Water Source Alternative Options Assessment for the Metropolitan Supply Rainwater Tanks Concept Report Prepared for Watercare Services Ltd Prepared by Beca Limited 9 December 2020 Creative people together transforming our world | Rainwater use assessment | Revision History Revision Prepared By Description Date Nº 1 Haddon Smith Frist draft 18 th Nov 2020 2 Haddon Smith Final draft 27 th Nov 2020 3 Haddon Smith Final 9th Dec 2020 Document Acceptance Action Name Signed Date Prepared by Haddon Smith 9th Dec 2020 Reviewed by Jon Reed 9th Dec 2020 Approved by Clive Rundle 9th Dec 2020 on behalf of Beca Limited © Beca 2020 (unless Beca has expressly agreed otherwise with the Client in writing). This report has been prepared by Beca on the specific instructions of our Client. It is solely for our Client’s use for the purpose for which it is intended in accordance with the agreed scope of work. Any use or reliance by any person contrary to the above, to which Beca has not given its prior written consent, is at that person's own risk. Waikato River Water Take and Discharge Proposal – Board of Inquiry | i Contents Executive Summary ........................................................................................ 1 1 Introduction ................................................................................................ 3 1.1 Background............................................................................................................................ 3 1.2 This report .............................................................................................................................. 4 1.3 Purpose of this report ............................................................................................................ 5 1.4 Scenarios modelled in the 2015 report .................................................................................. 6 1.5 Storage developed by rainwater tanks .................................................................................. 8 2 Tanker demand during dry periods ....................................................... 10 3 Modelled yield of rainwater tanks at Watercare’s Peak Level of Service ...................................................................................................... 13 4 Modelled yield of rainwater tanks at Watercare’s Annual average drought Level of Service ......................................................................... 19 5 Advantages and disadvantages of rainwater tanks ............................. 22 5.1 Potential benefits of rainwater tanks ................................................................................... 22 5.2 Disadvantages of rainwater tanks ....................................................................................... 22 6 Yield recommendations .......................................................................... 24 7 Cost estimate ........................................................................................... 26 7.1 Capital costs ........................................................................................................................ 26 7.2 Operational costs ................................................................................................................. 26 7.3 Optimistic scenario costing .................................................................................................. 28 8 Conclusions ............................................................................................. 29 Appendices Appendix A – Peak results tables Appendix B – Annual average yield plots for scenarios 1-4 Waikato River Water Take and Discharge Proposal – Board of Inquiry | ii Tables Table 1-1: Definition of tank sizes ........................................................................................................... 7 Table 4-1: Annual average drought yields obtained under the optimistic scenario for differnce use types ...................................................................................................................................................... 20 Table 6-1: Summary of different use types ........................................................................................... 24 Table 7-1: Capital costs of rain tank installations by tank size .............................................................. 27 Table 7-2: Average capital costs by development type based on the optimistic scenario .................... 27 Table 7-3: Operational costs ................................................................................................................. 27 Table 7-5: Optimistic scenario cost analysis summary ......................................................................... 28 Table A1: 2019 rain tank peak results under outdoor use .................................................................... 32 Table A2: 2020 rain tank peak results under outdoor use .................................................................... 33 Table A3: 2019 rain tank peak results under non-potable use.............................................................. 34 Table A4: 2020 rain tank peak results non-potable use ........................................................................ 35 Table A5: 2019 rain tank peak results all use ....................................................................................... 36 Table A6: 2020 rain tank peak results under all use ............................................................................. 37 Waikato River Water Take and Discharge Proposal – Board of Inquiry | iii Figures Figure 1-1: How this report feeds into the overall options assessment process in the “Water Source Options Assessment for the Metropolitan Supply” report ........................................................................ 6 Figure 1-2: Definition of the modelled scenarios in the 2015 report, note that the uptake dates shown here have been moved forward by five years for the purpose of this 2020 update (i.e. references to 2050 in the table are 2055 in results produced for this report)................................................................ 7 Figure 1-3: Summary of rainwater tank penetration over a 35 year period (optimistic scenario) ........... 8 Figure 1-4: Simplified model schematic .................................................................................................. 8 Figure 1-5: Total rain tank storage volume under the Optimistic uptake scenario, compared to Watercare's total lake storage volume and Watercare’s smallest storage lake (Hays Creek) ................ 9 Figure 2-1: Tanker consumption by financial year ................................................................................ 10 Figure 2-2: Normalised monthly tanker consumption for the 2016 to 2020 financial years .................. 11 Figure 2-3: Timeseries showing relationship between total tanker consumption and monthly rainfall . 11 Figure 2-4: Relationship between tanker consumption and monthly rainfall between February 2015 and June 2020 ....................................................................................................................................... 12 Figure 3-1: Average yield over peak 5 days in various recent dry years under the optimistic scenario (note that the 5 days averaged are the highest individual 5 days of demand, not the highest 5 consecutive days) .................................................................................................................................. 14 Figure 3-2: Average yield in February in various recent dry years under the optimistic scenario ........ 14 Figure 3-3: Average yield in January, February and March in various recent dry years under the optimistic scenario ................................................................................................................................. 15 Figure 3-4: Average volume and demand met by medium sized tanks at single residential properties during the 2020 summer ........................................................................................................................ 16 Figure 3-5: Average volume and demand met by medium tanks at single residential properties during the 2014 summer ................................................................................................................................... 17 Figure 3-6: Average yield over different peak periods under different tank sizes in 2019 and 2020 with rainwater tanks supplying non-potable use ........................................................................................... 18 Figure 4-1: Optimistic scenario rainwater tank annual average drought yield at 2055 - 36% of properties by 2055 ................................................................................................................................. 20 Figure 4-2: Average yield through the year from simulations corresponding to dry [99% series] median [50% series] and wet [1% series] years under the optimistic scenario supplying non-potable demand. ............................................................................................................................................................... 21 Figure 6-1: Growth in the annual average drought yield of rainwater tanks under the ‘optimistic’ scenario ................................................................................................................................................. 25 Figure 7-1: Annual capital and operation costs of rainwater