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

6. Calculation of Stormwater Recharge Water level sensors in the basins coupled with Basin geometry provide the necessary data to determine inflows and outflows  S = I - O S t+1 - S t = (  I t,t+1 -  O t,t+1 ) *  t + (R t,t+1 - P t,t+1 - E t,t+1 ) * A t,t+1 *  t

7. 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.

8. Example of stormwater-only computation – Brooks Basin

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

16. 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 30 th, 2004.

17. 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 30 th – one month to get through the Watermaster process

18. 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

19. “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

20. “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

21. “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

22. 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

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

24. How would a long-term annual average estimate of new yield be estimated? For example 1) Use average for first five years 2) Recalibrate simulation tools based on recharge performance data from basins 3) Prepare new model estimated average for use in years six through ten 4) Repeat Steps 1 to 3 for the next five years and so on…

25. Questions?