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HomeMy WebLinkAbout02/07/1989, 2 - COORDINATED OPERATIONS STUDY FOR THE SALINAS AND WHALE ROCK RESERVOIRS MEETING DATE: IIINIIIIN���I�����j l� City Of San LUIS OBISPO February NUMBER: 1989 COUNCIL AGENDA REPORT - From: William T. Hetland, Utilities Director Subject Coordinated Operations Study for the Salinas and Whale Rock Reservoirs Recommendation: Receive and file report. Direct staff to continue its efforts in maximizing the yield of our supplies and request the Whale Rock Commission begin studies to increase the pumping capacity of its conveyance system. Staff also recommends that no adjustments to the City's safe annual yield be made at this time. SUMMARY The City retained the firm of Leedshill-Herkenhoff to perform a safe annual yield study on the Salinas reservoir and on the coordinated use of the Salinas and Whale Rock Reservoirs. The studies showed a reduction in the independant yield of the Salinas Reservoir to 4450 AFY and an increase in the independant yield of Whale Rock Reservoir to 4960AFY. The studies also determined alternative coordinated yields based on four different combinations of minimum storage volumes for the two reservoirs. At conservative storage volumes of 3000 AF for Salinas and 5000 AF for Whale Rock Reservoirs, the coordinated yield for the City of San Luis Obispo is 7460 AFY or 103 AFY greater than the currently accepted value of 7357 AFY.. The coordinated yield can be increased to 8210 AFY, at these storage volumes, by making pumping modifcations to the Whale Rock conveyance system. Staff is also pursuing treatment plant changes and intake modifications at the Salinas Reservoir to increase the flexibility in using that facility. Downstream water use and its impact on the live stream is also being investigated. Staff is recommending we continue to maximize our yields and request the Whale Rock Commission to undertake modifcations to their conveyance system. No changes in the safe annual yield of the City is being recommended at this time. BACKGROUND Salinas Reservoir At the December 20, 1988 Council meeting, staff presented tentative results of a new safe annual yield study on the Salinas Reservoir. The final report was received in January and distributed to staff and the Council. The report concluded that the safe annual yield of the Salinas reservoir has been reduced by 350 acre-feet per year (AFY) to a level of 4450 AFY from the existing 4800 AFY. The reduction was the result of increased siltation in the reservoir due to some large storms we have experienced in the last few years. Staff also indicated that this loss of safe annual yield may be offset by an increase in yield due to the coordinated use of the Salinas and Whale Rock Reservoirs. The major conclusions reached in the study are as follows: 1. Based on appliction of a mathematical regression equation developed by the United States Geological Survey in 1975, approximately 1500 acre-feet of usable storage capacity has been lost to accumulated sediment from the upstream watershed since 1975. Therefore, the current usable storage capacity is estimated to be approximately 21,800 AF. i�iIIIIIfII Pilll ow 0� SM Luis 081sp0 COUNCIL AGENDA REPORT Coordinated Operations Study Page 2 2. The impact of the "live stream" requirement is difficult to determine due to the relative lack of historical data and the possibility of continuously changing conditions along the downstream reaches of the Salinas River. Therefore, hydrologic data related to the live stream releases should be closely monitored and further analysis should be performed once more information is available in o4der to better understand the impact of the live stream requirement. 3. Based on the revised estimate of storage capacity and the projected impact of the live stream requirement, the current safe annual yield of Salinas Reservoir is estimated to be 4450 acre-feet per year. Coordinated Operations Study The City's consultant, Leedhill-Herkenhoff, has also completed a study updating the safe annual yield of the City based on a coordinated use concept. The Coordinated Operations Study looked at what the yield of the Salinas and Whale Rock Reservoirs would be if they were operated in a managed, coordinated manner. The basic concept is that water from the Salinas Reservoir is used as much as possible because it will fill faster and more often than the Whale Rock Reservoir. Also there is more loss of storage due to evaporation at Salinas Reservoir and by keeping the reservoir down minimizes the evaporation loss. A preliminary analysis on this concept was performed for the City's Draft Water Management Plan. That analysis estimated that 300 to 800 AFY in yield could be gained. The Draft Water Management Plan used the amount of 500 AFY. Since revised yield models for both the Salinas and Whale Rock Reservoirs were developed and a new operating policy has been adopted by the Whale Rock Commission, a more thorough evaluation of the coordinated use concept was appropriate. The Coordinated Operations Study used the computer model that was developed in LH Salinas Reservoir study. Four minimum storage volumes of 400, 2000, 3000, and 5,000 AF were used. These amounts were based on a combination of different factors including dead storage, fish habitat, water quality, physical constraints of the reservoir facilities. The safe annual yield of the Whale Rock Reservoir was recalculated based on monthly data instead of annual data as had been done in the 1974 Department of Water Resources study. This placed the Whale Rock analysis on the same basis as Salinas Reservoir. A number of statistical correlations were also done to improve the accuracy and reliability of the precipitation, evaporation, and reservoir inflow input data. This check on the input data showed that DWR overstated the evaporation loses and understated the inflows at the reservoir. The results of this recalculation and revised input data increased the independent safe annual yield for Whale Rock Reservoir from the old value of 4400 AFY to 4960 AFY. This increase of 560 AFY is due to the higher inflows and lower evaporation rates over the critical period. �';2, 1u1t1111111114§ city of San LUIS OBISpo N"InA COUNCIL AGENDA REPORT Coordinated Operations Study Page 3 Coordinated Operations Model The coordinated operations model included four minimum storage volumes for the Salinas and Whale Rock Reservoirs. They are summarized below. Minimum Storage Scenario Salinas Whale Rock A 5000 5000 B 3000 5000 C 2000 2000 D 400 500 These volumes represent the lowest possible and a combination of other volumes based on water quality, fish habitat, or reservoir facilities. Scenario A represents a "worst case" posssibility, while scenario D was included to provide consistent comparisons with previous studies. Scenarios B and C are the most realistic. The operations model also showed that at the higher flow rates that hydraulic restrictions existed in the Whale Rock conveyance system. Therefore two different runs were made based on the existing hydraulic capacities and future hydraulic capacities. Additional pumps would have to be added to the Whale Rock system to meet the future hydraulic capacities. i The results of the coordinated operations study are summarized below. The minimum storage volumes for each scenario are identified and the yield for the existing hydraulic conditions and the future hydraulic conditions are shown.. City of San Luis Obispo Coordinated Operations Study Min Storage (AF) Coord SAY (AFY) Coord SAY Less Current (AFY) Scenario Salinas Whale Rock Existing Future Existing Future Current 400 500 7357 7357 0 0 A 5000 5000 6860 7810 (497) 453 B 3000 5000 7460 8210 103 853 C 2000 2000 7800 8580 443 1223 D 400 500 8250 8990 893 1633 • I �����i iVVIIIIIfI�pn ��Ulll MY Of San WIS OBispo : WaGe COUNCIL AGENDA REPORT Coordinated Operations Study Page 4 The safe annual yield for the City under existing hydraulic conditions, ranges from a decrease of 497 AFY to an increase of 893 AFY. Under the most logical scenarios of B and C the yield has increased 103 and 442 AFY, respectively. These increases take into account the revised Salinas and Whale Rock Reservoirs indepentant safe annual yield studies. Scenario B is a conservative approach which is based primarily on water quality considerations. City staff feel that it is possible to treat the water at the Salinas Reservoir to a level of 3000 AF of storage and may be possible to get to the 2000 AF level. The Whale Rock Reservoir has never been drawn down far enough to give staff any experience with what the water quality concerns may be at the lower levels. But based on our experience at Salinas we feel that 5000 AF of storage is a conservative level. Both of these levels also meet minimum storage volumes for fish habitat. The hydraulic restrictions in the Whale Rock conveyance system occur when the reservoir levels are down and we are trying to deliver the maximum amount of water through the system. This is because the existing pumps do not have adequate head (ie ability to pump at higher pressures) for the mount of water being delivered. Alternative ways to improve the system may include modifying existing pumps, installing new pumps, adding additional pumps or installing an in-line booster pump station. If these restrictions are resolved, the yield for scenarios B and C would be increase over our current yield by 853 and 1223 AFY, respectively. The consultant is recommending that a study be done to determine the most efficient method of resolving this problem. A yield of 7460 AFY could be supported based on scenario B with minimum storage volumes of 3000 AF for Salinas and 5000 AF for Whale Rock and existing pumping conditions on the Whale Rock conveyance system. This would represent an increase of only 103 AFY. Since the City is still pursuing actions to maximize our yield and will be coming back to Council in May with the City Annual Water Operations Plan, it is not appropriate to take any additional action at this time. Maximizing the Safe Annual Yield There are a number of actions staff is currently pursuing to maximize the yield of the existing reservoirs. 1. Treatment - The primary concerns at the Salinas Reservoir are the taste and odor problems and manganese levels. Laboratory analysis has shown that these problems can be addressed by the addition of potassium permanganate. Temporary feed equipment and chemicals have been ordered to do full scale testing. This should be on line by the middle or end of February. This will allow us to treat water down to the 2000 to 3000 AF storage level. I 1111ellhIgpNil N city of San-11J IS OBIspo COUNCIL AGENDA REPORT Coordinated Operations Study Page 5 2. Intake - Another problem at the Salinas Reservoir is the lack of flexibility at the lower levels of the lake to withdraw the water. By having greater flexibility in the withdrawl, it is possible to choose the level at which the water quality is the best and easiest to treat. Staff is currently investigating the addition of an intake tube which will give us this flexibility. 3. Down Stream Uses - Storage at the Salinas Reservoir is dependent on a live stream being established downstream of the dam. The use of water downstream influences the establishment of the live stream. Staff is investigating the water rights and use along the river. 4. Groundwater - By utilizing groundwater during peak months it is possible to relieve the load on the surface water sources. The groundwater wells currently under construction will help this situation. Those wells will be completed by the end of March. Recommendations Staff recommends that the Council receive and file this report plus direct staff to continue its efforts in maximizing the yield of our supplies and request the Whale Rock Commission begin studies to increase the pumping capacity of it's conveyance system. _ Staff also recommends that no adjustments to the City's safe annual yield be made at this time. attachment say2789/n _ i