Seepage Remediation Case Studies

8/13/2019 Seepage Remediation Case Studies

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Case studies of projects by cotton growers

to remedy seepage losses from on-farm storages

Seepage RemediationCase Studies of Grower Practices

COTTON STORAGES PROJECT 2011

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ContentsIntroduction ............................................. 1

Caithness, Moree .................................... 3

Red Bank, Moree ..................................... 4

Boolooroo, Moree .................................... 5

Warren, NSW ........................................... 6

Bethel, Moree .......................................... 8

Baroma Park, Moree ............................... 9

Balmoral, Brookstead ............................10

Fairford, Moree .......................................11

Brighann, Moree .....................................12

St George, Qld ........................................13

Kensington Park, Dalby ..........................14

Long Meadows, Bourke..........................16

Disclaimer

The views and opinions expressed in this publication are those of

the authors and do not necessarily reflect those of the Australian

Government, the Minister for Sustainability, Environment, Water,

Population and Communities or the National Water Commission.

While reasonable efforts have been made to ensure that

the contents of this publication are factually correct, the

Commonwealth does not accept responsibility for the accuracy or

completeness of the contents, and shall not be liable for any loss

or damage that may be occasioned directly or indirectly through

the use of, or reliance on, the contents of this publication.

Acknowledgement

This work was funded by the Australian Government through the

National Water Commissions Raising National Water Standards

Program.

Copyright Cotton Catchment Communities CRC 2011

This publication is copyright. Except as permitted under

the Copyright Act 1968, no part of this publication may be

reproduced by any process, electronic or otherwise, without the

specific written permission of the copyright owner. Neither may

information be stored electronically in anyway whatever with out

such permission.


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About the Project

On-farm water storages are an integral component of mostirrigated cotton farms in Australia. However recent whole farmwater balance studies have indicated that around 30 to 40% ofall water on farm can be lost in storages. This comprises thebiggest proportion of on farm water loss out of any component ofthe irrigation system.

To determine the extent of storage losses, the National WaterCommission, through its Raising National Water StandardsProgram, funded the Cotton Catchment Communities CRC toundertake this project Measurement to improve the waterefficiency of on-farm storages in the cotton industry.

The project has used commercial consultants to determineevaporation and seepage losses from individual storages usingthe Irrimate Seepage and Evaporation Meter. The project hasnow measured over 135 storages to determine the magnitude ofthese losses.

To complement this new knowledge, the case studies in thisbooklet provide examples of works that growers have undertakenin the past to remedy storages with unacceptable seepage losses.As the causes of seepage issues are often difficult to identify,some of these case studies have been effectively resolved whilst

others remain a work in progress. It is hoped that the lessonsthat these growers have been able to provide might help otherswho are also looking to remedy their own seepage problems.

Acknowledgement

Many thanks go to the growers and consultants who haveprovided very insightful information for these case studies andwithout whom this publication would not be possible. Also to thewriters and photographers who contributed to this publicationand to Broons for supplying images of their square impact roller.

Featured Seepage Remediation Options

This publication includes a range of works that growers haveimplemented in order to address seepage issues. Note thatother options are available which may not be discussed here (forexample plastic liners) although there were no examples of theiruse within these case studies.

Measurement and Identification

The first step in seepage remediation is identification of the

problem. Measurement of seepage losses has traditionally beenchallenging as it is difficult to differentiate seepage losses fromevaporation losses. For storages with very high seepage, thisassessment is often made visually, as water levels may drop veryrapidly over a period of weeks.

However, an accurate measure of seepage is still very useful fordetermining the cost effectiveness of possible solutions. Untilrecently, there was no widely available technology for undertakingsuch measurements. However a new technology, the IrrimateSeepage and Evaporation Meter, has been used with successwithin this project and is able to cost effectively separate seepageand evaporation losses within a storage.

Once a seepage problem is identified, the next challenge isdetermining the nature of the seepage loss. Evidence in the casestudies in this publication suggests that most seepage problemsoccur in discrete locations within a storage, rather than uniformlyacross the storage floor. Such problems are often due to thepresence of small sections of sandy or gravelly soil.

In many of the case studies, a combination of EM surveys andphysical inspections (test holes or excavation pits) were used toidentify these regions. As one of the case study growers noted,EM surveys can be very useful for identifying particular problemareas, but they are not completely foolproof, and ground truthingthe results is important to ensure that potential issues do not gounnoticed.

Another method of investigation, resistivity imaging, was used byone grower to look at cross sections of soil profile in significantdetail.

Clay lining and compaction

The most predominant type of seepage solution employed bygrowers involved the application of additional clay materialover suspect areas, sometimes with additional compaction.Compaction of existing materials was also used on someoccasions.

The case studies indicate that the methods for undertaking theseworks can vary significantly. The depth of clay lining varied from0.25m up to 2m. Some growers chose to overlay this compactedclay with additional material of around 0.5m thick to prevent thecompacted area from drying out.

Introduction

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Introduction

Compaction was provided by various means, with some growersrelying on the compaction provided by earthmoving machinery(bulldozers, scrapers or laser buckets) whilst others appliedadditional compaction with sheepsfoot rollers or square impactrollers.

The level of compaction provided by different equipment shouldbe considered when undertaking this type of work. In particular,tractors and bulldozers are designed to spread their load over alarge area to avoid compaction and ensure traction. As can beseen in Figure 1, equipment designed for compaction, such asthe sheepsfoot roller, provide many times more compaction than

a bulldozer, even though the machine weight is lower.

Figure 1 - Compaction pressures applied by different equipment(Source: Guidelines for Ring Tank Storages, Irrigation Australia Limited)

Soil type is also a key consideration. Many clay soils in cottongrowing regions have a large shrink-swell capacity. Therefore ifcompacted clay is allowed to dry out, it will most likely crack openand the effectiveness of the compaction will be diminished. Thisis why some growers have chosen to overlay their compacted soilwith additional material to try and prevent cracking.

Planting crops in empty storages will dry the soil more than

evaporation alone and will almost surely reduce or completelyremove the effectiveness of compaction. For this reason, plantingcrops in storages is strongly discouraged.

Bentonite

Bentonite is a type of clay which has a very large shrink-swellcharacteristic that results in a very low permeability when wet.Bentonite suppliers should be able to provide advice regardingthe best application method for specific applications and soiltypes. The most common methods of application are:

Pure Blanket a layer of pure bentonite of around 10mm

thickness is used with a protective compacted covering ofsoil.

Mixed Blanket Bentonite is incorporated into the existing

soil at a rate of around 50 to 150 t/ha depending upon theexisting soil characteristics.

Broadcast Bentonite is applied to the surface of a storage

which contains water and allowed to settle to the bottom ofthe storage.

It is suggested that blanket techniques are more effective, withthe potential to reduce seepage by 65 to 95%, whilst broadcastingis more likely to result in a 30 to 50% reduction. It is critical toensure that bentonite is applied at the recommended rates and inthe recommended manner as the results may not be satisfactorywhen the rate of application is too low. As with clay lining,a protective cover of at least 0.5m of soil is likely to improve

performance and longevity.

Polyacrylamide

Polyacrylamides (PAM) are chemicals used in a variety ofindustries including the food and water industries. Specific PAMformulations, typically high molecular weight products, havebeen found to provide seepage reduction in some cases.

PAM can be applied to the soil surface, where it may or may notbe incorporated in to the soil. It can also be broadcast over a bodyof water. Whilst evidence of PAM effectiveness exists, the only useof the product within these case studies does not seem to have

reduced seepage loss.

The use of PAM may be of lower cost than some structuralsolutions, although the PAM is likely to need reapplication atregular intervals and the seepage reduction effectiveness maybe variable.


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Property: Caithness, Moree

Grower: Kelly Humphries

Background

In an effort to increase on farm storageafter purchasing Caithness northwest ofMoree in NSW, owner Kelly Humphriesselected an existing storage to renovate.The storage was relatively shallow andhad an irregular shape that reflected thecourse of a nearby waterway.

Kelly says the original storage structuredid not leak. However, when renovationsto increase storage capacity were beingcarried out a few years ago, water wasnoticed seeping into the dam from asection of the storage floor that wasadjacent to the river.

Prior to commencing renovations to theexisting storage, Kelly commissionedSMK Consultants in Moree to carry out anEM-31 survey on the dam to check thatthe soil material was likely to be suitable.The EM-31 survey revealed some variationin the soil conductivity across the storagearea. Immediately following the EM-31

survey, soil trenches were dug using abackhoe to approximately 3 meters toinvestigate the soils corresponding todifferent colours on the EM-31 map.These trenches did not reveal any soilmaterial that would be unsuitable forholding water.

The Problem

Construction began to increase thestorage capacity by excavating a further1.8m of material from the storage floorand an additional 2.5m of material wasadded to the wall height. As the excavationwas taking place, it was discovered thatwater was seeping into the dam.

The original EM-31 survey map was thenreviewed and it was realised that someof the green areas on the south easterncorner of the map corresponded with thearea where the water was being seen inthe dam floor. Using the backhoe thatwas onsite for excavations, Kelly hadnumerous pits dug to investigate the soilat depth in those areas revealing a seamof sandy soil in that corner of the storage.It is believed that this sandy seam waspart of a previous watercourse that ranunderground through to the nearbyriverbed and that water must have beenseeping into the excavated area from the

river. It was likely that once the storagewas filled, water would move out of thestorage in the same way.

The Solution

To prevent seepage from the renovatedstructure, the area in the south easterncorner of the storage, where sand hadbeen found at depth, was clay lined.Suitable clay material was taken fromother areas of the storage to create a1meter deep lining which raised thestorage floor to the height of the naturalground level outside the dam wall. Theclay was spread using a laser bucket

which Kelly believes also providedadequate compaction so no furthercompaction was required.

The Outcome

The dam currently has a water levelof approximately 3m. Measurementstaken recently by John Doble fromGwydir Valley Irrigators Association(GVIA) using the Irrimate Seepage andEvaporation Meter, indicate seepage

to be approximately 200mm/year (lessthan 1 mm/day) demonstrating that theremediation work was successful.

The seepage remediation was estimatedto have cost approximately $30,000 whichKelly says was well worth the expense.

The Future

Kelly questions whether the rate ofseepage will be greater when the storageis at full capacity but is happy with the

outcome of clay lining.

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Property: Red Bank, Moree

Grower: Ray Fox

Background

Red Bank is a property owned byAustralian Food and Fibre located nearMoree. The propertys only on-farm waterstorage is 300 ML with an area of 12.5ha. The storage is built on red clay overa sandy base and has a creek nearby. Itis believed to have been constructed inthe late 1980s and has been consistentlyused every year. It is usually dry for threeto four months over winter.

The Problem

There was no abnormal water lossobserved or recorded until around 2004/05when it was noticed that the water levelwas dropping more than Ray believedcould be attributed to evaporation. Thechange in water depth was measured anda loss of approximately 10mm/day wasestimated.

Seepage was believed to be occurring in

the vicinity of the original pump site whichwas moved in the late 1990s. Due to thenearby creek, visual evidence of seepagewas generally not noticed. However, onoccasion the outside wall would lookdamp low on the base of the storageto the east of the old pump site. Raybelieved that the wall was not compactedsufficiently when the pump site wasmoved.

The Solution

Renovation work was initiated in 2005 torepair the area believed to be responsiblefor the leak. The storage was emptied andthe inside wall adjacent to the old pumpsite was covered with 30cm of black claywhich was cut from the storage floor. Thework was completed using a laser bucketwith no additional compaction of the clay.The storage was utilised immediatelyafter the work was completed.

The Outcome

The renovation significantly reducedthe seepage losses for the next 2 to3 years. However, losses were againobserved when the storage was filled forthe 2008/09 season. Losses are againestimated at around 10mm/day and areevident when the storage is more thanone third full. Ray initially noted that theredid not seem to be any seepage occurring

when the storage level was below onethird capacity. However during Novemberand December of 2010 Ray noticed thatwater losses actually seemed to beoccurring regardless of the water volumestored in the dam.

The Future

AFF have now contracted surveyors SMKto conduct an EM survey. Soil pits willalso be dug to identify the full extent ofthe problem. The intention is to repairthe area identified in the EM survey withclay. They will also ensure that the clay iscompacted more thoroughly than it wasin 2005. This work is expected to takeplace during 2011.



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Property: Boolooroo, Moree

Grower: Ray Fox

Background

Boolooroo is an irrigated cotton propertynorth of Moree in the Gwydir Valley, whichhas been recently leased by AustralianFood and Fibre (AFF). Manager Ray Foxnoticed water levels on a 30 ha, 700 MLstorage were dropping more rapidlythan he believed could be attributed toevaporation.

The Problem

Ray observed that the storage lost waterregardless of how full it was, whichsuggested to him that the seepage wasoccurring through the floor. He measuredwater height changes and estimatedseepage losses of approximately 6 mm/day. The storage was built around 2001,but as Boolooroo had only recently beenleased by AFF, Ray was unsure of howlong it had been losing water.

The Solution

The storage was emptied to allow soil pitsto be dug and an EM survey conducted. Itwas identified that the water losses werelikely to be attributed to some gravellysoil found on the storage floor.

In 2008, remediation work was initiated.The entire floor of the storage wascovered with a 30-40cm layer of clayimported from elsewhere on the property.The spreading and levelling work wascompleted using a scraper to compactthe clay. The storage was utilisedimmediately after completion of the workand has not been completely empty sincerenovations took place.

The Outcome

To date the renovation has beensuccessful and only evaporation lossesare now being observed from the storagesays Ray.




Background

In 1994 a water storage dam wasconstructed on a property near Warrenin NSW. Prior to construction, anengineering consultant was engagedto investigate the site and design asuitable water storage dam. Following acursory inspection and 2 test pits, it wasconsidered that material at the site wouldbe suitable for construction of the waterstorage and a design was supplied.

Elevating bowl scrapers were usedto construct the storage. Material forthe walls was dug from a borrow pitand sourced from the cheapest sitesto transfer soil from. A key trench wasbuilt approximately 0.5m deep under thewalls around the entire perimeter of thestorage. No additional compaction wascarried out during this initial constructionphase. The final storage was 650m by290m with a 2m high wall and a capacityof 350ML. Within a few months of

completion the water storage was filled.

The Problem

After the next seasons cotton crop wasplanted, prolific growth of the cottonplants was observed in a specific area ofthe field adjacent to the water storage.The soil was boggy and wet and thereforeit was assumed that water was somehowleaking from the newly filled waterstorage.

The Solution

In May 1995, Pat Hulme, a local soilconsultant was contracted to assist inidentifying the problem.

An EM31 survey was carried out whichshowed a strip of material with lowelectrical conductivity running throughthe water storage area. Pat followed upon this with permeameter tests, 5 testpits and more than 40 test holes.

The pits revealed sand at approximately2m in some areas, but more than 3.5mof continuous clay in others. One test sitehad clay over sand whilst another site hadsand over clay. It was surmised that waterwas moving through these sand layersinto the nearby field.

A square impact roller was hired in aneffort to compact the storage floor andslow seepage losses. However afterrefilling the storage, permeametermeasurements confirmed that this had

not been effective.In 1996, to better understand themovement of water through the differentsand layers, the Department of Land andWater Conservation drilled 6 test holesaround the water storage and adjacentfield to a depth of 20m or until the firstaquifer was penetrated. The test holeswere then monitored with piezometers.In some cases 2 pipes were installed 1m

Property: Located near Warren, NSW

Consultant: Pat Hulme,Sustainable Soils Management

Water leaks into the green area at the top of the photo, but not into the redder crop at the bottom of the photo


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apart. In these cases, one of the holesmeasured changes to the deeper aquiferand the other measured changes to thewater table closer to the ground surfacelevel. It was hoped that this would revealhow well the two aquifers were connected.

The pattern varied between the sites.The water level rose very quickly in bothpiezometers in the part of the field thatwet quickly (the blue area near the bottomright of the EM survey). The water level

in this piezometer followed the storagewater level very closely. In contrast, therewas little movement in the water level ofthe piezometer in the dry part of the field(the yellow area near the bottom left ofthe EM survey).

These observations indicated that waterfrom the storage was seeping throughthe floor material down to the underlyingsand layers where interconnected localaquifers were present. It is thought thatthe sand layers are the remains of priorstream beach areas where curves in the

stream channel cause sand to accumulateinside bends and then facilitatemovement of water underground. Thisexplains the clearly delineated wet areain the adjacent field. Although the floormaterial was largely clay, it was allowingwater seepage into the aquifer.

In this case, compaction alone, did notreduce seepage sufficiently to preventthe problem of water leaking into thefield. This is consistent with the generalperformance of compaction, which

generally reduces seepage, but otherthan a few exceptions, does not stop itsays Pat.

The problem was managed for a fewyears by emptying the water storage intime to allow pick and other operationsto be carried out. However, eventually itwas decided to cut off the worst sectionof the water storage by moving part ofthe storage wall. The EM-31 survey mapand test pit results were used to selectthe area of the storage to remove. Theremediation design proved challenging as

the leaky areas were running diagonallyacross the storage floor and around theinlet area.

A supply channel had to be constructedto take water to the new inlet area whichmeant crossing the area of sandy soil.Although this would be expensive it wasrealised that by reducing the area ofproblematic soil that required lining, claycould be brought in for the supply channelat less of a cost than lining the entireproblem area if the wall was not moved.

The site was remediated using elevatingscrapers with 200mm lifts. Clay soil was

sourced from an area adjacent to thereservoir and used to line the supplychannel and a few small areas within thestorage that were identified on the EM-31map and test holes to have sandy soils.

The remediated areas of the storage andthe supply channel were then compactedusing a self-propelled sheepsfoot roller.To maximise compaction, the work wascarried out when the soil was moist.

Capacity of the storage was reduced from350ML to 300ML however seepage was

no longer occurring.

The Outcome

Moving the wall, clay lining andcompaction have successfully minimisedseepage from this storage. Pat Hulmeremarks that It is important to note thatthe problem was found by soil coringdifferent parts of the water storage andthat the low conductivity results from theEM31 survey were caused by 2 differentsoil problems. One was sand over clay;the other was clay over sand. Where

sand lays over clay there is likely to be aproblem with water seeping through thestorage floor and moving through thesandy layer. However, if there is relativelyimpermeable clay over sand, the claylayer is likely to prevent seepage intothe sand layer. This can only be realisedby soil coring areas identified as suspectfrom the EM31 survey.



Property: Bethel, Moree

Grower: Mark and Peter Winter

Background

Brothers Mark and Peter Winter farmthree properties along Carole Creek,North West of Moree. On one of theseproperties, Bethel, they have 500ML and2500ML storages. Whilst they believedthe 2500ML storage held water quitewell, losses from the 500ML seemedunaccepetably high, most likely the resultof seepage loss.

The Problem

Construction of this storage started in theearly 80s when Peter and Mark startedto push up the walls with dozers. Whileworking in the area of the North Westcorner, they discovered a seam of gravelwhich would not have been suitablematerial to have the storage built upon.

They proceeded to bore a number of holesinside the proposed wall location. Fromthese holes, they determined that if they

were to cut the corner off the proposedstorage design, they would be able to moveaway from the area of gravel and have thestorage sited on suitable clay soil. Henceby the late 80s they had a new storagedesign that had a wall approximately100m from where the original cornerwould have been. Scrapers were broughtin to finish wall construction and ensureappropriate compaction of the clay core

in the wall.

However, once the storage was filled,it appeared that seepage could still bea problem. By measuring the changein depth of water over a period of time,Peter determined that perhaps thestorage was losing 20ML of water perweek . He believed that this amountwould be well in excess of the potentialloss to evaporation, indicating that someseepage must be occurring.

Furthermore, evidence of moist soil wasoccasionally noticeable at some pointsoutside of the storage, near the base ofthe wall. This occurred not only in thecorner of the storage near where thegravel had been previously found, but alsoalong other sections of wall altogether.

The Solution

In around 1994, the Winters brought ina square impact roller to provide some

compaction over the storage base. Theentire storage floor to about halfway upthe batters was first ripped to a depth of14 or 15 inches (350 to 380 mm). Thenthe square impact roller was used overthis entire area to provide compaction.Mark notes that in some areas of lighterred soil, 3 passes of the impact rollerwas sufficient to provide substantialcompaction. At this point, the roller was

providing little additional compactionwith the force of the strike being passedthrough to the tractor.

However the black clay areas required7 passes of the impact roller to providesimilar compaction. In this same soil type,the roller was also used to compact asection of channel, where the compactionresulted in a drop of the channel soilheight of around 8 to 10 inches (200 to250 mm).

Following the use of the impact roller,Peter recalculated the losses, and judgedthat the total loss was more or lesshalved, but was still not satisfied that theseepage was completely under control.

Some years later, an EM survey wascompleted to see if any significant soildifferences could be identified whichmight be causing seepage in particularareas. The EM survey indicated that anarea of lighter soil in the North Westcorner might have an increased potential

for seepage.This time, Mark and Peter tried usingBentonite, as this was more cost effectivefor a smaller area than the use of theimpact roller. Bentonite was spread overthis area and offset discs were used toincorporate it into the soil, before theirown machinery was used to provide somecompaction.

The Outcome

Although the seepage has been reducedsince the storage was first constructed,Mark and Peter are still not satisfiedthat they have completely rectified theseepage problem, and therefore thisstorage is not regularly used. They arecurrently carrying out further works tominimise losses through more efficientwater transfer between storages.



Property: Baroma Park, Moree

Grower: Gary Taunton

Background

The water storage at Baroma Park wasconstructed in the mid 1980s. It is an800 ML storage, with 3.5 to 4m highwalls. It was built on alluvial river flatsand originally had trees growing in thestorage at one end.

The Problem

Sometime between 1985 and 1989 a wallwas constructed across the centre of thestorage. This was constructed as waterwas seeping from the end of the storagewhich contained the trees.

In 1989 after Gary had purchased theproperty he siphoned water into theproblem area of the storage. Gary foundthat the storage did not hold even 1m ofwater for a week. There was no evidenceof water outside the storage so heconcluded that the seepage was goingdirectly down.

The borrow pit in this part of the storagewas particularly deep, almost 2m deeperthan the floor. Gary also observed that thesoil in the borrow pit was more gravelythan the remainder of the floor area. It ispossible that the borrow pit extended intoan old river bed.

Because of the high losses, this part of

the storage was not used again until afterrenovation could take place.

The Solution

In 1991 Gary renovated the storage. Thetrees were removed and the borrow pitwas filled with soil from the higher areasof the floor. The work was done with ascraper with no additional compaction. Atthe completion of the work the floor waseven and it sloped to the pipe through thedividing wall. A gate was installed in thepipe to enable water management.

The Outcome

The renovated area of the storagewas filled straight after the work wascompleted and has been used continuallyever since. The storage is used to holdboth bore and river water so there areconstant changes in the storage duringsummer.

During autumn there is normally no wateradded to the storage. Gary has noticedduring this time that there are some

minor water losses which may possiblybe more than expected from evaporationalone. However they are only very minimaland have not been measured.



Property: Balmoral, Brookstead

Grower: Russell Clapham

Background

Balmoral is an irrigation propertylocated near Brookstead on the DarlingDowns. It is owned and operated by theClapham family. Russell Clapham hasbeen growing cotton for 20 years, withirrigated production for the last 13 yearson Balmoral. The soils on Balmoralare cracking clays typical of the region.The property has four storages whichcurrently all lose water at similar rates.

The Problem

When the Clapham family purchasedBalmoral 13 years ago, a 500ML, two-celled water storage had recently beenconstructed. However, the previousowner reported that the storage wasleaking. One cell had much higherseepage losses, losing more than doublethe amount from the other cell. WhileRussell did not have any evidence of the

extent of the leakage he decided to tryand identify the cause of the seepage lossbefore filling the dam.

An excavator was used to dig pilottrenches to explore the base of the dam.A sand bed was found approximately 1.5m below the surface of the dam base.This sand bed was at least three metresdeep and originated from a prior streamadjacent to the storage.

The Solution

Once Russell had identified the sand bedhe decided to line this area with clay.Clay was sourced from another areaof the storage that was identified to bestable and have good quality clay. Helayered 600 mm of this clay over the sandbed. This clay layer was then compactedusing a Broons square impact roller. Anadditional 400-600mm of soil was thenlayered over the compacted clay liner.

Russell carries out opportunemaintenance on the dams to furtherminimise seepage losses. When thedam is empty and they receive sufficientrainfall to wet the base of the dam hewill compact the base by trafficking withtractors to help seal it. He finds that thisis effective ongoing maintenance to helpreduce seepage losses but it does not fixthe problem.

He performs a similar operation aroundthe banks of the storage if it has been dry

for extended periods. A tractor with widespread duals will be used with one wheelbelow the water surface to compact thebank around the water level.

The Outcome

The clay lining to address seepage losseswas moderately successful for a limitedtime. It reduced the seepage losses forthree years before the storage startedleaking again.

It is estimated that the storage is currentlylosing approximately 13 mm per day. Thisis based on dam water height lossesover the five months of March to July2010. According to Russell the storagelost 2 m in height during this period. Itis likely that losses from the storagewill be greater over summer months asevaporation losses increase.

The Future

The next step is to identify more preciselywhat component of the losses is due toseepage and what is due to evaporation.This will require some more detailedmonitoring of the dam using technology

such as the Irrimate Seepage andEvaporation Meter, which was used toundertake these types of measurementsin the Cotton Storages Project. Otheroptions to stop the seepage may thenhave to be identified. Russell says that hewill have to stop the seepage but first Ineed to know what is seepage loss andwhat is evaporation loss



Background

Stephen Seery recently renovated a 25haon-farm storage as he changed thestorage configuration on his propertyFairford in the Gwydir Valley. The originalstorage, which had been built around1980, did not have a seepage problem.

The Problem

Prior to commencing the reconstructionin 2007/08, Stephen had an EM surveycarried out to assist with identifying areasof soil that may not have had good sealingproperties. Stephen also dug a number ofsoil pits up to 3 meters using a backhoeas he suspected that there may havebeen gravel on the dam floor that wasnot showing up on the EM survey. The soilpits confirmed Stephens suspicions.

Gravelly soil was found using soil pits inplaces that had been identified as suitablefor use in the EM survey. Stephen says he

believed that An EM survey could alertyou to possible problem areas, but wouldnot necessarily identify all the potentiallyproblematic soil types as demonstratedin this case.

The Solution

During construction it was ensured thatthey left 1 meter of clay cover over anyof the areas where they had identifiedunsuitable gravelly soil. In other areas ofthe storage, the floor was dug out usingbulldozers to a depth of 1.8m below theoriginal floor. Scrapers were used to finishthe storage and no other compaction wascarried out.

A few months after construction thestorage was trialled with approximately1300 ML of water, filling it to ground level.The water level dropped significantly overthe following 2 weeks so it was decidedto move the water. Stephen estimatesapproximately 300 ML was lost duringthis short time.

Once the storage was empty Stephenwas able to visually determine where onthe floor the seepage was occurring. Onthe inside of one wall at the bottom of thebatter and across the borrow pit there were

a series of sink holes, approximately 5-10cm deep, with smaller tunnels off these.

Investigation of these sink holes with asoil probe indicated that there was a layerof gravel underneath these depressions.To identify all the problem areas thewhole floor of the storage was visuallyassessed and probed, which confirmedthe presence of gravel at a number ofother sites.

To remediate the problem, 1 meter ofblack clay sourced from outside thestorage was back filled over the gravellysoil areas. Clay was also added acrossthe remaining area which was cut deeperin the initial development. In total, theremediation work required 50,000 cubicmetres of clay. A 70 tonne bulldozer wasused to spread the clay but no furthercompaction was undertaken.

The OutcomeThe storage has now been filledover the 2010-11 season since theseepage remediation was completed.Unfortunately the seepage has beenslowed down but has not been stoppedcompletely. Inspecting the storage againhas indicated that the work that wasundertaken was successful, but that therewere some other areas in the storagewhich were missed during the previousinspection. Stephen believes that if he

now goes back in and completes thesame work in these areas, the problemwill be solved.

Stephen comments that in hindsight, theideal situation would have been to haveavoided the seepage completely by notdigging down the 1.8 meters.

Property: Fairford, Moree

Grower: Stephen Seery


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Property: Brighann, Moree

Grower: Michael Seery

The Problem

A 500 megalitre storage constructedin 1985 on Michael Seerys propertyBrighann, west of Moree, was known tohave a seepage issue. Filling the storagebeyond 50% of its capacity caused thewater height to drop more quickly thancould be attributed to evaporation alone.Furthermore, as the water height wasdropping, a wet patch became evident inthe field next to the dam. As the water in

the storage increased to 75% of capacitythe water level decreased more rapidlyand the wet spot in the field became moreobvious.

In 1998 Michael began to address theseepage issue in the storage. Additionally,it was decided to increase the storagecapacity to 700 megalitres and improvethe efficiency with which it could bedrained.

Prior to commencing the renovations, anEM survey was conducted across the floor

and around the perimeter of the storage.The survey identified sandy patches whichwere generally found to correspond withlow spots across the storage floor.

The Solution

The entire floor of the storage was linedwith 1 meter of black clay sourced fromoutside the storage. The low spots on thefloor where sand was identified in the EMsurvey were lined with a thicker 1.5 - 2m ofclay. The whole floor was then compactedwith a sheepsfoot roller. The wall heightwas increased by approximately 1.5m andthe batters were improved.

Refilling the storage began soon afterconstruction was completed. As thewater level reached approximately 50-75cm, fifty tons of bentonite was appliedby plane over the 20ha area of the storage(a rate of 2.5t/ha). The objective wasto create a laminate across the wholestorage floor. The storage was then filledcompletely.

The Outcome

Michael says The renovation work hasslowed the leak but has not stoppedit. The work seems to have stoppedthe seepage losses when the storage isup to half full. However, above this levelseepage losses still occur and there isstill evidence of moisture in the fieldnext to the storage, although the rateof loss is significantly less than prior tothe renovations. At 75% capacity in the

renovated storage, the water level is thesame height as when the original storagewas full. The wet spot in the adjacentfield now becomes more evident as thestorage capacity increases above 75%.

The Future

Given the current inconsistency in wateravailability there are no plans in place todo more renovations. Should conditionschange Michael believes there are several

alternatives which could be considered.Firstly, more bentonite could be added.However he is not confident that thiswould be successful. Secondly, anotherclay layer could be applied although thecost of moving additional clay and thereduction in storage capacity make thisan unattractive solution. Thirdly, thereis the potential of lining the floor with aplastic membrane. However, he is notsure that this would be an economicallyviable option.



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Local irrigation consultant Justin Schultz,Waterbiz


Property: Located near St George, Qld

Background

This family owned and operated drylandand irrigation property is located northof St George. Production consists ofprimarily winter crops such as wheat andchickpeas with some peanuts, cotton andmungbeans. Water storage tends to beonly short term.

The Problem

This property has a 1000ML dam that wasconstructed after the family purchasedthe property. Whilst it was known thatthere was soil of marginal quality for theconstruction of the dam, the plan was tohave a shallower dam so that they did notexcavate deeper into this marginal soil.However during construction, excavationoccurred in this marginal soil type whichhas resulted in subsequent seepageproblems. Despite only being used forshort term water storage, as much as

half of the water pumped into the storagewas being lost before the water could beused. The grower believed that the site ofthe problem was in the borrow pit, whichis approximately 5 hectares and over 1metre deep.

The Solution

The grower has tried different options tofix the seepage losses. The first attemptinvolved lining the borrow pit of the damwith 100 tonnes of Bentonite, which wasapplied as a pure blanket. Approximately2 hectares of the borrow pit had double therate of Bentonite applied (approximately30, 000kg/ha) where the grower believedthe leakage was more severe because ofthe soil type in this area.

The thickness of the Bentonite wasapproximately 5mm as it was not costeffective to increase the applicationrate to achieve greater thickness. TheBentonite was spread using a Marshallspreader to achieve good coverage. Oncespread, the base of the dam was given alight harrowing and then filled with water.The Bentonite lining was not successfulin fixing the problem.

The second attempt involved lining thebase of the dam with black clay. The

entire base of the dam was lined withgreater depths applied to the borrowareas. In the borrow areas the clay liningwas to a depth of 450mm. The rest of thedam base was lined with 250mm. The claymaterial was not compacted when it wasfirst layered. It has since been compactedusing a 25 tonne trailing sheepsfoot roller.

The grower currently carries outopportune maintenance of the storagebase when empty. If sufficient rainfall isreceived to wet the base of the dam, the

grower will compact it using a squareimpact roller to help seal the base. Whilethis maintenance is carried out whenmoisture is sufficient on average this isundertaken twice each year.

The square impact roller is run over thebase of the dam multiple times untilcompaction is to a point that the growerthinks is satisfactory. This is assessedusing a spike. To achieve this level ofcompaction six passes of the roller isusually required. This maintenanceprogram helps to reduce seepage losses

but does not fix the problem.

In 2005 the grower had an EM surveyconducted on the base of the storage toidentify the leaking areas. The borrow

areas in particular were identified asbeing prone to seepage losses confirmingthe growers suspicion that this was thearea that needed to be addressed. Therest of the dam base was identified assuitable material for water storage.It appears that in the borrow pit area,removal of the suitable material hadexposed more marginal soil underneath.

The Outcome

Both the Bentonite lining and the blackclay lining reduced the seepage losses butdid not fix the problem. The grower hasused gauge board readings to estimatelosses at an average of 12mm per dayduring the autumn and winter months(March to July). Specialist irrigationconsultant Justin Schultz from Waterbiz,has estimated that approximately 3.5mmper day is due to evaporation losses andthe rest is due to seepage.

The Future

The grower believes that the next stepto address the seepage issue is togroundtruth some of the EM survey work.The EM survey report outlined furtheroptions that could be undertaken tominimise seepage from the storage.

One option is to increase the depth ofthe clay lining. Another is to use a lowerpermeability lining material to furtherline the dam. The black clay that has

been used to line the dam is very suitablefor agricultural production and has goodstructure which limits its suitability asa lining material. It was not originallycompacted and it also contains weedswhich dry and crack the lining materialallowing water through the liner.

The grower believes that he will have toget some professional help into the futureand that there is some great stuff in theEM survey report that they could look attrying.



Property: Kensington Park, Dalby

Grower: Ian Hayllor

Background

Ian Hayllor grows irrigated and drylandcotton and grain crops on his property onthe banks of the Condamine River, westof Dalby. Over the years Ian has put a lotof time and effort into ensuring his farmis as water use efficient as possible, withmuch of that effort spent trying to reduceseepage loss from one of his on-farmstorages. Ian has two on-farm storageson this property; his first was constructed

in 1984 with a capacity of 500ML and theother was constructed in 1996 with acapacity of approximately 1500ML.

The Problem

After constructing his first storage, Ianmonitored his water levels manuallyand determined that water losses due toseepage were unacceptably high.

Until recently it has been extremelydifficult to measure the precise seepagerate of an entire storage, let alonedetermine the location of any specificproblems. Ian has therefore tried toremedy the problem over a period ofyears using whatever new technology wasavailable at the time.

When the storage was constructed, thematerial all seemed to be of a suitablenature, with sufficient clay to preventsignificant losses, so Ian thought thatperhaps there were one or more sectionswhere a thin layer of clay disguised sandyregions under the surface.

The Solution

Ian used an excavator to dig down toin excess of 5 metres in a number oflocations across the storage to determineany potential sandy areas, but found onlyone. He then ripped this area and addedsome additional clay material beforecompacting with a sheepsfoot roller.

Whilst this may have made someimprovement, Ian was still unhappywith the level of loss, so over the nextfew years he repeated this process overmuch of the storage base. At one stage,in a section of the storage that typicallystays quite moist, Ian found a small zonethat appeared to be quite dry, perhapsindicating a sandy spot that allowed moredrainage.

He excavated this spot and did find anarea of almost pure sand below, so hesubsequently covered this area with 1-2metres of clay loam material and againcompacted with the sheepsfoot roller.

However yet again upon next filling thestorage he was not satisfied that theseepage losses had been adequatelyaddressed.



By this time, Ian had already built hissecond storage, and was happy thatseepage in this storage was not a majorproblem. A recent measurement ofseepage, undertaken using the IrrimateSeepage and Evaporation Meter as partof the Cotton CRC Storages project,has supported this view with seepagemeasured as less than 1mm/day. Thismeant that Ian was able to use his betterstorage on a day to day basis, only usingthe other storage sporadically as more

water became available. Over the lastdecade, this has meant that his olderstorage has been unused most of thetime.

During this period, as newer technologiesbecame available, Ian employed some ofthese to try and determine where losseswere occurring. He had an EM38 surveyundertaken in 2005, which did not seemto indicate significant variation in soilcharacteristics. However high resolutionresistivity measurements also taken

around this time did provide a very highlevel of detail regarding differences in soiltype for certain storage transects.

Ian has now used this informationto perform additional clay lining andcompaction activities in certain areasacross the storage, this time using asquare impact roller to try and providefurther compaction than the sheepsfootroller. Visually, the square impact roller

seemed to provide significant compaction.

Previously, the soil had distinct channelsthroughout which looked like waterpathways, but after impact rolling, thesoil was like plasticine, it was completelychanged said Ian.

One concern in shrink-swell soils suchas these is that the advantage obtainedthrough compaction might be easily lostthe next time soil dries out and cracksopen, so in this case about 6 to 8 inches

of soil was placed over the compaction totry and protect and maintain it.

Unfortunately, Ian still does not believehe has got to the bottom of the problem.I dont think we have slowed it down onelittle bit, there has to be somewhere thatwe havent looked he said. Ian measuredthe change in water level over a fewweeks in October 2010. After accountingfor evaporation losses at the time, heestimated the seepage rate was around15mm/day.

Ian then tried broadcasting polyacrylamide(PAM), which is marketed as a potentialseepage mitigation technology when usedat appropriate rates. Unfortunately, thePAM application was also unsuccessful,with an accurate measurement ofseepage conducted as part of the CottonStorages Project immediately after thePAM had been applied confirming Iansearlier estimation of 15 mm/day seepage.

The Future

Ian is disappointed that the PAM did notwork, but was happy to give it a try. If ithad worked it could have potentially savedus hundreds of thousands of dollars, butnow well go back to the drawing boardand look for other solutions.

The key is that we need to know how toinvest our money when looking for potentialsolutions. The resistivity measurementsseemed to provide good data, so perhapswe use EM to find potential problem spotsand then something like the resistivitymeasurements in these areas to providemore detail.



Property: Long Meadows, Bourke

Grower: Mitch Abbo

Background

In 2003 Clyde Agriculture had access toa Broons impact roller and decided tocompact several storage floors and torepair the damage caused to storagewalls due to wash. The decision torenovate was opportunistic; there hadnot been any significant seepage issuesobserved.

The Long Meadows storage (cell 1) wasone of the storages that was renovatedin 2003. The storage has a capacity of4,700 megalitres and covers an area ofapproximately 137ha. The wall height is4.5m, with a water storage depth of 3.5mand originally a three in one batter.

The storage was constructed in 1990 andsoil tests were undertaken at that time.

By 2003, there was considerable washon the downwind storage walls. Soil wasbeing washed into the storage which wasstarting to impact on the storage capacity

and the road around the wall.The Problem

The wash from the prevailing windshad started to significantly damage thedownwind storage walls. It had removed asignificant about of soil from the walls. Acliff face was starting to form and storagecapacity was being lost. Additionally theroad around the storage wall was beingaffected.

There may also have been some seepagefrom the storage floor, but there were

no accurate measure of how much waspossibly being lost. Some moisture hadbeen observed outside the storage, whichmay have been due to seepage.

The Solution

The work focused primarily on thedownwind storage wall where the washdamage was most significant. Theoriginal batter had been three in one. Therenovations adjusted this so that the top

two meters of the wall had a batter of fivein one. The lower two meters had a batterof three in one. This was done to createmore of a beach like effect. Soil neededto make these adjustments was sourced

from the centre of the storage.

The Broons Impact roller was used acrossthe entire storage floor. After the initialpasses, holes were dug with an excavatorin a grid like pattern. These holes wereused to assess the effect of the rollerpasses and were focused primarily on theareas where Mitch expected losses couldhave been occurring. These locationscorrelated with where seepage had beenobserved in isolated points outside the

storage.The storage walls were not compactedbecause it was felt that there was not a lotto be gained by compacting a completedwall. They could not justify rebuilding thewalls and compacting the core, as thismay have created more issues and wasnot cost effective.

The Outcome

In 2004 the storage was filled to capacity.

It remained with water in it until 2006.There was no seepage observedduring this time, although no specificmeasurements were taken.

The storage was dry again for two yearsduring 2007 and into 2008. During this drycycle there was considerable crackingwith cracks to a depth of at least onemeter observed. The storage floor formeda block like structure. The blocks werequite well compacted but were brokenby deep expansion cracks. There was anexpectation for a reasonable amount of

seepage.

In 2009 the storage was dry again.During this most recent dry cycle ClydeAgriculture sourced funding from theWestern Catchment ManagementAuthority. The funding was designed todo water balance calculations on farms.Additionally there was investment inmetering equipment and informationcollected on the suitability of different soiltypes for storage construction.

During 2009 there were quite a number ofmeasurements taken. There was an EMsurvey conducted by Terrabyte Services.Core samples were taken of the areasidentified in the EM survey as suspect.

Additional to this a Geo Tech engineerused the EM survey as a basis to selectsites for excavator pits. These pits wereused to assess soil types, infiltrationcharacteristics and the feasibility ofincreasing wall height and hence storedwater depth. Soil samples were collectedand soil analysis completed at each of thepits.

The 2009 funding provided for IrrimateSeepage and Evaporation meters,

storage volume meters and mace metersfor inlets and outlets.

The storage was again filled in late 2009.The seepage and evaporation readingsindicate that seepage is very low (


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Documents

Seepage Remediation Case Studies