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Determination of New Recharge

Determination of New Recharge. February 14, 2003. When will new stormwater recharge occur?. Basins will be constructed in Watermaster fiscal 2002/03 and 2003/04 – final construction completed around December 2004.

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Determination of New Recharge

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  1. Determination of New Recharge February 14, 2003

  2. When will new stormwater recharge occur? • Basins will be constructed in Watermaster fiscal 2002/03 and 2003/04 – final construction completed around December 2004. • It is unlikely that there will be new recharge from these facilities in 2002/03 due to the timing of the construction • New recharge will occur in 2003/04

  3. How is new stormwater recharge calculated? • Two step process: • Calculate the volume of stormwater recharge after improvements • Calculate the volume of stormwater recharge before improvements • New recharge equals difference

  4. Calculation of Stormwater Recharge • Key relationships between water surface elevation, inundated area and storage are developed from Basin geometry • Elevation – area – storage • Elevation – outflow

  5. Calculation of Stormwater Recharge • Water level sensors in the basins coupled with Basin geometry provide the necessary data to determine inflows and outflows DS = I - O St+1 - St = (SIt,t+1 - SOt,t+1) * Dt + (Rt,t+1 - Pt,t+1 - Et,t+1) * At,t+1 *Dt

  6. Have the calculations been done before? • Over the last few years Watermaster staff has performed these computations at the Brooks, Montclair and Turner 1 Basins • The computations are straightforward for basins that receive storm water only and are more difficult for basins that receive storm and supplemental water.

  7. Example of stormwater-only computation – Brooks Basin

  8. Example of stormwater-only computation – Brooks Basin

  9. Example of stormwater-only computation – Brooks Basin

  10. Example of stormwater-only computation – Brooks Basin

  11. Example of storm and supplemental water computation – Montclair 1 Basin

  12. Example of storm and supplemental water computation – Montclair 1 Basin

  13. Example of storm and supplemental water computation – Montclair 1 Basin

  14. Example of storm and supplemental water computation – Montclair 1 Basin

  15. When can these calculations be done for the improved and new Basins? • Recharge from the Chino Basin Recharge Facilities improvement project will occur in 2003/04. • First data set for this recharge will be complete on June 30th, 2004.

  16. When can these calculations be done for the improved and new Basins? • Computations should be started during the rainy season and could be completed by September of 2004 • two months to complete the calculations of storm and supplemental water after end of fiscal year – June 30th • one month to get through the Watermaster process

  17. What should Watermaster allocate as New Yield from new stormwater recharge? • Two schools of thought • Allocate estimated new stormwater that is captured in the prior year • Allocate the estimated average annual new stormwater that is captured over a long period, say a 40 to 50 year hydrologic period

  18. “Allocate estimated new stormwater that is captured in the prior year” • Pros • simple accounting • no out-year surprises • Cons • volume allocated to appropriators will be highly variable from year to year • more difficult for appropriators budget for expenses and to set water rates • New recharge will not be available to appropriators until 2004/05 assessments

  19. “Allocate the estimated average annual new stormwater that is captured over a long period, say 40 to 50 year hydrologic period” • Pros • volume allocated to appropriators will be uniform from year to year • creates certainty for appropriators for planning budgeting and water rates • uses the groundwater storage to manage the variability of storm water recharge • new recharge could be available to appropriators for 2003/04 assessments

  20. “Allocate the estimated average annual new stormwater that is captured over a long period, say 40 to 50 year hydrologic period” • Cons • could be surprise in out-years if estimated average annual recharge is substantially different than actual average – estimate could be low or high

  21. How would a long-term annual average estimate of new yield be estimated? • Use simulation models to compute recharge under existing and improved conditions – new yield is the difference • Use a long precipitation period, say 50 years • Use a set of assumptions that produce estimates of recharge that range from conservatively low to aggressively high – Watermaster policy decision

  22. How would a long-term annual average estimate of new yield be estimated? • Alternatively, Watermaster could just use an arbitrary value for new recharge

  23. How would a long-term annual average estimate of new yield be estimated? For example • Use average for first five years • Recalibrate simulation tools based on recharge performance data from basins • Prepare new model estimated average for use in years six through ten • Repeat Steps 1 to 3 for the next five years and so on…

  24. Questions?

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