Australia; Integrated Water Cycle Management Analysis of Resource Security
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MARCH 2005 21 Abstract This paper summarises a systems analysis of the impact of Integrated Water Cycle Management approaches on the security of regional water supplies. The synergistic impacts of supply and demand management approaches on the security of regional water supply systems can be accurately evaluated using a combination of non-parametric regional demand methods: the PURRS lot scale water balance simulator and the WATHNET network linear headworks model. The systems methodologies described in this paper have widespread application. A case study analyses regional water security in the Greater Sydney region to demonstrate the capability of the methodologies. The use of different pump marks for extractions from the Shoalhaven River, various frequencies of water restrictions, rainwater tanks and demand management measures has been investigated. An increase in acceptable frequency of water restriction to 5% and a pump mark of 70% will defer the requirement to augment the water supply headworks system by 26 years. The use of demand management measures alone will not defer augmentation whilst installation of 5 kL rainwater tanks for hot water, toilet, laundry and outdoor uses can defer augmentation beyond 2090. A Pareto diagram is employed to examine conflicting environmental and economic objectives. Introduction About 4 million people currently occupy the Greater Sydney region that extends from the Hawkesbury River in the north to Gerroa in the south and from Mt. Victoria in the west to the east coast. Sydney Water Corporation (SWC) is responsible for the provision of reliable water supply to people living in the Sydney region and for managing water demand. The Sydney Catchment Authority (SCA) supply bulk water from the water supply catchments (see Figure 1) to SWC. Since the 1960s Sydney’s water consumption increased dramatically due to growth in population, prosperity and subsequent urban development. The increased consumption was driven by use of water consuming domestic appliances and a water inefficient heavy industry. Water demand decreased following the 1978 - 1983 drought and during economic recession that led to restructure of heavy industry. During the late 1980s and early 1990s public education programs and pricing policies also assisted in management of water demand. Deen [2000] reported that the introduction of user pays pricing for water, accompanying media campaigns and water restrictions during the 1992- 1998 drought reduced water demand by 10% - 15% during the mid 1990s. Sydney’s water demand has increased by over 11.5% since 1995. It is an operating license requirement that SWC reduce per capita water demand by 35% over 1991 water demand in order to avoid construction of the Welcome Reef Dam on the Shoalhaven River. Note that the triggers to augment a regional water supply system are an unacceptable change of water restrictions and risk of failing to supply water. A Least Cost Planning (LCP) model was developed to rank various demand management strategies on a unique cost effectiveness basis. Using the Least Cost Planning Model as a guide SWC began to implement a demand management strategy using a limited range of demand side options in 1999. Nonetheless water demand increased by 5.4% since 1999 in response to population growth. Reviews of the Demand Management Strategy found that a wider range of demand and supply management options was required to avoid augmentation of the water supply headworks system. Selection of demand and supply management methods should also consider the long term system impacts on the environment, the water supply headworks system and the community. Rainwater collected from roofs and stored in tanks to supplement mains water supplies for domestic consumption has been shown to significantly reduce household mains water use. Importantly Coombes et al. [2000] and Spinks et al. [2003] found that the quality of water supply from rainwater tanks was acceptable for hot water, toilet and outdoor uses. Coombes et al. [2002] found that the use of rainwater tanks will defer the requirement to augment the Lower Hunter and Central Coast water supply headworks systems by 28-100 years. Many authors including White et al. [1998] claim that the use of dual flush toilets, and AAA rated shower roses and washing machines will significantly reduce domestic mains water demand. This study examines the economic, environmental and water supply systems impact of the use of demand management measures and rainwater tanks in the demand management refereed paper INTEGRATED WATER CYCLE MANAGEMENT: ANALYSIS OF RESOURCE SECURITY P J Coombes Figure 1. Sydney headworks system.
Transcript
MARCH 2005 21
Abstract This paper summarises a
systems analysis of the impact ofIntegrated Water CycleManagement approaches on thesecurity of regional water supplies.The synergistic impacts of supplyand demand managementapproaches on the security ofregional water supply systems canbe accurately evaluated using acombination of non-parametricregional demand methods: thePURRS lot scale water balancesimulator and the WATHNETnetwork linear headworks model.The systems methodologiesdescribed in this paper havewidespread application.
A case study analyses regionalwater security in the GreaterSydney region to demonstrate thecapability of the methodologies.The use of different pump marks forextractions from the Shoalhaven River,various frequencies of water restrictions,rainwater tanks and demand managementmeasures has been investigated. An increasein acceptable frequency of water restrictionto 5% and a pump mark of 70% will deferthe requirement to augment the watersupply headworks system by 26 years. Theuse of demand management measures alonewill not defer augmentation whilstinstallation of 5 kL rainwater tanks for hotwater, toilet, laundry and outdoor uses candefer augmentation beyond 2090. A Paretodiagram is employed to examine conflictingenvironmental and economic objectives.
IntroductionAbout 4 million people currently occupy
the Greater Sydney region that extendsfrom the Hawkesbury River in the north toGerroa in the south and from Mt. Victoriain the west to the east coast. Sydney WaterCorporation (SWC) is responsible for theprovision of reliable water supply to peopleliving in the Sydney region and formanaging water demand. The SydneyCatchment Authority (SCA) supply bulk
water from the water supply catchments(see Figure 1) to SWC.
Since the 1960s Sydney’s waterconsumption increased dramatically due togrowth in population, prosperity andsubsequent urban development. Theincreased consumption was driven by use ofwater consuming domestic appliances and awater inefficient heavy industry. Waterdemand decreased following the 1978 -1983 drought and during economicrecession that led to restructure of heavyindustry. During the late 1980s and early1990s public education programs andpricing policies also assisted in managementof water demand. Deen [2000] reportedthat the introduction of user pays pricingfor water, accompanying media campaignsand water restrictions during the 1992-1998 drought reduced water demand by10% - 15% during the mid 1990s. Sydney’swater demand has increased by over 11.5%since 1995.
It is an operating license requirement thatSWC reduce per capita water demand by35% over 1991 water demand in order toavoid construction of the Welcome ReefDam on the Shoalhaven River. Note that
the triggers to augment a regionalwater supply system are anunacceptable change of waterrestrictions and risk of failing tosupply water. A Least CostPlanning (LCP) model wasdeveloped to rank variousdemand management strategieson a unique cost effectivenessbasis. Using the Least CostPlanning Model as a guide SWCbegan to implement a demandmanagement strategy using alimited range of demand sideoptions in 1999. Nonethelesswater demand increased by 5.4%since 1999 in response topopulation growth.
Reviews of the DemandManagement Strategy found thata wider range of demand andsupply management options wasrequired to avoid augmentation ofthe water supply headworks
system. Selection of demand and supplymanagement methods should also considerthe long term system impacts on theenvironment, the water supply headworkssystem and the community.
Rainwater collected from roofs and storedin tanks to supplement mains watersupplies for domestic consumption has beenshown to significantly reduce householdmains water use. Importantly Coombes etal. [2000] and Spinks et al. [2003] foundthat the quality of water supply fromrainwater tanks was acceptable for hotwater, toilet and outdoor uses. Coombes etal. [2002] found that the use of rainwatertanks will defer the requirement to augmentthe Lower Hunter and Central Coast watersupply headworks systems by 28-100 years.Many authors including White et al. [1998]claim that the use of dual flush toilets, andAAA rated shower roses and washingmachines will significantly reduce domesticmains water demand.
This study examines the economic,environmental and water supply systemsimpact of the use of demand managementmeasures and rainwater tanks in the
d e m a n d m a n a g e m e n t
refereed paper
INTEGRATED WATER CYCLEMANAGEMENT: ANALYSIS OF
RESOURCE SECURITYP J Coombes
Figure 1. Sydney headworks system.
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regional water supply system; namely theGreater Sydney region. The non-parametricregional demand model developed byCoombes et al. [2002] and the networklinear program for headworks simulationWATHNET by Kuczera [1992] was usedto analyse water demand, streamflows andheadworks security. The Pareto analysispresented by Kuczera and Coombes [2001]is used to compare the environmental andeconomic performance of differentscenarios. A more complete description ofthis study is provided by Coombes et al.[2003].
The Headworks SystemWater is currently supplied to the Sydney
region from the Warragamba, UpperNepean, Shoalhaven and Woronora rivercatchments that have a combined area of16,850 km2 (Figure 1). Streamflow fromthe Warragamba catchment is captured inWarragamba Reservoir that has a storagecapacity of 1890 gigalitres (GL). Waterfrom the Cataract, Cordeaux, Avon andNepean Dams located in the UpperNepean catchment is conveyed via a systemof pipes, natural river channels, weirs,tunnels and aqueducts to ProspectReservoir whilst also supplying variouscommunities along the routes. The SouthCoast region is supplied with water fromthe Avon and Cordeaux Dams and NepeanDam via the Nepean-Avon tunnel.
Streamflow from the Shoalhavencatchment is captured in Lake Yarrungaand Tallowa dam where water is raised 612metres to Wingecarribee Reservoir viaFitzroy Falls Reservoir when the waterstorage volume in Warragamba Dam is lessthan 65%. Water from the WingecarribeeReservoir is distributed to Nepean dam andLake Burragorang via the Wingecarribeeand Wollondilly Rivers. The townships ofMittagong and Bowral are also suppliedwith water from the WingecarribeeReservoir.
Simulation of Headworks SystemPerformance
Performance of the water supplyheadworks system and impact of urbanwater demand on streamflow inthe water supply catchment wassimulated using the WATHNETnetwork linear program forheadworks simulation by Kuczera[1992].
The streamflow records andclimate data (rain depth, rain daysand daily maximum temperature)from the period 1909 to 2000were used in this study. Topreserve the climatic correlationbetween the urban and water
supply catchments 2000 replicates ofstreamflow and climatic variables in bothcatchments were simultaneously generatedfor the period 2001 to 2090.
It is important to highlight thesignificance of using replicates ofstreamflow and climatic variables inpreference to the use of a single historicalsequence of information. The use of asingle historical sequence to evaluate thesecurity of a regional water supply can onlyprovide understanding of the water system’sresponse to a single given sequence ofclimatic events. In contrast, the use ofreplicates will allow a reliableunderstanding of system responses to arange of different climate sequences thatmay occur in the future and allowevaluation of the systems failureprobabilities.
Headworks System ReliabilityIn this study reliability is defined as the
probability that water restrictions will notbe imposed in a particular year. Restrictionson urban water demand are triggered whenstorage levels in Warragamba Dam andAvon Dam fall below 60%. The reportedeffectiveness of water restrictions in the
Sydney region during the 1992-1998drought by Deen [2000] was used todevelop restriction criteria and subsequentdemand reductions for domestic outdoordemand. Water restrictions were onlyapplied to domestic outdoor demand andnon-domestic demand (Tables 1 and 2).
The trigger to augment Sydney’s watersupply system with the construction of theWelcome Reef Dam was an unacceptablechance of water restrictions and risk offailing to supply water.
Water DemandThe Sydney region was divided into ten
water supply zones with different climaticconditions (monthly rain depth,temperature and rain days) that coincidedwith trunk distribution system monitoringdata provided by the SCA. These zonesinclude: Prospect East, Prospect South,Prospect North, Blue Mountains, OrchardHills, Avon, Nepean, Macarthur,Warragamba and Woronora. The NorthRichmond zone was not included in thestudy.
Monthly daily average domestic waterdemand for different dwelling types withinthe various demand zones was estimated
using climate data from the NSWoffice of the Bureau ofMeteorology, socio-economic datafrom the Australian Bureau ofStatistics and the methodsdeveloped by Coombes et al.[2002].
Daily water balance results forhouseholds was derived using thePURRS (probabilistic urbanrainwater and wastewater reusesimulator) allotment water balancemodel and historical climate data
Figure 2. Impact of pump marks on the Shoalhaven River in the year 2020.
Table 1. Water restriction criteria for domestic outdoordemand.
Storage less than (%) 60 55 50 40Reduction in demand (%) 33 57 75 100
Table 2. Water restriction criteria for non-domesticdemand.
Storage less than (%) 50 40 30 20Reduction in demand (%) 5 10 15 20
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was compiled into resource files.Resource files were also created forhouseholds with demandmanagement measures andrainwater tanks.
The method of non-parametricaggregation created by Coombes etal. [2002] was used to generatemonthly domestic water use foreach dwelling type in each climatezone using the historical resourcefiles and the climate replicatesgenerated for the headworkssimulation.
Importantly, the use of climatereplicates and the non-parametricmethods ensures that waterdemands are temporally andspatially consistent with therainfall and stream flows in thewater supply catchments.Population data used in this study wasprovided by the Australian Bureau ofStatistics, Planning NSW and SCA.
Pump Marks and Frequency ofWater Restrictions
The performance of the water supplyheadworks system was evaluated using 2000replicates of streamflow and water demandsin the WATHNET program. Variation inthe Shoalhaven pump marks and frequencyof water restrictions were considered. Thepump mark in the base system is consideredto be 65% which means when storage levelsin Avon and Warragamba Dams fall below65% pumping from the Shoalhaven River iscommenced. Performance of the headworkssystem subject to variation in pump marksand frequency of restrictions is shown inTable 3.
Table 3 shows that increased pumpmarks and frequency of water restrictionsdelays the requirement for augmentation byup to 66 years. At the currently acceptedfrequency of water restrictions of 3%increasing pump marks can delayaugmentation of the water supplyheadworks system by 24 years. At a pumpmark of 65% increasing the frequency ofwater restrictions can defer the requirementto augment the water supply headworkssystem by up to 40 years. The impact ofvariation in pump marks on streamflow inthe Shoalhaven River in January 2020 withacceptance of a 3% chance of waterrestrictions is shown in Figure 2.
Figure 2 shows the cumulative percentilesof streamflows that exceed a given value as aproportion of natural flows. Waterextractions from the Shoalhaven River inresponse to pump marks ranging from 65%to 90% result in very significant reductionsin streamflow. Increasing pump marks to
80% and 90% will result in up to 85%depletion of medium range streamflow.Increasing the pump marks will alsoincrease energy consumption, costs andgreenhouse gas emissions (Table 4).
Table 4 shows that higher pump markswill increase annual energy costs by $0.7Mto $6.9M and greenhouse gas emissions by39% to 280% in the year 2020. The cost topump water from the Shoalhaven River toWingecarribee Reservoir was estimated torange from $62/ML to $84/ML withenergy consumption of 1624 kWh/ML.About 0.89 kg of greenhouse gases (CO2)is generated for each kWh of electricityconsumption.
Adoption of a 70% pump mark andacceptance of a 5% frequency of waterrestrictions will defer augmentation of theheadworks system by 26 years withincreases in annual pumping costs of$0.7M to $1M, greenhouse gas emissions
increase of 40% and the smallestadditional reduction in streamflowin Shoalhaven River.
The Impact of Demand andSupply ManagementMeasures
The impact of various demandand supply management measureson mains water demand in theSydney region was determinedusing the regional demand method.A limited selection of approacheswas evaluated including 1% and2% per annum installation of AAArated shower roses (AAA_1%,AAA_2%), demand managementmeasures including 6/3 litre flushtoilets, AAA rated shower roses andwashing machines (DM_1%,DM_2%), 5 kL rainwater tanks
with mains water trickle top up fordomestic toilet and outdoor demand(T_TO_1%, T_TO_2%) and 5 kLrainwater tanks with mains water trickle topup for domestic hot water, toilet, laundryand outdoor demand (T_HTLO_1%,T_HTLO_2%).
Combinations of measures were alsoconsidered including 1% per annuminstallation of demand managementmeasures in combination with 0.25%,0.5% and 1% per annum uptake of 5 kLrainwater tanks with mains water trickle topup for hot water, toilet, laundry andoutdoor uses (T_0.25%DM_1%,T_0.5%DM_1%, T_1%_DM_1%). Apump mark of 65% was used. Regionalaverage annual water demand from some ofthese scenarios is shown in Figure 3.
Figure 3 shows that a 2% per annuminstallation of AAA rated shower roses(AAA_2%), demand management measures
Table 3. Variation in pump marks and frequency ofwater restrictions.
Pump mark Augmentation year by frequency of restrictions1% 3% 5% 10%
Figure 3. Regional mains water demand in the Sydney region.
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(DM_2%) and 5 kL rainwatertanks for toilet and outdoor uses(T_TO_2%) will have a moderateimpact on regional water demand.The 1% and 2% installation perannum of 5 kL rainwater tanks forhot water, toilet, laundry andoutdoor uses (T_HTLO_1%,T_HTLO_2%) producessubstantial reductions in regionalwater demand. Combinations ofdemand management measures and5 kL rainwater tanks used to supplydomestic hot water, toilet, laundryand outdoor uses, especially theT_1%DM_1% scenario, alsoproduce considerable reductions inregional mains water demand.
Using the WATHNET programthe impact of demand and supplymanagement scenarios on thereliability of the water supply headworkssystem was evaluated. The impact of thedifferent scenarios on augmentation timingis shown in Table 5.
Table 5 shows that under reliabilitycriteria of 3% (similar to current criteria)only the scenarios T_HTLO_1%,T_HTLO_2%, T_0.5%DM_1% andT_1%DM_1% that include 5 kL rainwatertanks used to supply hot water, toilet,laundry and outdoor uses deferaugmentation. The T_HTLO_2% andT_1%_DM_1% scenarios result in longterm deferral of augmentation by 71 to 84years. Note that the scenarios with AAArated shower roses and demandmanagement measures will not defer therequirement to augment the water supplyheadworks system subject to currentreliability criteria. Similar results apply tothe scenarios with 5 kL rainwater tanks tosupply toilet and outdoor uses.
Interestingly, acceptance of a 5% chanceof water restrictions produces the greatestdeferral of augmentation timing (5 to 8years) for scenarios with demandmanagement or rainwater tanks for toiletand outdoor uses. For these scenarios a10% reliability criteria diminishes therelative impact on augmentation timing.The scenarios with 5 kL rainwater tanks forhot water, toilet, laundry and outdoorsupply and/or demand managementmeasures provide greater deferment ofaugmentation with increases in frequenciesof water restrictions from 3% to 5% or10%. Note that a combination of a 5%reliability criteria and scenariosT_HTLO_1%, T_HTLO_2% andT_1%DM_1% defer the requirement toaugment the water supply headworkssystem beyond the 90 year planninghorizon.
Economic ImpactsThe investment model developed by
Coombes et al. [2002] compares economicbenefits accruing to the community from atraditional Base scenario to alternativescenarios that include installation ofrainwater tanks and demand managementmeasures. The Base scenario considers thestatus quo: provision of traditionalstormwater systems to areas undergoingurbanisation and provision of additionalmains water supply by further regulation ofriver systems.
Costs and benefits for the provision ofmains water and the disposal of stormwaterconsidered common to the base andalternative scenarios were not included inthe analysis. The costs and benefits thatdiffer from the base scenario are consideredin analysis of the alternative scenarios. Inthe alternative investment scenario ahousehold can purchase water from a waterutility, use rainwater tanks for water supplyand install demand management measuresto reduce water use. The community paysthe cost of installing, operating,maintaining and replacing rainwater tankand demand management systems whilstgaining benefits from reductions in mainswater use and the requirement for watercycle infrastructure. The reducedrequirement for infrastructure results indecreased depreciation and maintenancecosts.
Installation of 3A rated shower roses wasestimated to reduce water distributioninfrastructure installation costs by $21.1per device at an installation cost of $80each. 3A rated shower roses have anestimated 10 year life with a replacementcost of $45 per device.
Installation costs for 3A rated washingmachines and 6/3 litre toilets were $800
and $85 per device respectively.The washing machines wereestimated to have a ten yeardesign life. The demandmanagement scenarios wereexpected to produce waterdistribution infrastructureinstallation savings of $54.40 perdwelling respectively. Theinstallation of rainwater tanks wasestimated to cost $2,500 eachproviding stormwater and waterdistribution infrastructure savingsof $1,300 per dwelling. The tankhas a design life of 50 years with areplacement cost of $800 and thepump has a design life of 10 yearswith a replacement cost of $350.Augmentation of the water supplyheadworks system by theconstruction of the Welcome Reef
Dam was expected to cost $226M (basedon NSW Treasury estimates from 2003,note that the current estimated cost is over$2 billion).
A 5% frequency of water restrictions wasaccepted for the economic analysis. Thepresent benefits of the demandmanagement scenarios ranged from -$527M to $144.9 and cost of water supplyfrom rainwater tanks varied from -$985Mto $774M.
Environmental ImpactThe impact of demand and supply
management measures on theenvironmental health of the Sydney regionin the year 2020 was considered in terms ofstreamflow in the Shoalhaven River,stormwater runoff in urban areas, thevolume of sewage generated and greenhousegas emissions. A 5% frequency of waterrestrictions was accepted for theenvironmental analysis.
Streamflow in the Shoalhaven RiverIncreasing water urban demands or the
construction of Welcome Reef Dam has thepotential to further degrade the ShoalhavenRiver system. Although the monthly timestep used in the streamflow analysis in thisstudy is unsatisfactory from an ecologicalperspective the changes in streamflow inresponse to urban water demand willprovide an indicator of river health. Thegreatest reduction in streamflow for January2020 from each scenario was calculated as apercentage of natural streamflow. Thesepercentages from each scenario were usedto develop an environmental flow score thatranged from 75% to 80%.
Frequent Stormwater DischargesThe use of rainwater tanks can result in
substantial reductions in stormwater runoff.
Table 5. Augmentation requirement for the water supplyheadworks system.
Scenario Augmentation year by frequency of restrictions1% 3% 5% 10%
A stormwater discharge score was developedthat determined the percentage reductionin 3 month ARI stormwater discharges inthe Sydney region resulting frominstallation of rainwater tanks. Values forthe stormwater discharge score ranged from14% to 30%.
The Volume of Sewage DischargesInstallation of demand management
measures such as 6/3 flush toilets, 3A ratedshower roses and washing machines willreduce the magnitude of indoor water use.The water savings become a reduction inthe volume of sewage discharges that willreduce impacts on the environment. Thesewage score represents the reduction insewage discharges in the Sydney region thatresult from demand management measures.Values for the sewage score range from1.28% to 6.6%.
Greenhouse Gas EmissionsChanges in energy usage resulting from
reduced pumping from the ShoalhavenRiver, in rainwater tank systems (smallpumps that use less energy than deliveringwater via the mains distribution system)and in the sewage and water reticulatedsystems and reduced water heating in hotwater systems will reduce greenhouse gasemissions. The greenhouse gas scoredetermines the percentage reduction ingreen house gas emissions in comparison toemission from the Base water supplyscenario. Values for the score range from0.02% to 133% for the T_TO_1% andAAA_2% scenarios respectively. Use of 3Arated shower roses achieved a considerableenergy saving. Note that 3A rated showerroses generate additional energy savingsderived from heating less water.
The Pareto FrontierThe results from the environmental
impact scores were combined with equalweight with the exception of thegreenhouse gas score which was given anarbitrary weight of 0.01 in recognition ofthe relative significance of the otherenvironmental scores to form anenvironmental criterion. The economicresults reported as the present value ofalternative solutions were combined withthe environmental criteria in the ParetoDiagram shown in Figure 4.
The Pareto Diagram provides a methodof comparing conflicting environmentaland economic objectives. Inferior solutionsare those that have lower economic valuesand environmental scores than othersolutions.
Figure 4 shows that the scenario with 2%per annum installation of rainwater tanksfor hot water, toilet, laundry and outdoor
uses is a Pareto optimum solution and thedisturbing realisation that the currentlypreferred water industry solutions are farfrom optimum. Although this study has notanalysed enough scenarios to accuratelylocate the Pareto Optimum a number ofobservations can be made. It is clear thatscenarios with 5 kL rainwater tanks forsupply of hot water, toilet, laundry andoutdoor uses (T_HTLO_1%;T_HTLO_2%) are close to ParetoOptimum solutions. Similarly scenariosthat combine demand managementmeasures and 5 kL rainwater tanks for hotwater, toilet, laundry and outdoor usesapproach the Pareto Optimum.
Figure 4 also shows that scenarios with 5kL rainwater tanks for supply of toilet andoutdoor uses or AAA rated shower roses ordemand management measures alone areinferior solutions and should therefore bediscarded.
ConclusionsThe most significant contribution of this
paper is an explanation of systemsmethodologies to evaluate the performanceof integrated water cycle managementscenarios. These methodologies and modelshave generic application to evaluation ofregional water security at any location.Although the systems methodologies havebeen used in the analysis that evaluated alimited range of water managementscenarios, the results are instructive.
Acceptance of a greater frequency ofwater restrictions will defer the requirementto augment the water supply headworkssystem by up to 43 years. Increasing thepump mark for water extractions from theShoalhaven River with current frequency of
restrictions will defer augmentation by upto 24 years with substantial impact on theShoalhaven River. A pump mark of 70%with acceptance of a 5% chance of waterrestrictions will defer augmentation by 23years.
Use of demand management measures or5 kL rainwater tanks for toilet and outdooruses, and retention of the 3% chance ofwater restriction rules will not result indeferment of Welcome Reef Dam.However the installation of 5 kL rainwatertanks for hot water, toilet, laundry andoutdoor uses with or without demandmanagement measures at rates of 1% and2% per annum will defer augmentation by21 to 84 years. If the acceptable chance ofwater restrictions is increased to 5% thesescenarios will defer the requirement toconstruct Welcome Reef Dam beyond2090. The present value of scenarios withdemand management measures ranged from-$527M to $133.3M and with rainwatertanks varied from -$985M to $774M.
The results of this study indicate that theurban water industry is operating in aconstrained solution space resulting in sub-optimal solutions. This observation isparticularly relevant given that the waterindustry claim that rainwater tanks areinferior solutions in comparison to demandmanagement measures. Installation ofdemand management measures alone willhave minimal impact on the requirement toaugment Sydney’s water supply headworkssystem. The adoption of a wide range ofsupply and demand management measures,including recycling of wastewater, will havea significant impact on the security ofSydney’s water supply. Importantly, the useof methods outlined in this paper will allow
Figure 4. Pareto Diagram of alternative solutions.
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improved understanding of the synergisticand systems benefits of a wide range ofwater management approaches.
The AuthorDr Peter Coombes is Conjoint Senior
Fellow in Integrated Water CycleManagement, School of Environmental andLife Sciences, University of Newcastle.Email [email protected]. He isalso the managing director of theconsulting company Urban Water CycleSolutions. Dr Coombes has a PhD in watersystems engineering and microbiology,degrees in Civil Engineering and Surveying,and an Associate Diploma in Engineering.
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