Evaporation basins: opportunities for cost minimisation in siting, design and construction

IRRIGATION AND DRAINAGE

Irrig. and Drain. 50: 19–29 (2001)

EVAPORATION BASINS: OPPORTUNITIES FOR COST MINIMISATIONIN SITING, DESIGN AND CONSTRUCTION1

JAI SINGH1 AND E.W. CHRISTEN2,*1 Haryana Agril Uni6ersity, Hisar, India

2 CSIRO Land and Water, PMB No. 3, Griffith, NSW 2680, Australia

ABSTRACT

To reduce adverse downstream impacts of saline subsurface drainage water, farmers developingnew horticultural developments in the Murrumbidgee Irrigation Area are required to constructevaporation basins to hold the subsurface drainage water on their property. This creates anadditional cost burden upon farmers. This paper reports on a detailed investigation into the costcomponents of evaporation basin construction. Costs can be minimised by careful site selectionand appropriate design. Cost components with high potential for cost minimisation were foundto be the site geotechnical investigations, leakage control measures and basin design in terms ofshape and number of cells. Copyright © 2001 John Wiley & Sons, Ltd.

KEY WORDS: cost minimisation; design; evaporation basins; geotechnical investigation

RESUME

Afin de reduire les impacts resultant du drainage d’eaux salines, les horticulteurs de la zoned’irrigation du Murrumbidgee sont tenus de construire des bassins d’evaporation recevant leseaux de drainage de leurs proprietes. Les couts associes au developpement des ces bassins sontsouvent prohibitifs. La presente publication detaille les couts associes aux differents stages dedeveloppement de bassins d’evaporation et propose une strategie de minimalisation de ces coutspar une selection soignee de sites d’implementation ainsi qu’une conception appropriee. Lescouts les plus eleves de l’implementation de bassins, et par la meme les plus susceptibles d’offrirdes reductions de couts significatifs si soigneusement planifies, sont l’etude geotechnique, lesmesures de controle de drainage ainsi que la geometrie et le nombre de cellules du bassin.Copyright © 2001 John Wiley & Sons, Ltd.

MOTS CLES: bassins d’evaporation; etude geotechnique; controle de fuites; geometrie de bassins; rationalisation des couts

INTRODUCTION

The management of saline drainage waters is a complex problem with no readily available lowcost solution. To date options considered for the disposal of saline water from irrigated areas ofthe Southern Murray Darling Basin, Australia have been: river disposal, disposal bores,

* Correspondence to: CSIRO Land and Water, PMB No. 3, Griffith, NSW 2680, Australia. Tel.: +61 2 69601500; fax: +61 269601600; e-mail: [email protected] Bassins d’evaporation: une opportunite de minimaliser les couts de localisation, conception et de construction.

Copyright © 2001 John Wiley & Sons, Ltd.

J. SINGH AND E.W. CHRISTEN20

evaporation basins, pipeline to the sea, and desalination. Of these only the use of evaporationbasins is currently accepted as a viable, short- and long-term disposal option. However, there isconcern about the cost involved in the use of evaporation basins. Although there are numerousevaporation basins in the riverine plain of the Murray Darling Basin, detailed costings are notoften available. The reported costs for different basins vary markedly (Table I). The largevariation in costs found in the literature is confusing, thus an investigation into the reasons whybasin costs may vary so markedly will be useful to those proposing the use of evaporationbasins.

There is evidence that evaporation basins can be an effective way of handling drainage water,especially with greater efforts being made to locate basins at sites where hydrogeological effectswill be minimal, there are large expenses involved with the detailed investigations required. Alsoassociated with new basins are construction costs (mainly the costs associated with controllingexcessive leakage), maintenance and operating costs. When these expenses are added to the costsof the drainage system, the total costs may become prohibitive (RWC 1992; Muirhead et al.,1997). Therefore, a detailed investigation is needed to investigate the possible scope for costminimisation.

OBJECTIVES

The objectives of this study were: (1) determine the cost of siting, design and construction of anevaporation basin, and the relationship between basin size and cost; (2) examine the sensitivityof evaporation basin cost to individual items and the potential for cost minimisation; and (3)determine the range of likely evaporation basin costs for different basin sizes, under a variety ofsiting and design criteria.

METHODOLOGY

In conducting these assessments of basin costs it was assumed that the basins were sited,designed and managed according to the guidelines presented by Jolly et al. (2000). Of particularimportance is the relationship between basin size and leakage. Jolly et al. (2000) show that forbasins in the riverine plain of the southern Murray Darling Basin leakage reduces with basin sizedue to a decreasing perimeter to area ratio. They also state that a desirable leakage rate is 0.5–1mm day−1. This leakage rate is generally what is observed for basins greater than 50 ha in size.Basins smaller than this will leak at higher rates which may lead to unacceptable environmentalimpacts, thus basins smaller than 50 ha are assumed to require additional leakage controlmeasures such as soil compaction.

Table I. Reported salt disposal basin costs

SourceBasin size Basin locationCost/ha(ha) (A$ 000’s)

Nauton et al. (1995)5 Wakool, NSW770Sinclair Knight Merz (1995)30 21 Girgarre, VictoriaTrewhella (1989)15 9 VictoriaPoulton (1998)Kerrang, Victoria310Muirhead et al. (1997)10 18 Griffith, NSWDepartment of Food and Agriculture (undated)2.8 Pyramid Hill, Victoria21Muirhead et al. (1997)Griffith, NSW252

Copyright © 2001 John Wiley & Sons, Ltd. Irrig. and Drain. 50: 19–29 (2001)

EVAPORATION BASINS: COST MINIMISATION 21

Four different basin sizes (2, 5, 20 and 200 ha) were used to examine the relationship betweenbasin size, siting, design and cost. Detailed estimates of cost were determined in consultationwith surveyors, consultants, engineering suppliers and water and electricity supply authorities.The capital and net present cost estimates of evaporation basins are based on actual costs in1998 Australian dollars.

To identify major components determining the cost of evaporation basin, sensitivity analysisusing the @RISK® EXCEL spreadsheet ‘add-in’ program was undertaken. For the ‘riskanalysis’, @RISK generates a set of random numbers for each iteration and replaces each inputwith a value taken from the input range defined by the distribution function, and it thencalculates new output values. These analyses are based on 500 iterations and a Latin Hypercubedistribution (Palisade Corporation, 1996). The specification of output and input variables forthis analysis was as follows:

Net present cost (NPC)= f(Geotechnical investigation, Stripping of vegetation Floor andbank formation, Floor and bank compaction, Interception of leakage)

Based on the sensitivity analysis results, the extent of variability in basin cost was determinedby allowing variations in the major cost components and then selecting the ‘best’ with lowestcost case and the ‘worst’ with highest cost case scenarios. A probability distribution functionwas used for considering the likely variation in construction cost due to contractors and regionalfactors. Detailed methodology and comprehensive results can be found in Singh and Christen(2000).

RESULTS AND DISCUSSION

Cost components of an e6aporation basin

This section gives an account of the various steps involved in construction of an evaporationbasin and estimates of the costs associated with each step.

Site selection. Site selection involves a geotechnical survey of the proposed area. Thegeotechnical investigations required for evaporation basin siting have been discussed by Christenet al. (1998). They suggest two levels of site assessment:

1. Macro scale : the suitability of the general locality. Used to assess the broad potential risk ofbasin leakage. This needs to consider the environmental sensitivity of the area such asconservation value, floodplains, wetlands and swamps, remnant native vegetation andresidential areas. An understanding of local hydrogeology, including the general extent andcharacter of deep aquifers and likely existence of shallow aquifers, is critical to setperformance criteria for leakage and risk assessment.

2. Micro scale : assessment of on-site factors. This is a set of on-site factors that endeavour toestimate potential leakage rates, the direction and extent of leakage and the likelihood ofcausing environmental degradation. The level of on-site investigation required dependslargely upon the scale of the project and the extent of economic and environmental riskinvolved.

Table II shows the factors that should be considered to determine if a proposed basin will fallinto a high or low risk category and as such the extent of geotechnical investigations required.



Table II. Factors determining the possible risk category for an evaporation basin site (Christen et al.,1998)

Criterion Low risk High risk

1. Locality assessment Detailed Simple2. Design Locally developed guidelines No local guidelines3. Potential off-site leakage effects Small Large4. Size Small Large5. Hydrogeology Well documented Uncertain6. Management plan Good Poor

Site layout. After site selection, the basin area needs to be surveyed before earthworkscommence so that the areas of cut and fill can be determined for laser levelling. A survey gridof 40×40 m is used for the basin layout at a cost of A$29.40 ha−1 (Polkinghorne, pers. comm.).

Earthworks. The top 100–200 mm of soil including vegetation, is stripped from the surface ofthe area. This operation is done with a scraper or bucket. Topsoil is removed to expose lesspermeable clay subsoil. The cost of stripping is A$0.30 m−3 (Polkinghorne, pers. comm.).

Bank formation. Banks can be formed to typical dam or basin design, or as detailed by theDepartment of Land and Water Conservation (undated) that banks should be about 1 m highand 2.4 m wide at the crest, bank slope should be 1:5 internally and 1:2 externally. Banksformed to these specifications use 5.9 m3 of soil per metre length. Using a scraper, up to 90–93%of total potential compaction can be achieved by forming the banks at the right soil moistureconditions (Polkinghorne, pers. comm.). The use of bulldozers to construct banks is notrecommended, as the banks will not be adequately compacted. Formation of banks using ascraper costs A$0.70 m−3. The bottom of the basin is then levelled flat to promote an evenspread of water to increase evaporation. This costs A$0.70 m−3 (Polkinghorne, pers. comm.).

Compaction. If required, additional compaction of banks and floor can be achieved using awater truck and sheep’s-foot roller, at A$2.00 m−3 (Polkinghorne, pers. comm.). The soil type,local conditions, and desired seepage rate determine whether the basin requires further com-paction. Large basins are less likely to need compaction, whereas small basins (less than 50 ha)tend to have high leakage rates and thus require more compaction (Jolly et al., 2000). Asignificant cost of the earthwork component of construction is the cost of extra compaction witha roller. Some compaction takes place with the scraper during construction, but investigationsinto the effects of additional compaction have not been undertaken.

Interception of lateral leakage. There are two modes of basin leakage, lateral and vertical.Lateral seepage is undesirable as it affects the environment immediately surrounding the basinwithin a short period of time (Jolly et al., 2000; RWC, 1992). Lateral seepage is generallycontrolled using subsurface interceptor pipe drains, although open drains are sometimes used forlarger basins such as Wakool (30 ha) and Girgarre (2100 ha) (Evans, 1989). A pipe drain canbe installed around the basin perimeter at a depth of around 2 m. This drain returns lateralseepage water to the basin via a sump and pump. The cost of installing pipe drains was foundto be A$4.60 m−1 for basins of up to 20 ha (includes cost of trenching and installing slotted pipeof 100 mm diameter) and A$7 m−1 for large basins of 200 ha (150 mm diameter pipe isrequired).

Recurring expenses. Recurring costs include: (1) pump repair, maintenance and running costs;(2) maintenance of the basin banks – annual spraying of weedicide and rebuilding (it wasassumed that 10% of the banks will need to be rebuilt every 10 years); (3) public liability



insurance – farmers in the Murrumbidgee Irrigation Area are required to maintain publicliability insurance for an amount of not less than A$1 million in the joint names of thelandholder and Murrumbidgee Irrigation against surface runoff and seepage into the surfacedrainage system; (4) miscellaneous expenses – 1% of the capital cost of the basin was taken asnecessary to meet additional recurring expenses such as labour for basin management.

En6ironmental impact statement (EIS). In New South Wales a development consent/EIS isrequired under the Environmental Planning and Assessment Act 1979 for carrying out develop-ment in an environmentally sensitive area for a storage structure of more than 100 Ml capacity(Department of Urban Affairs and Planning, 1998). No development consent is required forstorages of up to 800 Ml if they are outside an environmentally sensitive area. The minimumcost for an EIS is around A$15000 (Polkinghorne, pers. comm.). In this study only the 200 habasin will require an EIS.

Total basin costs

All the individual cost components of evaporation basins are combined to determine the totalcost for the four basin sizes (Table III). The result shows that basin cost per ha and also per Mlof storage capacity declines with increasing basin size. The earthworks, geotechnical investiga-tions and interception of lateral leakage are the major cost constituents of an evaporation basin.The earthworks are the largest cost varying from 64–71% in smaller basins (2–5 ha) to 73% inthe 200 ha basin, within this component the compaction of banks and floor accounts for45–50% of the total cost (Figure 1). The cost per hectare of floor compaction increases while thecost of bank compaction decreases with increasing basin size. The geotechnical investigation cost(high-risk situation) accounts for about 20% of the total cost per hectare. The cost ofintercepting lateral leakage declines from 12% in a 2 ha basin to 3% in a 200 ha basin. Therecurring costs account for about 2% of the total cost.

Net present cost (NPC)

The total cost of evaporation basins, based upon the previous sections, was estimated forbasins from 2 to 200 ha, over a 30-year period at a 7% discount rate to give the net present cost

Table III. Total cost of an evaporation basin, investigation costs as for a high-risk situation (A$ ha−1)

Items Basin size (ha)

200 (1000 Ml)20 (100 Ml)5 (25 Ml)2 (10 Ml)

Geotechnical investigation 3 310 1 970 1 871 1 77230303030Site layout survey

Stripping of vegetation 450 450 450 450Floor and bank formation 2 506 1 975 1 604 1 371

3 000a3 0003 0003 000Floor compactionBank compaction 4 160 2 643 1 582 918

1 297 824 411Pipe drain installation 198Pump and sump 700 280 70 13Recurring costs 505 292 179 123Environmental impact statement – 75––

15 402Total per ha cost 11 164 9 017 7 8383 080Total cost per Ml 1 5671 8032 232

a Note that floor compaction is unlikely to be required for a 200 ha basin



Figure 1. Distribution of evaporation basin costs

(NPC). It is assumed that the 2, 5 and 20 ha basins require compaction to control leakage toacceptable levels, while the 200 ha basin is large enough not to require compaction (Jolly et al.,2000). Table IV shows that the initial construction cost (earthworks) increased from A$19000 toA$517600 as the size of evaporation basin increased from 2 to 200 ha, however the NPC per hadeclined from A$21000 to A$6000.

Sensiti6ity analysis for cost minimisation

The sensitivity analysis of evaporation basin cost on the basis of NPC was performed byvarying the scale and cost of the following: (a) geotechnical investigation; (b) leakage control; (c)basin geometry; (d) bank height; (e) lateral leakage control.

Geotechnical in6estigation. Intensive geotechnical investigation is generally recommended forsiting larger evaporation basins (Christen et al., 1998). However, smaller basins can be sited inlow- or high-risk environments depending upon the level of understanding of the biophysicalsystem of the area. If risks are low then minimal investigations are needed (Christen et al., 1998).The increase in NPC of different basin sizes ranged from 8 to 10% when siting was done witha full geotechnical assessment compared to minimal investigation (Table V). This cost increasemay be justified to avoid adverse environmental effects. It may also provide enough confidenceto avoid expensive leakage control measures such as compaction or lining.

Leakage control. Compaction to control leakage is a major cost. Uncompacted basins are thecheapest, however this assumes that the basin siting and design are such that it will not leak

Table IV. Effect of salt disposal basin size on the net present cost (A$)

Item Basin size (ha)

200 ha2 ha 5 ha 20 ha

331 200Geotechnical investigationa 6 200 9 200 35 000517 600124 60037 80019 000Earthworksb

Interceptor drain+pumpc 3 700 5 200 9 000 39 400Recurring 12 400 16 900 40 100 324 800

Total NPC 41 300 1 213 000208 70069 100NPC per ha 20 600 13 800 10 400 6 065

a High-risk situation – full investigation.b Floor compaction not included for 200 ha basin.c Subsurface pipe drains for 2, 5, 20 ha and open drains for 200 ha.



Table V. Effect of geotechnical investigations on NPC of evaporation basins (A$ ha−1)

Level of investigation Basin size (ha)

2 5 20 200

Minimum 19 000 12 800 9 500 –Full 20 600 13 800 10 400 8 900

% increase 8.4 7.8 9.5 –

excessively. It is assumed that larger basins do not require compaction as their large sizegenerally results in leakage at acceptable levels (Jolly et al., 2000). Also siting of large basins isoften based on a more intensive geotechnical investigation than undertaken for a small basin.Table VI shows that choosing a site that avoids the need for leakage control can approximatelyhalve the cost of a large evaporation basin. Thus expenditure on a full geotechnical investigationmay be justified if it provides confidence that leakage control measures are not necessary.Smaller basins due to their geometry will nearly always need full compaction regardless of thelevel of geotechnical investigation.

Basin geometry. Basin geometry has a significant effect on the ultimate cost of an evaporationbasin. The geometry includes the shape of the basin and the number and size of internal cells.This affects the total length of bank required. Table VII shows that basin shape has significantimpact on the NPC. A square or rectangular basin is more cost effective than a triangular basinin terms of perimeter and length of internal banks to create cells. The cost difference betweenbasin shapes increases with basin size. The cost of compacting the floor and banks (A$2 m−3)to reduce leakage was the largest cost in the construction of an evaporation basin. This cost islargely determined by the total bank length, thus the cell size and hence total length of internalbanks is important (Table VIII). This shows that the cost of an evaporation basin is reduced

Table VI. Effect of seepage control measures on NPC of evaporation basins (A$ ha−1)

Leakage control measure Basin size (ha)

2002 5 20

NA 4 700 NAaNANo compaction, minimum geotechnical investigation (low risk)No compaction, full geotechnical investigation (high risk) 5 600 4 700NA NA

12 800Floor and bank compaction (minimum geotechnical investigation) 9 50019 000 8 900a

a For 200 ha basin full geotechnical investigation cost is used as it is assumed to be high risk.NA denotes not applicable, as these small basins will require compaction to control leakage.

Table VII. Effect of basin shape on NPC of evaporation basins (A$ ha−1)

Basin shape Basin size (ha)

52 20 200

8 900 (12 626)Square 19 000 (705) 12 800 (1 118) 9 500 (2 682)Rectangulara 11 700 (2 844) 11 400 (12 003)18 900 (700) 14 500 (1 000)

14 500 (3 053)Triangularb 15 600 (14 920)20 100 (825) 16 000 (1 211)

a Sides are twice the end lengths.b Equal length sides; figures in parentheses are the total length of bank in metres.



Table VIII. Effect of cell size on NPC of a square evaporation basin (A$ ha−1)

Cell size (ha) Basin size (ha)

2 5 20 200

1 19 000 15 300 12 800 11 6002 17 700 12 900 12 400 10 3005 – 12 000 9 500 9 400

10 – – 9 100 8 90020 – – 8 700 8 600

considerably by increasing cell size. However, there are a minimum number of cells required inany evaporation basin in order to provide management flexibility. This may be in order to allowcells to dry out periodically or to provide a sequence of ponds of increasing salinity. Internalcells are also required inside the outer banks to help prevent wave formation and resultingerosion.

Bank height. These basins function by evaporation that is constrained by the area of openwater surface, not by the storage volume for the drainage water. However, basins do requirecertain storage so that drainage pumping can continue during periods of low evaporation. Thusadded storage volume by increasing the bank height may be useful in critical periods, butexcessive storage is costly and unnecessary as the primary mode of water disposal is byevaporation. Cost sensitivity to bank height was carried out for heights ranging from 0.7 to 1.5m (Figure 2). The results show that bank height has considerable impact on basin cost. Withincreasing basin size the cost per ha decreases due to a decreasing total bank length per unitarea. There are considerable savings per Ml storage by increasing bank height; however, in thelong term it is the evaporation area that is important. The extra storage merely reduces the riskof short-term waterlogging in the drained area.

Lateral leakage control. Two types of lateral leakage control measures, namely subsurface pipedrains and open ditch drains, are often used in controlling lateral leakage from evaporationbasins. The NPC of using these two alternatives on different basin sizes is shown in Table IX.Subsurface pipe drains were found to be least expensive in smaller basins (2–20 ha) whereas thecost of pipe and open drains were the same for a 200 ha basin. The use of an open drain could

Figure 2. Effect of bank height on net present cost



Table IX. Effect of lateral leakage control measures on NPC of evaporation basin (A$ha−1)

Basin size (ha) Pipe drain Open drain

2 19 000 19 9005 12 800 13 500

20 9 500 9 900200 8 900 8 900

be more economical for larger basins due to the larger capacity of open drains compared to pipedrains. However, the use of open drains requires more land and achieving adequate depth toeffectively intercept leakage may be more costly.

Variability in e6aporation basin cost

From the previous analysis it is clear that the cost of any particular evaporation basin willdepend upon the site conditions, compaction requirements, geometry and lateral leakage controlmeasures. The cost will vary greatly depending upon selection of any of these items. To show thevariability of costs, best and worst case scenarios were compared by selecting the factorsapplying to a bad design and poor site and a good design and suitable site (Table X). Apartfrom variations in costs due to siting and design, there will be variations in the constructioncosts between contractors and also regional cost factors. Variations in these factors wereinvestigated by applying a lowest, highest, and most likely cost to each individual item (TableXI). By combining all of the possible price variations for each scenario a cost probabilityfunction was determined for each basin size (Table XII). This showed that the siting and designof an evaporation basin, together with price variations, can cause the cost to vary greatly.Therefore, careful site selection and appropriate design are critical to minimise costs.

CONCLUSIONS

Large basins cost less to construct on a per unit area basis, a well-designed and sited 2 haevaporation basin will cost about A$19000 ha−1 whereas a 200 ha basin under the sameconditions would cost about A$5000 ha−1. This is due to economies of scale in construction,

Table X. Best and worst case scenarios for evaporation basin siting and construction

Basin area (ha)Cost items Scenarios

2 5 20 200

MinimumMinimumMinimum FullBestGeotechnical investigationWorst Full Full FullFull

SquareBasin shape Best Square Square SquareTriangular TriangularWorst Triangular Triangular

52BestSize of cell (ha) 20101 2 5 5Worst

Floor compaction Best No No No NoYesWorst Yes Yes Yes

PipeLateral leakage interceptor drain PipeBest Pipe PipeOpen PipeWorst Open Open



Table XI. Summary of variables used to generate probability distribution function of basin cost

Variables Cost range Basin size (ha)

2 5 20 200

Geotechnical investigation (A$ ha−1) Lowest 1 573 953 916 1 595Most likely 1 748 1 059 1 018 1 772Highest 1 923 1 165 1 120 1 949

Stripping vegetation (A$ m−2) Lowest 0.2 0.2 0.2 0.2Most likely 0.3 0.3 0.3 0.3Highest 0.5 0.5 0.5 0.5

Floor and bank formation (A$ m−3) Lowest 0.5 0.5 0.5 0.5Most likely 0.7 0.7 0.7 0.7Highest 0.9 0.9 0.9 0.9

Floor and bank compaction (A$ m−3) Lowest 1.5 1.5 1.5 1.5Most likely 2.0 2.0 2.0 2.0Highest 2.5 2.5 2.5 2.5

Interception pipe drain (A$ ha−1) Lowest 1 795 994 433 1 795Most likely 1 997 1 104 481 1 997Highest 2 197 1 214 529 2 197

Table XII. Variability in the NPC of evaporation basins (A$ ha−1)

Scenarios Cost range Basin area (ha)

2 5 20 200

Best case Lowest 17 200 10 700 4 100 4 300Most likely 19 000 12 100 4 600 4 700Highest 21 300 14 000 5 200 5 300

Worst case Lowest 20 200 13 300 9 700 10 000Most likely 22 700 14 900 11 200 11 700Highest 24 600 16 800 12 700 13 300

especially with regard to bank length and also due to small basins requiring compaction tocontrol leakage. Thus there may be significant advantage in using a smaller number of largebasins compared with many smaller basins. This, however, will depend upon drainage watertransportation costs. The reduction in cost with larger basins also indicates that the overalldesign of the drainage network and basin will be critical in reducing costs.

Leakage control is an important factor in cost minimisation. Basin design that requires noadditional leakage control measures is cheapest. Therefore, it is important to find sites thatavoid the need for additional compaction. Larger basins are less likely to require compactiondue to their size limiting leakage rates and their siting being based on intensive investigation,whereas smaller basins will nearly always require compaction to control leakage.

Site selection and appropriate design are critical in cost minimisation of evaporation basins,the NPC of a 2 ha basin can increase from around A$19000 to around A$23000 ha−1 if thedesign and siting is not carefully considered, a 200 ha basin can increase from around A$5000to around A$12000 ha−1. These factors make it important that basins are designed and sitedwith a full understanding of the impacts of these costs.

Basin geometry, which includes the shape of the basin and the number and size of internalcells, has a significant impact on the ultimate cost. Square or rectangular basins are more costeffective than triangular basins. The cost of an evaporation basin is highly sensitive to the bank



length and hence number of internal cells. Therefore, selecting the best basin shape andappropriate size of internal cells will reduce costs.

Bank height will affect the cost of an evaporation basin considerably, however the storagecost per Ml of water is reduced with increasing bank height. The appropriate bank height shouldbe selected depending upon the required storage to maintain pumping from the drainage systemduring periods of low evaporation. For practical reasons a minimum bank height should be 1m, as this will provide a reasonable amount of storage and reduce the risk of overtopping dueto rainfall and wave action.

Intercepting lateral leakage by pipe drains was less costly than open drains for smaller basins,while for larger basins the costs were similar. The geotechnical investigation cost for siting anevaporation basin will increase with basin size.

ACKNOWLEDGEMENTS

This project is in collaboration with the CRC for Catchment Hydrology and is also funded by the NaturalResource Management Strategy of the Murray Darling Basin Commission. We are grateful to Mr BrettPolkinghorne, of Polkinghorne, Budd & Longhurst, Griffith.

REFERENCES

Christen EW, Singh J, Skehan D. 1998. Geotechnical investigations for siting salt disposal basins in the Riverine Plain. Discussionpaper, CSIRO Land and Water, Griffith, NSW 2680, Australia.

Department of Food and Agriculture. Undated. Tile drainage and evaporation basin research project. Department of Food andAgriculture, Kerang, Victoria.

Department of Land and Water Conservation. Undated. Horticulture on Large Area Farms. Manager, Murrumbidgee Region,Department of Land and Water Conservation.

Department of Urban Affairs and Planning. 1998. Draft SEPP 52 – Land and Water Management Plan. Sydney.Evans RS. 1989. Saline water disposal options in the Murray Darling Basin. BMR Journal of Australian Geology and Geophysics 11:

167–185.Jolly ID, Christen EW, Gilfedder M, Leaney FWJ, Walker GR. 2000. Guidelines for On-Farm and Community-Scale Salt Disposal

Basins on the Ri6erine Plain: 2. Guidelines. CRC for Catchment Hydrology Report 00/07/CSIRO Land and Water TechnicalReport 12/00.

Muirhead WA, Moll J, Madden JC. 1997. A Preliminary E6aluation of the Suitability of Salt Disposal Basins to Manage DrainageWater in the Murrumbidgee Irrigation Area. Technical Report 30/97, CSIRO Land and Water, Griffith, NSW 2680, Australia.

Nauton D and Co, Farmanco Pty Ltd, Jacob PH and Associates, McGuckian Rendall. 1995. Wakool Land and Water ManagementPlan – Economic Sur6ey. Bendigo, Victoria.

Palisade Corporation. 1996. @RISK Ad6anced Risk Analysis for Spreadsheets. USA.Poulton DC. 1998. A review of sub-surface drainage and ground water disposal options in the Pyramid Hill irrigation area of

Northern Victoria. Discussion Paper, Tragowel Plains sub-regional working group.RWC. 1992. Study and Appraisal of the Feasibility for Utilising Saline Water Disposed off to Existing and Future Salt Disposal Basins

for Salt Har6esting, Solar Ponds and Aquaculture. Report prepared for Rural Water Commission of Victoria by LMA PartnershipPty Ltd in association with JNM Consulting Pty Ltd and Mr Nathan Sammy, pp. 83+appendices.

Sinclair Knight Merz. 1995. Girgarre salinity control project. Draft report, Sinclair Knight Merz, Tatura, Victoria.Singh J, Christen EW. 2000. Minimising the Cost of E6aporation Basins: Siting, Design and Construction Factors. Technical Report

12/99, CSIRO Land and Water, Griffith, NSW 2680, Australia.Trewhella W. 1989. Development of sub-surface drainage plan. Paper C, background paper GW8 to the Shepparton Irrigation Land

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Evaporation basins: opportunities for cost minimisation in siting, design and construction