Identification of areas in Australia where soil loss from hillslope erosion … · 2009. 11. 17. · erosion by water. The process builds upon the 2008 expert panel’s work but,

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[Title]

Identification of areas in Australia where soil loss from hillslope erosion could be reduced Peter B. Hairsine, Michele Barson, Lucy Randall and Scott N. Wilkinson

CSIRO Land and Water Report 45/09 October 2009

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CSIRO Land and Water Science Report series ISSN: 1834-6618

Copyright and Disclaimer © 2008 CSIRO To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO.

Important Disclaimer: CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it.

Citation: Peter B. Hairsine1, Michele Barson2, Lucy Randall3 and Scott N. Wilkinson4.Identification of areas in Australia where soil loss from hillslope erosion could be reduced. . CSIRO Land and Water Science Report 45/09. 1 Peter Hairsine CSIRO Land and Water PO Box 1666 Canberra 2601 Australia [email protected] 2 Dr Michele Barson Science Adviser Australian Government Land and Coasts Division 3 Dr Lucy Randall Land and Forest Sciences Bureau of Rural Sciences GPO 858, Canberra ACT 2601 4 Dr Scott N. Wilkinson CSIRO Land and Water PMB Aitkenvale QLD 4814 Cover Photograph: Peter Hairsine (private collection)

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Acknowledgements The following State agency Expert panel participants are thanked for their contributions to the assessment process: Dr Dan Carter, Jim Dixon, Paul Novelly of the Western Australian Department of Agriculture and Food; Giles Forward and James Hall, South Australian Department of Water Land and Biodiversity Conservation; Darren Kidd, Tasmanian Department of Primary Industries, Parks, Water and Environment; Dr Brian Murphy, Greg Chapman, Dr Xihua Yang, NSW Department of Environment and Climate Change; Jason Hill, NT Natural Resources, Environment, Arts and Sport, Bernie Powell, Dr Mark Silburn, Queensland Department of Environment and Resource Management; David Rees, Clem Sturmfels, Victorian Department of Primary Industries. The state and regional natural resource management organisations which provided additional maps of hillslope erosion for consideration in the Expert Panel process are also thanked for their assistance.

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Executive summary This report describes the 2009 expert panel process that underpins the spatial targeting of the Caring for Our Country (C4OC) investment concerning hillslope soil erosion by water. The process builds upon the 2008 expert panel’s work but, in response to feedback, produces a national map concerning the severity of hillslope erosion by water that reflects very recent research and is of a finer spatial resolution. In most of the Australian landscape the rate of soil erosion far exceeds the rate of soil formation. As a result, soil erosion is a fundamental threat to the sustainability of Australia’s lands and the ecosystem services it supports. Soil erosion by water, including sheet and rill erosion, is a major, often-dominant, form of soil erosion in the Australian landscape. The process described in this report is confined to sheet and rill erosion (also known, in combination, as hillslope erosion). Hillslope erosion impacts both the productive ability of the soil and the quality of environments at that location and downstream.

The expert panel concluded that the National Land and Water Resources Audit (NLWRA) 2001 dataset of mean annual sheet and rill erosion rate is currently the most up to date available dataset available for national comparative assessments. Its limitations have been demonstrated in the assessment undertaken during this process. These limitations are reflected in the product maps and tables of this report. While a number of regional natural resource management organisations have invested in mapping or modelling the extent of hillslope erosion for their areas since 2001, the variety of approaches used means that these data sets can not be readily compared and are thus not suitable for national assessments. The primary product of the expert panel’s work is a national map of the severity of hillslope erosion, presented as those areas assessed to have a hillslope erosion rate of greater than 5 tonnes per hectare per annum. This map is shown in figure 2. This product is intended for use in region to region and district to district comparisons. It is not intended for use in property to property comparisons. The panel concluded that the limitations of the primary national assessment of hillslope soil erosion in the 2001 NLWRA were a significant constraint to the expert panel’s task and that investment in a major update to this product is warranted.

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Purpose of this process Here we describe the 2009 expert panel process that underpins the guidelines concerning the management of soil erosion by water for the 2010-2011 Caring for our Country Business Plan. Sustainable farm practices are a key aspect of the Caring for our Country Initiative. To address this issue the business plan for the initiative guides applicants to address specific targets. The process reported here supports the target: Improving Land Management Practices. This report identifies at a national scale where in the agricultural landscape hillslope (sheet and rill) erosion is likely to be a significant issue.

What is different from last year? The maps prepared for the 2009-2010 Caring for Our Country Business Plan have been revised to identify locations within each region where improving land management practices to reduce soil loss by controlling hillslope erosion will result in the biggest benefits. The expert panel also took into consideration recent research into hillslope erosion and information provided by some state and regional natural resources management organisations. This data served to provide more specific guidance as to the limitations of the current national mapping.

Background Soil provides an essential physical and biological component of all rural landscapes. Soils form from parent materials over time scales of thousands of years. It is widely recognised that soil erosion in human impacted landscapes is occurring at many times the rate of soil formation, so soil is being depleted. The reduction of soil loss by good land management practices is vital to preserve this resource and stop downstream impacts of eroded soil. Soil erosion by water is widespread in Australian landscapes. It has many forms including sheet and rill erosion of hillslopes, gullies, tunnels, and stream bank erosion. Rainfall and runoff, as agents of erosion, are supplied to the Australian landscape in a highly variable manner. An important feature of the erosion processes in the Australian landscape is that erosive episodes are frequently linked with preceding prolonged dry periods. At these times, soils are especially exposed to water erosion where vegetative ground cover is sparse and offers little protection. The process described in this report is limited to hillslope erosion, that is, the processes of sheet-wash and rill erosion. These processes directly impact on the productive capacity of the land, and are directly influenced by broad-scale land management practices including grazing management and cropping practices. Other forms of water erosion (streambank and gully erosion) are being addressed in the Great Barrier Reef and Gippsland Lakes catchments where more specific information is available on the location of sediment sources and the impact of these processes on water quality. Elsewhere gully and streambank erosion is a significant problem for downstream impacts of soil erosion. While the panel recognised these forms of erosion as important the scope of the panel’s work was limited to hillslope erosion by the emphasis in the policy process and the availability of a suitable national data set to support the assessment of gully and streambank erosion.

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The Australian Agriculture Assessment 2001 was conducted as part of the National Land and Water Resources Audit (NLWRA 2001). This assessment mapped the spatial patterns in erosion processes, and the off-farm exports and fluxes of sediments, carbon and nutrients across the Australian continent. A national map of hillslope erosion was produced as part of the NLWRA. This map provided the first detailed national assessment of hillslope erosion severity. Much of the 2001 soil erosion assessment remains current, but in recent years there have been some new regional assessments with improved data and interpretation. Details of these assessments and their influence on the deliberations of the panel are set out below.

The expert panel process In June 2009 Australian Government Land and Coasts convened an expert panel to update the hillslope erosion maps for the Caring for our Country 2010-11 Business Plan. Invitations to join this panel were made to acknowledged regional experts in the field of soil erosion by water. All jurisdictions except the ACT provided one or two experts to this process. Most members of the panel also served in the 2008 expert panel process. Drs Scott Wilkinson and Peter Hairsine from the CSIRO joined the panel to provide a national overview. Dr Wilkinson was a lead member of the team who did the 2001 national assessment of soil erosion by water as part of the National Land and Water Resources Audit. Table 1 sets out the membership and roles of the 2009 panel. Table 1: Membership and roles of the 2009 expert panel for hillslope erosion Jurisdiction/role Expert Organisation Convenor Dr Michele Barson Australian Government

Land and Coasts Western Australia Dr Dan Carter, Jim Dixon,

Paul Novelly Department of Agriculture and Food

South Australia Giles Forward, James Hall Department of Water Land and Biodiversity Conservation

Chair Dr Peter Hairsine CSIRO Land and Water Tasmania Darren Kidd Department of Primary

Industries, Parks, Water and Environment

New South Wales Dr Brian Murphy, Greg Chapman, Dr Xihua Yang

Department of Environment, Climate Change and Water

Northern Territory Jason Hill Natural Resources, Environment, Arts and Sport

Queensland Bernie Powell, Dr Mark Silburn

Department of Environment and Resource Management

Spatial analyst Dr Lucy Randall Australian Government , Bureau of Rural Sciences

Victoria David Rees, Clem Sturmfels

Department of Primary Industries

National technical oversight

Dr Scott Wilkinson CSIRO Land and Water

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Preparatory steps As the most recent national assessment, the 2001 National Land and Water Resources maps of hillslope soil erosion by water formed the starting point for the panel’s work. This map is reproduced in Figure 1.

Figure 1 Mean annual sheetwash and rill erosion rate (Source: National Land and Water Resources Audit 2001). The digital data for mean annual sheet wash and rill erosion were reprocessed with catchment scale land use data (Bureau of Rural Sciences, 2009) to produce maps which identified agricultural areas where predicted average annual hillslope erosion rates were greater than 5 tonnes per hectare per year. This map was segmented into NRM regions for initial review by the panel. The panel were asked to assess the accuracy of the maps and provide an update and interpretation on the basis of local knowledge and more recently published regional studies.

Moderation process and results The expert panel met by teleconference to discuss the maps and panel members’ comments and to moderate them through cross comparison. In a national technical assessment, cross comparison and technical moderation is needed to ensure consistency of results across the country. Panel members were provided with the maps developed from the NLWRA and additional material provided by regional organisations (see Appendix 2). For each NRM region, the panel was tasked with commenting on whether the extent of erosion > 5 tonnes/ha/year shown on the maps produced by the Bureau of Rural Sciences was correct. If the maps were not correct, was the erosion under or over estimated? Panel members were asked to provide additional information in support of their assessments. The assessments for each region were then discussed by panel members to ensure that the approach had been applied consistently. Appendix 1 presents the results of this process.

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The panel agreed that for 32 of Australia’s 56 natural resources management regions, the mapped data (see Figure 2) was an adequate representation of the extent of hillslope erosion > 5 tonnes/ha/year on agricultural lands. For 13 regions it was agreed that the mapped data underestimated hillslope erosion (at > 5 tonnes/ha/year). The mapped data over-estimated hillslope erosion in four regions. For seven regions dominated by extensive grazing (regions 304, 306, 310, 313, 314, 503, and 701) it was agreed that the areas of hillslope erosion > 5 tonnes/ha/year were substantially over-estimated, and that these data would be excluded from the final map.

Outcomes of the Expert Panel Process Figure 2 presents the primary product of the expert panel process. This map shows the areas of Australia where hillslope erosion is likely to be greater than 5 tonnes per hectare per annum. The NLWRA hillslope erosion assessment identified rates of hillslope erosion > 5 tonnes/ha/year as “high”. It is the view of the panel that this is a key threshold above which it is appropriate that investment is justified for urgent intervention to manage this form of land degradation. The map in Figure 2 presents this assessment at a spatial resolution of 1:25,000,000 (1 cm represents 250 km). Most natural resource management regions have areas above and below the threshold. The spatial resolution of this assessment will help improve national targeting of resources needed to improve land management practices which will reduce soil loss through hillslope erosion. However, the panel cautions readers not to over interpret the assessment shown in Figure 2. This is useful for district comparisons (e.g. the upland versus the lowlands of a region), but is not suitable for comparisons between individual sites or properties. The map reflects the limitations for the current use of the NLWRA 2001 hillslope erosion assessment. In areas where the Audit data are considered an under estimate of the extent of high rates of hillslope erosion, predominantly in southern Australia, the resolution of the data may have been too coarse to capture some of the finer scaled patterning of agricultural land use or the land use has intensified since the Audit analysis. This is confirmed by the results of recent modelling (see Appendix 1 and references) using the same approach employed to produce the Audit data set and/or advice from state agency staff. The Audit data are thought to have over estimated the extent of hillslope erosion for four coastal Queensland regions because the vegetation cover values estimated from remote sensing for the modelling process were incorrect (too low). This has been confirmed by subsequent research in these regions. In the grazing lands of northern Australia, dead and dry vegetation was frequently incorrectly classified as bare ground from remotely sensed data. Use of these data in the Audit assessment overestimated the rates of hillslope erosion for these areas. However, comparison between the NLWRA assessment and plot erosion measurements confirm that northern regions have considerably more erosion potential than southern regions (Lu et al., 2003). The panel assessed that these regions had generally high erosion rates, particularly where pastoral lands are overgrazed or on bare slopes after fires; and that they would include some areas of high priority for erosion control. The panel agreed that no data on the extent of hillslope erosion would be presented for these regions. The overestimation of hillslope erosion in the grazing lands of northern Australia problem has been acknowledged by the authors of the 2001 NL&WRA. Development of new remote sensing methods for separating out bare ground, non photosynthetic

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(dry) and photosynthetic (green) vegetation (Guerschman et al., 2009) will enable this problem to be overcome for future assessments.

Concluding remarks The NLWRA 2001 dataset mean annual sheet and rill erosion rate is currently the most up to date available dataset available for national comparative assessments. Its limitations have been demonstrated in this assessment undertaken for Caring for our Country. While a number of regional natural resource management organisations have invested in mapping or modelling the extent of hillslope erosion for their areas, the variety of approaches used means that these data sets can not be readily compared and are thus not current suitable for national assessments. A number of the inputs used to develop the mean annual sheet and rill erosion rate data set are now available at better levels of resolution, and improved remotely sensed ground cover data are available. Many of these have been well demonstrated in recent regional assessments. Furthermore, there is a great deal of expertise in mapping hillslope erosion in the states and regions that can inform this new national effort. It is recommended that an improved version of this data set be developed at a higher level of resolution and that the limitations of the NLWRA 2001 assessment in grazing lands as identified here be addressed.

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Figure 2 – Locations where improving management practices on agricultural land to reduce soil loss from hillslope (sheet and rill erosion) will provide the biggest benefits.

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References Note that many of these references are drawn from the following appendices. Bureau of Rural Sciences (2009) Catchment scale land use mapping for Australia Update April 2009 (CLUM Update 04/09) dataset. Guerschman, J.P., Hill, M.J., Renzullo L.J., Barrett, D.J., Marks, A.S. and Botha, E.J.2009). Estimating fractional cover of photosynthetic vegetation, non-photosynthetic vegetation and bare soil in the Australian tropical savanna region upscaling the EO-1 Hyperion and MODIS sensors. Remote Sensing of Environment, Vol 113, 928-945

Lu, H., Prosser, I.P., Moran, C.J., Gallant, J., Priestley, G., Stevenson, J. (2003) Predicting sheetwash and rill erosion over the Australian continent. Australian Journal of Soil Research 41, 1037-1062.

NLWRA. 2001. Australian Agriculture Assessment (2001) National Land and Water Resources Audit, Canberra. http://www.anra.gov.au/topics/publications.

New South Wales Emery, Keith (1992) Land use and erosion survey. See http://www.canri.nsw.gov.au/nrdd/records/ANZNS0359000148.html Graham, O.P. 1989, Land Degradation Survey of NSW 1987-1988: Methodology, Soil Conservation Service of NSW (SCS) Technical Report No. 7, SCS, Sydney. Yang, X, Chapman G.A., Murphy, C. and Heemstra, S. (2006). Estimating soil erosion hazard for NSW coastal catchments using RUSLE in a GIS environment. Proceedings of 10th Annual SIA Conference on Urban Stormwater Management (on CD ROM), Parramatta, 28-30 June 2006. Northern Territory Dilshad M (2007). A preliminary assessment of hillslope (sheet and rill) erosion and associated suspended sediment movement in the Daly River catchment, Northern Territory Department of Natural Resources, Environment and the Arts technical report 18/2008D. Queensland Brodie, J., McKergow, L. A., Prosser, I. P., Furnas, M., Hughes, A.O., Hunter, H., 2003. Sources of sediment and nutrient exports to the Great Barrier Reef World Heritage Area. Report Number 03/11, Australian Centre for Tropical Freshwater Research, Townsville. Cogle A., L, Carroll C., Sherman B.S., (2006). The use of SedNet and ANNEX models to guide GBR catchment sediment and nutrient target setting. Department of Natural Resources, Mines and Water report Dougall, C., Carroll, C., Herring, M., Trevithick, R., Neilsen, S., Burger, P., 2008. Enhanced sediment and nutrient modelling and target setting in the Fitzroy Basin. Queensland Department of Natural Resources and Water, 70 pp. Hateley, L., 2007. Fingerprinting sources of sediment in the Tully River catchment, North Queensland, Honours Thesis, James Cook University. Kinsey-Henderson, A., Sherman, B., Bartley, R., 2007. Improved SedNet Modelling of Grazing Lands in the Burdekin Catchment. Science Report 63/07, CSIRO Land and Water. http://www.clw.csiro.au/publications/science/2007/sr63-07.pdf.

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Olley, J., Wilkinson, S., Caitcheon, G., Read, A., 2006. Protecting Moreton Bay: How can we reduce sediment and nutrient loads by 50%? 9th International River Symposium, 4-7 September 2006, Brisbane. Prosser, I.P., Wilkinson, L.J., Hughes, A.O., Caitcheon, G., 2003. Patterns of Erosion and Sediment and Nutrient Transport in the West Brisbane River Catchment, Queensland. Technical Report, CSIRO Land and Water, Canberra. Rohde, K., Masters, B., Sherman, B.S., Read, A., Chen, Y., Brodie, J., Cogle, A., 2006. Sediment and nutrient modelling in the Mackay Whitsunday NRM region. Volume 4. In: Cogle, A.L., Carroll, C., Sherman, B. (Eds.), The use of SedNet and ANNEX models to guide GBR catchment sediment and nutrient target setting, Queensland Department of Natural Resources, Mines and Water. QNRM06138, 218 pp. http://www.wqonline.info/products/short_term_modelling.html Rohde K, Windel J, Wake J Higham W and Trendell P (2008). Effectiveness of Best Management Practices for water quality in GBR Catchments: sugar cane in the Mackay region. Centre for Environmental Management, Central Queensland University, Rockhampton. South Australia DWLBC (2007). Land and Soil Spatial Data for Southern South Australia - GIS Format. Water Erosion Potential Spatial Data (mapped at 1:50,000 or 1:100,000 scale). Soil & Land Program. SA Dept of Water, Land & Biodiversity Conservation [CD ROM]. DWLBC (2008). Land Use Mapping of South Australia (mapped at 1:100,000 scale). Science, Monitoring & Information, Information Group. Dept of Water, Land & Biodiversity Conservation, South Australia. (DWLBC Web Feature Server http://10.92.14.22). DLWBC (2009). Estimated Water Erosion Severity - Map of South Australia's Agricultural Districts. Map representation of landscape model incorporating water erosion potential and land use spatial data (mapped at 1:50,000 and 1:100,000). Soil & Land Program. SA Dept of Water, Land & Biodiversity Conservation. Tasmania Cotching WE and Sims CC (2003). Linking water quality and land use in northwest Tasmania. Natural Resource Management 6(2): 12-20. Richley L, Loughran RJ, Elliott GL and Saynor MJ (1997). A national reconnaissance survey of soil erosion, Tasmanian. Australian National Landcare report, Department of Primary Industries and Energy. Victoria DeRose, R.C., Prosser, I.P., Wilkinson, L.J., Hughes, A.O., Young, W.J., 2003. Regional patterns of erosion and sediment and nutrient transport in the Goulburn and Broken River catchments, Victoria. Technical Report 11/03, CSIRO Land and Water, Canberra, 51 pp. Hancock, G., Wilkinson, S., Read, A., 2007. Sources of sediment and nutrients to the Gippsland Lakes assessed using catchment modelling and sediment tracers. Science Report 70/07, CSIRO Land and Water, Canberra.

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Western Australia Bligh KJ (1987).Water erosion in the Geraldton area during June-July 1986. Technical Report 59. Division of Resource Management, Western Australian Department of Agriculture. Loughran RJ, McFarlane DJ Campbell BL and R Shepherd (1993). The distribution of caesium-137 in rangeland soils at three sites in Western Australia. Rangeland J. 15, 24-38. McFarlane DJ and Ryder AT (1987). Water erosion survey in the Northam District after storms in June 1986. Technical Report 57. Division of Resource Management, Western Australian Department of Agriculture. McFarlane DJ, Delroy N, Gratte H, Middlemas JP, van Vreeswyk AME and I McKissock (1989). Water erosion on vegetable growing land in south Western Australia. Technical Report 107. Division of Resource Management, Western Australian Department of Agriculture. Payne AL, Curry PJ and GF Spencer (1987). An inventory and condition survey of rangelands in the Carnarvon Basin, Western Australia. Technical Bulletin No.73. Western Australian Department of Agriculture. Summers RN (1987). The incidence and severity of non-wetting soils of the south coast of Western Australia. MSc Thesis, University of Western Australia. Van Vreeswyk AME, Payne AL, Leighton KA and P Hennig (2004). An inventory and condition survey of rangelands of the Pilbara region, Western Australia. Technical Bulletin No.92. Western Australian Department of Agriculture.

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Appendix 1: Expert panel hillslope erosion assessment

Region Region name

Is the extent of the high erosion class (≥ 5 tonnes/ha/year correctly shown in

the Audit (2001) data? Comments

New South Wales

101 Border Rivers-Gwydir yes

Accords with estimates previously made: Peasley (pers. comm.), NSW land degradation survey (Graham 1989), land use and erosion survey (Emery 1992) See http://www.canri.nsw.gov.au/nrdd/records/ANZNS0359000148.html

102 Central West yes

103 Hawkesbury-Nepean yes

104 Hunter-Central Rivers yes

Spatial patterns are similar to those mapped by Yang et al. (2006).

105 Lachlan yes

106 Lower Murray Darling yes

107 Murray yes 108 Murrumbidgee yes

109 Namoi no

Expansion of cropping onto more sloping land is believed to have led to a larger area where mean annual hill slope erosion ≥ 5 tonnes/ha/year

110 Northern Rivers yes

111 Southern Rivers yes

112 Sydney Metro yes 113 Western yes

Victoria

201 Corangamite yes

202 East Gippsland no

Surface sediment tracing and high resolution SedNet modelling both indicate the long-term contribution of hillslope erosion in the Tambo River catchment is at least 2 times than indicated by the Audit map (Hancock et al., 2007).

203 Glenelg Hopkins yes

204 Goulburn Broken no

Significant areas of hillslope erosion on uplands areas see DeRose et al., (2003)

205 Mallee yes Wind erosion main issue in this region

206 North Central no

High rates of hillslope erosion believed to occur on granitic hillslopes around Pyalong and Harcourt

207 North East yes

208 Port Phillip and Westernport no

High rates of hillslope erosion believed to occur in the Parwan valley and Darraweit Guim areas.

209 West Gippsland yes Extent shown in Audit data about right.

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Region Region name



210 Wimmera no

Cropping has expanded onto previously grazed hilly country in the upper catchment of the Wimmera river. Mean annual hill slope erosion on marginal soils in this area is now ≥ 5 tonnes/ha/year.

Queensland

301

Border Rivers Maranoa - Balonne no

It is thought that the Audit data may have underestimated the area of hillslope erosion > 5 tonnes/ha/year in this diverse agricultural landscape.

302 Burdekin no

Audit data overestimates hillslope erosion here by 2–3 times because the cover values estimated from remote sensing were incorrect. See comparison with Kinsey-Henderson et al., 2007.

303 Burnett Mary no

Audit data overestimated hillslope erosion here because the cover values estimated from remote sensing were incorrect. Brodie et al (2003) suggest that annual rates of hillslope erosion in this region are mostly < 5 tonnes/ha.

304 Cape York no

Audit data significantly overestimated hillslope erosion here because the cover values estimated from remote sensing were incorrect.

305 Condamine yes

306 Desert Channels no

Audit data overestimated hillslope erosion here because the cover values estimated from remote sensing were incorrect.

307 Fitzroy no

Audit data overestimated hillslope erosion here by 2–3 times because the cover values estimated from remote sensing were incorrect. See comparison with Dougall et al., (2008).

308 Mackay Whitsunday no

Comparison with available water quality based load estimates indicates that the NLWRA over-estimated hillslope erosion in grazing areas by 2–3 times (Rohde et al., 2006).

310 Northern Gulf no


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Region Region name



311 South East Queensland yes

Audit data is probably about right here. Prosser et al., 2003 used high resolution land use and terrain data and found 25% of the area had >5 t/ha erosion rate (compared with ~30% for NLWRA). Prosser et al. (2003) and Olley et al. (2006) estimate that Moreton Bay on average is receiving about 280,000 tonnes of fine sediment a year; 80% of this sediment comes from 20% of the catchment area, mostly from streambank and gully erosion, not hillslope erosion.

312 South West Queensland yes

313 Southern Gulf no


314 Torres Strait no


315 Wet Tropics no

Recent SedNet modelling indicates twice the NLWRA hillslope erosion (Armour et al., 2007). This recent modelling is consistent with sediment tracing data (Hately et al. 2007).

South Australia

401 Alinytjara Wilurara yes

402 Eyre Peninsula no

The extent of the high erosion class shown in the Audit data is too low. The DWLBC Soil & Land Program landscape modelling (2009) estimated that there are 194,000 ha on the Lower Eyre Peninsula and the Cleve Hills where hillslope erosion rates are high (≥ 5 tonnes/ha/year).

403 Kangaroo Island yes

Audit data agrees with modelling done for the DWLBC Soil & Land Program June 2009.

404

Adelaide and Mount Lofty Ranges no

The extent of the high erosion class is too low. The SA modelling estimates that there are 73,000 ha of agricultural land in this region where hillslope erosion rates are high (≥ 5 tonnes/ha/year) (DWLBC Soil & Land Program landscape modelling 2009, using data from DWLBC (2007) and DWLBC (2008).

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Region Region name



405 Northern and Yorke no

The extent of the high erosion class shown in the Audit data is too low. The SA modelling estimates that there are 501,000 ha of agricultural land in this region where hillslope erosion rates are high (≥ 5 tonnes/ha/year) (DWLBC Soil & Land Program landscape modelling 2009, using data from DWLBC (2007) and DWLBC (2008).

406

South Australian Arid Lands yes

407

South Australian Murray Darling Basin yes


408 South East yes


Western Australia

501 Avon yes

Audit data generally in agreement with previous work; rates of hillslope erosion are generally higher on the western side of region (McFarlane and Ryder 1986) and lower in east (Kevin Bligh pers. comm.).

502 Northern Agricultural yes

The only significant area affected is north of Geraldton (Bligh1987).

503 Rangelands no

Audit data overestimated hillslope erosion in the northern parts of the rangelands because the cover values estimated from remote sensing were incorrect. Estimates from Cs137 studies indicate that soil loss could be >10t/ha/yr in Kimberley and West Pilbara-Gascoyne (Loughran et al.1993). Rangeland Condition Surveys (Payne et al. 1987 and Van Vreeswyk et al. 2004) show that in pastoral areas there is a strong relationship between high soil loss and grasslands, in shrublands soil losses are lower. In future, WA rangelands could be subdivided into smaller regions for assessment.

504 South Coast no

The Audit data may underestimate the areas affected by high rates of hillslope erosion. The south flowing rivers are well incised into landscapes and hillslope erosion on the change-of-slope is evident in some catchments. Extensive water repellent soils contribute to overland flow (Summers 1987).

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Region Region name



505 South West yes

Audit data are generally correct but have not picked up hillslope erosion associated with horticulture in Manjimup/Donnybrook areas (McFarlane et al. 1989). Erosion in the Kellerberrin area may be over-estimated.

506 Swan yes Few properties affected. Tasmania

601 North yes

602 North West no

Audit data provide insufficient detail in this region. Risk mapping using land use, slope class, soil parent material, and Tasmanian land capability rules shows that approximately 47% of the agricultural land has a high to severe erosion risk (however, no groundcover data are available to predict areas of actual erosion). C-137 trials (Richley et al. 1997) have shown long term soil losses on Tasmanian ferrosols in the north-west to be 2.3 to 5.2 t/ha/yr, with direct measurements of 10 to 142 t/ha/yr on bare or fallow ground (Cotching and Sims 2003).

603 South yes

701 Northern Territory no

Audit data significantly overestimated hillslope erosion in the north because the cover values estimated from remote sensing were incorrect. In the south, the extent of hillslope erosion is probably underestimated. There are some cropped lands in the Daly catchment where hillslope erosion is ≥ 5 tonnes/ha/year (Dilshad 2007). On low slopes in the Daly, soil loss from conventionally tilled croplands without soil conservation banks can exceed 100 tonnes/ha/year. With conservation banks, losses range from 2-13 tonnes/ha/year. Cropping in the Daly basin is a small (2-3%) but expanding proportion of the catchment.

801 ACT yes There are relatively small areas of modified pastures in the ACT.

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Appendix 3 Additional maps provided for comparison with the Audit 2001

hillslope (sheetwash and rill) erosion data

Region Organisation (Data Source)

Map

NSW DECC LSC/Water quality region Tasmania DPIW Areas of potential hillslope (water) erosion under

grazing and cropping land N. Tasmania DPIPWE Tas Flood erosion image August 2005 North Western Tasmania

University of Tasmania and TIAR

Percentage sub-catchment supporting cropland with erosion potential

South East Queensland

SEQ catchments Hillslope erosion – SPOT 2006 imagery South East Queensland

South East Queensland

SEQ catchments Erosion priorities South East Queensland Region

Namoi Namoi CMA Sheet erosion in the Namoi catchment Namoi DLWC Excerpt from Banks, R G (2001) Soil landscapes of the

Tamworth 1:100,000 sheet Western Australia

Agriculture WA Areas of high, very high or extreme susceptibility to water erosion

Mount Lofty Ranges

CSIRO Land and Water

High resolution predicted hillslope erosion

Great Barrier Reef catchments

Australian Centre for Tropical Freshwater Research

Predicted hillslope erosion under natural conditions in the GBR catchment

Western Port Bay


Predicted hillslope erosion (using the Revised Universal Soil Loss Equation) in Western Port Bay

Murrumbidgee catchment


Mean annual hillslope erosion rate used in SedNet

Murray region (NSW)


Predicted hillslope erosion (using the revised Universal Soil Loss Equation) fro the NSW Murray region

West Brisbane catchment


Predicted soil erosion hazard in the west Brisbane River catchment

Goulburn-Broken catchment


Mean annual hillslope erosion rate used in SedNet

Border River - Gwydir

DECC High risk water erosion area at NRM Region 101 (Border River – Gwydir, NSW)

Southern Rivers, NSW

DECC High risk water erosion area at NRM Region 111 (Southern Rivers, NSW)

NSW DECC High risk water erosion area in NSW and Bar chart of Percent of high risk water erosion in NSW

Southern South Australia

DWLBC Water erosion potential map and Excel spreadsheet SA Water erosion potential data statistics by NRM region

Queensland DERM Hillslope erosion dataset Lake Argyle, WA

ANU Wasson et al. 2002 Sourcing sediment using multiple tracers in the catchment of Lake Argyle, Northwestern Australia. Environmental Management 29 (5): 634-646

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Identification of areas in Australia where soil loss from hillslope erosion … · 2009. 11. 17. · erosion by water. The process builds upon the 2008 expert panel’s work but,