C S I R O L A N D a nd WAT E R
Water erosion in the Murray-Darling Basin:Learning from the past
By Anthony Scott
CSIRO Land and Water, Canberra
Technical Report 43/01, November 2001
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Water erosion in the Murray-Darling Basin:Learning from the past
By Anthony ScottCSIRO Land & Water, CRC for Catchment Hydrology
CSIRO Land & Water Technical Report No 43/01(ISBN 0 643 06098 7)
November 2001
AcknowledgementsThis report was funded by the Murray-Darling Basin Commission and the Cooperative Research Centrefor Catchment Hydrology. The author would also like to thank the following people and organizationsfor kindly providing information, reviewing the draft report or contributing photos;
• Jon Olley, Ian Prosser, Chris Moran, Jacqui Olley (CSIRO Land & Water),• Carolyn Young, Greg Bowman (Department of Land & Water Conservation, NSW),• Pat Feehan (Goulburn-Murray Water, Victoria),• Geoff Titmarsh, Bernie Powell, Bruce Carey (Department of Natural Resources and Mines,
QLD),• Lisa Robins (Robins Consulting),• Tony Jakeman, Lachlan Newham, Barry Croke (CRES, Australian National University),• Klaus Koop (Environment Protection Agency, NSW),• Nicki Taws (Taws Botanical Research),• Peter Russell,• Mitchell Library - State Library of NSW,• National Library of Australia,• State Library of Victoria,• Museum Victoria.
Copyright: © 2001 CSIRO Land and Water.To the extent permitted by law, all rights are reserved and no part of this publication covered bycopyright may be reproduced or copied in any form or by any means except with the written permissionof CSIRO Land and Water.
CSIRO Disclaimer: To the extent permitted by law, CSIRO Land and Water (including its employeesand consultants) excludes all liability to any person for any consequences, including but not limited to alllosses, damages, costs, expenses and any other compensation, arising directly or indirectly from usingthis publication (in part or in whole) and any information or material contained in it.
MDBC disclaimer: The contents of this publication do not purport to represent the position of theMurray-Darling Basin Commission. They are presented solely to stimulate discussion for improvedmanagement of the Basin's natural resources.
Front cover photo; Gully erosion along a tributary of Merrill Creek, near Gunning, NSW(photo; Nicki Taws)
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Table of Contents
SUMMARY ................................................................................................................................... 41. INTRODUCTION TO EROSION PROCESSES .............................................................................. 52. THE LANDSCAPE AT THE TIME OF EUROPEAN SETTLEMENT ................................................. 8
2.1 Previous episodes of gully erosion ............................................................................. 82.2 Impacts of Aboriginal land use .................................................................................. 82.3 The shape and size of streams and drainage lines ..................................................... 92.4 Chains of ponds in Southern Tablelands of NSW..................................................... 122.5 River turbidity prior to European settlement ........................................................... 15
3. EXPLORATION FOLLOWED BY PASTORAL EXPANSION; 1813 TO 1850S .............................. 173.1 Explorers and settlers move into the Murray-Darling Basin................................... 173.2 Early forms of pastoralism ....................................................................................... 203.3 Early attempts at cropping ....................................................................................... 213.4 The first signs of landscape change ......................................................................... 22
4 THE GOLD RUSH ERA ......................................................................................................... 244.1 Discovery of gold...................................................................................................... 244.2 Environmental impact on rivers and streams........................................................... 264.3 Loss of forests in gold mining districts..................................................................... 304.4 Growing concern about the sludge problem ............................................................ 33
5. 1860S – 1920S; CLOSER SETTLEMENT AND ACCELERATED LAND DEGRADATION .............. 375.1 The Free Selection Acts and closer settlement ......................................................... 375.2 Expanding frontiers .................................................................................................. 385.3 Accelerated erosion from overgrazing and land clearing........................................ 395.4 Further notes on land clearing................................................................................. 485.5 Eroded gullies initiated by animal tracks, roads and drains ................................... 525.6 The introduction of rabbits....................................................................................... 565.7 Expansion of cropping.............................................................................................. 585.8 The effects of droughts and floods............................................................................ 635.9 Land degradation on the Western Plains ................................................................. 66
6. THE CAMPAIGN FOR SOIL CONSERVATION ......................................................................... 716.1 Setting up Agricultural Colleges and Departments ................................................. 716.2 NSW sets up Soil Conservation Service ................................................................... 716.3 Soil Conservation Board established in Victoria ..................................................... 746.4 Soil Conservation Act of South Australia................................................................. 786.5 Growing awareness of soil conservation in Queensland ......................................... 796.6 Erosion problems in the high country ...................................................................... 81
7. IMPROVED MANAGEMENT FROM 1945 ONWARDS .............................................................. 857.1 Overview of improvements ....................................................................................... 857.2 Rates of erosion declining in most regions .............................................................. 927.3 Improved pastures and fertilizer use ........................................................................ 987.4 Erosion associated with increased cropping.......................................................... 1007.5 Farm dams and water storages reduce sediment yield .......................................... 102
8. INVESTIGATING THE SOURCES AND YIELDS OF SEDIMENT. ............................................... 1058.1 Sediment yields for different land uses................................................................... 1058.2 Effects of logging and plantation forests on stream sediment concentrations....... 1068.3 Streambank erosion – another source of sediment in rivers .................................. 1078.4 Sediment surveys of reservoirs ............................................................................... 1088.5 Erosion studies using small plots or paddocks ...................................................... 109
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8.6 Studying the impact of single storm events .............................................................1108.7 Recent surveys of erosion in NSW and Victoria .....................................................1118.8 Sediment budgets ....................................................................................................113
9. LOOKING TO THE FUTURE ................................................................................................118REFERENCES ............................................................................................................................123
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SummaryWhen travelling across the Murray-Darling Basin, it becomes clear that many regions sufferfrom extensive soil erosion. What isn’t so clear is that much of this erosion commenced over150 years ago when European settlers started farming (and later mining) the land. Tounderstand the current condition of the landscape it is essential that we have a knowledge ofwhat has happened in the past.
In the first half of the 19th century, European farmers and pastoralists took possession of landthroughout the Murray-Darling Basin. The large numbers of sheep and cattle that they broughtwith them, grazed the perennial grasses and reduced the ground cover that protects the soil. Thehard hooves of the stock also disturbed the soil surface, particularly along streamlines andaround waterholes. Disturbance to the land accelerated in the second half of the 19th century assettlement and associated land clearing intensified and this was exacerbated by the huge plaguesof rabbits which ate any remaining vegetation.
In some regions, particularly along the western slopes of New South Wales and Victoria,alluvial gold was discovered in the 1850s, and this led to long stretches of creeks andsurrounding floodplains being completely dug up and processed through primitive ‘puddlingmachines’.
All of these disturbances resulted in a massive increase in soil erosion, which probably reached apeak during the second half of the 19th century and the first half of the 20th century. By theearly to mid 20th century there was a growing awareness of the problems associated with soilerosion and this eventually led to the establishment of soil conservation agencies in each state.From the 1940s onwards there has been a concerted effort to repair the damage caused by soilerosion. Today, the landscape appears to be gradually adjusting towards a new ‘equilibrium’ andthe rates of erosion are slowly declining from their peaks. However, these new rates of erosionare still many times higher than those of pre-European times, and the legacy of the past 180years continues to have a significant impact on both the environment and agriculturalproductivity.
This report documents these major events, and the changes to land use since Europeansettlement, that led to the increase in soil erosion throughout the Murray-Darling Basin. A betterknowledge of the history of soil erosion not only helps to understand the processes that lead toaccelerated erosion, but should also assist with the prediction of future trends. It also provides along term perspective (over a timeframe of 150-200 years) which can complement morequantitative but shorter term studies (of 5 to 10 years) that might be undertaken in a specificcatchment or paddock. Most importantly, by learning about the mistakes made in the past, wemight be able avoid them in the future.
“We could not have made a bigger mess of the soil of the country if its destruction had beencarried out under supervision.”
(Henry Bolte, Premier of Victoria, introducing legislation in 1949 which replaced the original SoilConservation Board with the new Victorian Soil Conservation Authority.)
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1. Introduction to erosion processes
Erosion, by water or wind, is a natural process. While volcanic and tectonic processes build upland surfaces, erosive processes wear them away. However, the effect of European settlement inthe Murray-Darling Basin (and elsewhere in Australia) has been to drastically increase the rateof erosion, and this has resulted in significant land degradation (Woods 1983). There are twomain forms of erosion in the Murray-Darling Basin, wind erosion and water erosion. This reportexamines the history of water erosion.
Increased water erosion has been caused by a number of factors, the most important being;- land clearance and the loss of the protective vegetation cover due to grazing,- increased runoff from cleared areas and,- increased erodibility of disturbed soils (eg. cropping land).
The potential soil loss increases sharply when ground cover falls below 70% (Lang andMcCaffery 1984), and bare, tilled soil is particularly prone to high rates of erosion.
Soil erosion by water is a complex process being dependent on many factors, such as climate,soil, topography, plant cover and land use. Initial detachment of soil occurs when the erosiveforces of raindrop impact, or of flowing water, exceed the soil’s resistance to erosion. Detachedparticles are then transported downslope by surface runoff, the quantity and size of particlestransported being dependent on the velocity and turbulence of the water flow.
There are four main types of water erosion, and these are;
• Sheet erosion is the removal of a fairly uniform layer of soil from the land surface byraindrop splash or surface runoff. It is often less visible than rill or gully erosion. Sheeterosion often occurs on cropping land where the soil is loosened by tillage. In someregions, sheet erosion is also associated with the presence of salt scalds (van Dijk 1969,Graham et al 1989, Bullock and Neil 1990, Neil and Richardson 1990).
• Rill erosion is the formation of small eroded channels that could be obliterated by normaltillage. A depth of less than 30 cm is normally used as a criterion to distinguish rillsfrom gullies. Rill erosion occurs when soil is detached by concentrated runoff. Rillscommonly develop along tillage lines and on the edges of roads and tracks where the soilhas been disturbed and runoff is concentrated. (Sheet and rill erosion are sometimescombined under the more general term of ‘hillslope erosion’.)
• Gully erosion is the removal of soil by flowing water, resulting in the formation ofchannels sufficiently large that they disrupt normal farming operations and are too largeto be filled during normal cultivation. Incision of gullies tends to occur when thevegetation along drainage lines is disturbed or when changes in land use within thecatchment causes an increase in surface runoff. Once gullies have started to form, theyare difficult to control.
• Streambank erosion refers to the undermining and collapse of banks along rivers andstreams. This is a natural process but has been accelerated by the removal of riparian
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vegetation, trampling of river banks by stock, and increases in bankfull discharges inregulated rivers. (Gully and streambank erosion are sometimes combined under themore general term of ‘channel erosion’.)
The direct or ‘on-site’ consequences of accelerated soil erosion are;
• loss of nutrients required for plants to grow,• a loss of organic matter which plays a vital role in sustaining the desirable physical and
chemical characteristics of soil,• decrease in soil depth which reduces water storage capacity, and• damage to infra-structure such as fences, roads and buildings.
The Soil Conservation Service of NSW has found that, on the black soils of the Namoi Valley ina season following bad erosion, a fall of up to 30% in wheat yields is possible (Seymour 1993).Fertilisers can be added to the soil to compensate for the loss of nutrients associated with soilerosion, but the reduction in water holding capacity (caused by a decrease in soil depth) is moredifficult to address.
Accelerated soil erosion can also cause ‘off-site’ impacts, in particular the increased turbidity inrivers and streams, and the sedimentation of reservoirs, lakes and estuaries. In some estuaries,increased quantities of sediment has led to the smothering of valuable seagrass beds. Increasedsediment loads have also changed the nature of streams and wetland habitats by filling deepwaterholes that used to be drought refuges for plants and animals. The sediment also transportsnitrogen and phosphorus into streams, which can lead to increased growth of algae. Increasedwater turbidity can also interfere with aquatic organisms, for instance the reduced visibility canaffect the foraging habits of many fish species.
High sediment loads also reduce the storage capacity of reservoirs, and the increase in turbiditycan add substantially to the cost of water treatment. In summary, accelerated soil erosion has asubstantial economic, ecological and social cost to society.
Why study the history of erosion in the Murray-Darling Basin?Studying the history of erosion over the last 150-200 years, helps develop a better understandingof the causes and processes that led to accelerated erosion rates. To understand the currentcondition of the landscape it is essential that we have a knowledge of what has happened in thepast. A better knowledge of the past also assists with the prediction of future trends. It providesa much longer term perspective of the issue which can complement more quantitative studieswhich might only investigate a shorter time scale of 5 to 10 years, or even just one storm event.
A Basin-wide study provides a useful overview of general trends and major events that affectedthe entire region and can this complement more detailed studies of a specific catchment orpaddock. Most importantly, by learning about the mistakes made in the past, we might be ableavoid them in the future.
The following chapters describe the landscape at the time of European settlement, and then tracethe activities and events that led to the disturbance of the land, and hence accelerated erosionrates. This includes details of;
• The initial pastoral expansion across the Murray-Darling Basin and the grazing ofpastures by large numbers of hard hoofed stock.
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• The gold rush eras and the massive disturbance to gullies in the gold mining districts.• Accelerated clearing and intensification of settlement after the Land Acts of the 1860s.• Overgrazing and degradation of the western plains in the late 19th century.• Increasing areas of cropping land and the impacts of the bare-fallow rotation.• Growing awareness of land degradation followed by the establishment of Soil
Conservation Agencies in the mid 20th century.• Introduction of restoration works to repair badly eroded land and attempts at better land
management practices in the second half of the 20th century.
Finally, a discussion of current land management activities and research is presented, along witha brief look at future issues and trends.
Namoi R.
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Figure 1. Murray-Darling Basin.
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2. The landscape at the time of Europeansettlement
2.1 Previous episodes of gully erosion
Today, many valleys in the Murray-Darling Basin contain eroded gullies, some up to 10 metresdeep. At the time of European settlement, most of these gullies did not exist. Clearly, there hasbeen a major change in geomorphic processes over the last 200 years, causing considerableproblems with soil loss from paddocks and reduced water quality in rivers.
Studies of the landscape indicate that earlier episodes of gully erosion have also occurredthroughout many regions of eastern Australia (Erskine 1986, Wasson 1979, Coventry andWalker 1977, Prosser 1991). In the Southern Tablelands of NSW, past gullies were of a similarsize to those of today but were not as widespread across the region (Prosser et al 1994, Prosser1996). These episodes of erosion were followed by 1,000 to 4,000 years of relatively stableconditions, with continuous sedimentation and the gradual formation of swampy meadows alongthe drainage lines. In some other regions there is little or no evidence of previous phases ofgully erosion, and the current phase of gullying may be unique in terms of landscape history(Fanning 1999).
The present episode of gully erosion in eastern Australia is the result of major environmentalchange caused by European settlement, and this has had a greater effect on erosion processesthan any other environmental change over the last 10,000 to 20,000 years.
2.2 Impacts of Aboriginal land use
Evidence uncovered at Lake Mungo in south-western NSW suggests that Aborigines have beenpresent in the Basin for at least 40,000 years (Powell 1993). This is equivalent to over 1000generations of Aborigines who have successfully lived within the Murray-Darling Basin. Theirtotal population was relatively small and sparsely settled, and as subsistence hunter-gatherers,their overall impact on the environment was minimal.
Their biggest impact was the change in the fire regime. This changed from one of rare, highintensity natural fires to one of more frequent low intensity fires. These fires were used to flushout animals while hunting and also to encourage a new growth of grass, which would attractkangaroos and other grazing animals. The frequent, low intensity fires allowed a quick recoveryof vegetative cover.
Studies of some archaeological sites indicate that there was an increase in sedimentaccumulation which coincided with the initial occupation of these camp sites (Hughes andSullivan 1986). However, any increase in erosion associated with disturbance of vegetationaround these sites would have been localised in extent, and unlikely to have had an impact on aregional scale.
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A detailed stratigraphic study of Wangrah Creek in the Southern Tablelands of NSW wasundertaken by Prosser (1988, 1990) to investigate the effects of Aboriginal settlement and theiruse of ‘fire stick farming’. An increase in fire frequency was detected, beginning at 3,000 to4,000 yrs BP, but this did not change the rates of erosion or cause widespread alluviation in thevalleys.
Figure 2. Prior to European settlement, the western slopes of the Murray-Darling Basin contained largeareas of grassy woodland. Today, only small remnants remain, such as this reserve near Tarcutta, NSW.(photo; Nicki Taws)
2.3 The shape and size of streams and drainage lines
The initial period of settlement in the Murray-Darling Basin, between 1813 and 1850, isrecorded in the journals and diaries of explorers and early settlers, and also in the reports andmaps of government surveyors. One of the most important issues they reported on was theavailability and permanence of water, and their records provide descriptions of the rivers andstreams. These descriptions provide evidence of what these drainage lines looked like prior tothe introduction of the pastoral and agricultural activities of the first settlers.
The early reports indicate that the broad valleys in upland regions often contained swampymeadows and ‘chains of ponds’ (Eyles 1977b, Page and Carden 1998). In drier areas along thewestern slopes, valleys often contained ephemeral channels which linked deeper water holes(Davis and Finlayson 2000, Randell 1980). Some larger streams had well defined channels anda semi-permanent flow of water during wetter periods. In the drier semi-arid regions throughoutthe western half of the Murray-Darling Basin, flow is highly ephemeral, and drainage linesconsisted of shallow meandering sandy streams bordered by trees (Williams et al. 1991).
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Most importantly, however, detailed studies of historical evidence (for example Beavis et al.1999; Davis and Finlayson 2000, Starr et al. 1999) indicate that the continuous networks ofdeeply eroded gullies now found in many catchments of the Basin, were not present prior toEuropean settlement.
‘Chains of ponds’ described by explorers and settlers of VictoriaMajor Thomas Mitchell was the first European to explore central and western Victoria duringhis expedition of 1836. On returning to Sydney he described this region as follows;
“The land is, in short, open and available in its present state, for the purposes of civilized man.We traversed it in two directions with heavy carts, meeting no other obstruction than thesoftness of the rich soil; and in returning over flowery plains and green hills, fanned by breezesof early spring, I named this region Australia Felix, the better to distinguish it from the parcheddeserts of the interior country, where we had wandered so unprofitably, and so long.” (Mitchell1839)
Mitchell made no mention of encountering networks of deeply incised gullies, whichpresumably would have posed a major obstacle to his carts. He did however describe crossingnumerous ‘chains of ponds’ as well as some running streams. It is not exactly clear whatMitchell meant by the term ‘chain of ponds’. He may have been referring to ephemeral channelswith large pools in which water remained, or he may have been describing the true ‘chain ofponds’ form still evident along a few of the less disturbed creeks in Victoria (Davis andFinlayson 2000).
Mitchell’s expedition and his report of ‘Australia Felix’ prompted many people to move fromSydney along ‘The Major’s Line’ and settle in the newly discovered land in the Port Phillipdistrict. One of these overlanders was Alexander Mollison who travelled south in 1837. In hisdiary he describes the creeks near Euroa;
“I observe that those creeks and chains of ponds which have large water ponds and a broad,shallow water course, are now full and running, while those which have deep channels, steepbanks cut into the earth and ponds small in proportion to their channels, are now quite dry, withthe exception of a few ponds in some of them in which there may be found a little muddy water”(Randell 1980)
Mollison’s description indicates that some streams consisted of ‘chains of ponds’ along broadshallow streamlines, but some others did in fact have steep earth banks.
Early descriptions of Tarcutta Creek, NSWThe earliest descriptions of Tarcutta Creek were made by the first explorers in the 1820s and30s. The channel then consisted of a connected chain of ponds and swamps. Remnants of theswamps persist in the upper catchment at Courabyra (10km north of Tumbarumba) and upstreamof Tarcutta township. Evidence of their former existence is found in exposures of dark organicsoil in present cut banks at Parsons, Borambola and elsewhere. (Page and Carden, 1998)
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Chains of ponds in the Darling DownsIn 1827, Allan Cunningham, the distinguished and intrepid explorer and botanist, set out fromSegenhoe (near the present town of Scone in the Hunter Valley, NSW) and travelled north overthe Liverpool Plains. After crossing the Namoi and Gwydir Rivers, the arid drought strickencountry forced him to swing east, and crossed the Dumaresq River near Beebo. Soon after, heentered the Darling Downs, which he named in honour of Governor Darling. A few hours later,he camped on the bank of the Condamine near Toolburra. The explorer actually gave the name‘Darling Downs’ only to the narrow valley along Glengallan Creek, about 29 km long, and 2.5to 5 km wide. The Downs were defined, he wrote, by “their lightly wooded ridge, and on theiropposite margin by a level forest of box and white gum. A chain of deep ponds passes along thecentral lower flats”.
Cunningham spent the next week traveling through the Darling Downs and discovered some ofthe finest pasturage he had ever seen in the colony of New South Wales. On his return toSegenhoe, he passed through the Canning Downs (near the township of Warwick) and continuedsouth through heavily timbered forest of box and casuarinas, and camped at a “chain of smallponds”. (From Allen and Skerman 1986)
Figure 3. An undisturbed drainage line in Roseburg State Forest near Cowra, NSW.(photo; Anthony Scott)
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Figure 4. Undisturbed drainage line in a Travelling Stock Reserve near Yass, NSW.(photo; Nicki Taws)
2.4 Chains of ponds in Southern Tablelands of NSW
On the Southern Tablelands of NSW, explorers and pioneer settlers made frequent reference to“chains of ponds” (Eyles 1977a, b, c; Starr et al 1999). While it is clear that some of thesefeatures were pools within river channels, other ponds were described as being sunk in grassyalluvial flats with no connecting channels. The ponds were generally long (10-100 metres) andnarrow and separated by bars of fine sediment vegetated with species such as Juncus, Typha,Phragmites and Poa. Except during wet weather, there was little or no flow between the ponds.Maps produced by the early surveyors also show ‘chains of ponds’ along many of the drainagelines in the broad, flat valleys typical of the Southern Tablelands.
Most valleys which previously contained these ‘chains of ponds’ now contain continuous gulliesincised to bedrock, and up to 10 m deep. However, there are some valleys which remainunaffected by channel incision and still contain ‘swampy meadows’ interspersed with ‘chains ofponds’. Here, alluvial flats have a dense cover of tussock grass and sedge up to 1m high and theflows of water twist between the vegetation (Prosser et al 1994). Larger meadows, those withcatchment areas of greater than 10 km2, often contain drainage ways of concentrated flow asmuch as 0.5 m deep and 1-10 metres wide but with no discernible banks. Within drainage ways,sedge is more prevalent than tussock grass, and 3-40 cm high aquatic plants predominate at sitesof standing water (Costin 1954).
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Figure 5. This pond on Murrumbateman Ck, north of Canberra, shows little sign of incision andcontains a variety of aquatic plants. In pre-European times, many streams in the Southern Tablelandscontained ‘chains of ponds’ similar to this. (photo; Ian Prosser)
Chains of ponds on the ‘Yas’ Plains“…. There is a small and new species of lobster, which is also procured in large quantities fromthe muddy ponds on the Yas Plains; they are delicious eating, and taken readily by placing apiece of raw meat on a bent pin…… The ponds in which the lobsters are taken are always fullof water being supplied by springs; one of them is about 50 yards in length by 20 in breadth, butof no great depth at any part. They form a chain along the plains during the dry season of theyear; but during heavy rains they unite into a running stream which empties itself into the YasRiver. It is only at the season when there is merely a chain of ponds or swamps, with but littlewater, that the lobsters can be caught with facility.” (Bennett 1834)
Chains of Ponds – near Lake George in the 1830s“The first part of our day’s journey lay through a bush, between McFarlane’s and the ranges, ofan ordinary character, and along a chain of ponds, called Cavan River. We then entered a gapwhich led through the ranges, and in due time descended on the other side; there emerging fromthe bush, we suddenly came upon the plain of Lake George....” (Walker 1838)
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Early description of ‘chain of ponds’In 1834, the naturalist Dr John Lhotsky gave the following account;
It was at the Pack Inn, and afterwards at Lockyer's Farm, that I first observed those highlycharacteristic chain of ponds, which would deserve a geological examination of months, as theyare a phenomenon not to be found, to my knowledge, in any other part of the world. They arecommonly round or oval basins, of from 20 to 200 feet in diameter, or length, excavated or sunkin the superficies of an alluvial soil, which is commonly of a rich kind, fed by subterraneoussprings; often indeed generally very deep, and not at all to be confounded with water holesowing their origin to the accumulation of atmospheric water.
The Pack Inn and Lockyers Farm are in the catchment of the Lachlan River to the immediatenorth of the Murrumbidgee, but similar chains-of-ponds were observed in the UpperMurrumbidgee Catchment. The ponds not only existed in chains, but also as single features. Inthe lower reaches of Ingelara Creek, which flows into the Murrumbidgee south of Michelago,Lhotsky ‘found finally one of those circular deep waterholes, I characterised in page 25.’(Andrews 1979, Starr et al 1999)
‘Chains of Ponds’ and ‘Swampy Meadows’ in Wangrah CreekWangrah Creek is a headwater catchment of the Murrumbidgee River, on the SouthernTablelands of NSW, covering an area of 50 km2. An 1842 map produced by the Governmentsurveyor WK Wright, shows that a sequence of pools preceded the present gully in the lowerreaches of Wangrah Creek. The original form of the valleys is preserved locally at sites thathave escaped gully erosion in historical times, including a section of Limekiln Creek and theheadwaters of Wangrah Creek, and sections of other creeks in the region. Floors of all thesevalleys are covered to their full widths by swamp ground with a rough surface of tall sedge andtussock grass up to 80 cm high, and flows spread through the vegetation, often in severalpreferred pathways which may include shallow scour pools. These wet valleys withoutcontinuous channels are termed ‘swamp meadows’. (Prosser et al 1994)
Early records of Jerrabomberra Creek and Molonglo RiverThe lower reaches of Jerrabomberra Creek were described in a surveyors letter as a swamp flatthat contained chains-of-ponds (Eyles 1977b). This term was also used by Lhotsky who wrote“After 7 miles we reached Giribombery, which lies on the banks of a distant creek, or chain ofponds.” In 1822 Kearns described the Molonglo River where it flowed across the MolongloPlain as “a chain of connected ponds running from the south end of the plains.” Along differentreaches, Allan Cunningham (1824) described the Molonglo River as a “reedy creek”, a “largecreek” and a “fine brook” flowing over a plain that was “low and swampy”.(From Starr et al 1999)
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Burra Creek – once a chain of ponds now deeply incisedAlong almost its entire course Burra Creek is today incised to bedrock leaving its former alluvialflood plain as a prominent terrace which averages 2.8 metres in height above the presentchannel. In the earliest survey plans of the catchment (eg Hoddle 1836, cited by Eyles 1977c)Burra Creek is represented as a chain of ponds. It seems likely that Burra Creek, in the first fewdecades of settlement, may have had steep 1 to 2 metre high banks and a channel consisting ofponds separated by ‘bars’ of fine sediment stabilized by various species of native reeds. Thiswould explain the considerable difficulties bullock trains experienced in crossing the creekduring the early years of settlement. (Eyles 1977c)
Figure 6. A swampy meadow along the upper reaches of Merrill Creek, near Gunning, NSW.(photo; Nicki Taws)
2.5 River turbidity prior to European settlement
In the early 19th century, when the first explorers headed westward from Sydney to discover newlands beyond the Great Dividing Range, they often followed the large inland rivers, either onhorseback or in small boats. In their journals, Charles Sturt, John Oxley and Thomas Mitchell,for instance, all provided quite detailed descriptions of these rivers, and in some instances alsomentioned the clarity of the water. Also, some of early settlers, and a few natural scientists whoexplored the region, also provided descriptions of the rivers. Many of these reports describecobble and gravel bedded rivers with clear flowing water, and this indicates that in many of therivers the supply of fine suspended sediment was limited, and sediment transport exceeded thesupply of sand and mud (Olley and Scott, in press). Sturt, for instance (in 1829), described thewaters of the Murrumbidgee at Jugiong as “hard and transparent” and for the Murray at the
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Murrumbidgee confluence, he reported that, “its transparent waters were running over a sandybed.”
The Lachlan River, however, is one river which appears to have always been more turbid thanmost, and Oxley (in 1818) refers to this when he describes the Macquarie River as being, “inevery respect different from the Lachlan; its waters are pure and transparent.” The DarlingRiver was also often described as turbid as illustrated by Sturt’s (in 1829) comparison of theMurray and Darling Rivers at their confluence;
“there was as distinct a line between their respective waters, to a considerable distance belowthe junction, as if a thin board alone separated them. The one half of the channel contained theturbid waters of the northern stream, the other still preserved their original transparency.”
Although many of the reports by early explorers and settlers indicate that the rivers of theMurray-Darling Basin were less turbid than in present times, heavy rainfall could quicklychange their appearance, as Oxley discovered when camping on the banks of the Castlereaghriver in 1818;
“The river during the night had risen upwards of eight feet; and still continued rising withsurprising rapidity, running at the rate of from five to six miles per hour, bringing down with itgreat quantities of driftwood and other wreck. …. The water was so extremely turbid, that wecould not use it; but were forced to send back to the marshes for what we wanted. …… Now thequantity of matter is astonishing, and such as must take some years to remove.”
In summary, there is historical evidence which indicates that prior to European settlement, manyof the rivers within the Murray-Darling contained less turbid water, due to the lower supply offine sediment from the upper catchments.
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3. Exploration followed by pastoral expansion;1813 to 1850s
3.1 Explorers and settlers move into the Murray-Darling Basin.
Although the First Fleet arrived at Port Jackson (Sydney) in 1788, it was not until 1813 thatBlaxland, Lawson and Wentworth crossed the Blue Mountains and established a gateway to theinterior of New South Wales. Governor Macquarie then commissioned the surveyor GW Evansto undertake further exploration in 1813 and 1815. This resulted in the discovery of the upperreaches of the Macquarie and Lachlan Rivers. Then, in 1817, Surveyor-General John Oxleyfollowed the Lachlan River westward, almost as far as its junction with the Murrumbidgee. Thefollowing year Oxley followed the Macquarie River down to the Macquarie Marshes.
Initially, settlers were slow to follow in the footsteps of the explorers, and in 1819, there wereonly about 8 settlers in the Bathurst district, along with 24 flocks of sheep and about 1,400 headof cattle. Ten of the flocks belonged to William Cox and the remainder to 7 other individuals(King 1957). By the 1820s, however, explorers such as Hume and Hovell, Allan Cunninghamand Charles Sturt were discovering new lands to the south, west and north of Port Jackson (seeTable 1), and settlers were following soon after. The pastoral expansion of the colony hadcommenced. This phase of exploration and settlement expanded rapidly in the 1830s, withThomas Mitchell conducting expeditions into the north-west of NSW in 1831 and 1832, andthen in 1836 travelling through south-west NSW and into western Victoria. Within months ofMitchell’s return, squatters with large herds of cattle and flocks of sheep followed his tracks tothe new pastoral lands.
Initially, the Government had tried to restrict settlement to the official ‘Nineteen Counties’which only extended inland as far as Yass, Bathurst and the southern edge of the LiverpoolPlains. However, squatters were occupying large tracts of pastoral land well beyond theseofficial limits. In 1836 the first attempt to regulate squatting beyond these boundaries wasmade, when by ‘Act of Council’, it was decided to admit the right of the squatters to graze theirstock, but imposed annual licence fees of 10 pounds each (King 1957). Nine squatting districtswere proclaimed, and Commissioners of Crown Lands were appointed to safeguard governmentinterests in each. Squatting had been officially recognized by the government. Since squattersdid not own their runs, they hesitated to develop their holdings and they usually remaineduncleared and unfenced.
By 1840, settlers had established themselves in a continuous belt from Port Phillip in the south,sweeping up between the Lachlan River and the coast, to the Darling Downs in the north. Thenext ten years was an era of consolidation within this region as well as further expansion west.After considerable political pressure, the famous ‘Order in Council’ of 1847 provided furthersecurity of tenure to squatters outside the ‘settled districts’ in the form of 8 and 14 year leases.In 1848 the Government Gazette listed the successful applicants for leases. In the Monarodistrict on the Southern Tablelands of NSW for instance, there were 42 runs, many of whichwere close to 50 sq miles (13,000 ha) and at least one, Michelago, which was closer to 150 sqmiles (38,800 ha). There was no restriction on the number of runs a person could lease sosquatters could control vast properties if they could afford the rent (Hancock 1972).
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In 1821 NSW only had 139,000 sheep, essentially producing meat for a restricted local market(WRC 1984). In the 1830s, improved shipping and increased British investment allowed woolgrowing to establish itself as the main pursuit of the pastoral industry, and by 1850 there weremore than 12 million sheep grazing the whole of south-eastern Australia. This expansionrequired little capital apart from livestock itself. Land cost either nothing or a nominal amountfor a lease, shepherds were employed instead of building fences, and accommodation wasprimitive.
Table 1. Exploration and settlement of the Murray-Darling BasinDate Event1788 First Fleet arrived at Port Jackson.1813 Blue Mountains crossed by Blaxland, Lawson and Wentworth, and they were the
first Europeans to enter the Murray-Darling Basin.1815 George Evans explored from Bathurst, south to Abercrombie River, reached the
Lachlan River and returned to Bathurst.1817 Oxley expedition. From Bathurst to the lower reaches of the Lachlan River.1818 Oxley travels from Bathurst to Macquarie Marshes, then eastwards through the
Liverpool Plains to Port Macquarie on the coast.1820 Throsby explores Lake George and Canberra region in the Southern Tablelands of
NSW, and by 1825 herds and flocks were being depastured in the region.1824 Hume and Hovell expedition starting from Yass, first to cross the Murray River and
then down to Port Phillip Bay.1827 Alan Cunningham discovers the Darling Downs in southern Queensland.1829 Governor Darling issued Government order defining the 19 Counties, the limit of
permissible settlement until 1840. Yass, Bathurst, Wellington and the southern endof the Liverpool Plains were within this boundary.
1829-30 Sturt travels down the Murrumbidgee and Murray, reaching the sea at LakeAlexandrina.
1831-2 Liverpool Plains and north-west NSW explored by Thomas Mitchell. Settlers arrivein Liverpool Plains soon after.
1835 Mitchell follows the Bogan River down the Darling, erects a stockade at ‘FortBurke’ and travels down the Darling to Menindee.
1836 First squatting Act to help control the ‘squatting’ boom. Licence fee set at £10 perannum.
1836 Mitchell travels down Lachlan, Murrumbidgee, Murray and back through Victoria.This opens up most of Victoria, and squatters follow in his footsteps.
1836 Colony of South Australia proclaimed. The Colony’s first land sale is held atWellington, on the Murray River, in 1837.
1838 Horton and Bonney are the first to move cattle overland from NSW, down theMurray River, to South Australia. Within a few years, hundreds of thousands ofsheep and cattle had followed the same route.
1840s Settlement of the Western Division of NSW begins, initially along the major rivers.1840s By the early 1840s, squatters had established more than 20 stations in the Darling
Downs in QLD.1845-46 Thomas Mitchell explores westward, discovers Maranoa River, which flows into the
Darling.1847 The 1847 ‘Order in Council’ improved security of tenure for squatters outside the
settled districts by establishing 8 and 14 year leases.1847 Stewart – explored the back country between the Lachlan and Murrumbidgee in
search of grazing territory.1851 The goldrush era begins when Edward Hargreaves discovers gold near Bathurst.
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Gwydir R
Namoi R.
MacIntyre R
Macquarie
R.
Lachlan R
Culgoa R.
Murrumbidgee R
War
rego
R.
Par
ooR
.
Goulburn R.
Darling R
Cam
pasp
eR
Edward R
Murray R
Lodd
onR
Avo
caR
Mur
ray
RSettlement of the Murray-Darling Basin
1830
1840
1850
1860
Figure 7. Settlement of the Murray-Darling Basin from 1830 to 1860.
Murrumbidgee valley already settled – 1837“The whole of the Murrumbidgee has long since been fully stocked (every four or five miles wecome to a head station), at all events as far down as seventy or eighty mile below this, afterwhich the country becomes dead level, and in wet seasons almost an entire swamp and unfit forpasturage.”
From the journal of Thomas Walker, one of a party of gentlemen who travelled from Sydney toPort Phillip in 1837. The observation was made while camping downstream of the present siteof Gundagai, NSW. (Walker 1838)
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3.2 Early forms of pastoralism
The rural industry in the Murray-Darling Basin began when outstations for the more establishedproperties near Sydney were set up in the 1820s near Bathurst in the west and Yass in the south-west. Pastoral methods were simple, and for those who were squatting or leasing the land,investment was kept to a minimum. There was little incentive to fence paddocks or to outlaycapital on extensive clearing.
Cattle roamed at will, usually forming their own camps near water, and were mustered whenneeded. Sheep were shepherded. They were held in flocks ranging from 400 to 1000 sheep withseveral flocks folded each night in the care of a night watchman (Gallagher 1989). They werecounted out to the shepherds in the morning, taken to fresh pastures to graze and returned to thefold again at night. For shearing, flocks were taken in rotation to a home station, to be washedand shorn (Fitzhardinge 1941). Home stations were established near rivers or creeks so thewashing could be carried out.
Quite large areas of land were allowed for each head of stock, three and half acres (1.4 hectares)frequently being allowed for one sheep. The leasehold regulations of 1847 allowed four acres(1.6 hectares) per sheep and 34 acres (14 hectares) per head of cattle (Jeans 1972). Initiallythere was ample land for all and the runs must have been understocked. However, stock numbersincreased rapidly. In the first nine years the stock on the Duntroon property near Canberra,multiplied 35 times (Moore 1977) and by 1838 Campbell of Duntroon had 60 or 70 shepherdsworking for him (Fitzhardinge 1941).
The pastoral system meant that up to 2,000 sheep were folded each night on an area rarelyexceeding a hectare, for several nights at a time. The two or more flocks folded at a station weretaken out in opposite directions soon after sunrise, kept slowly moving all day and returned eachnight. Because of the shortage of labour the flocks were generally larger than the optimum sizeand the larger the flock the more trampled the vegetation became and the further the sheep hadto be taken each day (Roberts 1935). Due to the belief that yarding in one spot led to foot rot(Roberts 1935) the whole station was moved every few days. The grazing system would havecreated severely trampled and denuded areas of one or two hectares in extent. These bare anddisturbed areas were left to recover, or erode, as the station moved to repeat the process(Gallagher 1989).
Fewer cattle were run per hectare than sheep as they require more feed per head. The cattlewere not held in closely bunched herds, and therefore generally spread out more than sheep(Roberts 1935, Jeans 1972, Hancock 1972). While one head of cattle might consume as much asten sheep, the ten sheep could trample more vegetation and disturb more soil (Gallagher 1989).However, the cattle tended to feed along the moister valley floors where disturbance to sensitivevegetation in swampy meadows and along streamlines was greatest.
The movement patterns and grazing habits of herds of cattle were different from thoseof sheep. The Rev. Henry William Haygarth (1848) noted that:
“The usual feeding times [of cattle] are in the morning and evening, and during the first part ofthe night; at mid-day they congregate on the low grounds in the vicinity of water... Here theybask for hours, lying closely grouped together until the heat begins to abate, when they draw offtowards the forest in all directions, moving leisurely, and grazing as they go.”
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The cattle congregated to rest on the valley floors. Haygarth wrote about the impact of thiscongregation:
“A spot on which cattle are thus in the habit of assembling and basking during the day is calleda 'rendezvous' and is easily known, for, from the constant pressure of innumerable vast bodies,the surface of the ground becomes smooth and hard, resembling a blighted ring in the midst ofverdure; these marks still remain on stations from which the cattle have long been removed andbeing seen from a considerable distance, are frequently used as a means of direction for thelonely traveler.”
The impact of grazing of sheep and cattle was soon being noticed by astute writers. AlfredMcFarland’s (1872) words on seasonal variations and drought in the area south of Michelago onthe Monaro, are cautionary to those using stocking rates based on seasons of plenty;
“But there are other sides to the picture which should also be given; for it must not be supposedthat Manaro is always green. On the contrary, in mid-winter the withered grass converts into ahalf-white and half-brown appearance; and then, when the sun is shining strongly on a hill sideor plain, it sometimes looks as if it were covered with snow. During a drought the face of theland is changed still more; there is scarcely a blade of grass to be seen, the hills are glisteningwith red iron stone, the creeks are dry, most of the rivers are shriveled up, and the sheep andcattle half dead from starvation, or away on the mountains.”
And…
“The tall waving grass of the plains bending before the wind, and reflecting the passing clouds,is one of the commonest and not the least beautiful of the sights in Manaro; and in the paddocksat Bibbenluke, as well as other places, I have seen acres of grass up to my horses shoulders –though in times of drought, the whole country is bare enough – as bare as bare can be.”
3.3 Early attempts at cropping
The first crops planted in the Murray-Darling Basin were small gardens of vegetables for localconsumption. In the early 1830s Lhotsky noted one such garden on an outstation that containedcabbages and watermelons (Andrews 1979). He also noted that it had been planted in the richhumus soil that was associated with many of the drainage lines.
Planting of cereal crops followed. The method of cultivation was primitive. The first wheatcrop in Wagga Wagga was planted in 1846 and demonstrated some of the methods used at thistime (Irvin 1962). The plough was homemade using wood and a bolted-on iron blade. Teamsfor ploughing consisted of up to eight bullocks which could turn over four acres (1.6 hectares) aweek. Roots and stumps left in the roughly cleared land often wrecked the plough, delayingplanting. Hand-made wooden harrows could be used for cultivation, which was completed byusing a mallet to break up any soil clods left. The seed was broadcast and rolled in with a log. Ifit was a cereal crop it was cut by hand using a sickle, then bound and stacked. Threshing wasdone using a simple flail of two saplings bound together at two ends with a piece of greenhide.A bushel of grain could be threshed in an hour. The grain was then winnowed by tossing it inthe air with a shovel.
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Even with convict labour these labour intensive methods must have restricted the area of landcultivated. For instance in 1832 the County of Murray (578,000 ha covering Yass and theCanberra region on the Southern Tablelands) had only 200 hectares under cultivation (NSWColonial Secretary 1832). Wheat, maize, barley, oats, potatoes and tobacco were the main cropsgrown.
Through the 1840s and 1850s the area of land cultivated for crops steadily increased, butpastoralism remained the dominant land use. Although the area cultivated was small, almost allthe cropping occurred along the river flats, and on the rich humus soils of the swampy meadowsof valley floors. Drainage of these was necessary and was carried out as a deliberate operation.These drains often developed into deeply eroded gullies over the following decades.
3.4 The first signs of landscape change
Even the simple early forms of agriculture and pastoralism carried out in the 1820s and 30s werea radical change from what had gone before. Stocking rates were often set in ignorance of theextremes of the climate and the complex interactions of a long established ecosystem. The stockwere different to the indigenous grazing animals. They had hard hooves and they grazed indifferent ways. Animal movements became more confined and more directed. The pastoralistswere dealing with an environment vastly different to that in Europe with which they werefamiliar and their methods did not always successfully transfer from one environment toanother.
Early erosion in the Upper Murrumbidgee catchmentThe first evidence of accelerated erosion in the catchment of the Upper Murrumbidgee Riverappeared soon after settlement. The 1848 diary of John William Buckle Bunn contains a sketchtitled ‘The well in the deep creek’. This shows a four to five metre deep gully with exposedroots of a large tree, indicating recent incision.
In 1851, Rev. WB Clarke (1860) witnessed a major storm when he was camped near the‘Berudba’ (Bredbo) River. Of the effects of that storm Clarke wrote;
“…. the masses of rock and earth that had been washed down to the Berudba, and also a mile ortwo to the southward, especially about Mr Cosgrove’s, where the torrent had sought a way tothe Murrumbidgee, were perfectly astonishing.”
(Starr et al 1999)
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First signs of degradation in the ‘Wannon’ country of Victoria – 1850sIn 1840, John Robertson settled on 11,000 acres (4400 hectares) in the Portland District ofwestern Victoria (which is to the south of the Murray-Darling Basin). In 1853 he wrote a letterto Governor Latrobe which described his experiences over the previous 13 years as he set up asheep grazing farm. This included a description of his concerns about the loss of perennialgrasses, the commencement of gully erosion and the appearance of salt water springs in lowlying areas. The land degradation, now widespread across much of eastern Australia, hadcommenced on his farm only a decade after it was first settled.
“….the long deep-rooted grasses that held our strong clay hill together have died out; theground is now exposed to the sun, and it has cracked in all directions, and the clay hills areslipping in all directions; also the sides of precipitous creeks - long slips, taking trees and allwith them. When I first came here, I knew of but two landslips, both of which I went to see; nowthere are hundreds found within the last three years. A rather strange thing is going on now.One day all the creeks and little watercourses were covered with a large tussocky grass, withother grasses and plants, to the middle of every watercourse but the Glenelg and Wannon, andin many places of these rivers; now that the only soil is getting trodden hard with stock, springsof salt water are bursting out in every hollow or watercourse, and as it trickles down thewatercourse in summer, the strong tussocky grasses die before it, with all others. The clay is leftperfectly bare in summer. The strong clay cracks; the winter rain washes out the clay; nowmostly every little gully has a deep rut; when rain falls it runs off the hard ground, rushes downthese ruts, runs into larger creeks, and is carrying earth, trees, and all before it. Over Wannoncountry is now as difficult a ride as if it were fenced. Ruts, seven, eight and ten feet deep, and aswide, are found for miles, where two years ago it was covered with tussocky grass like a landmarsh.” (From Bride 1983)
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4. The gold rush era
4.1 Discovery of gold
In 1851, Edward Hargreaves discovered gold in a creek at Ophir, not far from Bathurst. Thiswas the first publicly recognized gold discovery in Australia, and signified the start of the goldrush era. Over the next few years, gold was discovered at numerous sites in the uplands andslopes of NSW and Victoria (see Figure 8), and tens of thousands of people flocked to thesegoldfields, taking away labourers from the fledgling pastoral industries.
AvocaStawell
Maryborough
MoliagulDunolly
Wedderburn
St Arnaud
Creswick
ClunesTalbot
Maldon
Inglewood
Castlemaine
Daylesford
Bendigo
Rushworth
Alexandra
Melbourne
Chiltern
Eldorado
GulgongMurray-Darling Basin
Bright
Junee
YackandandahBeechworth
Forbes
Parkes
Harden
Young
Adelong
Tumbarumba
Hill EndSofala
Lucknow
Ophir
Junction Reefs
Grenfell
Sydney
Nundle
Bingara
Uralla
Figure 8. Major goldfields discovered in the 19th century within the Murray-Darling Basin
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Figure 9. Goldfields of central Victoria in the 19th century (source; Flett 1970)
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Figure 10. Part of the great complex of gold workings of the Castlemaine –Mt Alexander field. (The map covers and area of 8.5km by 12.5km. Source; Flett 1970)
4.2 Environmental impact on rivers and streams
The land degradation during the gold rush period differed from that of pastoralism in that theeffects were very dramatic but localized in extent. The mining activities and associatedsettlements quickly degraded the streams and surrounding countryside. The initial phase ofmining involved surface digging and washing from shallow alluvial deposits by individuals orsmall parties. This required a great deal of water to sort the gold from the washdirt using smallwooden puddling tubs, cradles and pans.
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Later, the horse driven puddling machine was introduced wherever a sufficient water supply wasavailable. In the peak year of puddling in 1858 over 5,000 puddling machines were used inVictoria and, at Bendigo alone, some 10,000 men and 5,000 horses worked 2,000 machines(Powell 1976). The creek beds themselves were often so ravaged that the evidence persiststoday. In some instances the entire stream was diverted so that the alluvium in the stream bedand banks could be processed more easily. Beautiful valleys were stripped bare of soil,processed in the puddlers and then flushed downstream. Vast quantities of sludge moved downthe valleys, frequently blocking the natural watercourses and depositing on the lower floodplains(Brough Smyth, 1869).
With advances in technology during the latter half of the 19th century, a second phase of alluvialmining occurred. ‘Hydraulic mining’, including a variety of sluicing operations, was introducedinto Victoria’s north-eastern fields by Californian miners. The method depended upon reliablewater supplies of good volume and was not widely employed elsewhere. Its most devastatingprocedure involved the undercutting of hillsides and steep stream banks down to bedrock, usingpowerful jets fed by water races which stretched for between three and twenty miles across thecountryside. Depending on the nature of the material involved, hydraulic sluicing enabled asingle worker to shift between 50 and 100 cubic yards daily, twice the amount obtained by othersluicing methods (Powell 1976).
Where the source of gold was traced to underlying rocks, companies were formed to sink deepshafts. The underground mining industry produced huge quantities of tailings and sludge whichflowed into nearby streams.
Figure 11. A miner sluicing for gold along a creek in the Castlemaine district in 1894.(Reproduced courtesy of Museum Victoria)
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Impact of gold mining commenced in 1851Only two months after the discovery of gold at Ophir, near Bathurst, the magnitude ofenvironmental disturbance was noted by John Erskine, a naval officer who visited the diggings.“The whole of the sides of the creek, here 80 to 90 yards wide… were dug and turned up to adepth of five and six feet, like a stone quarry, the slate rock lying about in heaps.” (Keesing1967)
Whole valley torn up in 1851-52“The whole valley had been torn up by the diggers: in the bed of the creek, and on the risingground on either side, and up the lesser valleys which led into it, holes and pits were dug, fromone to twenty feet deep.” Written by two travellers, Samuel Mossman and Thomas Banister(reprinted 1974), as they visited the goldfields along Forest Creek, part of the Mt Alexanderdiggings in Central Victoria, in 1851-52.
Spring Creek, Ovens Diggings in Victoria“On reaching the brow of a hill, we see a broad valley lying below us, and white tents scatteredalong it for a mile or more. The tents, right and left, glance out of the woods on all sides. In theopen valley they stand thick, and there is a long stretch up the center of the valley, where all theground has been turned up, and looks like a desert of pale clay. … We go on, - huts, dustyground, all trodden, trees felled and withering up in the sun, with all their foliage; here andthere a round hole like a well, a few feet deep, where they have been trying for gold, and havenot found it. Down we go, - more tents, more dust, more stores, heaps of trees felled and lyingabout; lean horses grazing about on a sward that a goose could not lay hold of; hole after holewhere gold has been dug for, and now abandoned; washes hanging out; horrid stenches frombutchers’ shops, and holes into which they have flung their garbage. …. all the ground isperforated with holes, round or square, some deeper, some shallower, some dry, some full ofwater, but in few of which work now seems going on…. All between the holes, the hard clay-coloured sand lies in ridges; and you must thread your way carefully amongst them. … There isthe creek or little stream, - Spring Creek, - no longer translucent as it comes from the hills, but athick clay puddle, with rows of puddling-tubs standing by it, and men busy working their earthin tins and cradles.” (written by William Howitt, 25th Dec. 1852)
Digging for gold at Spring Creek“…. We have wandered about amongst the diggings. No language can describe the scene ofchaos where they principally are. The creek that is a considerable brook is diverted from itscourse; and all the bed of the old course is dug up. Then each side of the creek is dug up, andholes sunk as close to each other as they can possibly be, so as to leave room for the earth thatis thrown out….. The course of the creek is lined with other diggers washing out their gold.There are whole rows, almost miles, of puddling-tubs and cradles at work. The earth containingthe gold is thrown into the puddling-tubs – half hogsheads – and stirred about with the water, todissolve the hard lumps, then it is put through the cradle, and the gold deposited in the slide ofthe cradle, then washed out in tin dishes.” (Written by William Howitt, 25th Dec. 1852)
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Destroying Yackandandah Creek“We have begun to destroy the beauty of this creek. It will no longer run clear between itsbanks, covered with wattles and tea-trees, and amongst its shallow parts overgrown withforeign-looking shrubs, flags and cypress-grass. A little while, and its whole course will exhibitnothing but nakedness, and heaps of gravel and mud. We diggers are horribly destructive of thepicturesque.” (Discovering gold at ‘Upper Yackandanda’, written by William Howitt on 28th
February, 1853)
Degradation of Bendigo Creek“Little more than a year ago, the whole of this valley on the Bendigo Creek, seven miles long byone and a half wide, was an unbroken wood! It is now perfectly bare of trees, and the whole ofit riddled with holes of from ten to eighty feet deep – all one huge chaos of clay, gravel, stonesand pipeclay, thrown up out of the bowels of the earth! So much has been done on this oneforest in one year; and not only so much but a dozen other valleys as large… It is thus that afew months sees the most wonderful metamorphosis of the country where gold is. It is thus thatone of those tremendous rushes which takes place whenever there is the least rumour of successanywhere, brings tens and tens of thousands speedily together, like a flight of locusts, who tearup and leave the earth desert in a few weeks.” (Written by William Howitt, 30th October 1853)
Digging up the hill sides“We observed, with astonishment, as we went on, how the diggers had followed the traces ofgold up the very hill sides, over the hills; sometimes cutting deep openings, which must havecost enormous labour, and following them down again into the open valley, where all was dugand thrown up in the wildest manner. Hill after hill, and gully after gully, we passed over,everywhere the trees felled, the ground turned topsy-turvy, deep pits and huge openworkdelvings, as if they had been making reservoirs, with strange, rude machinery and dams forwashing out gold. Everywhere, amongst the ravaged and desolated woods, tents andnondescript huts, and people leading a rude, wild sort of life, which no one can realise tohimself without seeing it.” (William Howitt describing the Bendigo gold fields in November1853)
The creek has been dug and sluiced“For many miles the woods between this creek and Spring Creek have been felled, and theground dug up for gold. Where we used to travel through unbroken forest with the compass nowextend the tents and the delvings of the digger race. Nuggety Gully, New Rush, Europa Gully,and a whole succession of gullies are dug up, and all their woodland scenery desolated. NineMile Creek has been dug out again and again, and has been sluiced three times. This creek,which has acquired the cognomen of Back Creek, and Snake Valley has also been amazinglyworked. Whole miles of its banks that a year ago were wild and desolate, shrouded in densethicket of tea-trees and wattles and lightwood, and thick with sedge and jungle, are now butheaps of clay; the trees prostrate, the whole scene laid bare; the stream deviated from itscourse; and the bed of the creek has been dug and sluiced, and it’s banks themselves cut downand put through the sluice.” (Upper Yackandanda, as described by William Howitt, December1853)
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Effect of gold mining on the Avoca RiverAvoca River is located in north-western Victoria and is a terminal, anabranching river systemwith highly variable stream flow from a large catchment covering 12,340 km2. The first settlersmoved into the Avoca catchment in the 1840s. In the early 1850s gold mining commenced andtens of thousands of miners began working the creeks of the catchment, particularly atAmpitheatre, Avoca and St Arnaud. Most of the mining was not actually in the stream lines asin other parts of Victoria, but the mining would have released large amounts of sediment into thestreams. The gold was almost exhausted by the 1890s, but from 1953 to 1956 large scaledredging was used to re-work alluvial deposits just north of Ampitheatre. (Rutherfurd andSmith 1992)
Figure 12. ‘Australian Gold Diggings’, in about 1855. A painting by Edwin Stocqueler, from the RexNan Kivell Collection. (By permission of the National Library of Australia)
4.3 Loss of forests in gold mining districts
Gold mining created a huge appetite for timber, and the surrounding forests rapidly disappeared.Initially timber was used for firewood and for building shelters, but when reef and deep leadmining commenced in the 1860s, timber was also needed as boiler feed and as props inmineshafts. Throughout the gold mining districts, and in particular Central Victoria, hundreds
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of square kilometres of forest disappeared, leaving the fragile soils prone to sheet and gullyerosion.
Tree felling at goldfields“The diggers seem to have two especial propensities, those of firing guns, and felling trees. It isamazing what a number of trees they fell. No sooner have they done their day’s work, than theycommence felling trees, which you hear falling continually with a crash, on one side of you orthe other… you see numbers of stringy bark trees standing with the bark stripped off for six oreight feet high, and others felled and completely stripped…” (Howitt 1855)
Reckless destruction of forest“Wherever the miners have pursued their labors the trees have been cut down; and we see acresof bare short stumps where a few years ago there was a stately growth of eucalypti. There hasbeen so much waste, and so much almost wanton destruction, that no time should be lost inrepairing the damage, if indeed there is yet time to repair it with any hope of the new growthbeing available before some of the mines are abandoned. The general interests of the minershave been sacrificed to the greed or caprice of those who, until lately, ravaged the beautifulforests, as if the loftiest tree were the growth of a single night, and was placed there merely to beirreparably damaged or destroyed as soon as found. A giant of the forest has been killed inorder to furnish a sheet of bark, and the smaller kinds have been burnt for the purpose of boilinga kettle.” (From ‘Gold Fields and Mineral Districts of Victoria’, 1869, written by Victoria’sSecretary for Mines, Robert Brough Smyth)
Figure 13. ‘Mt Alexander gold diggings, 1853’, a painting by William Bentley. (By permission of theNational Library of Australia)
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Figure 14. Gold was first discovered at Chewton, Victoria in 1851. 150 years later, the area has slowlyrevegetated and many of the eroded gullies have stabilized. Chewton was part of the ‘Mount AlexanderDiggings’ which covered a large area around the township of Castlemaine. (photo; Anthony Scott)
Figure 15. Deep erosion gullies at Sailor’s Diggings near Daylesford, Victoria, which formed during thegold rush era in the late 19th century. (photo; Anthony Scott)
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4.4 Growing concern about the sludge problem
About 1885, public concern had been aroused about the siltation of some Victorian streamscaused by the alluvial mining operations then in full swing. Alluvial mining was active alongtributary streams and gullies in the catchments of the Avoca, Loddon, Campaspe, Goulburn andOvens Rivers. In 1887 an official Board was appointed by the State Government to enquire intothe sludge question and a report was produced. In this report the following comments weremade about the siltation of rivers (Thompson 1979);
“The injuries already inflicted and which, unfortunately, in many cases cannot be cured, consistof the filling up of the large clear watercourses in the creeks and river, the silting up of the riverbeds causing sludge to overflow on the adjacent lands, to the destruction of vegetation and fruittrees; the liability of horses and cattle going to water in the creeks being bogged in the sludgeand perishing there, or contracting disease by drinking the muddy and often mineralizedwater…. these, and the destruction of roads and bridges, are some of the evils arising from theabsence of foresight on the part of the legislature in years gone by, and the want of care on thepart of the miners.”
No immediate legislation for the control of these operations resulted from this report but some ofthe larger mining companies, which were working deep alluvials and operating crushingbatteries, were persuaded to, and in fact did, construct a series of sludge dams which werereasonably effective.
However, severe floods in the 1890s accentuated erosion of the banks of many Victorian riversand streams.
It was not until 1904 that the Mines Act was amended to provide for some control over thequantity of sludge, from mining operations, that would be permitted to enter any naturalwatercourse. The Sludge Abatement Board was established in 1905, under the provisions of thislegislation. The appointment of this Board was the first positive action taken in Victoriatowards the control of soil loss caused by erosion.
However, Victoria’s ‘sludge problem’ continued into the twentieth century, with the operationof hydraulic mining and dredging. Hydraulic mining used pressurized water jets to displacealluvial deposits for the purposes of sluicing (Shakespear et al 1887). This technique could onlybe used where there was a reliable water supply and consequently was not widely practised.However, in areas where it was used, such as the Upper Loddon catchment, the damage to theriverbanks and floodplains was severe (Davis 1996). After gold extraction, the muddy effluentwould often drain into the nearby creeks and rivers, and large quantities of sediment wouldmove downstream.
Giant dredges were also being used to rework enormous quantities of sediment both in the riverbeds and on the floodplains, and once again, large quantities of fine sediment would bedischarged into the river system. The peak period for hydraulic mining and dredging was from1907-1909 and Table 2 indicates the scale and location of this mining during 1907.
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Table 2. Dredge Mining and Hydraulic Mining, operating in Victoria, December 1907District
Bucket dredge Hydraulic pumpsluice
Jet elevator Total
Ararat & Stawell 0 4 0 4Ballarat 1 20 0 21Beechworth 37 11 2 50Bendigo 0 4 0 4Castlemaine 2 28 2 32Gippsland 5 3 0 8Maryborough 0 14 0 14(From a report issued by the Victorian Sludge Abatement Board in 1908 and cited by Davis 1996)
The large quantities of sediment originating from alluvial mining, hydraulic mining anddredging, contributed towards the siltation of Laanecoorie Reservoir on the Loddon River.Constructed in 1891, the initial capacity of 17,000 ML was reduced by over half during its first41 years of operation (see section 7.5 for more details).
In relation to instream mining, the Beechworth District, in northern Victoria, was probably theworst case, with 50 dredging and sluicing operation operating in the district in 1907 (see Table2). An Inquiry in 1913 by the Sludge Abatement Board reported many instances of seriousstream and floodplain siltation throughout the Beechworth area (Davis 1996). One example wasSandy Creek, a tributary to the Mitta Mitta River with a catchment area of approximately 155km2, where there were extensive dredge mining operations. It was reported that from theconfluence of Sandy Creek with the Mitta Mitta River, to a point 5 km upstream, a deposit ofmining sediment had been laid down. The total size of the deposit was 1.2 km wide, 5km longand 1.2 m deep, or 7.2 million m3 (Sludge Abatement Board 1915, cited by Davis 1996).Another example was the Reids Creek catchment where it was reported that much of thesediment had moved downstream into the Ovens River and had deposited onto the floodplains inthe Wangaratta and Tarrawingee districts, all the way down to the Murray River (Davis 1996).
Dredges were still operating in the Avoca River as late as the 1950s (Rutherfurd and Smith1992), while an abandoned dredge on the outskirts of Maldon was operating until 1984 (seeFigure 16).
Fish in creeks choked with ‘gold dust’ - 1852“There used to be fish in the creeks, but our washings must have choked them all with golddust.” (James Bonwick describing the impact of alluvial gold mining on a creek near Bendigoin 1852. Extract from Keesing, 1967)
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Figure 16. This abandoned dredge is located on the outskirts of Maldon, Victoria. It processed thesurrounding alluvial soils in the 1970s and was finally abandoned in 1984. (photo; Anthony Scott)
Figure 17. Between the 1930s and 1954, high pressure water jets were used to cut into the embankmentof alluvial soils at Red Hill in the Forest Creek diggings near Castlemaine, Victoria. The resulting slurrywas collected and passed through a series of traps to separate the gold. The roar from the jet could beheard 3-4 kilometres away. (photo; Anthony Scott)
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Figure 18. The goldfields of the 19th century, such as this valley at Chewton, Victoria, have slowlyrevegetated, often with weeds such as blackberry and gorse bushes. However, many of the steep sidedbanks continue to be active sources of sediment. (photo; Anthony Scott)
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5. 1860s – 1920s; Closer settlement andaccelerated land degradation
5.1 The Free Selection Acts and closer settlement
In NSW the Crown Lands Alienation Act and the Crown Lands Occupation Act (commonlyreferred to as the Robertson Land Acts or Free Selection Acts) were passed in 1861. Theoutcome of these Acts was that any person could select a holding of between 40 and 320 acres(16 to 130 ha) on any vacant Crown Land, even land that had previously been under pastorallease. Existing leases had to expire before the land was available for selection. Ascompensation, the pastoralists were able to buy the land on which their buildings, tanks, damsand stockyards stood. These Acts were introduced as a response to the very large pastoralholdings that were held by a small number of people. They were intended to assist ruraldevelopment by encouraging more people onto the land.
Up until the introduction of the Free Selection Acts, many large landholders had done little toimprove the land or to increase its productivity, except for the small cleared and fencedcultivation paddocks close to the homestead, simply because they had so much land and alsobecause they did not own it. However, the new farmers soon realised that to make a living onthese smaller sized farms required more intensive farming practices, including higher stockingrates and the clearing of trees to encourage pasture growth. This led to an accelerated rate ofland clearing and a higher potential for land degradation.
The Commissioner of Crown Lands in Monaro described this problem in 1879;
“There is a very great number of stock now kept on the same area of land than formerly,throughout the whole of the Monaro, on those parts where selection has been going on rapidly,as the lessees of the runs have not decreased their stock in the same proportion that large areasof their runs have been taken from them by conditional purchasers, and as most of the selectorshave got sheep the land has been made to carry twice the number it formerly did, and whichoverstocking is, and has done, an immense harm to the grazing capabilities of the country..”(NSW Department of Mines 1879 and cited by Gallagher 1989).
In Victoria, Queensland and South Australia, similar Land Acts slowly came into force duringthe 1860s and 70s, and this led to the gradual replacement of the large squatting runs held underleasehold, with a greater number of new settlers who had purchased smaller blocks of land(Roberts 1968). In Victoria, a series of Land Acts were progressively introduced in the 1860s,but the system was initially abused by squatters who submitted a series of ‘dummy’ names toselect all of their original land. In 1869 fresh legislation was introduced, and in the followingtwo years, thousands of new settlers had been placed on the land. By June 1872, there had been19,420 selections for 1,916,860 acres (766,700 ha) and this resulted in increased pressure ontimber resources for domestic fuel, fencing and building materials, as well as widespreadclearing for cultivation and grazing paddocks (Powell 1976).
From the 1870s onwards, pastoralists started to use ringbarking as a quick and cheap method ofclearing the land. William Farrer was one who, in 1873, promoted ringbarking as the cheapestand easiest method of improving pasture growth by the removal of competition of trees for soil,
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water and sunlight (Hancock 1972). In a number of districts gangs of travelling Chinese, nolonger able to make a living from gold mining, offered their services as cheap and hard-workingcontractors for ringbarking.
With the continuing belief in the virtue of closer settlement, renewed efforts were made to createsmall farms by soldier settlement after World War I. The size of farms were set on the basis ofwhat was considered to be sufficient to maintain a family, an area calculated on the optimisticbasis of temporarily high prices. Falling prices during the Depression inevitably led to heavylosses.
Closer settlement and ‘land improvement’ encouraged by Government - 1869“Let a man take his 320 acres, at a shilling a year if you like, but let him remain on the land;make him cultivate it, because, if he does not cultivate it, it may be very reasonably assumed thathe does not want it.” (Victorian Parliamentary Debates 1869: 956, cited by Powell 1976)
5.2 Expanding frontiers
By the 1850s nearly all the suitable grazing land on the highlands and slopes in the eastern halfof the Basin had been occupied. Most of the river frontages in the drier, western half of theBasin were also occupied, but the ‘back blocks’ (those with no border along a river) were onlyutilized during wet seasons. The introduction of well sinking, construction of earth dams anderection of galvanized tanks in the late 1860s enabled these ‘back blocks’ to be stocked on amore permanent basis. The most spectacular developments were achieved following thediscovery of the Great Artesian Basin in 1879, which had the effect of opening up the north-westof NSW and the south-west of QLD. Much of this land however, was marginal and sensitive todrought.
In the 1860s the railway system started to rapidly expand from Melbourne, Sydney andBrisbane, and by the 1890s most large towns in the Murray-Darling Basin were connected via anetwork of railway lines (Jeans 1972). With better transport and prices, wool production alsobecame an increasingly popular rural enterprise, outstripping beef and sheep meat production,which had been stimulated by demand from the gold fields. Sheep numbers in NSW rose from8.5 million in 1855 to almost 62 million in 1891 (Jeffcoat 1988).
The development of riverboat services also assisted with the pastoral occupation along theDarling and Murray Rivers. In 1853 there were two steamboats on the Murray, and by 1861there were 30 (Jeans 1972). The trade created new towns along the rivers, boosted agricultureby providing better access to markets and thus allowed more land to be opened up for farming.
Due to the high costs of transport, in the first half of the 19th century crops were mostly grownalong the coastal valleys, close to the larger towns. However, the introduction of railwaysopened up the western slopes and plains to cropping. Further developments such as thestumpjump plough (1876) and HV McKay’s combine harvester (1885) reinforced the move tothe west. In NSW, 91% of wheat was grown on the coast and tablelands in 1860. By 1890,71% was grown on the western slopes and plains (Dunsdorfs 1956, Jeans 1972, Robinson 1976).However, clear trends of declining crop yields soon emerged and by 1902 wheat yields in south-eastern Australia had plummeted to about one third (ie 0.5 t/ha/hr) of yields obtained a few
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decades earlier. The practice of frequent cropping without adequate fallowing encouraged soilborne diseases, and the lack of fertilizers or rotation with legumes reduced the supply ofavailable nutrients.
From its high point in 1891 the wool industry also started to slump. Overgrazing and the arrivalof rabbits in the mid-1880s caused problems, but it was the drought in the second half of the1890s that triggered the collapse, halving the number of sheep shorn between 1895 and 1900(WRC 1984). Many graziers went broke and their pastoral leases were passed on to the banksor larger pastoral companies.
Agricultural development in Australia in the late 19th century“In central Queensland and the dry interior of New South Wales and South Australia thediscovery and exploitation of extensive artesian basins further increased the potential forgreater intensification, and in higher rainfall regions such as Victoria’s Western District, thewell established grazing freeholds consolidated their reputations for stud-breeding by confidentinvestments in water storages, elaborate subdivisioning and management research. Thecumulative benefits of all these efforts were obvious enough: the sheep population of Australiaincreased from 42 million in 1872 to about 106 million in 1892. What the industry lacked,however, was the ability to adjust to drought, and the concurrence in the ‘nineties of dryseasons, rabbit plagues and the economic depression proved that far too many holdings,especially in the outback, had become over-financed and over-grazed.” (Powell 1976)
5.3 Accelerated erosion from overgrazing and land clearing
The exact timing of accelerated erosion after European settlement is difficult to determine butanecdotal evidence and archival records indicate that in many places it coincided with the periodof rapid agricultural expansion of the late 19th century (Bird 1985, Prosser 1991, Williams et al1991, Wasson et al 1998, Starr et al 1999, Beavis et al 1999). Many erosion gullies thatformed during this period, continued to expand during the early 20th century.
Under natural conditions, prior to European settlement, most of the hills and valleys werecovered by forest or woodland. The trees, and perennial grasses (such as Kangaroo and Wallabygrass) had extensive, deep rooted systems. The roots had two main effects – they bound the soiltogether, and used up most of the moisture in the ground. Because the soil was kept fairly dry,most of the rain was soaked up, and runoff occurred only during heavy storms.
By 1900 many of the forests and woodlands throughout the Murray-Darling Basin, particularlyin the highlands and western slopes, had been ring-barked or cleared to improve productivity forgrazing. The deep rooted perennial grasses also slowly disappeared under the heavy grazingpressure, and were replaced by faster growing annual grasses which have a shallower rootsystem. From the 1870s onwards, the impact of grazing was exacerbated by the increasingpresence of rabbits, which rapidly spread throughout eastern Australia.
The reduction in soil moisture being taken up by the vegetation led to increased surface runoff.Many soils also suffered a reduction in permeability because of compaction by stock, and thediminished ground cover during summer (when the annual grasses died off) allowed surfacewater to flow away rapidly, before it could soak in.
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The overall effects of clearing and grazing were to increase the amount and speed of surfacerunoff, and to remove most of the binding effects of root systems. This led to accelerated ratesof erosion, particularly along drainage lines where cattle tended to congregate and trample thestreambank vegetation. Other factors, - such as the ploughing of hill slopes, digging channels todrain swampy meadows, the construction of roads, and the formation of animal tracks, - oftenaccelerated the erosion process by disturbing the soil and concentrating the surface flow along aparticular line.
In September 1892 A.G. Hamilton wrote in a paper presented to the Royal Society ofNSW, which described the erosion process:
“In clearing land and during the progress of settlement, the surface of the ground is injured inmany ways; in the formation of paths and roads; and in ploughing the ground. When thesurface is broken on a slope, no matter how gentle, the protection afforded by the grasses andherbaceous plants to the soil is removed and the surface drainage is altered. Small runlets ofwater begin to travel along the line of disturbance and to cut channels which become deeperand deeper. The amount of earth cut away of course depends greatly on the slope, the nature ofthe soil and the amount of rainfall; being greatest in light soils and on steep slopes. In a lightsandy soil I have seen on a very slight slope, channels nine feet deep and twelve or fourteen feetwide cut in a single wet winter.” (Hamilton 1892)
It is assumed that Hamilton' s understanding of erosion processes was gained through directobservation. The statement describes the process of surface disturbance, the creation of a smallrill, and concentration of flow to form a gully.
The observations of Hamilton are supported by more recent experiments undertaken by Prosserand Slade (1994) which investigated the causes of gully erosion. They concluded that thegrazing of the vegetation cover along streamlines and valleys was a major factor in the rapidformation of gullies in the 19th century.
The greatest risk of erosion was when heavy rains fell after an extended drought. Duringdrought, vast expanses of land were laid bare by overgrazing, leaving soils exposed to theerosive forces of surface runoff.
Erosion caused by overstocking on the Darling Downs – late 19th centuryPrior to European settlement, runoff from the upland sectors of the Darling Downs slowlyfiltered through the densely grassed flood plains. However, during the middle and late 19th
century, a rapid expansion in livestock population occurred, and there is evidence to suggest thatserious overstocking took place, particularly in the higher rainfall (and upland) sections of theDowns. The Warwick/Allora area appears to have suffered the most, and evidence of this isprovided by the residual scars of old gullies which appear to have originated from that time.(Skinner et al 1977)
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Figure 19. Severe erosion of pastoral land near Wellington, NSW, in 1960. (Mitchell Library, StateLibrary of NSW)
Overgrazing and loss of vegetation during droughtWriting in 1892, Hamilton noted that “the pasturing of sheep and cattle damages the indigenousflora in much the same way as the rabbits do. Given a few good seasons and owners let theirflocks and herds increase to the verge of the carrying capabilities of their holdings. Whendrought comes, the starving animals devour every vestige of green herbage, pull the roots out ofthe ground and eat them and even lick the seeds off the surface.” (Hamilton 1892)
Causes for the initiation of gully erosionIt is impossible to determine the exact causes of incision in each valley, but the results ofexperiments undertaken in the southern tablelands of NSW demonstrate a strong control ofvalley-floor vegetation on susceptibility to gully formation. Swampy meadows covered bytussock and sedge are very resistant to incision. Tussock and sedge are only susceptible toincision if there is heavy degradation of vegetation coupled with increased discharge, or if thesurface is laid bare. On larger swampy meadows, vegetation cover in drainage ways is naturallyreduced by persistent base flow. The reduced vegetation cover increases the sensitivity of asurface to incision during large flood events. There are also many recorded instances of swampymeadow degradation by ploughing and early road and drain construction in addition to theimpact of livestock. (Prosser and Slade 1994)
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Erosion of duplex soilsUnder natural conditions, the surfaces of soils are protected by litter and vegetative cover. Whenthe vegetation is removed, the surface is exposed to rainfall impact and soil structure breaksdown rapidly, resulting in a sealed, impermeable surface condition. This is characteristic ofduplex soils which cover large areas of agricultural land within the Murray-Darling Basin. Oneimportant consequence of this condition is that soils have reduced infiltration capacity and aremore prone to generate run-off and accelerated erosion.
Erosion of duplex soils in some areas has caused deep rills and gullies to form and this exposesthe clay-rich subsoils. The subsoils tend to disperse readily in flowing water so that advancedstages of erosion are characterized by subsoil collapse and ‘piping’. Because textural B horizonsof duplex soils contain a high proportion of clay mineral colloid, fine grained erosion productsare released in large quantities and are capable of long distance transport as suspended load torivers and water storages. (Walker 1986)
Gully erosion near Bredbo in the late 19th centuryA 1913 plan of the Bredbo village – the field work of which was completed in 1887 – shows aseries of gullies on surrounding farmland, including Cosgroves Gully, which was mentioned bythe Rev. WB Clarke (1860) during a storm in 1851. Comparison of the village plan with 1944aerial photos shows that these gullies had reached their headward extent by the time of the 1887survey. More recent aerial photographs show no further headward extension since 1944. Theupper and lower reaches of Cosgrove’s gully is stabilizing and revegetating naturally. The mid-section however is still producing sediment, principally through gully wall undercutting andcollapse.
Two gullies within the village of Bredbo are also shown on the 1913 plan. The original surveyrecord includes measurements of the widths of the gullies. A recent measurement of the deeperof these gullies has shown no lateral movement and no measurable change of width since the1887 survey. (Starr et al 1999)
The catchment problem in VictoriaMost Victorian rivers still suffer from a legacy of catchment mis-management, which beganwith the indiscriminate wielding of the settlers axe last century. The effects of clearing weremade worse by overgrazing, overcropping and rabbits. Also swamp drainage, gold mining bythe diggers and the dredges, droughts, floods and fires (most of them deliberately lit toencourage grass growth) have all taken their toll. As the consequence of a hundred years ofneglect and abuse, Victorian catchments became more vulnerable than ever before to the effectsof drought and flood. (From “The State of the Rivers, Victoria, Australia”, SCCRI 1984)
Sheet erosion in 1882Early descriptions of sheet erosion are sometimes provided as part of a report on a large storm orflood. In 1882 for instance, after a great storm at Ginninderra near Canberra, five feet (1.5metres) of debris was removed from each of two recently constructed dams. Grass growth didnot evidently follow the storm because ‘runoff carried away the loose surface’. (Eyles 1977b)
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Origin of incised channels in the Burra catchmentIn the Burra Creek catchment south of Queanbeyan, active gully erosion has occurred in valleyswhich today contain vigorous dry sclerophyll forest. All of these gullies are located in or nearareas which were chosen as selections between 1869 and 1895. This is good circumstantialevidence that the initiation of channel incision was related to the brief period of ringbarking,burning and grazing before these farms were abandoned at around the beginning of the 20th
century. (Eyles 1977b, 1977c)
Effects of denuding a country of its natural vegetation - 1896‘The earlier settler found everywhere the country more or less well clothed with some kind ofperennial (notably woody) vegetation, the soil loose and porous, the banks of watercoursesthickly overgrown and lined with shrubs. When the rain or waterspout descended over hill orplain, the water found numberless obstacles on its road to the lower levels, and had to flowslowly. Hence a large proportion soaked into the sieve-like soil to be saved and stored as areserve supply. The remainder, reaching the bed of creek or river gradually, could also onlyadvance slowly, because obstructed by the rank vegetation lining the banks. Here againopportunities were afforded for abundant soakage and loss of volume. When reaching the levelground, the limpid or but slightly muddy flood-waters arrived with small momentum, and somuch reduced in mass, that they could do little harm. The flow lasted also much longer thannow, and much more drained, therefore, into the ground, enabling it to resist subsequentdroughts much longer. Now the hills are more or less completely denuded of the despised‘scrub’, the ground hard and firm, the surface bare, or bearing a mere apology for grass thegreater part of the year, the beds of watercourses devoid or nearly so of all obstructions. ….The rain or thunderstorm descends; down it rushes unobstructed from the hillsides, carryingwith it part of the still remaining fertile surface soil. Of the precious moisture, a very smallproportion finds its way into the ground, and to very slight depths. The larger volume gets mud-(fertility) laden into creek and river. Rushing along cleared unobstructed bed it gathers volumeand momentum rapidly, and carries destruction instead of blessings to the low-lying level, whereit becomes heaped up much faster, than it can escape. Here the mud is deposited, choking everycrevice of the soil and making it impervious.’ (From Tepper 1896, p33)
The costs of settlementThe settlers slowly adapted what they knew from another country to their new land. However,because the frontier was so vast, little thought was given to preventing land degradation. Itsresources seemed endless. Change was also legitimized by the firmly held belief that rainfollowed the plough and that livestock improved the soil. Such powerful myths about theAustralian environment persisted for a long time. In 1874 the Premier of NSW and future PrimeMinister, GH Reid, wrote:
“The soil of the plains is loose, and in very dry weather the grass nearly disappears; but as thecountry becomes stocked the tread of the animals binds the surface; the grass acquires closenessand strength, and the saltbush gives way to the characteristics of the slopes. As a consequencethe rain that falls begins to form watercourses, waterholes become creeks and the streamsincrease in volume.”
Reid was quite correct, the rain did form new watercourses but they were of no benefit becausethey were erosion gullies and the soil was lost downstream. (Breckwoldt 1988)
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Land use and sediment yield in the Upper Yass catchmentIn the Upper Yass River catchment on the Southern Tablelands, grazing of native pastures waswidespread by the 1830s. Following the introduction of free selection under the Robertson LandActs in the 1860s, grazing intensity increased rapidly as the small number of large holdings weresubdivided into numerous smaller holdings. Cultivation of land for crops such as wheat andpotatoes also commenced on a small scale. Ringbarking, burning and draining of swamps werewidely practiced. Forest clearing in the region is thought to have reached its maximum in themid to late 19th century. Rabbits first appeared in the 1890s and soon reached plagueproportions. Along with these changes there was a period of drought in the late 1890s. Much ofthe gully erosion and stream incision now apparent in the area occurred or was initiated in theperiod between 1860 and 1900. This situation continued with little improvement until the late1950s. (Neil and Fogarty 1991)
Figure 20. Chain-o-ponds Creek near Yass, NSW. The name of this creek provides an indication of itsoriginal appearance when the first settlers arrived in the first half of the 19th century. (photo, Nicki Taws)
Siltation of Junction Reefs DamThe Junction Reefs Dam, on the Belubula River near Lyndhurst, NSW, was among the firstmajor dams built west of the Great Dividing Range. Water from the 200 megalitre storage wasconveyed by a 2km pipeline to the Junction Reefs goldmine. There it operated a Pelton waterwheel which powered a series of driving belts connected to mining equipment such as rockcrushers, stamper battery, shaking tables, conveyor belts and sludge activators. Water providedthe motive force for this mine for more than 20 years. The dam silted up in 1920 and miningoperations ceased in 1937. (Jeffcoat 1988)
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Erosional history of Warrah catchment, Liverpool Plains.Warrah Creek is an upland catchment (150km2) of the Mooki River on the Liverpool Plains,NSW. It was first settled in 1833 by the Australian Agricultural Company. Limited sheepgrazing was practiced until 1861 when major development of the property commenced.Development included running large numbers of sheep and cattle, and the enclosure of the estateby wire fencing. Two dams were built in the Warrah catchment, together with a series ofwashpools on or immediately adjacent to the creek for washing sheep prior to shearing.Although ‘the forests of Warrah were not particularly extensive’ (from correspondence in 1862),they were sufficient to supply almost all the fencing needs of the company (correspondence from1868).
Maps and surveys from 1881 indicate that Warrah Creek was a meandering entrenched streamwith a number of major tributaries. Two discontinuous gullies were apparent at this time.Further downstream, 5km E-N-E of Warrah homestead, the creek ‘meandered along a barelydefined watercourse’.
After 1885, exotic weeds had become problematic, and by 1903 rabbits had arrived in the area.Severe droughts occurred in 1885 and in 1901-02, with the latter being reported as the worstsince 1838. Surveys of the upper catchment, completed in 1912, depict a number of ephemeralgullies, suggesting that land degradation in response to land clearing, total grazing pressure anddrought was manifest by this date. Furthermore, the main channel downstream of the homesteadhad become entrenched. Clearing of the catchment continued until 1926, when the supply ofmature timber was exhausted and the sawmill, which had been operating in the middlecatchment, was closed.
The earliest aerial photography was taken in January 1943. These photographs show a highlydegraded catchment almost devoid of timber, including an almost complete absence ofvegetation in drainage lines. Extensive gully systems comprising deep incisions with abundantsecondary offshoots occurred throughout the catchment. These gullies were often associatedwith multiples of rills which were oriented generally in the direction of slope. The condition ofnative pasture was very poor, with large areas of bare ground. This can be partly attributed torabbits which had reached plague proportions by the 1940s. Grazing was the primary land usealthough limited areas of cropping were restricted to small holdings adjacent to the creek in themiddle to lower parts of the catchment. (From Beavis et al 1999)
Incision of Jerrabomberra CreekA typical example of the change in stream channel form since 1840 is Jerrabomberra Creek nearQueanbeyan, NSW. Between 1835 and 1862 various surveyors and explorers reported a ‘chainof ponds’ and a ‘swamp flat’. The first hint of change is given in a survey plan dated 1878 withthe description of the catchment of a tributary of the Jerrabomberra as containing ‘deepstormwater gullies’. In 1910 Griffith Taylor described ‘the small canyon, about 12 feet deep,cut by the Jerrabomberra Creek into a soft alluvial plain’. By 1944 channel incision had affectedalmost every drainage line in the catchment. Further examples such as this have been reportedfor other streams in the Southern Tablelands. (Eyles 1977b)
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Birchams Creek; the transition from a chain of ponds to a gullyOn the Southern Tablelands of NSW, chains of ponds have often been replaced by incisedchannels since European settlement. Birchams Creek, a tributary of the Yass River, is noexception. Dry sclerophyll forest covered the entire catchment during the 1830s, the time of thefirst extensive sheep grazing. However, the first 40 acre selections were not surveyed until 1877along the lower reaches of the creek. Trees on most of the remaining catchment area were notring barked till the 20th century, and, particularly in the upper portion of the catchment, grazingpressure between 1925 and 1972 was intense with three to four sheep per acre being run withoutthe application of fertilizer or grass seed.
Dramatic changes in channel form since 1880 have occurred in Birchams Creek. Aerialphotographs taken in 1941 show a gully to have advanced upstream approximately 500 metresfrom the Yass River, a chain of large ponds to occupy the middle reaches of the creek and shortdiscontinuous gullies and some ponds to exist in upper reaches. Fieldwork in 1975 revealed thatthe incision of the main channel had continued its advance from the Yass River by a further 150metres. Signs of local instability were also evident with the headwalls of a number of pondsbeginning to erode and advance up valley. The farm dam which was a prominent feature in1941 photographs had, by 1975 been completely infilled with sediment.
It is only possible to speculate on the causes. The lower portion of the catchment is farmed bydescendants of one of the original selectors and the present landowner comments; “the maingully has been working upstream since at least 1910, and ponds which extended much furtherdownstream have been either cut out or filled in”. The supply of water of the main valley floorhas apparently increased, thus increasing stream discharges and triggering the present phase ofchannel incision. The replacement of dry sclerophyll forest by pasture, and the introduction ofstock would have increased soil compaction, reduced surface storage and reduced rates ofevapotranspiration, perhaps sufficiently to influence the flow regime of the stream. (Eyles1977a)
Gully erosion and sediment movement in the Michelago Creek, NSWThe northern section of Michelago Creek and its tributaries, Margarets and Teatree Creeks, risein the well forested and steep Tinderry Mountains of the Southern Tablelands. The firstEuropean settlers were recorded in the Michelago district in 1828 and as elsewhere in the region,sheep grazing was the main pastoral occupation. Following the passing of the Free SelectionAct in 1861, six families settled in the northern Michelago Creek and Teatree Creek catchmentsand three along Margarets Creek. Most of the gullies in this catchment were incised in theperiod between 1860 and 1900, triggered by cultivation, swamp drainage, soil disturbance bysheep and rabbits, land clearing and grazing. The deep gullying of Margarets Creek adjacent tothe Spring Valley homestead, for instance, was initiated soon after settlement by a ploughfurrow cut either as a deliberate action to form a drain or as the last furrow of a cultivationblock. Major runoff events during the first four decades of settlement would have ensured rapidincision and extension of the gully network. Major flooding occurred in 1851, 1870 (twice) andin 1891. These events are likely to have been a major factor in the extension of the gullynetworks. Some gullies were also highly active in the first half of the 20th century. A limitednumber of sites have continued eroding, but with the rate of activity decreasing over time. Mostsediment production in the Michelago Creek catchment now originates from existing instreamsites. (Starr 1989)
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Formation of gullies at Bango Creek near YassThe Bango Creek catchment was settled in the 1850s. At this time, there was no indication oferoded gullies along the stream-lines, and water movement across the flats at the head of BangoCreek was predominantly sheet flow. Mr Grieves, the original settler, began clearing the nativewoody vegetation and by 1899 he had cleared some 1,600 hectares. In 1882 and 1884, extensionof a nearby goldfield took in part of Grieves property ‘Bango’. In 1900 Grieves went bankruptand the bank manager, JR Ross took over ‘Bango’. Ross, unlike Grieves who was a grazier,believed in cultivation, and cropped the flats at the head of Bango Creek for wheat, oats andbarley.
During the tenancy of Ross, folk from the neighbouring farms travelled across the flats on theirway to the nearby village of Coolalie. However, by 1915, gully erosion at the head of BangoCreek prevented the passing of horse and buggy and an alternative route had to be found. In1960 the farm was sold to the McReynolds family. Under the McReynolds management wascompletely changed. The land was pasture improved and fertilized, rabbits controlled andploughing of the flats ceased. In 1961, soil conservation work was undertaken and the gullyhead advancement stopped. Since 1962, aerial photographs record no appreciable increase ingully size to the present.
The main gully was active for 46 years, 1915 to 1961. The length of this gully was 800 metres,and the width (at top of gully profile) varied between 5 and 13 metres. Depth varied between2.1 and 7.0 metres. On average, the gully head moved 17.5 metres upstream each year.(Gillespie 1981)
Figure 21. Sheep and cattle grazing along the Murrumbidgee River near Coolac, NSW. Theintroduction of livestock to the mid-Murrumbidgee catchment from the 1830s onwards, causedovergrazing along the valleys and this ultimately led to increased erosion of drainage lines and riverbanks. (photo; Anthony Scott)
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Figure 22. Deep erosion gully near Colinton, south of Michelago on the Southern Tablelands, NSW.The Monaro district, between Michelago and Cooma, has been badly affected by gully erosion, probablydue to the poor soils, low and erratic rainfall and poor vegetation cover. (photo; Anthony Scott)
5.4 Further notes on land clearing
From the mid-1860s there was growing concern from some scientists and academics about therapid rate of land clearing and ringbarking. This attracted the attention of the Age and Argusnewspapers and resulted in a number of editorials being published (Powell 1976). The primaryconcern was about the perceived effect of land clearing on rainfall and water supply in streams.But issues such as increased soil erosion were also addressed.
“Over and over again we have urged that steps should be taken to protect our forest lands, notonly because extravagance will lead to scarcity, but also because the local climate will beaffected in all those places where the forests are removed. In protecting the forests we do morethan increase the growth of timber – we prevent waste of soil, we conserve the natural streams,it is not improbable that we prevent decrease in the rainfall, and it is certain that we largelyaffect the distribution of storm waters. A covering of shrubs and grass protects the loose soilfrom being carried away by floods. Anyone who has looked at the wheel-ruts in the friable soil
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covering our Palaeozoic rocks must have observed how rapidly the rain, having once found itsway under the roots of the grass, cuts large unsightly channels in places where for ages therehas been but a slight depression. The physiognomy of many districts of the colony has beengreatly changed in this manner. But far more effective in altering the physiognomy of a countryis the removal of forest timber. The Italian hydrographers have made mention very often of thedisastrous results attendant on destruction of forests – Frisi relates that when the natural woodswere removed from the declivities of the Upper Val d’Arno, in Tuscany, the soil of the hills waswashed down into the Arno in vast quantities, to the great injury of the riparian proprietors.Some districts of Catalonia have suffered even more by the incautious operations of man; and,on the other hand, we know by what has been done in Italy, in France, in Germany and inAlgeria, how much the local climate may be ameliorated, and the fruitfulness of gardens andfields increased by judicious planting. Mining, ploughing, roadmaking, the cutting of drains,the formation of tracks, all aid in diminishing the conservative powers of the natural herbage,and it is not surprising that our best streams, such as the Loddon, Campaspe, and Avoca, arefast becoming mere channels for the efflux of sludge and sand. Even in those parts not touchedby the gold-miner, the rivers are rapidly changing their character. The mere occupation of thecountry for pastoral purposes has produced great changes, and it is well to consider whetheranything can be done to compensate for, if we cannot check, this kind of devastation. Thereservation of large tracts of forest land is our first duty. By keeping the hills clothed we maymake fruitful the valleys, and provide stores of moisture for the parched plains….. (Argus16/10/1865)
The concern prompted the convening of a special committee to investigate the whole issue offorest conservation in Victoria. A report was issued in November 1865, and the dominatingconcern was with ‘needless destruction of timber’. The continuing wasteful ways of the‘improvident diggers’ (then about 85,000 strong) were now matched and sometimes surpassedby those of pioneer settlers and a host of bush workers. The committee made a number ofrecommendations about the creation of forest reservations near the larger mining towns, andeventually led to the State Forests Act of 1876. However, there was little or no effect on the rateof clearing in the pastoral and agricultural districts of the State.
Similar protests about the rapid loss of forests were being made with less clamour in New SouthWales. The Director of Sydney’s Botanic Gardens, pointed the bone at the pioneer farmer; “Theaxe of the settler has no discrimination; - every tree disappears under its rude sway when theland is required for a homestead”. Once again, these concerns originated from a very smallnumber of scientists in Sydney and had no effect on the rate of land clearing out west.
The South Australians did not have the problems associated with major gold mining activity, buttheir agricultural economy was rapidly expanding and the small area of natural forest andwoodland was rapidly disappearing. Several leading politicians and public servants campaignedthroughout the 1860s for the promotion of new plantations and the reservation of natural forest.Foremost among these were G Goyder (the Surveyor General), R Schomburgk (Director ofAdelaide’s Botanic Gardens), and F Krichauff (a long serving member of the House ofAssembly). In 1870 these three associates recommended the reservation of some 300,000 acresof forest, and this scheme, with modifications, was incorporated into the Forest Trees Act of1873 and Forest Board Act of 1875.
Despite the farsighted statements by a few scientists and the creation of some forest reserves, theprimary aim of the state governments was for rural development and the clearing of land inpastoral and agricultural districts continued unrestricted.
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Timber resources were not only being cleared for farming, but with the expansion of the railwaynetwork throughout the countryside, there was a large demand for railway sleepers. A big redgum could produce as many as three hundred sleepers but contractors usually took the nearesttimber to hand, thus helping to clear the land for pioneer farmers (Bolton 1981). Timber wasalso needed for domestic firewood to fuel kitchen stoves, bath heaters and sitting roomfireplaces. There are no early estimates for domestic consumption of timber, but in 1925, whengas and electricity were already available in all major cities, and coal briquettes were cominginto common use in Melbourne, it was calculated that NSW and Victoria between themconsumed a million tonnes of firewood each year (Commonwealth Year Book, 1925, cited byBolton 1981).
In 1892 AG Hamilton estimated that 9.5 million hectares of New South Wales forests had beendestroyed by clearing or ringbarking, almost a third of the total area which was under forestwhen European settlement commenced a century earlier. In his view, commercial exploitation oftimber for export was a minor cause, and that clearance for farming and ringbarking for grazingwere the main agents of destruction.
Land cleared in NSW by 1890“In New South Wales it is probably safe to assume that the whole of the coast district, tablelands and mountains, and a narrow fringe of the plains were forest-clad, and that the majorportion of the plains were treeless. Now this tree covered part is probably not less than one-third of the total surface, that is to say, 103,000 square miles, or 65,920,000 acres of forest. Thearea cleared for, or under cultivation in 1890 was 2,688,486 acres; and that ringbarked andpartially cleared was 21,823,690 acres, making a total of 23,512,176 acres upon which theforest has been destroyed. … On the whole it is probably within the mark to say that in NSWalone, probably one third of the total forests have been swept away since the colony wasfounded.” (Hamilton 1892)
William Farrer advocates ringbarkingThe abnormally wet seasons of the early 1870s were a great spur to the pioneer wheat farmers inthe west, but they hit the high country pastoralists of Victoria and NSW very hard indeed. In thehighlands of Victoria and New South Wales, foot rot and liver fluke decimated many flocksduring the abnormally wet seasons of the early 1870s. In 1873 William Farrer, better knownlater for his experimentation with new wheat strains, joined other scientists and livestockfarmers in advocating ring-barking as the cheapest and most efficient method of combating thedisease – especially via an improvement in the quality of the native grassland after the removalof the ‘competitor’, the subsequent increase in light and so on. The idea was rapidly acceptedand was soon widely credited with the ‘sweetening’ of pastures and the eradication of ‘thefluke’. Ring barking had long been practiced in the Australian Colonies, but its extension in the1870s caused great alarm in some quarters, especially among scientists who still held to thebelief that the forests were the principal causative agent in precipitation and moisture retention.(Powell 1976)
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Development of land near EuroaThe development of farms in the Euroa district, Victoria, started to accelerate in the second halfof the 1800s with construction of the north-east railway and the advent of the Land Selectionlegislation. Most of the flat country had been ringbarked and some of it cleared by the 1890sand by the 1920s there was little commercially valuable timber left. In the hilly country, mostland had been ring-barked by the 1890s, however timber remained on a number of allotments inthe area through to at least the 1920s. (Davis and Finlayson 2000)
Work of destruction in South Australia - 1870“Will anyone who knew the country a dozen years ago say we have nothing to fear if the work ofdestruction goes on at the same rate for some 20 to 30 years to come?” 15 January, 1870,Border Watch, a weekly newspaper from Mt Gambier, South Australia. Although Mt Gambieris not in the Murray-Darling Basin, this comment reflects the accelerated rate of clearing thatwas occurring throughout much of the south-eastern portion of the State.
Figure 23. Gully erosion near Gulgong, NSW, 1945. (Mitchell Library, State Library of NSW)
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The Gwydir RaftA remarkable feature of the lower Gwydir Valley is the ‘Raft’, an immense obstruction oftimber, sediment and debris which has formed in the Gwydir anabranch. There are a number oftheories as to how and when the Raft commenced, but it is generally agreed that its formationcoincided with settlement and land clearing at the end of the 19th century. Appreciable clearingof timber by ringbarking took place as settlers began to cultivate on the upper slopes of theValley, and led to an increased silt load being carried by the Gwydir. A sharply diminishingriver channel capacity at the point of transition into swampland, together with the rapidlyflattening bed gradient and accompanying drop in flow velocity, made this section of the riverthe perfect trap for water-borne debris which included logs, rubbish and silt. (Jeffcoat 1995)
Figure 24. The Gwydir Raft. (photo; Department of Land & Water Conservation, NSW)
5.5 Eroded gullies initiated by animal tracks, roads and drains
The habit of stock to continually move along the same paths, which slowly forms a network ofruts across the countryside, appears to have initiated the formation of many erosion gullies.Hamilton (1892) wrote of sheep and cattle tracks:
“The tracks made by these animals carry off the rainwater, and when there is a slight incline,these tracks deepen into gullies... Any one familiar with sheep runs in hilly country willremember the network of paths on the hillsides; and by the formation of these tracks, drainage islargely affected.”
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Even minor stock movements were observed to initiate gullies. Hamilton continued:
“ ... where the cattle of the settler cross a well grassed slope in any part of which is naturallymoist, immediate changes are effected. The surface waters begin their work at some small holemade by the hoof of an ox, and gradually enlarge to deepen it, (always working backwardtowards the hill) until a dry channel several feet deep is excavated. In this way thousands ofcubic feet of soil are carried into the low-lying valleys by streams in places where for ages therehas been no current or denudation.”
Trampling of stream banks by the hard hoofed livestock also increased the risk of erosion duringhigh flows.
Vehicle tracks worn by constant use were another source of disturbance, because vegetation wasworn away and a depression was formed which could capture and concentrate flow, resulting inincision. Where streams were directed under narrow culverts along roads or railway lines, theconcentration of flow also had the potential to cause channel incision.
The plough was also used to form surface drains through swampy meadows, and improve thepasture for sheep. The following account describes such practices at Yarralumla in the Canberraregion in the late 19th century;
“In the beginning much of his property was poor sheep country, being wet, flukey, cold flats...five hundred miles of plough furrows opened out and cleaned with shovels were run through thelands, from which all scrub, timber and refuse had previously been burned off. The work wasgreat, but so was the reward for all that poor country is now most excellent sheep land …”(Fitzhardinge 1941)
The risks of constructing these surface drains had been noted at a very early date:
“Drainage is very little practiced; indeed in many parts of the country it is not much needed;open ditches to carry off the surface-water is all that is required. The sides of these should beformed with a considerable slope, as the force of water is so great in heavy rains, that it willfrequently undermine and wash away the sides, and small ditches are by this means sometimesconverted into immense gullies.” (Atkinson 1826)
In summary, the initial formation of many erosion gullies was often catalysed by a localdisturbance to the soil surface, such as sheep and cattle tracks, vehicle tracks, or the constructionof drains through swampy meadows.
Roads cause erosion“The making of roads causes a great alteration of surface drainage. Everyone who has traveledmuch on bush roads must have seen deep gullies cut along the road sides by the rush of water inthe drainage channels on each side, and this of course acts in the same way as above.”(Hamilton 1892)
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Figure 25. Gully erosion along the gutter of a vehicle tracknext to a pine plantation in the Southern Tablelands, NSW.(photo; Anthony Scott)
Origin of incised channels on the southern tablelandsThe origin of individual incised channels can occasionally be related to specific events. Forexample, during the drought year of 1901 a mob of cattle spent some time on agistment in alarge paddock of oats north of Michelago, and the track they formed in walking to WaterholeCreek each day is now a large gully. Some incised channels resulted from early methods ofcultivation. In the days of the horse-drawn one or two furrow moldboard plough, crops werealways grown in the same paddocks commonly located on valley floors. The same procedurewas followed each year with a hollow ‘V’ being left at the end of a day’s work at the sameposition in the paddock. Over the years these hollows developed into quite distinct lineardepressions that tended to concentrate surface runoff and allow the formation of channels. Anumber of incised channels along gently sloping valley floors was probably initiated by thedraining of swamps. It was common practice around the turn of the century simply to plough afurrow along the valley axis thus concentrating flow and allowing the development of a gully.(Eyles 1977b)
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Figure 26. Sheet and rill erosion along a road-side near Gundagai, NSW. (photo; Anthony Scott)
Draining of swamps caused channel incision of Tarcutta CreekWith increased runoff caused by changes in land use, the main streams near Tarcutta (NSW)incised their courses and progressively destroyed the original chains of ponds and swamps. Inplaces the destruction of the swamps was accelerated by the deliberate burning of reed beds andby attempts to encourage channelisation of the flow. One such exercise occurred in the 1930s,when an extensive swamp near the junction of Umbango and Tarcutta Creeks was drained.Subsequent channel incision quickly scoured a deep channel through the swamp.(Page and Carden, 1998)
Sites of gully erosion at Wangrah CreekA survey plan made in 1842 shows a sequence of ponds in the channel of Wangrah Creek on theSouthern Tablelands (Prosser et al 1994). By 1910, portion plans of the catchment indicatedthe major valleys as ‘washed out gullies’ (Prosser 1991). Bridge abutments on the original road,constructed in the 1890s, indicate that gullies along Good Good and Limekiln Creeks were 2 to3 metres deep at the time this road was constructed.
None of the points of major gully initiation were at sites particularly susceptible to erosion, so itis likely that incision was a result of site specific disturbances, not catchment wide changes torunoff. It is only possible to speculate on what the specific causes were. Two points of incisionare sites where the original road crossed the valley. Other points possibly coincide with theconstruction of drains, a practice used at Wangrah Station in the late 19th century to supply waterto the vegetable gardens. (Prosser 1991)
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Figure 27. Gully erosion near Orange, NSW, 1962 (Mitchell Library, State Library of NSW)
5.6 The introduction of rabbits
Although rabbits had been introduced previously, it was the wild grey rabbits which ThomasAustin brought out from England in 1860 that acclimatized so successfully and rapidly spreadthroughout the countryside (Reeve 1988, Bolton 1981). In 1865 Austin had 20,000 rabbits onhis property near Geelong, and by 1874 they were spreading north into the Horsham district. Bythe end of the 1870s, they had crossed the border into South Australia and by 1880 were over theMurray and heading north across NSW (Bolton 1981; Jervis 1956; Kiddle 1931, cited by Driver1999). By 1886 they were reported in QLD. Between 1884 and 1886, the government ofVictoria spent £30,000 on a campaign of eradication, partly through poisoning and partlythrough a bounty, and although claims were made for 1,884,000 rabbits in two years, theycontinued to flourish. From the early 1880s canneries were established, and in the 1890sVictoria was exporting 1,500 tonnes of rabbit meat annually.
Many farmers erected netting along the boundaries of their properties and used poisoning andother methods of destruction. However, in most districts of the Murray-Darling Basin, rabbitshad reached plague proportions by the 1890s or early 1900s.
The main effect of the rabbit was to exacerbate the overgrazing already being caused by thesheep and cattle during dry periods. This left the land bare and prone to erosion from wind or
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water. In the semi-arid zone, rabbits also ringbarked edible trees and contributed to the loss ofperennial grasses and bushes.
Rabbit plague on the Steam Plains property in the Riverina“Rabbits were first known on Steam Plains in 1880, and in 1882, 29 scalps were paid for at 2s.6d each; in the same year 884 kangaroos and 136 emus were paid for at 1s each. In 1890 theproperty was rabbit netted on the boundaries, and continual but ineffective methods ofdestroying the pest were adopted, and the whole district became badly infested, it being nothingunusual to poison from ten to twelve thousand at one waterhole. The result was that during anydry period both the rabbits and sheep were underfed and the country was being eaten out. Itwas not fully realised what damage the rabbits were doing, but many of the edible trees wereringbarked and killed, and practically all bush and perennial grasses were killed.” (Kiddle1931, cited by Driver 1999)
Figure 28. On a property in the Albury-Corowa area, a farmhouse and shearing shed are surrounded bybare ground denuded by rabbits. Rabbit plagues continued throughout the first half of the 20th century,and were particularly bad after World War 2 in the late 1940s. Farmers and graziers had been away at thewar, unable to carry out normal trapping, shooting and poisoning, and rabbits swarmed aroundwaterholes like a seething carpet of brown fur (McKay 1976). This scene changed in 1950 when themyxomatosis virus was introduced to control the rabbit population. (drawing by Robert Ingpen, fromMcKay 1976. Reproduced courtesy of CSIRO)
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Rabbits ringbarking trees“In the drought of 1895, when all grass and herbage had disappeared, the rabbits in theWyalong district turned their attention to the bark of various shrubs and small trees, but thespecies which suffered most from these rodents was Myoporum deserti (Dogwood). The barkwas eaten off right round the stem and as far up as Bunny could reach when standing on twolegs.” (Cambage 1902)
Rabbits in the Upper Murrumbidgee catchmentAlthough stock numbers dropped in the early 20th century, grazing pressure did not decreasegreatly as rabbits were spreading rapidly throughout the catchment and began to reach plaguelevels in some areas. A report from the Cooma Express (May 2, 1902) describes the scenenoting that rabbits “.. raided even the orchards and ate the bark of the fruit trees, and utterlydestroyed the roots and foliage of ground plants”. By May 1902 lack of feed caused the rabbitsto invade Queanbeyan's suburban gardens (Franklin, 1978). By the early 1920s the rabbitnumbers seemed to be held in check, mainly by hard work with netting of fences, poisoning anddigging out warrens. (Gallagher 1989, and The Queanbeyan Age, Feb. 19, and March 21, 1924).
5.7 Expansion of cropping
The first crops planted by pioneer settlers tended to be vegetables and cereals for personal use,and hence only small areas of land were cultivated. In 1834 Lhotsky, for instance, mentioned anoutstation garden that contained cabbages and watermelons (Andrews 1979). Much of the earlycropping occurred on the rich humus soils of the swampy meadows or alluvial floodplains, andwhen disturbed by the plough they soon became some of the most unstable parts of thelandscape.
With the introduction of the Free Selection Acts of the 1860s and 1870s, the amount of croppingstarted to accelerate. Many selectors planted subsistence crops of cereals and vegetables on theirblocks, and the impact of the plough was soon taking effect. The ploughing of the land formedridges and furrows and if not properly managed, led to a concentration of flow and ultimatelythe formation of rills or gullies. The loose layer of soil was also prone to sheet erosion if a largestorm immediately followed ploughing.
It was only in the second half of the nineteenth century that the present wheat growing practicesstarted to evolve. In the Murray-Darling Basin, the expansion in cropping was dependent on thedevelopment of the railway network to provide a viable form of transport to markets. Also, withthe introduction of new strains of wheat, there was a movement away from the leached soils ofthe humid coastal regions to the extensive subhumid inland area of calcareous clays and loams(Jeans 1972, Robinson 1976). In south-eastern Australia the main period of expansion occurredbetween 1880 and 1930. In South Australia and New South Wales, late in the 19th century andup to the First World War, the wheat frontier was pushed well beyond its present limits, butoften with disastrous results, particularly during the drought of the 1890s. At this time, thefarming frontier was steadily transforming massive areas of grassland, mallee scrub and openwoodland into cropland.
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During the early 1900s further advances in farming methods and improvements in machinerywere made, including the general availability of the McKay Stripper Harvester and theintroduction of tractors. Increasing mechanisation reduced the labour costs of harvest andincreased the speed at which it could be carried out. During the 1920s and 30s the increasingnumbers of tractors combined with furrowed ploughs, allowed for a rapid agricultural expansionand this coincided with a growing worldwide demand for food (Jeans 1972, Hepworth andGraham 1985). Between 1920 and 1940, large areas of pasture land were converted to cropland,particularly on the ‘black soil’ plains of the Darling Downs in Queensland and the LiverpoolPlain in northern NSW.
Between the early 1880s and the 1920s, the use of ‘bare fallow’ in wheat production to increasesoil moisture, break down organic matter, and to control weeds, was actively promoted by theState Departments of Agriculture. Some even held district fallowing competitions, wherefallows were judged on moisture retention, tilth and freedom of weeds. Unfortunately, onsloping land this technique left the soils exposed to the forces of running water – every stormhad the potential to remove large quantities of topsoil. In a few hours of heavy rain, soil whichhad taken many thousands of years to form, was washed off the paddocks and down the neareststream. Similarly, on the plains, the loosened topsoils were quickly removed and carried awayby strong winds.
For instance, heavy rainfall in the summers of 1927-1930 caused severe erosion in the wheatgrowing areas of the south-west slopes of New South Wales;
“Land that ten years ago could be cultivated and drilled across is now in many instances cut bygullies 7 and 8 feet deep and 9 and 10 feet wide. The damage has to be seen to be believed.”(Clayton 1931)
The NSW Department of Agriculture was, however, reluctant to abandon fallowing as therecommended practice. In an article in the Agricultural Gazette of 1929 the Departmentadmitted that surface vegetation reduced erosion, but still concluded that any “drastic alteration”in the Departmental recommendation regarding fallowing in undulating country was “notadvisable” (Kerle 1929). It suggested ploughing on the contour and rotations as possiblesolutions.
The expansion of cropping, combined with the increasing use of machinery and the promotionof bare fallowing, led to a period of severe and widespread erosion throughout the fertile plainsof the Basin, particularly during the 1920s to 1940s.
Bare fallow – proclaimed advantages - 1890Bare fallow was promoted in the 1890 issue of the NSW Agricultural Gazette as a necessarypractice for wheat farmers (Pudney 1890). The advantages of a period of bare fallow after eachwheat crop were stated to be:
- Ploughing the land exposes the soil to air, sun and moisture which helps break upfragments of rocky mineral matter and release nutrients;
- Improves the natural formation of nitrates or ‘nitrification’ of the soil;- Increases the absorption of water, thus retaining more soil moisture for the nextcrop;
- Weeds germinate and are then ploughed into the soil, thus reducing the weedcontamination of the next crop.
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Expansion of cultivation in Australia in late 19th centuryBetween 1880 and 1900 the area under cultivation in Australia almost doubled, to 8,750,000acres (3,500,000 ha). This was principally due to the migration of wheat growing from theleached soils of the coastal regions to an extensive subhumid inland area of calcareous claysand loams, assisted by the trial and error development in South Australia of early maturingstrains of wheat to minimize the effects of the summer drought. Subsequently, in western NSW,William Farrer produced a number of successful new strains by the application of morescientific cross-breeding techniques, although his major achievement came from ‘Federation’wheat after the turn of the century. Novel implements were developed by the pioneer farmersthemselves, to clear, cultivate and harvest. But the new regions were less fertile and the newwheat strains normally lower yielding than those favoured before, so that increasingly largerareas were required to rest the land, while at the same time maintaining good returns to repayinvestment in mechanization. From the time they turned the first sod on the wheat frontier,pioneer settlers were hungrily searching for more land. In South Australia a widespreaddrought shook the confidence of the wheat farmers and some of them appealed in vain forGovernment assistance. …..Rain did not follow the plough, after all, and the frontier advancewas stalled and then repelled. (Powell 1976)
Fallowing -1895“We plough and fallow like our European forefathers. Moreover, before doing so, we feed offall the weeds and stubble, or rake them together and burn them, leaving ashes and cinders, to beblown away by the winds, and to be washed away by the floods, leaving the soil as bare as afloor…” (Tepper 1895)
Fallow erosion - 1929“One of the greatest problems confronting the wheat grower on undulating country is thewashing away or erosion of his fallow ground by heavy summer rains. It is frequently the casethat the ideal fallow to-day is, with the advent of a heavy storm, a network of irregular guttersto-morrow. More-over, a continuance of heavy storms may result in such huge gutters beingmade, that it is impossible to fill them in. It is common in such country to see watercourses thathad their origin in this way, and paddocks cut into many irregular shapes. The difficultiesencountered in such paddocks in ploughing, sowing, harvesting, &c, are apparent, and thecultivation paddocks are often considerably reduced in area.
“After continuous heavy summer rains, as in February 1928, it is common to see fallowpaddocks with extensive areas of subsoil showing through, the surface soil having beentransported to lower levels, and often into other paddocks, or to roadways, dams etc. Theamount of surface soil lost in this way is very considerable….
“Perhaps one of the most common sources of erosion and channeling of fallowed ground isploughing round a paddock irrespective of its contour, and ploughing out or deeply cultivatingthe corners. These provide the foundation for very severe erosion and the creation of hugegutters.” (from Kerle, 1929. WD Kerle was a senior agricultural instructor within the NSWGovernment.)
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Murrumbidgee River runs ‘liquid mud’ – 1914In 1914 the wheat growing fashion advocated by the Department of Agriculture was to growwheat on long fallow. At the time, the Junee, Ganmain and Coolamon area was regarded as theheart of the wheat farm area….. Houlaghan’s Creek drains some of the area and flows into theMurrumbidgee. A heavy storm dumped over four inches of rain over the catchment area in avery short time and it is not hard to imagine the result with about half the area under longfallow. The rolling country eroded and the river virtually ran liquid mud, rose about six feet ina few hours and fell again almost as quickly. The mud killed every living thing in the river. Fishlined the banks with their heads out of the water in the morning, and were all dead floatingupside down by lunch time. (Recollections by Max Leitch (1985). Max grew up on BulgaryStation, between Wagga Wagga and Narrandera on the Murrumbidgee River)
Soil erosion on 90ha farm in RiverinaA 90ha paddock in the Riverina, NSW was selected as a case study of soil erosion. Thepaddock had been severely affected by sheet, rill and gully erosion. Much of this erosionoccurred in the 1930s when the conventional wheat-fallow-wheat-fallow rotation was practised.In one incident, during either late summer or autumn, the paddock had been worked with aneight horse team and a mouldboard plough, and was under fallow awaiting the May sowing. Aheavy thunderstorm, in which a total precipitation of 125mm fell in a matter of hours, occurred.The storm devastated the paddock. On the more gently sloping area along the western boundaryso much sheet erosion occurred that the lower boundary fence had to be replaced.
By the early 1980s, when the paddock was studied, there were three large gullies, generallybetween 1m and 2m depth and 5m to 10m width across the top. There were also three smallergullies approx 0.5 metres deep and 5 metres wide. Another pronounced feature of the paddockwas the mature rills. These occurred over much of the area at spacings of as little as 5m to 20m.In the southern half of the paddock the rills were generally 5m in width at the top and varied indepth usually from 0.15m to 0.3m. Many of these latter rills formed continuous flow lines,approx 600m in length.
Sheet erosion had completely removed the Ao horizon from the soil profile. Evidence suggestedthat 2-8cm of topsoil had been lost with an estimated average of between 3-4cm. The totalextent of soil erosion was estimated at more than 97,000 tonnes which was equivalent to anaverage annual rate of 21.7 tonnes/ha/yr. (Ring 1982)
Cropland erodes on the Darling Downs – 1920s – 1940sA period of severe erosion on the Darling Downs is thought to have occurred between 1920 and1940 with the expansion of cropping across the ‘black-soil’ plains. Shallow working discimplements replaced the mouldboard plough, and together with the introduction of tractors,enabled farmers to cover greater areas in less time, producing a “better and finer” fallow.Summer bare fallowing of land was seen as an essential part of winter crop production, as itallowed for the storing of summer rainfall in the soil to meet the needs of winter crops.However, the exposure of bare, and finely worked fallows to the high intensity summer stormsexperienced locally, was a dangerous practice and resulted in serious and widespread erosion.Land was often stripped to cultivation depth with gully formation in some areas, and massivedeposition of eroded soil in others. (Skinner et al 1977)
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Erosion of cropping land in South Australia - 1937“The winter of 1937 was very wet, and one paddock on the property (near Tarlee, SA) was justsown when a very heavy rain fell, which washed a lot of gutters. As soon as it was dry enoughthe gutters were sown again, and yet another heavy rain fell, which washed all the soil that hadbeen loosened with re-sowing. During the winter, heavy showers fell, and by harvest , all of thegutters were creeks, and it was necessary to reap the crop in a lot of small patches. This wasmost annoying. After the stubble had been burnt, and the seriousness of the position wasrevealed, it was obvious that simply filling in the gutters would be so much lost time, as theywould have probably washed out again in the next heavy rain. Anyhow, the job of carting soil tothe creeks would have been very expensive. Therefore, the creeks were simply ploughed in, andcontour banks were constructed.” (from CR Kelly, 1940. Although the farm described above isjust outside the Murray-Darling Basin, the problems encountered were experienced by farmersthroughout Eastern Australia.)
Figure 29. This cultivated paddock in the Darling Downs, QLD, suffered heavylosses of topsoil during a high intensity thunderstorm. (photo; L Coxen, DNR&M QLD)
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5.8 The effects of droughts and floods
When the early settlers were establishing their farms, they were generally unaware of theclimatic extremes of their local area. Stocking rates were often set in better seasons when therewas an abundance of grass. However during extended droughts, severe overgrazing wouldoccur, leaving the ground bare and vulnerable to erosion. For instance, William Brodribb wroteof a drought in the Monaro district on the Southern Tablelands, that extended from 1846 to1848; “For upwards of two years very little rain had fallen; the whole country looked like adesert; I began to fancy the roots of the grass were destroyed.” (Brodribb 1883)
Alfred McFarland, the district court judge in the Monaro district also described thetransformation during drought time; “But there are other sides to the picture which should alsobe given; for it must not be supposed that Manaro is always green... During a drought the faceof the land is changed still more; there is scarcely a blade of grass to be seen, the hills areglistening with red iron stone, the creeks are dry, most of the rivers are shrivelled up, and thesheep and cattle half dead from starvation, or away on the mountains.. (McFarland 1872)
The drought of the late 1840s in the Monaro district was followed by a series of wet years, andin 1851 the Reverend WB Clarke observed severe erosion of a small stream near Bredbo whichwas caused by a short but intense storm;
“I measured excavations at the stockyard behind the house, which had formed by the rain thatfell from 6 to 8 p.m. on 2nd January, 1851, and by which blocks of granite and prophery (sic),some two cubic feet in contents, with earth and pebbles, were removed, leaving a hollow in oneplace 12 feet deep, 8 to 30 feet wide, and 272 long and another 2 to 3 feet deep, 17 wide, and282 feet long, with minor excavations. I calculated that nearly 200,000 cubic feet had thus beenremoved from little Stockyard Creek.” (Clarke 1860)
In the Upper Murrumbidgee severe flooding occurred six times in the 19-year period between1851 and 1870, including the devastating flood of 1852 which wiped out the township ofGundagai. A further two - one in 1853 and another in 1870 - may have approached or exceededthat level (Starr et al 1999).
These flood events would have been more than adequate to trigger extensive erosion. Theextreme nature of some of the events suggests that many gully networks may have eroded totheir headward extent during this period. In addition, the current channel dimensions of somegullies may well have been established then (Starr et al 1999).
Lost £247 and 10,000 tons of soil in 15 minutesA 15 minute storm yielding 90 points (23 mm) of rain cost a Bell (in the Darling Downs) farmer£247 and 10,000 tons of rich topsoil. This loss occurred because the newly planted 80 acre (32ha) paddock in fine tilth was not protected by contour banks. After the storm, an inspectionshowed that, in a quarter of an hour, a sheet of topsoil varying in thickness from ½ inch to 2inches (12mm to 50 mm) was stripped off. (Hoogvliet 1965)
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Drastic changes to the Murrumbidgee River in the great flood of 1852The Murrumbidgee River at Lanyon Estate (about 30km south of Canberra), during JamesWright’s occupancy (from 1833 to 1847), consisted of large deep water holes, between whichthe stream flowed gently over gravel beds during normal summer flow. Some of the holes wereso deep that when two of the longest bamboo sticks were joined together they would not touchthe bottom. The river abounded with fish and water fowl, it is on record that Michael Gallagherlanded a fish that was so large that when a sapling passed through its gills and carried on theshoulders of two men the tail of the fish dragged on the ground. It was a giant Murray Cod; theyinhabited the river and were known to reach weights of over 100 lbs. The river was lined withlarge gum and mimosa trees along its gently sloping banks.
This peaceful scene altered dramatically after the record flood of 1852, the flood that has gonedown in history as the Great Gundagai flood which caused the deaths of over ninety persons inthat town. The bed of the river doubled in width, steep banks arose where formerly there hadbeen only gentle sloping banks. Many of the giant trees that lined the stream were swept awayand the pebbly bed of the stream disappeared, being covered by large quantities of sand whichcompletely filled the whole bed of the river for several miles. The deep holes disappeared andthe large fish population were swept away and never returned to this stretch of the river.Another large flood in 1860, which rose to a height of only one foot below the 1852 height,completed the destruction of the original river structure. Many large floods have occurred overthe ensuing years, bringing large quantities of sand to choke the stream. During the 1970s theriver was surveyed to assess the quantity of sand available to be used in the Canberraconstruction programme. Probing of the river located many of the original holes, in some casesthe probes disclosed depths of sand to over thirty feet. (from ‘The Lanyon Saga’ by BruceMoore, 1982, and the Queanbeyan Observer, 29/3/1895.)
Drought of 1895-1915 in Queanbeyan district and its importance to channel incisionGrazing pressure must have been especially severe during the drought of 1895-1915.Throughout this period Queanbeyan received more than the long term (1871-1973) mean annualrainfall in only three years and for the first time rabbits were competing with domestic stock forfeed. Destruction of the vegetation was so widespread that wind erosion became a problem.Dust storms were reported in Cooma on three occasions in 1896-97, at Gundaroo in 1902 and‘sand drifts were a common phenomena on parts of the Cooma-Bredbo Road and the adjacentland’. Channel incision is most effectively triggered by rainfall when the ground surface is bareof vegetation and exposed to raindrop impact and sheet wash. A number of violent summerstorms during or at the end of severe droughts were recorded in this district. Gundaroo had itsown great flood after a terrific thunderstorm on 2 March 1894, although the district was thengripped by the worst drought experienced.(Information from Durham 1961, Lea-Scarlett 1972, Eyles 1977b)
Creightons Creek – flood in 1916 incised channelsMajor changes in the upper catchment of Creightons Creek near Euroa, northern Victoria,coincided with the 1916 flood, one of the largest on record. Anecdotal evidence suggests that theflood resulted in massive channel incision on Creightons Creek above the Ramages Creekjunction. This event must have scoured out large volumes of sediment and had a catastrophicimpact downstream. (Davis and Finlayson 2000)
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Heavy rainstorm in the Cowra District – January 1981Very heavy rainfall events are something that every Soil Conservationist fears, for many verygood reasons. One such storm occurred in the Cowra District (NSW) during January 1981, in acatchment known locally as the Nanami Valley. Although the storm lasted only 30 minutes, onelandholder recorded a fall of 90 millimetres during that period. The return period for a storm ofthis magnitude is certainly well in excess of 1 in 100 years. Considerable soil erosion occurredon low lying cultivation land inundated by floodwaters. This land had previously been cultivatedand topsoil was stripped off to a plough depth of approximately 10 cm. The majority of suchcountry in the catchment escaped serious damage only because cultivation had not commencedin earnest. Those areas which were cultivated suffered severe sheet and rill erosion, while thosenot cultivated still suffered moderate sheet erosion because of a lack of ground cover. Grazinglands higher in the catchment, which had varying amounts of erosion on them, suffered severesheeting and extension of existing gully erosion. The erosion led to considerable silt depositionin water storages throughout the catchment. (Colless 1983)
Figure 30. May 28, 1925. A tremendous flood roars defiance, spilling over Burrinjuck Dam, on theMurrumbidgee River. During floods such as this, massive quantities of soil are eroded from the uppercatchment and transported downstream. (photo; Mitchell Library, State Library of New South Wales)
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5.9 Land degradation on the Western Plains
Settlement of the western plains followed the explorations of the first half of the 19th century. Bythe 1840s, settlement had extended along the frontages of the Barwon, Murray and the lowerreaches of the Murrumbidgee and Lachlan Rivers. By the 1850s, settlers had also occupied theDarling River frontages. Initially, the hinterland away from the rivers was occupied only on asporadic basis in favourable seasons.
The early period of settlement was characterized by unfenced pastoral runs, meat productionfrom sheep and cattle, and homesteads and towns scattered along river frontages.
In the 1870s, occupation of the hinterland became possible with the introduction of well, boreand tank sinking techniques. Favourable seasons, higher wool prices and improved transport byrail and river steamboat, led to a change in production from meat to wool, causing a decline incattle numbers.
State government policies tended strongly towards closer settlement in rural areas and in NSWthe 1884 Crown Lands Act initiated the compulsory subdivision and resumption of almost halfthe acreage of pastoral holdings in the western district. The redistribution of this land was aimedat establishing a permanent rural population. This tended to increase stocking pressure on theland, as new settlers moved in and tried to make a living on smaller sized farms. But in the earlyto mid 1880s came the first reports of invasion by woody shrubs and also of rabbit infestation(Jervis 1956). This was followed by drought and depressed wool prices, and the burgeoningpastoral industry started to collapse in the early 1890s. Severe economic depression coupledwith severe and prolonged drought brought the closure of many stations. This era of pastoralismleft a considerable legacy of land degradation. Overstocking of the western districts resulted insevere soil erosion and the spread of the ‘scalded’ plains.
Apart from the extremely high stock numbers, and a rapid increase in rabbit numbers to plagueproportions during this period, the size of the holdings and the state of development of the landmade conservative management difficult. Large numbers of livestock had to be concentrated ona limited number of watering places causing excessive destruction of the vegetation andtrampling of the soil for a considerable distance around the watering point. The mustering andmovement of large mobs into holding paddocks for shearing and other operations wouldlikewise cause severe depletion of vegetation cover. Under such conditions of stockmanagement, the onset of drought would leave these points of heavy stock concentration veryvulnerable to erosion, and it is probable that much of the severe erosion recorded in the past hasresulted from this cause.
Evidence to a Royal Commission in 1901 provides a graphic description of huge areas ofwindswept and scalded land, with sand drift covering fences, water troughs, stock yards andeven silting up earthen tanks. Extensive areas of the edible saltbushes and bluebushes, oftenfound on the more erodible soils, were also wiped out.
Although the formation of scalds has been largely attributed to wind erosion, in some areaswater erosion has also been responsible (Warren 1965, Beadle 1945). Scouring by water hasresulted in sheet erosion on flatter ground and the gullying of streamlines on undulating or hillycountry. (Fanning 1999, Williams et al 1991).
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Eating the haystack – destruction of perennials“In its virgin state with the saltbush and other edible bushes in their prime, there was hardly alimit, except as regards water, in the opinion of settlers there to what the country would carry,and in many cases it was stocked accordingly, but they forgot in doing this that they were eatingthe haystack, and there was no crop growing to building another. Then the rabbits camealong.” (veteran inspector of stations for Dalgetys, providing evidence to the RoyalCommission of Enquiry 1901, cited by Bolton 1981)
The start of land degradation in the 1870sGiven increasing stock numbers, it is not surprising that land degradation began to occur. In1876 GH Reid contrasted stocked and unstocked land and noted the already obvious trendtowards soil compaction and increased runoff;“The soil of the plains is loose, and in dry weather the grass nearly disappears; but as thecountry becomes stocked the tread of the animal binds the surface; the grass acquires closenessand strength, and the saltbush gives way to the characteristics of the slopes. As a consequence,the rain that falls begins to form watercourses, waterholes become creeks, and the streamsincrease in volume.” (Reid 1876 cited by Duyker 1983)
Grazing pressure, rabbits and drought cause widespread degradation of western landsIn 1891 there were 14 million sheep in the Western Division of NSW but this substantialpopulation soon found itself in desperate competition for pasture with the newly emergent rabbitpest. When the extended drought of the 1890s hit the area, it soon became clear that the WesternDivision was grossly overstocked. As the Royal Commission of 1901 reported, “The result ofthe united effort of sheep and rabbit has, it is only too plain, been terribly disastrous”. TheRoyal Commission also found that the effects of rabbits and overstocking had not only resultedin the “destruction of almost all the vegetation on the face of the drought-stricken country”, butcombined with the prevailing westerly winds had produced “calamitous” sand storms and sanddrifts. Not only did scrub infestation reduce the amount of pasture available to stock, but withdisappearing grass, rainfall run-off of between 30-40% caused extensive sheet erosion andrilling of surface soil. (From Duyker 1983)
Erosion in arid western NSWGullying of the valley floors and associated processes of land degradation in the arid rangelandsof western NSW appear to have been initiated by the change in landcover associated with theintroduction of domestic animals in the mid nineteenth century. The loss of groundcover andcutting of shrubs and trees triggered a shift in the hydrologic regime on the catchment slopes andincreased surface runoff. The associated increase in erosiveness of flows on the slopes resultedin widespread stripping of surface alluvium from the valley floors, which today are severelydegraded and subject to extremely high rates of soil loss. (Fanning 1999)
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Clearing of trees in the Western Division of NSWMining resulted in intensive clearing around some towns in the Western Division of NSW. Attheir peak in 1884, the smelters in Cobar were consuming 70,000 tons of wood each year andsupplies near the town were so scarce that a private railway was constructed almost 18kilometres east to search out and haul wood (Forestry Commission of NSW 1988). By 1889, itwas estimated that the Cobar smelters had consumed 850,000 tons of wood (Jervis 1956b).
Another aspect of timber use in the Western Division was the intensive cutting to fuel the manysteamboats which plied the major rivers. The boilers of the larger boats used up to a tonne ofwood in an hour and enormous quantities were needed to keep the trade operating with fulltimegangs maintaining supply depots along the rivers (Mudie 1961).
A common activity which accompanied the introduction of sheep into the Western Division wasringbarking; the most widespread form of clearing in the Western Division before the 1970s.Ringbarking reduces the density of live trees and improves the carrying capacity for stock.
Dryland cropping has also been a major reason for clearing in the region. Commercial wheatgrowing in the Western Division dates back to the 1890s but was not attempted on a large scaleuntil the post-war settlements of the 1920s. Cropping expanded after the late 1950s with the useof bulldozers and chains to clear dense timber. Further expansion was encouraged by theremoval of wheat quotas in the early 1970s, development of bigger and more fuel efficientmachinery and increased drought tolerance and yield of crop varieties.
In some areas clearing was still proceeding rapidly in the 1980s and early 90s, the main reasonsbeing for dryland cultivation and thinning for improved carrying capacity.(Information from Pressey 1990)
Degradation of western lands“Some of the greatest mistakes in exploiting the land were made in the west. Most of thepastoralists took up land during a run of good seasons that lasted from 1865 to 1883, and didnot realize that their sheep were slowly eating up their drought reserves. When the saltbushstarted to disappear the pastoralists hailed it as a sign of the desert retreating under the goodinfluence of their livestock. In reality it was a disaster. Selective grazing had eaten away thedrought reserves that lay stored in the saltbushes and Mitchell grass tussocks. Livestock died intheir millions once that buffer against dry seasons were destroyed. The early settlers had notadjusted their stocking rates to the slow growth rate of western fodder plants. Suddenly thecapital was gone and, as one observer put it, they had eaten their haystack.
Ruin to people, their livestock and the land was all that resulted and by 1894 eight million acresin the Western Division had been abandoned. The Royal Commission to Inquire into theCondition of the Crown Tenants of the Western Division held in 1900-01 took evidence thatshowed what a social and environmental failure attempts at closer settlement had been.”(Breckwoldt 1988)
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Impact of settlement debatedWhile the impact of settlement upon the character of the plains was never denied, the precisenature of that impact was vigorously debated over the years. Broadly, the protagonists formedtwo camps, one suggesting an improvement and the other a deterioration of the natural, ie pre-white settlement, conditions. The advocates, such as Rankin (1876), stated that the“consequence [of settlement on the plains] is nearly always more grass and more water – thepasture thickens, dry creeks fill, and swamps become standing lagoons.” The pessimists agreed,but added riders that the hooves were cleft, thus while the soil was consolidated it formedhardpan, increased runoff meant greater soil erosion, and the reservoirs were indeed filled, butwith silt. (From Heathcote 1965)
The deterioration of pastoral country - 1900“There is no doubt that over-stocking has ruined hundreds of thousands of acres of land in thepast, and the process is still going on. Take the lands bordering the Western Division – sayfrom Nyngan – and keep east of the Bogan, you will find that where once there were thousandsof acres of saltbush, now it is only found in the horse paddocks. The same disappearance istaking place on the Marra and Macquarie River country. …. What can one say to the recklessdestruction of edible scrub? … Every year sees the scalded plains growing bigger and bigger,every rainfall sees the surface soil swept away, leaving a sour subsoil behind, for the want ofplant-life to bind the loose surface soil together. The remedy I would suggest is light stocking –we must recognize that saltbush country is very light carrying country.” (Grigg 1900)
The western lands – their degradation in the late 19th century(This article was written during the 1895-1902 drought)“The present condition of the vast area of our western lands, as compared with its primevalcondition, when the aboriginal, kangaroo and emu reigned supreme, points to a period ofdeterioration unexampled in the history of New South Wales. In the early days of pastoraloccupation the pioneers found ample scope to depasture their scanty herds upon virgin pasturesof the west, which were looked upon at that time as some of the most profitable pasturesthroughout the country. Within the last decade the high opinion formerly held by the leadingpastoralists has been changed, to the extent that the once coveted western properties have inmany cases been abandoned by their former holders, and many millions of acres, under theirpresent condition, are beyond the scope of profitable occupation…..
In the early days of settlement, the cattle and sheep were kept almost solely upon the riverfrontages, they only going back into the red country when the rainfall allowed sufficient watersupply in shallow cowals and gilgais, and returning when the conditions were not so favourable.…When the means of communication were improved by the construction of railways etc, waterconservation by means of excavations and dams was made possible, thus enabling land whichwas valueless for the greater part of the year to be continuously stocked. From that period thedeterioration of the country, especially the red country, set in. … In places unprotected from theperpetual summer winds, and in situations calculated to allow excessive weathering, the everincreasing scalded plain consisting of a bared subsoil is to be found. All these are too familiarlandmarks, resulting from the mistakes of the past, and calculated to teach valuable lessons tothose willing to listen to the voice and teachings of Nature. ….Droughts in conjunction withoverstocking have been the principal factors, and the pioneers had not the severe lessons of thelast seventeen years to warn them.” (Peacock 1900)
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Degradation of the Warrego district in early 1880sThere were signs by 1883 that the Warrego vegetation was showing the effects of continuousstocking. The changes were the more serious since they were affecting the best country, thealluvial frontages. Here, where stock had been grazed longest, the extensive grass and saltbushplains showed some deterioration. The Darling and Warrego frontages dismayed Nisbet in1881; “The grass seems to go away utterly, there is no saltbush or cottonbush anywhere insight of the frontage and the paddocks which have been any way heavily stocked are as bare asthe roadway.” (Nisbet 1912, cited by Heathcote 1965)
Post-European Changes in Creeks of semi-arid rangelands, ‘Polpah Station’, western New SouthWalesIn the 1850s, Europeans introduced domestic stock into the semi-arid environment of PolpahStation near Wilcannia, where precipitation is irregular and highly variable. Settlement initiallycentred on the (almost) perennial rivers and a few waterholes. These were quickly augmentedby ground tanks and wells. For a short time, stock numbers rose very steeply until graziers wererudely awakened to the harsh realities of semi-arid ecosystems. The large biomass of perennialgrasses, herbs and small shrubs belied the very low annual productivity. Some watering pointscarried over 15,000 sheep which denuded circular areas of up to 10 km across. Palatable shrubswere lopped to provide feed for starving stock. Other trees and large shrubs were felled to fireboilers which powered steam pumps on the wells, and for fences.
By the 1890s, the lethal combination of drought and too many stock had effectively removed allthe feed. Up to 50% of the sheep died from starvation. Subsequently, stock numbers have neverrecovered to such levels.
Creeks on the property exhibit evidence of major channel changes over the last century, andlonger. Earth dams constructed in the 1880s and early 1890s were silting up badly by the late1890s. Buried fences also indicate considerable sedimentation on the floodplains. (Pickard1994)
Erosion in central western NSWErosion and sedimentation was studied in the Sandy Creek catchment, in the Belarabon Ranges,east of Wilcannia in central western NSW. The exposure of root systems indicates that the mostrecent and presently active period of erosion was initiated during the life of still living pine andeucalypt trees. Other evidence indicates that logging of pine also preceded the erosion of thiscatchment. Since then, the meandering ephemeral streams have incised and migrated laterallythroughout their length. The typical channel shape has changed from a stable shallow dish-shaped profile with presumably a stable bed, to an entrenched gully with a mobile sandy bed andvertical to undercut walls on one or both banks. Networks of active tributary gullies are alsocommon. Gullying is confined to the sandy sedimentary fill in the valleys.
The switch to the current erosional phase seems to be firmly linked to about the time of arrivalof the pastoral industry late last century. Vegetation depletion, soil structural breakdown, andchanneling of water along sheep tracks were probably important in triggering erosion. However,it may also reflect a change in drought frequency, or in the seasonal incidence of rainfall.(Williams et al 1991)
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6. The campaign for soil conservation
6.1 Setting up Agricultural Colleges and Departments
In 1882 Roseworthy Agricultural College was established in South Australia. This was followedin 1886 by the Dookie Agricultural College in Victoria, in 1888 by Hawkesbury AgriculturalCollege in NSW, and in 1897 by the Hermitage Research Station in Warwick, Queensland.Agricultural development was being put on a new scientific basis. In the dozen years before1900 every State government of Australia also set up a Department of Agriculture, whichincluded among their functions, the spread of information about sound farming practices (Bolton1981). In 1910 Sydney University’s Department of Agriculture was established and in 1926 theapplication of science to primary industry was given a great boost by the establishment of theCouncil for Scientific and Industrial Research.
The main task of the agricultural colleges and State Departments was to enhance primaryproduction by carrying out research and to pass on the results to farmers through trainedextension officers. This preoccupation with increasing production led to some early mistakes,such as the ‘bare fallow’ cropping technique, which caused high rates of soil erosion oncropping land. Gradually, however, the more discerning members of the farming and scientificcommunity started to question whether increased crop yields could be sustained when the basicresource upon which they depended, the soil, was being washed and blown away. There wasalso a slow but increasing awareness that the capacities of some dams were being threatened byhigh rates of siltation.
6.2 NSW sets up Soil Conservation Service
In the late 1920s, Sam Clayton, the senior experimentalist at the Department of Agricultureexperiment farm in Cowra, became acutely aware of the serious soil erosion throughout thewheatlands along the western slopes of NSW (Breckwoldt 1988). Despite reservations frommany of his colleagues, he began constructing contour banks in eroded wheat paddocks atCowra Experiment Farm to demonstrate the principles of soil conservation to farmers. In 1930Clayton organised the first soil conservation field day in Australia, and then continued hiscampaign by holding lectures in country towns and writing articles for newspapers and theAgricultural Gazette. Through Clayton’s work and publicity, along with the heavy dust stormsthrown up by the summer westerlies, the public at large came to realize that much of the NewSouth Wales wheatbelt’s topsoil was being steadily lost. Moves towards comprehensive soilconservation legislation began in NSW with the Cabinet appointment of a soil erosioncommittee in 1933, which included Sam Clayton. This committee travelled extensively in NewSouth Wales and also gathered information on similar problems in the USA and Canada. Alsoin 1933, the NSW Minister for Mines and Forests, Roy Vincent, organized the first conferenceon soil erosion, and in his opening address stated;
“Because of man’s destruction of nature’s protection against the elements the plain has becomedesert and the hill a barren forbidding mass of rock – a monument not to earlier man’swantonness, but rather to his tragic ignorance.”
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The social climate was now ready for some major government initiatives to combat soil erosion,and in 1937 a soil conservation bill was introduced into NSW Parliament. But there was stillsome opposition, mainly from members of parliament who believed that farmers had a right todo what they liked on their own land. For instance, the Member for Liverpool Plains arguedthat soil erosion merely assisted the development of better soils elsewhere (Breckwoldt 1988).The bill was finally passed in 1938 and the Soil Conservation Service was formed.
One of the first tasks of the newly formed Soil Conservation Service was to provide anassessment of erosion on a statewide basis, and identify the worst affected areas. An erosionsurvey of the Central and Eastern Zones of NSW was carried out in 1941-43, and a summary ofthe results are presented below;
District Severegullyerosion(%)
ModerateGullyerosion(%)
Sheeterosion(%)
Moderatewinderosion(%)
Severewinderosion(%)
Noappreciableerosion(%)
Total
North CoastCentral CoastSouth CoastHunter V.
0.00.40.12.4
0.44.73.636.2
29.120.29.219.4
0.00.00.00.0
0.00.00.00.0
70.574.787.142.0
100100100100
Total Coast 0.7 10.3 21.8 0.0 0.0 67.2 100North TablelandsCentral TablelandsSouth Tablelands
0.10.31.0
23.440.830.6
31.716.129.9
0.00.00.0
0.00.00.0
44.842.838.5
100100100
Total Tablelands 0.6 31.7 26.3 0.0 0.0 41.4 100North west SlopesCentral west SlopesSouth west slopes
1.70.20.2
35.026.035.6
19.238.317.3
5.82.30.1
0.10.30.0
38.232.946.8
100100100
Total Slopes 0.8 32.1 25.3 3.4 0.1 38.3 100North west plainsCentral west plainsSouth west plains
0.20.00.0
1.42.10.7
2.830.95.3
10.744.927.9
2.30.81.3
82.621.364.8
100100100
Total Plains 0.1 1.3 12.5 27.9 1.5 56.7 100Grand total forcentral and easternDivisions
0.5 16.6 20.4 10.3 0.5 51.7 100
Kaleski published these results in 1945, and concluded that; “Only 51.7% or a little over halfthe area of the Eastern and Central Divisions is free from accelerating erosion.”
Another task of the newly formed Service was to set up research stations where new methods oferosion control could be trailed and field days could be held to demonstrate these methods to thefarming community. Exclosure plots were also set up by fencing off plots along travelling stockroutes. These were used to study natural regeneration in the absence of rabbits and livestock.Grazing trials were also set up and these were often placed along railway lines so that peopletravelling to regional towns or Sydney could view the results (Breckwoldt 1988). By the end ofthe 1940s there was increasing awareness of alternative approaches to soil conservation and landmanagement, and these were influencing the making and implementation of policy at the stateand federal level. Change was in the air.
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Soil erosion depletes soil fertility - 1931“Soil erosion is a cause of grave concern to farmers in many parts of Australia, and is already aserious problem on undulating land. The fertility of many of our soils is being graduallydepleted by the slow removal of plant food as the result of cropping, but many soils are alsobeing damaged much more rapidly by the washing away of the surface soil by rain water. It hasbeen stated that in many instances twenty-one times as much plant food is washed away fromcultivated land by rain water as is removed by cropping.
This serious damage has been allowed to proceed unchecked and often unnoticed until in manycases the land has been robbed of its original fertility; sheet erosion has often taken off thevaluable surface layer before the damage has been noticed. Investigations have shown that theparticles removed by washing are the richest constituents of the soil.” (Clayton 1931)
Damage done in NSW - 1931“Sheet washing is serious on much of the wheat country of this State, and severe gullying even isalready apparent in many districts. At the present time on the fertile country of the South-western Slopes, deep gullies are to be seen that have been cut by water in the last two years.Land that ten years ago could be cultivated and drilled across is now in many instances cut bygullies 7 and 8 feet deep and 9 or 10 feet wide. ….
The problem is a serious one, and there is very urgent need for action, or thousands of acres ofthe best wheat lands in the state will be washed and gullied into barren wastes. Fortunately, apractical scheme of control, viz., the use of broad-base contour drains, has been evolved – onethat is widely adopted in the United States, and which has been tested on undulating wheatcountry which is gullying badly at Cowra Experiment farm.” (Clayton 1931)
Soil Erosion - 1941“The effects of severe thrashing our lands have been taking are becoming obvious to even theless observant. They can be seen in the cultivation lands cut by deep gullies, the bare anderoded grazing lands, the soil and erosional debris washed from hills overcleared of trees andovergrazed, the stone surfaced areas where once was deep rich soil, gullied roadsides and thefailing rivers and creeks, once deep, now shallow, often dry and with their beds filled up withsand and gravel….
Erosion control is essential if the rural industries of NSW are to be permanent and profitableand if the land is to provide a satisfactory standard of living for the people. ….
There is a fundamental cause of the serious proportions which erosion has already assumed inthis country. It lies in our attitude towards the land. It has been exploitary, our land use has notoften been wise. Those who love the land fear that unless this national and individual attitudetowards it is changed our hopes of national survival and prosperity can never be fulfilled. It isessential that we should understand how vital is the conservation of the soil and of the streams.
There is a need for careful planning in our development and use of the land if erosion is to bechecked. The need for planning is greater because the wrong thing has been frequently andrather thoroughly done, and the ill effects are now becoming very noticeable….” (Sam Clayton,Director of Soil Conservation Service, NSW, 1941)
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Figure 31. Gully erosion near Gulgong, 1945. (Mitchell Library, State Library of NSW)
6.3 Soil Conservation Board established in Victoria
Sand drift was noted in the Victorian Mallee district as early as 1878, and in 1892 acorrespondent in the Victorian Naturalist wrote of districts where bare dunes overwhelmedpasture formerly covered with she-oaks and blackwoods (Thompson 1979). In 1917 theVictorian Ministry for Public Works set up a committee to prepare a report on the effects oferosion, but nothing followed.
In about 1921, erosion in water supply catchments and consequent siltation of reservoirs becamea live matter (Thompson 1979). In 1925, the River Murray Commission requested that action betaken to prevent destruction of forests on Crown lands in the catchment of the Hume Dam, butlittle action was taken (Mitchell 1978).
Meanwhile the Mallee district was being taken up by wheat farmers who were slow to recognizethat the practices which had served them well in the Wimmera were not suited to the newenvironment. The rotational system of burn, fallow, crop and burn again, exhausted the humusof the soil, and the pressure of debt led the farmers to resort to over-frequent cropping. Theresulting sand drifts flowed over the roads and railway lines and blocked irrigation channels(Bolton 1981).
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The droughts of 1929-31 intensified the wind erosion right throughout the Mallee, and manymiles of stock and domestic water supply channels were filled with blown sand. Public andpolitical awareness increased dramatically as dust storms moved across Victoria.
A growing realization of the importance of soil erosion in relation to the national economy, ledto agitation by various public organizations, government departments and members ofParliament, that steps be taken towards its control.
In 1933 The State Rivers and Water Supply Commission had spent over £100,000 clearing sandfrom watercourses and irrigation channels in the Mallee district. That was a substantial piece oftaxpayers’ money. In the same year the ‘Sand-Drift Committee’ was appointed to investigateand report on the problem of wind erosion in the Mallee.
Yet when Victoria’s premier, Mr Albert Dunstan, was taken on a tour of the Mallee in 1935 toinvestigate the damage, he returned to Melbourne and stated; “I saw no erosion there”. The presspromptly labeled him “Albert the Ostrich” since his head must have been buried in the sand notto have noticed it. However, it is more likely that Dunstan, an experienced farmer himself, wassimply reluctant to admit that the agricultural development of the Mallee region had caused thisproblem.
In August 1936, soil erosion was one of the subjects discussed by a conference ofCommonwealth and State Ministers in Adelaide. The conference decided that all StateGovernments should be asked to form soil erosion committees.
Following this, in 1937, the Victorian Government appointed a committee to enquire into theincidence of soil erosion in Victoria. Comprehensive inspections of soil erosion of all kindsthroughout the state were made and the various measures that were being used by thelandowners and Departments, in their endeavours to slow the loss of soil and to prevent siltation,were noted. The committee’s report, submitted in 1938, depicted startling evidence of gully,sheet and river erosion and made several recommendations to the Government. However, onceagain no action was taken. The recommendations of this committee were reinforced by asymposium on soil erosion in Victoria, which was organized by a group of concerned surveyors,engineers and agricultural scientists in 1939. Also in 1939, the findings of the RoyalCommission investigating the catastrophic bushfires of that year, were released. In his report,Justice Stretton gave his opinion that the rapid acceleration of erosion after these bushfires wasdue to poor land management. He recommended the appointment of a committee of experts tohelp develop better land management practices.
Despite the increasing body of evidence, the Premier was still reluctant to act, and it tookstrenuous political pressure, notably from Harold Henslow, the Country Party nominee on theState Rivers and Water Supply Commission, before Dunstan yielded (Thompson 1979). TheSoil Conservation Act was finally passed by Parliament in 1940 and the Soil ConservationBoard was established.
After a slow start due to a lack of both funds and staff during the Second World War, the Boardset up demonstration sites, held field days, educated and advised farmers, and assisted with soilconservation works. In 1946, Judge Stretton was appointed a Royal Commissioner to inquireinto forest grazing. In the introduction to his report, Judge Stretton stated;
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“Destroy your forests and your water will destroy your soil. Destroy your soil and you destroyyour forests and your water supply. Destroy the sources of your water storages and your forestand soil will vanish.”
As a result of this Royal Commission, in 1949 new legislation was passed through Parliamentand the Soil Conservation Board was replaced with the Soil Conservation Authority. TheAuthority was given wider and firmer powers than the Board, both in respect to the carrying outof soil conservation works and in implementing other controls aimed at achieving soilconservation.
After a little more than a century of continuous degradation of its soil and water resources,Victoria was finally taking steps towards a practical approach to soil conservation.
It is interesting to note that it was the State Rivers and Water Supply Commission, and to alesser extent the Forests Commission, which had most actively sought the appointment of a soilconservation organization. This was due to a concern about the cost of digging out the sandfrom water supply channels in the Mallee District, and also the siltation of water supplyreservoirs. The Department of Agriculture had shown much less interest and apparently sawlittle need for the creation of such a body.
Figure 32. A dust storm approaching Mildura, Victoria in 1938. Public and political awarenessincreased dramatically as dust storms moved across Victoria in the 1920s and 30s. (Reproducedcourtesy of Museum Victoria)
Soil erosion in Victoria - 1949“We could not have made a bigger mess of the soil of the country if its destruction had beencarried out under supervision.” (Henry Bolte, introducing legislation in 1949 which replacedthe original Soil Conservation Board with the new Victorian Soil Conservation Authority. FromThompson 1979)
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Dookie Contour experiments and other demonstration sitesIn 1942, the first official contour work for erosion control was done in Victoria. This was a jointproject by the Dookie Agricultural College near Shepparton and the Soil Conservation Board.The contour works served for some years as a useful demonstration to visiting farmers, atraining experience for college students, and good practical experience for officers of theConservation Board.
The first field day held by the Soil Conservation Board was in 1943 at a farm near Avenel in theGoulburn River Region. The farmer had spent three years digging 80 kilometres of contourfurrows. Despite petrol rationing due to the war, 150 people attended, and this event set thepattern for many hundreds of similar field days in years to come.
In early 1944 The Board accepted an offer by the Council of Scientific and Industrial Research(as CSIRO was then named) to undertake a soil and erosion survey of 1500 square kilometres ofcountry in the Dookie district near Shepparton. This work was done by RG Downes, and hefound that almost 50% of the area surveyed was affected by sheet and gully erosion. He alsodrew attention to the presence of salinisation at some sites, a phenomenon that was to increaseand become a cause for popular concern forty years later. The results of this work werepublished in 1949 and became a valuable reference work for use by field and research staff.
By the late 1940s, steady progress was made in soil conservation throughout the State throughdemonstrations, advisory services and assistance to landowners, competitions and education invarious forms. (Thompson 1979, Reeve 1988)
Catastrophic erosion events in the period 1936 to 1950 in Victorian catchments“In Victoria, the period 1936 to 1950 saw a combination of environmental factors actingthroughout the State, that induced erosion. There was a prolonged dry spell, a poor ruraleconomy that led to poor land management practices such as overgrazing, and a severe rabbitplague. All of this left areas already vulnerable to degradation, exposed to erosion.Consequently, when severe rainfall events combined with such conditions, catastrophicsedimentation of rivers and water storages resulted. Such an event was recorded twice in thecatchment of the Melton Reservoir on the Werribee River, and once in the catchment of thePykes Creek Reservoir, over this period.” (From Davis 1996. The Melton Reservoir and PykesCreek Reservoir are both in the catchment of the Werribee River, just south of the of theMurray-Darling Basin.)
River Improvement Trusts in VictoriaIn 1948 the River Improvement Act was passed enabling local authorities, known as RiverImprovement Trusts, to be constituted. These trusts, consisting mainly of concerned locallandowners elected by the ratepayers within the Districts, accepted responsibility not only forimproving the courses and controlling erosion along rivers and streams, but also for the equallyimportant task of proper maintenance of the works carried out. (From ‘The State of the Rivers,Victoria, Australia’, SCCRI 1984)
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6.4 Soil Conservation Act of South Australia
In South Australia, legislation “to make provision for the abatement and prevention of sanddrifts” was passed as early as 1923 (Matheson 1978). The main concern being addressed by thislegislation, and its amendments in 1935, was the protection of public roads and other utilitiesfrom drifting sand caused by wind erosion. Wind erosion was a serious problem in the lightersoils of the Murray Mallee district, where frequent cropping, stubble burning and an 8 to 10month bare fallow tended to aggravate the problem.
It is significant that during the first couple of decades of the 20th century, water erosion was notmentioned in the numerous articles published in the South Australian Journal of Agriculture(Matheson 1978). Water erosion was first recognized as a serious problem in the 1930s,particularly in the cereal belt around the towns of Hawker and Gawler (Tideman 1990).Following the Ministerial conference in 1936, South Australia established a Soil ConservationCommittee which investigated the extent of erosion in the state and reported to Parliament in1938. The Committee advised a halt to clearing, the revegetation and re-afforestation of erodingupland areas, and contour banking of cultivated slopes. It did not, however, make anyrecommendations about the continuous wheat-bare fallow rotation being practiced over largeareas of the state (Reeve 1988).
A Soil Conservation Act was passed in South Australia in 1939, and gave the Minister ofAgriculture fairly wide powers for the control of soil erosion. It also made provision for theestablishment of an Advisory Committee on Soil Conservation “to advise the Minister on suchmatters relating to soil erosion and soil conservation as are referred to it by the Minister.”Extension work was carried out through the Department of Agriculture. Apart from providingtechnical assistance to farmers anxious to get something done, much of the work consisted ofdeveloping an awareness of the problem (Herriot 1943).
The seriousness of water erosion was highlighted in 1941. In the previous year there was amajor drought in South Australia and extensive areas were bare. In January 1941, torrentialstorms moved across the State, bringing 150 to 200 mm of rain in 24 hours. Mr RI Herriot, whohad been appointed Soil Conservator only two months earlier, labeled the resulting erosion ascatastrophic.
The water erosion problem was a result of the same basic farming deficiency that caused winderosion problems on the lighter soils, a fallow-wheat rotation, aggravated by the practice ofworking up and down slopes to avoid crossing gutters once they were too big to handle withcultivation machinery (Matheson 1978). In the early 1940s a few farmers started buildingcontour banks to control erosion, and slowly farmers were persuaded by the new SoilConservation Branch to try this technique.
The problem of soil erosion was brought home literally to the majority of people in the State bya series of frequent and spectacular dust storms over Adelaide during the summer of 1944. Soilerosion was highlighted in the newspapers, and the issue gained a higher priority in Governmentcircles (Williams 1974).
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Destruction of the land – 1942-43“We are at present spending colossal sums of money to prevent this country from falling intoalien hands but at the same time allowing this other enemy, just as dangerous, to apply a‘scorched earth’ policy, which if unchecked, will ultimately render it almost unusable toanyone.” (Paper presented by WV Roediger at a conference on the Lower Eyre Peninsula,South Australia, in 1942. The author compared the threat of invasion during World War 2 withthe more insidious threat of land degradation. South Australian Journal of Agriculture,December 1942, p 102)
Sand drift in the Mallee - 1945“It is very much the exception at the moment to see a perfectly stable farm in the mallee areas,and the present scene is distressing to settler and traveler alike. Roadways and railways havebeen frequently blocked by drifting sand dunes, and very large sums of money have been spentsimply to scoop the sand out of the way. ….. If as a result of our recent experiences, we havebecome erosion conscious; if we stay erosion conscious; and if we are prepared to adjust ouragricultural activities to the requirements of our soils and climate, then these recent experienceswill not have been in vain.” (RI Herriot, Soil Conservator of South Australia, 1945)
6.5 Growing awareness of soil conservation in Queensland
The first steps to apply soil conservation to farming lands in Queensland were taken in 1935,when contour banks were surveyed and constructed on 25 hectares of a demonstration area onthe Darling Downs by Mr AF Skinner, a cadet in the Queensland Department of Agriculture(Pauli 1978). In the next few years several farmers on the Darling Downs installed contourbanking systems on their farms, but otherwise there was little interest within the farmingcommunity or the State Department of Agriculture and Stock (Reeve 1988).
The first advisory article on soil conservation, written by Skinner, was published in theQueensland Agricultural Journal in 1939, and in the same year Mr Skinner used radio talks anddisplays at agricultural shows to promote the principles of soil conservation (Pauli 1978).However, interest declined with the outbreak of World War II.
In November 1945, after the war had ended, Mr Skinner was appointed by the QLD Governmentas ‘Soil Conservation Officer’ and during the next three years, he carried out erosion surveys inseveral areas of the State. He identified the Darling Downs as an area requiring the most urgenttreatment. In 1947, Mr JE Ladewig, a former officer of the Soil Conservation Service of NSW,was appointed as Soil Conservation Officer in the Department of Agriculture and Stock and overthe next few years this created the nucleus of a Soil Conservation Section in Queensland. Trialsin erosion control were commenced at Hermitage Research Station in Warwick and these wereused as demonstration sites for educating farmers (Borrell and Amos 1997). With theproclamation of ‘The Soil Conservation Act’ in 1951, Queensland became the last mainlandState to enact a soil conservation statute.
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‘The high cost of doing nothing’ – 1936 radio broadcast in QLD“Queensland has immense areas of fertile country, and every type of soil from the lighter loamsto heavy black alluvia and volcanic deposits of extraordinary depth and richness is represented.Is it not time that we calculated the cost of water erosion? Erosion takes twenty times as muchplant food from the soil as the hungriest crop. …
The causes of erosion are various, but the primary and most important cause is the widespreaddestruction of forests and other soil-binding and soil-retaining vegetation. Every farmer on ourcoastal river catchment areas, as well as every producer in our back country, can see in his ownneighbourhood what damage to both agricultural and grazing country unchecked soil erosioncan do – damage quite unnoticed until, in many cases, the land has been robbed of its naturalfertility by sheet erosion, or become so broken as to be useless not only for cultivation but forgrazing also. It is no exaggeration to say that in Australia almost every acre of sloping farmland, and much that is out of cultivation, in the higher rainfall zones is being affected by soilerosion. Only in recent years has any notice been taken of it, and only then by those to whomthe plain facts have become apparent. Through the action of wind and water, depreciation anddestruction of land have become definitely a serious national problem demanding immediateand adequate attention.” (extracts of a radio broadcast by the editor of the QueenslandAgricultural Journal, and reproduced in volume 45 of the same journal in April 1936)
Figure 33. Sheet and rill erosion in an overgrazed paddock near Roma, QLD. (photo; Anthony Scott)
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6.6 Erosion problems in the high country
It was not long after settlers moved into the Monaro district in the 1830s that they started tomove sheep and cattle into the high plains of the Snowy Mountains during summer (Hancock1972). A similar pattern of summer grazing commenced on the Bogong High Plains of Victoriain the 1850s (Cabena 1980, Lawrence 1994). Along with their stock, graziers also introducedregular burning-off to the alpine vegetation to encourage the growth of pasture. The use of thealpine regions intensified after the Robertson Land Acts of 1861 forced closer settlement andoverstocking in the Monaro district. Stock numbers increased progressively up to the 1930s.Although in 1889 the NSW Government commenced a system of snow leases, there were fewcontrols on these leases and degradation was inevitable.
During a severe drought in 1902-03, 100,000 sheep, in addition to large mobs of cattle andhorses were reported to have “eaten the mountains bare” (Johnson 1974). Many of the sheepcame from as far away as the Riverina. Large numbers of sheep and cattle were again on thehigh plains during the droughts of 1914, 1926 and 1939, the last being accompanied byextensive fires.
One of the first public alerts on the effects of uncontrolled grazing around Mt Kosciusko waspublished in the Agricultural Gazette of NSW in 1893. Richard Helms, a natural scientist fromthe Australian Museum, described the area as “splendid grazing country and covered on theopen parts with a dense coating of grass, assuming in many places a carpet-like compactness.”Helms added that the sweet grass sward was greedily eaten by horses, cattle and sheep. He alsoreported some disturbing changes caused by indiscriminate annual burning to bring on a burst ofgreen grass. Frequent fire was exposing soil to erosion and it could already be seen washinginto watercourses. He warned that; “The more or less constant diminution of humus in the soil ofthe slopes is a danger not generally recognized.”
Added to the concern expressed by people such as Helms was a growing awareness of the valueof the water that was being shed by the Alps. Vague steps were taken to protect the catchmentbut they were in name rather than action. In 1906 the NSW Government designated an area of160 sq km as the Snowy Mountains National Chase for the purposes of public recreation and thepreservation of game (Breckwoldt 1988). By 1925 this area had increased to 280 sq km and thepreservation of native flora was an added objective. However there were no staff to manage thearea and grazing and burning continued. In 1932, a forester, Baldur Byles, completed the firstobjective study of the impact of mountain grazing and the findings were not pleasing. Bylesnoted that the graziers knew full well that their fires dried out the alpine swamps and bogs;indeed, this improved access for stock and for horses. He concluded that fire was the mainreason for soil erosion and also impaired the value of the Alps as a water catchment (Breckwoldt1988).
A new group of people then emerged to covet the High Country. In the early 1930s adventurousbushwalkers from the city carried packs across the alpine meadows and camped along mountainstreams. One of their leaders, Myles Dunphy proposed that 400,000 hectares of the HighCountry should be set aside from grazing and preserved. Dunphy’s proposal received widesupport, including the NSW leader of the State Opposition, William McKell. More supportcame from a group of farmers from the Albury district who were concerned about the recentlybuilt Hume Dam silting up.
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In 1944 The Kosciusko State Park was formed, covering 541,600 hectares of the high country inNSW, to protect its catchment values and provide a recreational resource (Breckwoldt 1988).Grazing was only permitted where it did not conflict with these uses. Stocking rates were set foreach lease and an attempt was made to enforce these. However, not all of the members of theTrust formed to manage the Park were interested in conservation, and this became even moreapparent when the President of the Snow Lessees Association joined in the early 1950s. Theother impediment was a lack of funds to manage the Park. In fact the main source of incomewas the fees collected from graziers with snow leases.
Although the controls on stocking rates helped, one of the problems was that the sheep and cattlewould selectively graze certain areas. Livestock converged on areas that were moist and alwayshad green growth, or they would eat the palatable species while avoiding the less palatabletussocks, thus leaving bare areas of soil between the tussocks. The use of fire also continued tohave an impact.
In 1946 the Park Trust requested a Joint Advisory Committee of the Linnean and RoyalZoological Societies of NSW to carry out a natural history survey in the Park. The Committeerecommended the removal of grazing and the appointment of an ecologist as Director of thePark. These recommendations were rejected but the report represents one of the milestones inconsidering the natural values of the High Country.
The Snowy Mountains Hydro-electric Authority (SMA) was formally established in 1949 andwork on the Hydro-electric Scheme commenced shortly after. Initially the Soil ConservationService was concerned about the erosion that might be caused by the SMA’s construction works,but soon developed a close working relationship. The SMA had a strong interest in erosioncontrol since they were concerned about their water storages silting up.
In the 1950s two influential groups recommended that grazing in the high country should cease.The first was the Murray-Murrumbidgee Development Committee, which in 1955 carried out aninspection tour of the catchments within the Snowy Mountains Scheme. A set ofrecommendations was then published which stated that all high-altitude leases should berevoked and that soil conservation works should be undertaken. The second group was theAustralian Academy of Science which in 1957 reported on the condition of the high mountaincatchments of New South Wales and Victoria (Australian Academy of Science, 1957). In theirreport, they stated;
“Your Committee is unanimously of the opinion that there is serious deterioration of thevegetative cover of all these catchments and a decline in catchment efficiency; also, there iswidespread surface soil erosion, which is likely to reach extremely serious proportions if notchecked.”
The report compared the small revenue earned by graziers to the value of the water forgenerating electricity and irrigation, and recommended that all grazing should cease in areasabove 4500 ft (1370m). The recommendations in these reports were supported by the ecologicalstudies undertaken in the Alpine regions by scientist, Alec Costin (1954). In 1957, after muchheated political debate, all leases in NSW above 4500 ft were terminated. However, manygraziers did not accept this ban and took their stock back up the following summer. Others whooccupied adjoining leases wouldn’t bother to repair fences and their stock would stray onto thenow vacant leases. Controlling the illegal grazing was almost impossible due to the shortage ofOfficers monitoring the region.
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The debate over alpine grazing continued throughout the 1960s and it was only in 1967 whenthe NSW National Parks and Wildlife Service was formed that the most far reaching changescommenced. Kosciusko National Park was proclaimed and the Minister for Lands, Tom Lewis,held an inquiry into grazing throughout the entire Park. The Edgar report was presented to theGovernment in May 1969 and recommended that all grazing be banned in Kosciusko NationalPark. The Government accepted this report and the era of mountain grazing in NSW was ended.Despite some continuing breaches, the National Parks and Wildlife Service had more resourcesto carry out its work, and was also supported by the SMA, as well as the rapidly growingconservation movement of the time. With the grazing and associated burning now removed, thevegetative cover slowly but steadily improved.
Meanwhile, similar developments had been taking place in the Victorian High Country. In1941, Miss Maisie Fawcett, a senior lecturer at the Botany School of Melbourne University wasasked by the Victorian Soil Conservation Board to undertake an ecological survey of the Humecatchment, and particularly the Bogong High Plains (Thompson 1979). This was due to theconcern about erosion leading to sedimentation of the Hume reservoir. Her studies revealed theserious extent of degradation caused by the grazing of cattle and sheep brought up for summerde-pasturing on grazing leases.
In 1944, a sub-committee of the Victorian Soil Conservation Board made an inspection of theBogong High Plains and after observing the obvious deterioration of the area, recommended thatsteps be taken to limit the number of cattle allowed in this area (Thompson 1979). In 1946 anadvisory committee was formed, consisting of representatives of various governmentdepartments and three representatives of the cattlemen. Sheep, horses and burning-off werebanned and cattle numbers limited to 8000 (Wahren et al 1994). Over the following years, thenumber of cattle was steadily decreased and the grazing periods shortened. Eventually cattlewere also excluded from the highest and most vulnerable areas. In 1991 there were furtherreductions in cattle numbers, so that by 1994 a total of only 3100 cattle were allowed to graze onthe licence areas between December and April each year (Wahren et al 1994). The result hasbeen a slow but steady recovery of the vegetative cover and general condition in most parts ofthe high country in Victoria.
Grazing leases in Kosciusko; grazing causes erosion! - 1893“Up to the present time the ranges have been, so to say, a free country, and anyone who likedtook stock up there. This, of course, will not be so when the country is leased. A common, and,in my opinion, very improvident practice, will probably be continued as hitherto, viz, theconstant burning of the forest and scrubs. This proceeding has only temporarily beneficialeffect in regard to the improvement of the pasture by the springing up of young grass in theplaces so cleared, for after a year or two the scrub and underwood spring up more densely thanever. On the very high slopes the dense low scrub… which in common phraseology go by thename of heathers, certainly do not reappear quite so readily, on account of their slower growth,and in places when the burning is done with discretion a permanent improvement may beeffected by the removal of them in this way; however, I have seen some very detrimental effectsfrom this practice here, because the heavy rains wash the soil away from the steep declivities,and it is either carried into the creeks and rivers and entirely lost, or it accumulates in the boggyplaces, and thus become useless. The more or less constant diminution of humus in the soil ofthe slopes is a danger not generally recognized.” (Helms 1893)
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Alpine streamlines incised and widenedThe sub-alpine valleys of the Snowy Mountains, near Mt Kosciusko had wet peaty floors inwhich distinct channels were either poorly developed or absent before European settlement.Stream incision and widening followed the introduction of sheep and cattle which began inearnest in the mid 1860s. In 1957 sheep and cattle were removed to protect the area fromerosion, and the widespread practice of late summer burning stopped. However, the channelscontinued to enlarge between 1959 and 1978 when they were monitored by Wimbush andCostin (1983).
Figure 34. In 1969, the NSW State Government banned all grazing within Kosciusko National Park, andthis allowed the vegetation cover to slowly regenerate. (photo; Pascale Garaud)
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7. Improved management from 1945 onwards
7.1 Overview of improvements
By the end of World War II, it was recognized in most States that agriculture and pastoralismhad left the nation’s land resources in a state that threatened the long term sustainability ofprimary production. By this time, soil erosion was well understood, as demonstrated by thebook, “Soil Erosion in Australia and New Zealand” by Macdonald Holmes (1946), whichprovided detailed explanations of the causes of soil erosion and detailed descriptions of themethods of prevention and rehabilitation.
In the late 1940s and early 1950s, soil conservation efforts were centred around the constructionof mechanical protection works and rehabilitation of individual paddocks. In Queensland forinstance, 20 demonstration sites had been completed by 1949 (Anon 1949, cited by Reeve 1988)and a major education campaign was carried out in the early 1950s. Field days on thesedemonstration sites were particularly successful with up to 800 people attending (Skinner et al1977). The success of these field days was both welcome and necessary for the promotion ofthe developing extension programme. Soil Conservation Research stations with a demonstrationfunction were also established in NSW (Taylor 1945) and by 1952, 1.01 million hectares hadbeen treated with mechanical protection works by farmers co-operating with the NSW SoilConservation Service (Clayton 1952, cited by Reeve 1988). Similar activities had alsocommenced in the other states.
During the late 1940s it became apparent that on-farm soil conservation works needed to be co-ordinated over the whole farm. So the idea of complete farm planning developed. The first stepinvolved a survey of soil types, vegetation, existing erosion and history of land use. The planincluded changes in land use, relocation of paddock boundaries to conform with various landclasses and, if needed, construction of mechanical works to arrest the various forms of erosionwhich existed.
Farm planning had been introduced in the late 1940s in South Australia and by 1949, 27 farmscovering an area of 11,060 hectares had been planned (Reeve 1988). The first farm plans forVictoria were prepared in 1951 (Thompson 1979) and for NSW in 1958. By 1978, 4,400 farmplans had been completed in NSW (Wagner 1978).
The next step was to start developing erosion control works for larger catchment areas coveringseveral properties. This approach was adopted in Queensland in the mid 1950s, and by 1959catchment plans covering 80,940 hectares had been prepared (Hocking 1960, cited by Reeve1988). The first co-operative project in Victoria was started near Stawell in 1952, and by 1961,39 co-operative projects were in operation (Thompson 1979). In 1959, the VictorianGovernment approved the construction of the Eppalock Reservoir. Its catchment neededrehabilitation to avoid siltation of the reservoir. £500,000 was allocated for the work which wassupervised by the Soil Conservation Authority. Results achieved in the first few years of the 10year project were considered to be so successful that legislation was passed in 1962 to enable theSoil Conservation Authority to establish further Group Conservation Area projects. Similarprojects were set up by the NSW Soil Conservation Service to protect the catchments of majorwater supply reservoirs throughout the State (Wagner 1978).
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The move to planning soil conservation and land resource management activities on a wholecatchment basis was termed ‘whole environment planning’ in Victoria during the 1970s and hasemerged as ‘total catchment management’ in NSW in the 1980s (Morse and Outhet 1986, Reeve1988). This move was accompanied by the realization that extension efforts must be directed atthe whole community, not only the farmers who have a direct interest in the maintenance of soilresources. The community participation approach has been promoted by various forms of statelegislation which encourage the establishment of catchment committees, advisory groups andlocal action groups.
As a result of a national assessment of land degradation in the 1970s, the Federal Governmentestablished the National Soil Conservation Programme in 1983. This program provided fundsto tackle soil degradation and in the five years 1984-85 to 1988-89, the program contributed toover 400 projects (McTainsh and Boughton 1993).
In 1989, the Prime Minister of Australia issued a ‘Statement on the Environment’ in which 1990was declared to be the ‘Year of Landcare’ and the decade (to the year 2000) was declared to bethe ‘Decade of Landcare’. Landcare groups were set up throughout the Murray-Darling Basinand have been very active in planting trees and rehabilitating degraded land.
Soil conservation is now regarded as a necessary part of farm management. The implementationof soil conservation measures is an accepted initial step when developing new land for cropping.In established areas, contour bank systems, stubble mulching and minimum tillage are anintegral part of farming (Hepworth and Graham 1985). At the farm level, landholders can obtainadvice from soil conservation officers to plan how to protect the farm from soil erosion. StateConservation Services also prepare co-ordinated plans for the catchment using information suchas topography, land use, soil types and location of existing erosion. State agencies are alsocontinually refining their knowledge through research and field trials as well as undertakingeducation programs for both farmers and the general community.
NSW Soil Conservation Service grows after the 1940sIn 1941 the Service consisted of only 25 staff members, but by 1949 had grown to 250 staff and5 research stations (Breckwoldt 1988). Detailed erosion and land use studies of high priorityregions throughout the state were undertaken during the 1950s, 60s and 70s (for example,Morland 1960, Stannard 1958, Stannard 1963, James 1960 and Junor et al 1979). The results ofthese studies were used to identify the areas in most need of rehabilitation, and to providefarmers and other land managers with advice on better land management practices. The SoilConservation Service also provided assistance with the construction of erosion controlstructures. By 1978, inspections had been carried out on 42,000 different properties in the Stateand structural works had been constructed on approximately 1.5 million ha on 25,000 of theseproperties (Wagner 1978).
To encourage farmers to adopt erosion control practices, between 1945 and 1952 the SoilConservation Service set up 511 demonstration sites on severely eroded areas on farms andpublic land throughout the State (Wagner 1978). The techniques used to repair the erosioncould be demonstrated to other landholders through field days and other publicity.
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Figure 35. Erosion gully in the Wimmera region, Victoria, (ca. 1940s). (La Trobe Picture collection,State Library of Victoria)
Figure 36. Erosion control in the Wimmera region, Victoria (ca. 1940s). (La Trobe Picture collection,State Library of Victoria)
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C
D
F
G
B E
A
400 800
kilometres
0
The map was reconstructed chiefly from information obtained from ‘Conserve Your Soil’ (a bulletin from the Bankof New South Wales), the ‘Regional Boundaries Committee Report’, Victoria, 1944, and the ‘Commonwealth RuralReconstruction Commission Third Report’, 1944. The categories A to G give only the very general picture, asindicated below;A. Greatest erosion by water, in sheet erosion and gullying.B. Serious wind erosion in pastoral areas, often with hillside gullying.C. Wind erosion serious under cultivation.D. Some erosion by wind or water on cultivated and over-grazed land, generally not as serious as A, B and C.E. Generally not eroded seriously except in small areas. Minor depreciation of fodder plants in some sections.F. Soil erosion affects relatively small areas though depreciation of perennial fodder plants is widespread.G. Soil erosion is not a consideration, though dust storms are prevalent. The greater part of this area consists of
parallel sand ridges.
Figure 37. Distribution of soil erosion in eastern Australia in the 1940s, with the Murray-Darling Basinsuperimposed. (From Holmes 1946 textbook, ‘Soil erosion in Australia and New Zealand’)
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Figure 38. Soil conservation works in the Cowra district, NSW, in 1952. (Mitchell Library, StateLibrary of New South Wales)
Soil conservation in South AustraliaMr RI Herriot was appointed as the State’s first Soil Conservator in 1941, and for the firstcouple of years he had no assistance. He was a tireless worker and travelled throughout theState speaking to farmers about soil conservation. He also wrote numerous articles for theAgricultural Journal and gave many addresses on the ABC radio.
In the early 1940s, a few farmers were persuaded to build contour banks on their farms. Oncethis had been demonstrated as an effective measure against soil erosion, there was an increasingacceptance of the technique, particularly from the late 1950s onwards as large earth movingequipment became more readily available.
After World War II, when the Soil Conservation Branch could recruit more staff members, therange of activities undertaken by the Branch broadened greatly. This included farmer education,‘on the ground’ remedial work, reserving hazardous areas from clearing, undertaking erosionsurveys, the development of improved tillage techniques and advice on fertilizer requirements.(Matheson 1978)
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Controlling erosion in the ACTIn 1915, two years after the Territory was declared as the site for the National Capital, the slopesof Mt Stromlo were planted to Pinus radiata to arrest erosion and visually improve thelandscape. In the 1920s and early 1930s further plantings of Pinus radiata and native speciesoccurred on Mt Majura, Mt Mugga and also around Cotter Dam, Canberra’s water supply. Thenext major soil conservation programmes took place in the period 1944-47. Degraded hills anderoded areas along watercourses were withdrawn from rural leases, treated with earthworkstructures, fenced and planted with pines (Taylor 1947).
As part of a vigorous extension programme by the Department of Interior during the 1950s and1960s, landholders were encouraged to establish improved pasture as a means of increasingproduction and controlling runoff. At the same time, there was a concerted effort to controlrabbits.
From 1965 onwards, attention focused on the control of erosion in the catchment of Lake BurleyGriffin. The lake was turbid from sediment entering from the Molonglo and Queanbeyan Riversand was in danger of rapid siltation. The worst affected area was the Field Firing Range, whichwas used for military exercises and had considerable sheet and gully erosion. Gully controlstructures were constructed, along with earth dams and contour banks. Streams were fenced toprevent access by stock and trees planted. Stocking rates were reduced and superphosphateapplied to maintain pasture vigour. Similar treatment was applied to other areas of activeerosion, including the NSW portion of the catchment where the NSW Soil Conservation Serviceassisted (Sebire 1991). The erosion control programme was then extended to cover thecatchment of the Googong Reservoir along the Queanbeyan River.
Soil Conservation measures were also implemented in the new housing developments ofCanberra, to reduce the rates of siltation in the new urban lakes, Lake Ginninderra and LakeTuggeranong, and also protect the quality of urban stormwater flowing into the MurrumbidgeeRiver. (Forster and O’Meara 1978)
Keepit Dam – a catchment with soil erosion problemsIn 1944 The Premier of NSW, William McKell was taken on a tour of the catchment of theKeepit Dam, which was being built on the Namoi River near Manilla. The Premier was sodisturbed by the condition of the land and the silt being deposited in the Keepit storage, that hecalled an immediate halt to any further work on the dam wall until something was done aboutmanaging the catchment. The entire catchment was surveyed and classified according to itserosion potential under cropping or grazing. For each classification, the level of mitigationtechniques were specified, depending on how severe the erosion potential was. If the land wasused according to its capability, and if the appropriate soil conservation methods were applied,then farmers could conserve their soils and protect the catchment at the same time. This wascalled conservation farming. By 1958 over 400 properties had been treated with soilconservation works. (Breckboldt 1988)
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The Eppalock projectIn 1959, the Victorian Government had approved plans for the construction of the EppalockReservoir on the Campaspe River. However there were serious concerns that unless an effortwas made to control soil erosion within the catchment, the reservoir would suffer from severesiltation. This was already apparent in the small existing reservoir. When the dam wasapproved, the Government also allotted a large sum of money towards erosion control and soilconservation within the catchment. An Eppalock Catchment Committee was formed and workon the farms commenced in 1960. In the first year, about 5,000 acres of hilly land were sown toimproved pastures, fifty erosion control structures were built, 200 groynes and silt trapsconstructed in gullies, 1,500 chains of fencing erected and more than 1,800 trees planted. Thebasis of the assistance to farmers was that the Government would meet the cost of erosioncontrol works that did not in themselves improve farm productivity, but were necessary to thesuccess of the plan and so were in the public interest. The farmer met the cost of any soilconservation measures that would directly increase his farm production (Thompson 1979).
(It is interesting to note that a recent appraisal of the Eppalock project concluded that theseriousness of the siltation problem was probably over-stated in an attempt to secure funding forerosion control works within the catchment (Davis 1996)).
Figure 39. A tractor with a 2-furrow disc plough forming contour banks on the side of a hill to helpprevent further erosion. (Reproduced courtesy of Museum Victoria)
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Soil Conservation in the Burrinjuck Catchment areaIn May 1954, a programme of soil conservation was commenced on a group of properties nearthe village of Hall, and close to the border of the ACT. The control of erosion on propertiessuch as these is of great importance in protecting the Burrinjuck Dam from siltation. Erosion ismainly in the form of very deep gullies, many of them about 30 feet deep and up to 40 or 50 feetwide. Many of these gullies have formed on the sites of old roads and tracks which were usedyears ago by bullock and horse teams, and unfortunately were located in hollows where waterrunning off the hillsides concentrated to the greatest degree.
Erosion was successfully checked by means of earthworks such as absorption banks, silt damsand pasture furrows which greatly increase absorption of water and decrease runoff, and bydiversion banks which exclude water from existing gullies and turn it onto suitable grassy areaswhere it will cause no harm.
Mechanical control measures must be supported by sound farming methods such as pastureimprovement, eradication of rabbits, careful location of roads, woodlots and watering places,judicious stocking and perhaps even permanent fencing off of some vital areas where it isessential to preserve a good grass sward and prevent stock trampling and overgrazing. (Harris1956)
National assessment of land degradation – 1970sThe first national assessment of land degradation was undertaken by the Commonwealth andState governments from 1975 to 1977. About 66% of Australia’s cropland and 40% of grazingland required treatment for erosion control. Water erosion affected over 70% of cropland inNSW and Queensland, and 15% or less in Victoria and South Australia. The findings of thisnational survey, and the estimates of the costs of works required to prevent further damage,stimulated governments in Australia to increase their efforts to protect national land resources.(Woods 1983)
7.2 Rates of erosion declining in most regions
The exact timing of accelerated erosion after European settlement is difficult to determine butanecdotal evidence and archival records have constrained the incision and extension of gullynetworks in many places to the period of rapid agricultural expansion in the mid to late 1800sand early 1900s (Dragovich 1966, Bird 1985, Wasson and Galloway 1986, Starr 1989, Prosser1990, 1991, 1996, Williams et al 1991). The first aerial photography shows that many gullynetworks had almost reached their present extent by (or before) the late 1940s (Eyles 1977a,Prosser 1991, Prosser and Winchester 1996, Starr 1995, Starr et al 1996). This evidence is alsosupported by anecdotal reports (Starr et al 1999).
In some areas, particularly where poor land management practices continue, or recent landclearing has occurred, incision and extension of new gully networks does continue (Rutherfurdand Smith 1992). However in many other regions the existing gully networks are slowlystabilizing and starting to revegetate (Starr et al 1988, 1990; Starr 2000, Rutherfurd and Smith1992). In these areas active erosion is often limited to ‘hot spots’ where the collapse of unstable
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gully walls or stream banks occurs during heavy rainfall, or sediment that has been depositedalong the gully floors is re-worked and moves further downstream. Also, during heavy storms,very high erosion rates can still be experienced in most regions, particularly if the storm eventoccurs after an extended drought when ground cover is sparse.
There are a number of reasons why the overall rate of erosion, and in particular gully erosion,within the Murray-Darling Basin have started to decline from their peak rates at the end of the19th century. These are:
1) After initial incision, followed by deepening and widening, many gully networks haveadjusted to the increased rates of surface runoff and are now gradually stabilizing, and insome areas revegetating with wetland plants.
2) Better land management has increased the protective ground cover. This has includedlower stocking rates, pasture improvement, and the replacement of conventional tillagewith conservation farming practices.
3) Reduction in rabbit numbers. In the early 1950s, Myxomatosis was introduced andcaused a big reduction in the rabbit population (McKay 1976). Slowly the rabbitpopulation developed an immunity to Myxomatosis and numbers started to increaseagain. Recently however, (in 1996), the introduction of Calicivirus has once againbrought rabbit numbers under control, particularly in the drier regions of the Basin.
4) Erosion Control Works. Since the 1940s, many farmers have started to build contourbanks, and repair eroded gullies, with the assistance of State Soil ConservationAuthorities. Education programmes have also helped increase awareness of soil erosionand its impact on farm productivity. In some areas, a very large number of farm damshave been constructed over the last 50 years, and these tend to protect gullies from theerosive forces of stormflows. The farm dams also act as sediment traps, therebyreducing sediment transport into the larger streams within the catchment (see section7.5).
5) Changes in weather patterns over the last 50 years. Riley (1988) reported that long termchanges in the weather patterns had resulted in increased rainfall over the last 50 years.It has been suggested that this might have caused an increase in pasture cover and hencebetter protection of the soil (Wasson et al 1984, Wasson 1987). However, an analysis ofweather data for the period 1910 to 1995 by Hennessy et al (1999) indicates that someregions have also experienced increases in heavy rainfall, which is when the greatesterosion tends to occur. These conflicting factors make it difficult to draw any firmconclusions about the effect of increased rainfall on erosion rates.
Although many gully networks throughout the Murray-Darling Basin are showing signs ofstabilization, there are some catchments where the soils are highly erodible, and the gullynetworks remain highly active. An example of this is the Milburn Creek catchment, just belowWyangala Dam on the Lachlan River, NSW. Most of this catchment was cleared in the mid tolate 19th century, and a complex network of gullies had formed by the early 1940s. Over the last50 years the gully network has shown little sign of stabilizing and many gullies remain highlyactive. Although the extension of the gully network has slowed in the last 50 years, the existinggullies have cut deeper and wider into the highly erodible soils (Bush 2001).
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In regions where land clearing has continued in recent decades, the associated high rates oferosion will not start to decline for many years to come. This includes large areas of landcleared in southern Queensland during the 1990s (Barson et al 2000) and along the westernslopes and plains of New South Wales in the 1970s and 1980s (Pressey 1990, Turner et al1996). In some districts there is also a trend to convert previously cleared pastoral country intocropping land. The erosion rates from cropped land can be orders of magnitude higher than thatfrom native or improved pasture.
Better land management in the Warrah catchment, Liverpool PlainsWarrah Creek is an upland catchment (150km2) of the Mooki River in the Liverpool Plains,NSW. The earliest aerial photography, taken in January 1943, show a highly degradedcatchment almost devoid of timber, including an almost complete absence of vegetation indrainage lines. Extensive gully systems comprising deep incisions with abundant secondaryoffshoots occurred throughout the catchment.
Aerial photography for 1984 and 1994 suggest that regeneration of forest and woodland hasoccurred in the upper catchment. Cropping has expanded to include the alluvial flats and slopesof the lower part of the catchment. In recent decades, land management has included theconstruction of dams and contour banks, pasture improvement and management of total stockingrates. At a catchment scale, the erosional network appears to have retracted in response to thesemanagement practices.
Warrah catchment, 1943, 1984 and 1994
(from Beavis et al 1999)
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Reduction in sediment reaching Burrinjuck ReservoirBetween 1925 and 1983 the rate of sediment transport, as judged by stratigraphic analysis ofsediments in Burrinjuck Reservoir into which the Murrumbidgee River drains, has decreased.Wasson et al (1984,1987) suggested that; increased rainfall since 1950 leading to improvedvegetative cover, the control of rabbit numbers, better farm management, the introduction of soilconservation practices, and the construction of large numbers of farm dams had all contributedto the decline in sediments reaching Burrinjuck Reservoir.
Figure 40. Sheet and rill erosion associated with a salt scald at Dalton Park, near Gunning, NSW. Thisis a good example of how the various land degradation issues being faced by farmers throughout theMurray-Darling Basin are often inter-related. (photo; Nicki Taws)
In-stream wetlands reduce sediment loads in Jugiong CreekThe Jugiong Creek catchment (covering 2175 km2), on the south-western slopes of NSW,contains an extensive network of eroded gullies which formed in the period 1880 to 1920. In thelast 50 years, these gully floors have slowly been colonized by emergent aquatic plants whichhave now formed dense in-stream wetlands covering 25% of the channel network. The wetlandshave trapped almost 2,000,000 tonnes of nutrient enriched fine sediments, which is equivalent toalmost 5 years of annual sediment production across the catchment. In some tributaries morethan 20 years of annual yield is stored within the in-stream wetlands. The current formationand spread of in-stream wetlands is interpreted to be the onset of the next infill phase, but it isnot known whether the present conditions will allow complete channel filling and re-formationof the pre-existing swampy valley floors. Nevertheless, further spread of in-stream wetlands islikely to increase sediment trapping capacity and further reduce the discharge of sediments andnutrients into the Murrumbidgee River. (Zierholz et al, 2001)
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Declining sediment yields in Victorian catchments“The graphs of sediment yield for Pykes Creek, Melton, Eildon and Laancoorie Reservoircatchments have declined over the last 50 years. Peak yields were recorded for Pykes Creekand Melton Reservoir catchments between 1915 and 1945, for Laancoorie Reservoir catchmentbetween 1890 and 1932 and for the Lake Eildon catchment between 1939 and 1942. Eachsurvey since that peak period, has recorded lower sediment yields for each catchment, and inmany instances significantly lower. …… Improved land management techniques are cited as thelikely explanation for these declining yields.” (Davis 1996. Pykes Creek and Melton Reservoirsare located just to the south of the Murray-Darling Basin, while Laancoorie Reservoir and LakeEildon are in the Basin)
Creightons Creek - more erosion in the wet years of the 1950sDavis and Finlayson (2000) reported that in the Creightons Creek catchment near Euroa, asecond phase of channel incision appears to have coincided with the 1950s, which was aparticularly wet decade. It seems that a series of erosion heads moved up Creightons Creekduring the 1950s and 1960s, resulting in incision throughout much of the system. Sedimentdeposition from this second major phase of channel incision was noted at a number of locationsin the creek downstream of the Baronga Creek confluence. According to Brian Kelly, a localfarmer, there were a number of large pools (approx 6m diameter) along Creightons Creek justdownstream of Kelly’s Bridge in the 1940s and 1950s which started to fill with sediment in the1950s; and within a few years had disappeared completely. At other locations sedimentdeposition of 2.5-3m occurred following the 1950s, engulfing the old road bridge. (Davis andFinlayson 2000)
Figure 41. This erosion gully, on a property south of Yass, has been fenced off to exclude stock andthen planted with trees. The re-established vegetation cover helps stabilize the gully and reduces thesediment loads moving into the Murrumbidgee River downstream. (photo; Anthony Scott)
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Erosion in the Burra catchmentBy 1944 (the date of the first set of aerial photos of the catchment), all the main tributaries ofBurra Creek, (a tributary of the Queanbeyan River in the southern tablelands of NSW) wereincised. The total length of incised eroding channels was 184 km or a gully density of 2.96km/km2. By 1968 the total length had dropped to 134 km, that is by 27%. In the farmed portionof the Burra catchment the worst phase of erosion had probably passed, with improved pasturemanagement, control of rabbits and better control of runoff through the construction of farmdams. Much of the farmland was also treated by the NSW Soil Conservation Service. However,in the late 1970s, stream bank erosion remained intense along almost the full length of BurraCreek and gully head erosion was still active in the now largely unused dry sclerophyll forest ofthe southeastern portion of the catchment (this area had once been cleared in the 19th century).(Eyles 1977c)
Erosion survey of NSW Eastern and Central Divisions Re-assessment – 1967.In 1941-43 the Soil Conservation Service made a detailed survey of soil erosion in the easternand central divisions of NSW. Twenty-five years later this survey was repeated using the sameprocedures. The results indicated that there was an increase in gully erosion in the Northern andCentral Tablelands and also the Central Western Slopes, possibly caused by increased clearingand cultivation of hilly lands. In the Southern Tablelands, however, there was a decrease whichwas thought to be the result of the concentrated efforts by the Soil Conservation Service in thisarea. Throughout both the Central and Eastern Divisions, there was a reduction in the areaaffected by sheet erosion. (Stewart 1968)
Recent erosion and sedimentation of Tarcutta Creek – a case studyAlthough it is clear that the most significant changes in terms of erosion and sedimentation inthe alluvial reaches of Tarcutta Creek (in the Murrumbidgee catchment, NSW) were initiated inthe decades following European settlement, channel change has continued throughout thepresent century. Remnants of the pool and swamp system with extensive platypus habitatspersisted until the 1940s. Local residents recalled that near the village of Tarcutta, a deepchannel capable of being dived into safely from the Hume Highway bridge before the turn of thecentury, had shallowed considerably by the early 1930s. However, a deep pool at the junction ofTarcutta and Umbango Creeks, which was also used for swimming and fishing, only started tofill with sandy sediment in the late 1940s.
In Umbango Creek the channel was already incised deeply before 1950 with bedrock exposed inmany sections. However, a series of floods in the 1950s caused channel widening of up to 30 m,and the eroded material contributed to the large sediment slug currently moving through thelower reaches of Tarcutta Creek.
The most spectacular episode of recent incision on Tarcutta Creek occurred at Janey HarveyBridge following ‘channel improvement’ works designed to reduce overbank sedimentation andthe frequency of local flooding. In 1985, Wagga Wagga City Council removed trees and logsfrom the channel and carried out minor channel re-alignment works. These works reduced localflooding and sedimentation at the bridge, but by 1990 had caused channel incision of 3-4 m andthe wooden bridge collapsed into the stream. Incision also resulted in severe bank erosion andthe delivery of sediment to downstream reaches. (Extracts from Page and Carden, 1998)
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Figure 42. This farmland near Gundagai, NSW, was first settled in the early 1830s, and gully erosionprobably commenced not long after. 170 years later, grass cover in this gully has re-established and thebanks have stabilised. (photo; Anthony Scott)
7.3 Improved pastures and fertilizer use
In the 1930s, the era of subterranean clover and artificial fertilizers (as opposed to manures)commenced. This allowed the widespread nitrogen and phosphorus deficiencies to be remediedin many areas of southern Australia. However, it was not until after World War II that the use ofartificial fertilizers, in particular superphosphate, rapidly increased (McGarity and Storrier1986). Superphosphate use on pastures peaked in the 1960s and early 70s, and then declined in1974 when the government subsidy was removed (McLaughlin et al 1992, Gallagher 1989).Also in the 1960s and 70s, the benefits in southern Australia of perennial species such asphalaris and cocksfoot was recognized, and in the 1980s came the possibility of perenniallegumes.
All these developments resulted in better pasture and increased stock carrying capacity. Theimprovement in vegetative cover, combined with other factors, such as the control of rabbitsthrough the use of Myxomatosis, reduced the areas of overgrazed, bare soil and hence reducedthe risks of erosion.
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Figure 43. Contour banks are used to reduce streamflow velocities and trap sediments. (photo; AnthonyScott)
Pasture improvement reduces erosion on farm near Quirindi (NSW)Located on the northern side of the Liverpool Range, the farm was a typical sheep countryproperty. The native pasture was predominantly made up from redgrass (Bothriochloa spp),bluegrass (Dicanthium spp) and speargrass (Stipa spp). A serious erosion problem existed.Active gullies and advanced rilling were common on the foothills and I the flat country. Sheeterosion was widespread on the hill country. In 1976 a pasture improvement programme wasdrawn up, the main objectives being the introduction of productive pasture species, sub-divisionof the farm into smaller paddocks and reticulation of water to each paddock, the introduction ofa rotational grazing system, and a high economic return.
Aerial sowing of pasture species minimized soil disturbance, and fertilizer top-dressings werecarried out annually to correct soil mineral deficiencies. These improvements resulted in greaterground cover, reduced runoff rates, less soil erosion, as well as greater carrying capacity andincreased financial return. (Gardiner and Kawabe 1983)
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7.4 Erosion associated with increased cropping
From the 1960s onwards, there has been a steady expansion of cropping along the westernslopes and plains of NSW (Watt 1983, Junor et al 1979) and in the Darling Downs inQueensland (Cartledge et al 1975, Pauli 1978). For instance, in the Gwydir Soil ConservationArea, cropping has increased from 98,500 hectares in 1950 to 688,700 hectares in 1980; a 700%increase (Watt 1983). Similarly, Berndt and Stephens (1987) estimated that during the late1970s, land in central Queensland and the western Darling Downs was being developed at a rateof about 80,000 ha per year. The great majority of this land had long gentle slopes and shallowsoils which would be seriously damaged by erosion if soil conservation measures were notemployed. The expansion of cropping in the Murray-Darling Basin has continued through the1980s and 1990s.
The erosion rates from cropped land can be orders of magnitude higher than that from native orimproved pasture, particularly after ploughing when there is no vegetative cover and the soilsurface is very loose. This problem was highlighted on the Darling Downs whenever severeerosion occurred during heavy storms, such as in 1956 (Skinner et al 1977), 1964 and 1965(Kelsey 1964, Hoogvliet 1965), the early 1970s (Cartledge et al 1975), and again in 1980 and1981 (QDPI 1980, 1981). Littleboy et al (1992) estimated soil losses of 0.35 cm/yr for atraditional wheat cropping system at Emerald (QLD), and that 50% of production potentialwould be lost in less than 100 years.
Similar problems were occurring in the cropping districts of NSW (Colless 1983, Aveyard et al1983). On the North-West Slopes and South and Central Western Plains, the area subject tomoderate gully erosion increased by 7,739 sq km between 1940 and 1967, a spread attributedlargely to the increase in areas planted to wheat in this period (Stewart 1968 cited by Reeve1988). In the lower Namoi region between 1967 and 1975, the land area affected by sheeterosion increased from 14 to 23 %, while the area suffering gully erosion increased from 26 to39% (Junor et al 1979). These changes were attributed to the increases from grazing tobroadacre cropping in the region.
Under a traditional cropping rotation, stubble was grazed or burnt and the soil was worked witha disc implement. The objective of the ground preparation was to accumulate soil moistureduring the wet season (summer in the north of the Basin, and winter in the south), to produce amoist seed bed overlain by a loose mulch of soil about five centimetres deep (Molnar 1974).However, this left the bare soil surface highly susceptible to sheet erosion, and a large quantityof soil was lost if a heavy rainfall event occurred (Hairsine et al 1993).
In the mid 1970s stubble retention was introduced, as farm machinery capable of cultivating andplanting through stubble became commercially available (Berndt and Stephens 1987). From theearly 1980s onwards, traditional farming practices were gradually replaced by a range of‘conservation’ farming techniques (Aveyard et al 1983, Marschke 1987, QDPI 1995).Herbicides and direct drilling replaced cultivations in the cropping cycle (conservation tillage)leaving the soil in a less erodible state, and the retention of stubble improved surface cover,increased organic carbon content of the soil and increased infiltration (Packer et al 1992,MacLead et al 1993, Smith 2001). Conservation tillage has also been found to increase yieldsand improve nitrogen fixation when legume crops such as soybeans are grown (Macleod et al1993).
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Soil Erosion in the Darling Downs, QLDThe Darling Downs are a rich fertile tract of largely basaltic country west of Toowoomba,centred around Dalby. Since 1935, dairying and mixed farming have declined in favour of graingrowing, particularly on the Central Downs which consist of a highly fertile plain of deep blacksoil. Grain growing, and the resultant large areas of fallow ground has resulted in a soil erosionproblem. Three storms and follow-up rains in the early 1970s caused severe soil erosion damageto the area. After these storms, a number of public meetings were held to discuss the problem.Political interest at local and state level followed, and in March 1973 the Queensland cabinetdecided that all shires of the Darling Downs would be declared ‘Areas of Soil Erosion Hazard’(Cartledge et al 1975). Within these areas, farmers were eligible for Government assistance totackle the erosion problem. This concern resulted from the enormous scale of the problem.Large areas of land were being lost to production where gullying was occurring, while sheeterosion was removing valuable topsoil and lowering crop yields. Loss of seed and fertilizerwere also high where sheet erosion occurred. Severe erosion occurred yet again in 1980 and1981 (QDPI 1980, 1981; Marshall et al 1980).
In subsequent years a large amount of effort went into investigating ways of reducing erosion byemploying different farm management methods (Freebairn and Wockner 1991). This hasincluded; the use of contour banks, strip cropping, reducing the fallow period, conservationtillage, retaining stubble, improved land use planning, and better management of floodwaters(Cartledge et al 1975, Marshall 1988).
Figure 44. Sheet and rill erosion of cultivated land after a heavy thunderstormin the Darling Downs, QLD. (photo; L Coxen, DNR&M QLD)
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Expansion of cropping in the western district of NSWDryland cropping has been a major reason for clearing in the region and its development hasbeen reviewed by Condon (1982) and the Western Division Select Committee (1983, 1984).Commercial wheat growing in the Western Division dates back to the 1890s but was notattempted on a large scale until the post-war settlements of the 1920s. Cropping expanded afterthe late 1950s with the use of bulldozers and chains to clear dense timber. Further expansionwas encouraged by the removal of wheat quotas in the early 1970s, development of bigger andmore fuel efficient machinery, and increased drought tolerance and yield of crop varieties. TheWestern Lands Commission of NSW has estimated that there was a ten-fold increase in drylandcropping from 20,000 ha in 1965 to 228,000 ha in 1980 (Western Division Select Committee1984). This recent increase of cropping has been concentrated on land previously used forpastoral activities. The major reasons for clearing licences being granted between February1984 and October 1990 were; dryland cultivation (56% of total area approved) and thinning forimproved carrying capacity of pastoral land (39%). (from Pressey 1990)
Soil conservation improves yields – case study from 1985.Nev and Enid Ronnefeldt’s farm near Dalby on the Darling Downs (QLD) is subject to erosiveflooding. They have found that the only way to control the erosion problem is through acombination of strip cropping to spread floodwater, and stubble mulching to slow water downand protect the soil surface….
Nev avoids working the ground in the fallow period by using herbicides for weed control, thenhe usually cultivates twice before planting. When double cropping, he can often plant straightinto stubble from the previous crop without any cultivation. “The big bonus has been about a20% increase in yield over the conventional system.”(From Hepworth and Graham’s 1985 booklet entitled ‘Soil Conservation; caring for Queensland’.)
Conservation or conventional tillage?Traditional tillage has significantly contributed to production losses, soil degradation and theviability of agriculture in New South Wales. A project was undertaken on two adjacentproperties in the Upper Bogan River catchment to compare conservation farming with moreconventional farming practices. The conventionally tilled paddock demonstrated the mostdegraded characteristics while conservation farming techniques preserved soil structure,improved infiltration and produced a higher economic gross margin. (from Smith 2001)
7.5 Farm dams and water storages reduce sediment yield
Prior to mechanization, farm dams were dug by hand with some assistance from horse-drawnscoops. This was laborious and prior to World War 2 farm dams were neither numerous norlarge in storage capacity. With the introduction of the mechanical crawler tractors after WorldWar 2, there was a rapid increase in the construction of farm dams throughout many regions ofthe Murray-Darling Basin. In the Yass River, upstream of Gundaroo the number of dams hadincreased from 491 in 1976 to 2242 by 1998. This is equivalent to 6 dams per square kilometre.Similarly, in the Broadwater Creek catchment in southern Queensland, the density of farm dams
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increased from 1.7 per square km in 1988 to 3.5 in 1997, a doubling over a period of just 10years (Schreider et al 1999). The total volume of these farm dams is equivalent to 60% of theannual average discharge, and therefore has a significant effect on streamflows. The rapidincrease in the numbers of farm dams is typical of catchments throughout the tablelands andslopes of the Murray-Darling Basin.
Farm dams not only reduce the streamflow within a catchment, but also reduce the sedimenttransport, by capturing a proportion of the suspended sediments. Neil and Galloway (1989)studied 14 farm dams in the Yass catchment and estimated sediment trap efficiencies between21– 88%. This indicates that in catchments with a high density of farm dams, there will be asignificant reduction in catchment sediment yield.
Large water storages, such as Burrinjuck Dam or Lake Eildon, also act as sediment traps, andsome collect over 90% of the suspended solids entering from upstream. A few of the smallerwater storages within the Murray-Darling Basin had so much sediment enter from upstream thatthey filled up completely with silt and had to be abandoned. This includes the Junction ReefsDam near Lyndhurst, the Illalong Creek Dam near Binalong and the Cunningham Creek Damnear Harden (Chanson and James 1999). Moore Creek Dam near Tamworth, was initially a 220ML reservoir, but is now completely filled with sediment (Morse and Outhet 1986).
The construction of Little Eildon reservoir (377,450 ML) between 1915 and 1927 reduced thedownstream sediment load in the Goulburn River (Victoria) from 210,000 m3/yr to 12,300m3/yr (Erskine 1996). Between 1950 and 1955, Big Eildon Reservoir (3,390,000 ML) wasconstructed immediately below the old wall, further reducing the downstream sediment load to2140 m3/yr. This is equivalent to a sediment trap efficiency of 99%.
Sedimentation of the Laanecoorie Reservoir on the Loddon River, VictoriaConstructed in 1891, the Laanecoorie Reservoir had an initial capacity of 17,000 ML. However,by 1930 siltation had reduced the capacity by 53%, with a catchment sediment yield of 50t/km2/yr. During this period, alluvial gold mining was occurring throughout the catchment,including dredging and hydraulic mining with high pressure water jets. Such methods werebeing used in the Loddon River upstream of Newstead, at Campbells Creek, Fryers Creek andForest Creek. These practices contributed a significant volume of fine sediment to the riversystem, and some of which settled out in the Laanecoorie reservoir downstream. Later surveysof the Reservoir indicated that there was a significant reduction in sediment yield after 1930 andthe final survey in 1962 showed that sediment yield had declined to only 10 t/km2/yr. (FromDavis 1996, using old records from the Victorian Sludge Abatement Board)
Siltation of weirs and dams in northern NSWMassive siltation via streambank and general erosion (sheet, rill and gully) following extensivetree clearing for agriculture, as well as mining operations, has caused a 32% loss of capacity inthe Inverell town water supply weir on the Macintyre River over a 43 year period to 1981.
In the Namoi Valley, soil erosion was identified as a problem as early as 1950, causing streamsedimentation and turbidity levels. The Quipolly Dam near Werris Creek constructed in 1932 isnow completely silted up and streambank erosion and top soil loss from cultivated areas of theLiverpool Plains is a major concern. (From Arthington 1995)
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Figure 45. Farm dams, such as this one near Gundagai, NSW, reduce sediment transport, by capturing aproportion of the suspended sediments. (photo; Anthony Scott)
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8. Investigating the sources and yields ofsedimentOver the past 30-40 years there has been a large number of research projects undertaken to gaina better understanding of erosion processes. This has included investigations into;
- the rate of erosion under different land use scenarios- the rate of erosion during heavy rainfall- the yield of sediment entering farm dams, rivers and large reservoirs- the main sources of sediment, in particular gully erosion versus sheet erosion.
To provide an indication of the types of research projects undertaken and the conclusionsreached, some typical case studies have been presented in the following sections.
8.1 Sediment yields for different land uses
It was mentioned earlier that farm dams act as sediment traps and sediment accumulates in themover time. From the volume of sediment accumulated, the loss of soil per unit area of theupstream catchment can be estimated. The two weaknesses with this method are; a proportionof the sediment entering the farm dam is flushed through the system, and some of the sedimentswill originate from livestock trampling the water’s edge (Lloyd et al 1998). Despite theseweaknesses, this method provides the simplest measurement of sediment movement in a smallrural catchment.
Neil and Fogarty (1991) measured the volumes of sediment accumulated in 46 farm damswithin the lower part of the Lake Burley Griffin catchment and in the upper Yass Rivercatchment near Canberra on the Southern Tablelands. The area is undulating to hilly and thedominant land use is grazing, primarily by sheep. The age of the dams since construction, or thelast cleaning out, were mostly 20 to 40 years. The largest catchment was 1000 ha and 85% wereless than 100 ha. The volume of sediment in each dam was measured by taking a series of coresamples. The trap efficiency of each dam was also calculated so that the mean annual yield ofsediment entering each dam could be calculated. The sediment yield for each catchment wasgrouped by the predominant landuse, and the following results obtained;
Catchment class Number ofcatchments
Mean area ofcatchments (ha)
Sediment yield(t/km2/yr)
Increase from‘natural’ rate
Undisturbed nativeforest
4 88 2.5 1
Native pasture 13 60 9.6 3.8Improved pasture 3 401 13.5 5.4Overgrazed pasture 2 6.9 68 27Winter cropping 5 21 52 21Pine plantation 7 47 83 33Discontinuous gullies 5 46 21 11Continuous gullies 8 113 160 64Data from Neil and Fogarty (1991) and Salmon (1989). The bulk density for the sediment was measured as 0.9g/cm3.
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The ‘natural’ erosion rate obtained in this study was 2.5 t/km2/yr, and this is similar to the resultsof Prosser (1994) for a small undisturbed catchment in the Southern Tablelands. The resultsalso demonstrate the very large increase in erosion rates caused by activities such as overgrazing(27 times higher) or cropping (21 times higher).
For catchments with a network of continuous gullies, Neil and Fogarty obtained a mean valuewhich was 64 times the natural rate. This was significantly higher than that for discontinuousgullies (11 times the natural rate), and emphasizes the importance of connected gully systems indelivering sediment to larger watercourses. In discontinuous gully systems, a significant amountof the eroded material is deposited in gully mouth alluvial fans and does not reach the largerwatercourses downstream.
By comparing data from gullied and ungullied sites, it was estimated that 80% of the sedimentload was originating from gully erosion and only 20% was derived from surface erosion ofhillslopes.
Although a number of workers have discussed the relative stability of the post 1950s SouthernTablelands landscape by comparison with the active periods of the late 19th century and early20th century, the results of Neil and Fogarty indicate that many of the eroded gullies remainunstable and are still contributing a high proportion of the total sediment load.
8.2 Effects of logging and plantation forests on stream sedimentconcentrations
In the highlands along the Great Dividing Range, there are large areas of native forest, some ofwhich are periodically logged for timber. During logging operations there is disturbance to thevegetation and soil, and this can lead to increased erosion rates (Cornish 1989, Wilson 1999).Hartland et al (1991) studied the effects on stream sediment levels of logging alpine ash forestsin the Springs Creek catchment in north-east Victoria. Following roading in 1982 and loggingin 1983, the sediment load in Springs Creek increased by approximately two times over the next5 years, while an adjacent unlogged catchment only increased by 30% over the same period.Other studies have shown that the roads and tracks formed during logging operations can be oneof the dominant sources of sediment in these areas (Croke et al 1999, Campbell and Doeg 1989).
Neil and Fogarty (1991) measured sediment yields from 7 sub-catchments (average area of 47ha.) under pine plantation in the Canberra region, and reported an average yield 33 times higherthan the yields for undisturbed native forest. Analysis of these results indicated that one themain determinants of sediment yield was the amount of roading within each catchment.
Olive and Rieger (1987) found elevated stream sediment levels in logged catchments of southernNSW, but noted that the timing and intensity of rainfall events following harvesting operationshad a major influence on the amount of sediment which enters the stream.
Prosser and Soufi (1998) studied a native forest which had been clear-felled in preparation for aplantation of Pinus radiata. Very heavy rainfall occurred in the year immediately after theclear-fell operations, and widespread rill and gully erosion was initiated. After 12 months thearea had revegetated sufficiently to provide better soil protection and the rates of erosiondeclined. Cassells et al (1982) also reported increased erosion during the establishment of a
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plantation forest, but observed that stream sediment levels had dropped back to the same levelsas adjacent native forest after 2-3 years.
The sediment yields from harvested catchments also depends on site factors such as slope andsoil type and also on the intensity of the harvesting operation, partly because of the higherdensity of roading and partly because of the more intensive site preparation activities followingharvesting (Brown 1983, Blackburn et al 1986).
Another form of disturbance in forested areas are high intensity fires. These can lead toincreased rates of erosion if heavy rainfall occurs immediately after the fire (Prosser andWilliams 1998, Ronan 1986, Leitch et al 1983). However, burnt areas tend to recover fairlyquickly and erosion rates remain high for only a few years, until vegetation cover is re-established.
In summary, sediment yields from forested catchments tend to increase when there is adisturbance to vegetation cover or to the soil surface. This includes logging operations andwildfires. However, under careful forest management, these impacts can be minimized, andsediment yields should drop back to levels similar to undisturbed native forest within 3 to 5years.
8.3 Streambank erosion – another source of sediment in rivers
At high river flows, streambank erosion can be a significant source of sediment, particularlywhere riparian vegetation is absent (Barling and Moore 1993). Severe bank slumping is oftenassociated with water management practices, in particular, the maintenance of high water levelsfor extended periods of time followed by a rapid fall. The saturated streambank soils areweakened and prone to slumping.
Figure 46. Unstable channel banks along Hillas Creek near Tarcutta, NSW. (photo; Anthony Scott)
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Figure 47. Channel bank erosion along Keajura Creek, near Tarcutta, NSW. (photo; Anthony Scott)
8.4 Sediment surveys of reservoirs
The accumulation of sediment in large water storages provides the opportunity to estimatesediment yields for large catchments. By analyzing the different layers of sediment, it is alsopossible to determine the changing rates of sediment delivery over time (for example, Wasson etal 1984).
Using data from Joseph (1953a 1953b, 1960), Erskine (1996) estimated the sediment yield forthe catchment of Big Eildon Reservoir to be 55 m3/km2/yr. Using a bulk density for soil of 1.5,this is equivalent to 83 t/km2/yr (or 0.8 t/ha/yr). (Big Eildon Reservoir was completed in 1955and has a catchment area of 3885 km2).
Abrahams (1972) reported sediment yields based on rates of accumulation of sediment in 14storages in eastern Australia, 9 of which are in the Murray-Darling Basin (Table 3). Yieldsranged from 21 t/km2/yr for Lake Burley Griffin, Canberra, to 198 t/km2/yr for Stephens Creeknear Broken Hill.
An important point to note, is that the specific sediment yield for a catchment (in units oft/km2/yr or t/ha/yr) tends to decline as the area of the catchment increases. Large quantities ofsediment might be eroded from small sub-catchments on hillsides, but most of this sediment isprogressively deposited downstream onto the floodplain as the gradient of the stream flattensout.
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Table 3. Sediment yields for 9 catchments in the Murray-Darling BasinReservoir and location Catchment area
(km2)Sediment yield(t/km2/yr)
Wyangala (Lachlan River) 8300 120Burrinjuck (Murrumbidgee River) 12950 62Hume (Murray River) 15300 63Cunningham Creek (near Yass) 818 99Stephens Creek (near Broken Hill) 513 198Cotter River (ACT) 482 49Lake Burley Griffin (ACT) 1865 21Eildon (Goulburn River) 3885 82Cairn Curran (Loddon River) 1593 34(Data from Abrahams 1972, assuming a sediment bulk density of 1.5 t/m3)
8.5 Erosion studies using small plots or paddocks
Over the last 30 years there have been numerous erosion studies undertaken at plot (0.1 ha) orpaddock scale (1-200 ha), to investigate the rates of erosion for different crops and/or treatments(Edwards 1991, Freebairn and Wockner 1986a, 1986b, Logan 1960, Lang and McCaffery 1984).These studies have shown that the highest rates of erosion occur when the soil is bare and hasbeen recently ploughed (bare fallow). Erosion rates decline if the paddock has not beenploughed, or stubble from the previous crop is incorporated into the soil. Soil erosion is alsoreduced once the crops have grown sufficiently to provide surface cover for the soil.
A typical example of an erosion study undertaken at plot or paddock scale is the workundertaken in the Darling Downs in south-east Queensland during the 1980s. (Freebairn andWockner 1986a, 1986b; Freebairn, Wockner and Silburn 1986; Wockner and Freebairn 1991).Soil erosion is a severe problem on the black soils of the eastern Darling Downs due to thecombination of high intensity storms, large areas of unprotected fallow and the highly erodiblenature of the soils. Greenmount, a farm on a sloping (5-7%) black earth was studied between1976-1989. 5 plots were selected consisting of contour bay catchments (plot area = 0.7-1.4 ha).Treatments included bare fallow, stubble incorporation, stubble mulch, zero tillage, summercrop, and pasture. The results were;
Treatment Erosion rate (t/ha/yr)Bare fallow 49Summer crop 16Stubble incorporated 15.5Mulch 6Zero tillage 3
These results clearly demonstrate the high rates of erosion associated with bare fallow paddocks.It was also observed that summer crops of sorghum, sunflower or maize provided little surfacecover early in the summer storm period when the soil profile often approached saturation.Therefore considerable erosion occurred before the crop canopy covered the soil, if earlysummer storms occurred, unless these crops were planted into stubble.
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It was also observed that 80-90% of the soil which moved during a storm event, was retaineddownslope in the contour bank channel. In the absence of contour banks all the eroded soil wasdeposited at the bottom of the field or carried further downstream.
Once again it should be noted that the specific sediment yield (in units of t/km2/yr or t/ha/yr)tends to decline as the area of the catchment increases. Large quantities of sediment might beeroded from a small experimental plot but much of this sediment is progressively depositedfurther down the paddock or in a contour bank at the end of the paddock. Edwards (1991)estimated that sediment yields of catchments of the scale of 1 km2 are approximately an order ofmagnitude lower than those recorded on small scale plots (0.01 ha in size).
8.6 Studying the impact of single storm events
Adamson (1974) and Edwards (1980) noted that the bulk of soil erosion losses over a longperiod could be attributed to a few storm events. In his study at Wagga Wagga, NSW, Adamsonfound that for improved pasture with erosion control banks, 89% of soil loss was caused bystorms in 5 out of the 22 years of record. Similarly, on wheat plots at Wagga Wagga, the largestsoil loss from one storm event recorded by Edwards was 20% of the total loss of 63.3 t recordedover the entire duration of the 30 year trial. The four largest events accounted for 48% of thesoil loss. It is also interesting to note that large soil losses were almost entirely confined to thefallow period, especially to the warmer months. Losses tend to be small at other times and otherphases of cropping.
Investigations by Erskine and Saynor (1996) of three catastrophic floods on rivers in south-eastern Australia showed that such events can generate between 11 and 283 times the meanannual sediment yield from channel erosion alone.
The soil erosion caused by two major storm events near Cowra, in the wheat belt of NSW, wasmeasured by Hairsine et al (1993) as 342 tonnes per hectare for a paddock under traditionaltillage. This was 7 times greater than the estimated mean annual soil loss for the paddock.
Surveys after two major storm events on the Darling Downs in 1980 and 1981 pictoriallydocumented the damage done in the uplands and floodplains (QDPI 1980, 1981). Marshall et al(1980) examined the damage in some areas of the eastern Darling Downs after the two storms in1980 and concluded that 53% of contour banks failed – most of these in paddocks under barefallow. The banks were usually overtopped after extensive siltation, rather than being broken.In extreme cases where soil was devoid of cover and no contour banks had been constructed, upto 300 t/ha of soil movement was measured (Wockner and Freebairn 1991). High intensitystorms are a characteristic of rainfall in the summer months in the Darling Downs, and thisresults in sporadic runoff and erosion events. Over a 14 year period 81 rainfall events producedrunoff with 556 t/ha of soil movement measured from the stubble burnt treatment. More than70% of this erosion resulted from 6 storms (Wockner and Freebairn 1991).
The erratic nature of soil erosion poses the question of how long should erosion be monitored tosample a representative component of the climate? For example, Wockner and Freebairn (1991)measured soil movement for two consecutive four year periods (a common time period used forscientific studies), 1980-83 and 1984-87. The annual soil losses over these two periods were 78t/ha/yr and 14 t/ha/yr respectively, giving very different impressions of the severity of erosion.
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8.7 Recent surveys of erosion in NSW and Victoria
A survey of land degradation processes in New South Wales was undertaken by the NSW SoilConservation Service in 1987-88 (Graham 1989, Graham et al 1989). The survey used aerialphotographs and field observations, and included sheet and rill erosion, gully erosion, winderosion, scalding and mass movement. It was found that 2.8% of the state was affected bymoderate to extreme sheet and rill erosion, 11.9% by moderate to extreme gully erosion, 2.9%by various types of mass movements, 10.3% by scalding, and 25% by moderate to extreme winderosion. Gully erosion was most extensive along the tablelands and western slopes, and alsoalong the ranges of the semi-arid western region (see Figure 48). As expected, there was astrong association of gully erosion with areas where natural forest and woodland have beencleared for cropping and pasture. More recently, the NSW Department of Land & WaterConservation has mapped gully erosion for a large portion of the state and loaded the data into ageographic information system (GIS). An example of this mapping is shown in Figure 49.
The distribution of gully erosion in Victoria has been presented by Ford et al (1993) and wasderived from the unpublished work of Milton in the 1970s and Sargeant in the 1980s (see Figure50). Ford et al concluded that the pattern of gully density in Victoria was related to theoccurrence of sodic soils. It was also evident that the highest incidence of gully erosiongenerally (but not always) occurred in areas with at least 500mm mean annual rainfall. Areaswith a low incidence of gully erosion were associated with broad, alluvial and basaltic plains,uncleared land, or aeolian landscapes in the west of the State.
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Murray-Darling Basin
Figure 48. Mapping of gully erosion in NSW, undertaken by the NSW Soil Conservation Service in1988. (Data courtesy of the NSW Department of Land & Water Conservation)
112
Blackville
#################################################
#################################################
#################################################
Pine Ridge
Yarraman
#################################################
#################################################
#################################################
Quirindi
Willow Tree
Wallabadah
km
0 5 10
Figure 49. Gully erosion near Quirindi in the Upper Namoi catchment, NSW. Mapping conducted bythe NSW DLWC between 1985 and 1992. (Data courtesy of NSW DLWC)
kilometres< 0.2
0.2 - 0.5
>0.5
>0.5 (on lunettes)
500 100 150
Gully Density (km/km2)
Insignificant
Murray-Darling Basin
Horsham
Nhill
AvocaStawell
Hamilton
Swan Hill
Mildura
Daylesford
Geelong
Ballarat
BendigoEuroa
Echuca
Benalla
Melbourne
Sheparton
Omeo
Wodonga
Wangaratta
Figure 50. Gully erosion density in Victoria. Data was derived from the unpublished work of Milton inthe 1970s and Sargeant in the early 1980s. (Courtesy of the DNRE, Victoria.)
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8.8 Sediment budgets
A sediment budget for a catchment provides information on the amount of sediment eroded fromhillslopes, gullies and stream banks, the amount deposited further downstream, and the amounttransported out of the catchment by the river or stream. This information can be used in thefollowing ways;
- A sediment budget can be used to assess the relative contribution from sheet and rill,gully, stream bank and salt-scald erosion, and this can be used to assist with theprioritising of funding for erosion control works.
- If the sediment budget includes the relative contribution from each of the major sub-catchments, this information can be used to determine which parts of the catchment arein most need of conservation works.
- Information on sediment transport can be used to assess the impact of erosion on waterquality and on the aquatic ecosystem.
- The total load of sediment leaving a catchment provides valuable information on thedownstream impacts of erosion. This might include increased turbidities in rivers belowthe catchment, or siltation of water storages, lakes or estuaries.
- Sediment budgets for pre- and post-European settlement can be used to determine thescale of the impact caused by changes to the landscape over the last 200 years.
Some examples of the methods being used to estimate sediment budgets (past and present), aswell as the relative contributions from the different forms of erosion, are provided below.
a) Field measurements of erosion rates.The total load of sediment from erosion gullies can be estimated from the volume of the existinggully system. Measurements from experimental plots or paddocks can be used to estimate sheetand rill erosion for different land uses. Erosion of stream banks can be estimated by measuringthe rate of retreat (or collapse) by inserting ‘erosion pins’ into the bank walls. The total erosionrate for various sub-catchments can be estimated from the siltation rates of farm dams or waterstorages. Neil and Fogarty (1991) for instance, examined their data for siltation of farm dams inthe Southern Tablelands, and compared the results from gullied and ungullied catchments. Theyestimated that the gullies were contributing about 80% of the total sediment yield.
Prosser et al (1994) estimated the mean rate of sediment yield from Wangrah Creek sinceEuropean settlement, by measuring the dimensions and age of the present gully network. Gullyerosion commenced in the 1840s and the first aerial photographs, taken in 1944, show that thelength, width and depth of gullies were approximately the same as exist today. The length of thegully network is 22km, average depth 3m and average width 5m, giving a total volume of3.3x105m3. Assuming most of the erosion took place between 1842 and 1944, this rate oferosion is 33 times higher than the long term estimate for the undisturbed swampy meadow ofnearby Limekiln Creek.
Rutherfurd and Smith (1992) studied the sources of sediment in Bromley Stream, a tributary ofthe Avoca River in western Victoria. They estimated that almost 100,000 m3 of sediment hadbeen released from the surrounding catchment into Bromley Stream over the last century. Thisconsisted of about 56,000m3 of bedload (gravel and sand), 90% of which came from erodinggullies, and 39,000 m3 of suspended load (silt and clay), 50% of which came from the gullies.At least 80% of the coarse material (sand and gravel) had been deposited into Bromley Stream
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or onto the adjacent floodplain, and had not reached the Avoca River. The remaining 20% ofsand had entered the Avoca River, although much of it was deposited within 200 metres of thejunction. This was in contrast to the finer particles, the silt and clay, most of which hadprobably entered the Avoca River and moved further downstream.
b) Using radioactive tracers.Surface soils are labeled by the fallout of the radionuclide tracers caesium-137 (137Cs is aproduct of nuclear weapons testing), and lead-210 (210Pb is a natural product of decay of theuranium series). These radionuclides are at their highest concentrations in the top fewcentimeters of soil. Therefore, sediment originating from surface erosion contains high levels ofthese radionuclide tracers. On the other hand, sediment originating from subsoil erosion, such asgully erosion or riverbank collapse, contains very low concentrations of radionuclides. So bycomparing the radionuclide concentration found in river sediments with the concentrations forsurface soils and subsoils, it is possible to determine what proportion of the river sedimentsoriginated from surface erosion and subsoil erosion. Using this method, Wallbrink et al (1996)estimated that about 90% of the suspended sediment in transport in the lower MurrumbidgeeRiver comes from subsoil erosion.
Loughran and Elliot (1996) measured the levels of caesium-137 that remained in the topsoil,along transects in agricultural and pastoral districts of South Australia, Victoria, New SouthWales and Queensland. These measurements were used to estimate how much caesium-137 hasbeen eroded from the surface, which in turn provides an estimate of net soil loss from sheeterosion. The highest net soil losses were of the order of 8-15 t/ha/yr (or 800 to 1500 t/km2/yr)under conditions of cropping (wheat rotation, potatoes, vegetables and vines). The lowest soillosses, generally in the order of 0.0 to 2.0 t/ha/yr (0.0 to 200 t/km2/yr), were recorded for grazingand forested areas. This work suggests that land use is an important controlling factor for soilerosion.
c) Modelling erosion processes, sediment transport and sediment delivery.In recent years, concern over erosion and sediment transport has shifted from on-site effectssuch as farm productivity and damage to engineering works, to downstream effects on theaquatic ecosystems of rivers, lakes and estuaries (Prosser et al 2001a). As a first step inassessing these impacts, the CSIRO recently undertook a nationwide assessment of the sedimentregime of rivers within the intensive land use zone (Prosser et al 2001b). The project assessed;
- sediment supply to rivers from hillslope, gully and streambank erosion;- the extent of sand slugs formed by increased bedload transport;- the suspended sediment loads of rivers; and- sediment delivery to the coast.
For many catchments there was very little data on erosion rates and river sediment loads, and theassessment was therefore compelled to use some method to interpolate and extrapolate to areaswith no data.
The approach used was to collect as much data as possible and then apply a relatively simplephysically-based model of the main driving processes of sediment transport at the scale of largecatchments. Predictions for sheet and rill erosion were based on the Universal Soil LossEquation (USLE). Gully erosion predictions were based on selective mapping from aerialphotographs and an existing database of gully erosion in NSW.
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The SedNet model (Sediment delivery through River Networks) developed for the projectconstructed a mean annual sediment budget sequentially downstream through each link of ariver network. National grids of hillslope erosion (Lu et al 2001) and gully erosion (Hughes etal 2001) were used to determine sediment inputs into each link from the surrounding catchment.The other inputs are sediment yield from the tributaries to the link, and prediction of bankerosion along the link. Bank erosion rate was assessed using the relationship with bankfulldischarge of Rutherfurd (2000) and the length of bank cleared of riparian vegetation.
Observed sediment yields from river basins are far lower than the sediment inputs into the rivernetwork. It was therefore essential to model deposition through the river network. Suspendedsediment and bedload have quite different transport processes and thus were modelledseparately.
The final outputs from this model were estimates for each catchment of hillslope erosion, gullyerosion, riverbank erosion, the load of sediment deposited downstream and the sedimentdelivery to estuaries.
This provided the first national assessment of sediment supply, sediment transport and sedimentdelivery and will be used to assess the ecological impacts of sediment accumulation alongriverine and estuarine systems. It will also provide a valuable tool for identifying the highestpriority areas for future funding of erosion control.
As further data becomes available, more refined assessments can be re-calculated for catchmentsof particular interest.
Figure 51. Large quantities of sand have been deposited in the upper reaches of the MurrumbidgeeRiver at Tharwa. This sand originates from accelerated erosion of pastoral land in upstream catchments.Early descriptions of the Murrumbidgee River near Tharwa indicate that it previously contained a seriesof deep waterholes. (photo; Anthony Scott)
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d) Measurements of sediment transport in riversThoms and Walker (1992) used water quality measurements over 16 years at eight stations in themiddle and upper reaches of the Murray River, and in three major tributaries, to estimatesediment loads. Concentrations of suspended sediment were highly variable, ranging from 1 to269 mg/L. The average annual suspended sediment load for the Murray at Tocumwal, thefarthest downstream station was 134,400 tonnes. This is much less than loads recorded for othersemi-arid river systems and may reflect low rainfall erosion potential, low basin relief and thehigh trap efficiencies of the two large impoundments. There was considerable variation inannual sediment loads over the 16 years of record, with higher loads during wet years. Forinstance, at Yarrawonga, 43% of the 16 year cumulative sediment load was transported in 1974-75 when sustained major flooding occurred. Channel erosion was the single most importantcontributor of sediment, supplying 69% of the average annual load. Channel erosion ispromoted by the changed flow regime and by abrupt changes in water level associated withflow management. The two reservoirs on the Murray retained large quantities of sediment,totaling more than 1.47 million tonnes over the 16 years of record. The estimated trapefficiencies were 35% for Lake Hume and 52% for Lake Mulwala.
Figure 52. Highly turbid water in the Goulburn River at Murchison, Victoria. The turbidity of riversand streams has increased since pre-European times due to higher sediment loads from accelerated soilerosion of hillslopes, gullies and channel banks. (photo; Anthony Scott)
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e) Estimating the increase in erosion since European settlementThere have been numerous studies which have estimated the increase in erosion since Europeansettlement, some of which are described below;
• The data of Neil and Fogarty (1991) indicated that erosion rates have increased between4 and 60 times from ‘natural’ or pre-European rates, depending on the current land-usesin the catchment.
• Wasson et al (1996), using the results of Rosewell (1997), predicted that the rate ofhillslope erosion across Australia has increased 100-fold in historical times as a result ofcatchment clearing and agricultural land use.
• Prosser et al (1994) estimated a 30-fold increase in erosion rates for a headwatercatchment in the Southern Tablelands of NSW.
• Thoms et al (1999) analysed sediment deposited on the floodplain of the Murray Riverand estimated that sedimentation had increased by an order of magnitude since Europeansettlement.
• Haworth et al (1999) analysed Lead-210 in sediments of Black Mountain Lagoon on theNew England Tablelands of NSW, and concluded that the erosion rates for the 20th
century were at least an order of magnitude higher than those for pre-European times.
All of these results indicate that erosion rates have increased by an order of magnitude or moresince European settlement. There is also some evidence, both quantitative and anecdotal, that incatchments where land clearing and pastoral activities commenced over 100 years ago, erosionrates might have reached their peak and are now slowly declining (Wasson et al 1998).
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9. Looking to the FutureIn the early 19th century, European farmers and pastoralists started to settle in the Murray-Darling Basin. The large numbers of sheep and cattle that they brought with them, grazed theperennial grasses and reduced the protective cover of the soil. The hard hooves of the stock alsotended to disturb the soil, particularly along streamlines and near waterholes. Disturbance to theland accelerated in the second half of the 19th century as settlement intensified, land clearingbecame common practice and in some areas gold mining commenced. This resulted in amassive increase in soil erosion, which probably reached a peak during the second half of the19th century and the first half of the 20th century.
Today, many of the areas cleared during the 19th century are gradually stabilising as vegetationcover is re-established, and the rates of erosion are slowly declining from their peaks. However,the current levels of erosion are still many times higher than those of pre-European times, andthe legacy of the past 180 years continues to have a significant impact on both the environmentand agricultural productivity.
Although most areas which were cleared long ago are showing signs of stabilization, there aresome catchments which have eroded badly in the last few decades, and continue to supply highsediment loads to downstream rivers. In other parts of the Basin, land clearing has continuedthough the 20th century and these areas will remain unstable for many decades to come. In somedistricts, particularly along the western slopes of the Basin, the continuing trend of convertingpastoral land to cropping land will also result in increasing rates of erosion.
So, what are the lessons that we can learn from the mistakes of the past? Essentially, the past180 years has demonstrated that many of the agricultural practices have been unsuitable for thesoils and climate of the Murray-Darling Basin. Short term productivity was achieved at theexpense of long term sustainability. Improved farming practices which protect the soil fromerosion have now been developed and should be introduced throughout the Basin. This includespractices such as maintaining vegetation cover, avoiding overgrazing and minimizing tillage. Insome regions, however, long term sustainability might only be achieved by replacing existingland uses with a completely different type of farming that places less demands on the soil. Inother areas, particularly in the arid regions, sustainable agriculture might not be possible, andlarge sections of land might need to be taken out of production and replanted with nativevegetation.
A major source of the sediment in rivers is derived from erosion of channel banks. This has ledto an increased awareness of the importance of riparian vegetation along streams and rivers andit is essential that future land management continues to target the protection of this riparian land.
When the first Soil Conservation Agencies started to take action, they initially concentrated onearthworks that targeted highly eroded sections of specific farms. Although these efforts werequite successful in controlling erosion, it soon became clear that it would be far too expensive totreat every erosion gully on every farm. Therefore, an increasing amount of effort was placed onthe prevention of further erosion by treating the causes rather than the symptoms. The idea ofcatchment-wide planning, and the changing of land management practices on a large scale, wasgradually accepted as a better option for the long term reduction of erosion. This broadercatchment-wide perspective needs to be the basis of all land management in the future, not onlyfor the control of erosion, but also for other sustainability issues such as dryland salinity.
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Figure 53. Clearing of riparian vegetation along a creek near Miles, QLD.Such activities lead to unstable channel banks and increased risk oferosion during floods. (photo; Anthony Scott)
Since it will be impossible to treat all land affected by erosion, a simple method of identifyingthe major sources of sediment within each sub-catchment would provide a useful tool formanagement agencies in the future. The CSIRO is developing such a tool by using acombination of field data and computer models to construct a catchment-scale sediment budgetwhich includes sediment sources, sediment transport and sediment delivery. These models canalso be used to test different options for future management options within the catchment. Themodels can identify which parts of the catchment contribute the highest loads of sediment torivers, and hence where restoration works should be located to provide the greatestimprovement.
Although much of the early work by Soil Conservation Agencies concentrated on reducing theloss of soil from paddocks by developing better land management practices, it is clear that on
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most cropping land the rate of soil loss is still far greater than the long term rate of soilformation. The direct or ‘on-site’ consequences of this long term soil loss include;
• loss of nutrients required for plants to grow;• loss of organic matter which plays a vital role in sustaining the desirable physical and
chemical characteristics of soil; and• loss in the ability of the soil to store water which can be drawn on by plants between
rainfall events.
For a time, loss of soil productivity may be economically substituted by applying fertilizers.However, reduction in the depth of the topsoil which roots can penetrate, will ultimately reducethe effectiveness of such chemical substitution. If this is not addressed, the productivity of largeareas of cropping land will not be sustained. Further research is still needed to develop betterland management practices which reduce soil erosion rates to levels equivalent to the long termrates of soil formation.
Figure 54. Recent tree planting and fencing along an erosion gully on a property between Bendigo andMaldon in Central Victoria. In recent years, Federal and State funds, through community programmessuch as Landcare and Greening Australia, have assisted farmers with such work. (photo; Anthony Scott)
Initially erosion control concentrated on addressing the on-site effects such as loss of soil andformation of deep gullies across paddocks, but more recently there has also been an increasingawareness of off-site effects such as the increased sedimentation and turbidity of downstreamrivers, lakes and estuaries. Increased sediment loads in rivers can have the following effects onwater quality and physical habitat;
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• increased water turbidity,• increased nutrient concentrations,• the formation of large ‘sand slugs’ in river channels and the filling of pools, and• the siltation of downstream estuaries and lakes.
These effects are likely to have significant impacts on the aquatic ecology of the water bodies.Although some of the ecological impacts have been studied, there is a need to improve ourunderstanding so that cost effective solutions can be initiated.
Figure 55. Farmers, with the assistance of Greening Australia, plan future tree planting activities arounderoded gullies on the Glencoe property south-east of Murrumbateman, NSW. Funds for the tree plantingare being provided by the Federal Government’s Natural Heritage Trust (NHT). (photo; Nicki Taws)
An important lesson that must be learnt from the past, is that the repair of the land should not beleft to the individual farmer but is the responsibility of the whole community as well as the Stateand Federal governments. The poor land management practices of the last 180 years were aresult of government policies just as much as the activities of the farmers. The repair of the landcommenced in the 1940s only after the State and Federal governments recognized theseriousness of the problem and accepted that the costs were beyond that of individual farmers.It is vital that government funding of sustainable land management continues, and, hopefully inthe future, both the government and the community will take a more pro-active approach, ratherthan reacting after the damage has been done.
Unfortunately, there are some regions within the Basin, where the mistakes of the past are stillbeing repeated. While large amounts of money are being spent by State and Federal
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Governments to replant trees in areas of the Basin that were heavily cleared over 100 years ago,large scale land clearing continues in other areas. Most of this land clearing occurs in the moreremote western and northern parts of the Basin, but even in the more closely settled regions inthe east and south of the Basin, where very little native vegetation remains, the last largeeucalypts scattered around the paddocks are being removed to grow high value crops. It isessential that we protect the remaining native vegetation throughout the Basin, not only forerosion control but for a host of other reasons such as prevention of dryland salinity andprotection of the native flora and fauna.
This report has provided a brief history of European settlement and the associated agriculturaland mining activities within the Murray Darling Basin over the last 180 years. These activitiesled to a massive increase in soil erosion which potentially threatens the long term sustainabilityof the Basin. In the early to mid 20th century a growing awareness of soil erosion led to theformation of Soil Conservation Agencies and increasing efforts to improve our management ofthe land. Although we have (hopefully) learnt from the mistakes made in the past, soil erosioncontinues to be a serious environmental problem in many regions of the Murray-Darling Basin,and this requires ongoing attention and continued financial support. Caring for the land is theresponsibility of the farmers, the governments and the whole community.
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