ITEM:

ACTION ITEMS

 

18.

CONSIDER REQUEST FROM DIRECTOR BROWER TO PRIORITIZE COORDINATION WITH CALIFONIA AMERICAN WATER ON INCREASING THE HEIGHT OF LOS PADRES DAM

 

Meeting Date:
October 20, 2008

Budgeted: 

No

 

From:

Darby Fuerst

Program/

N/A

 

General Manager

Line Item No.:

 

 

 

Prepared by:

Darby Fuerst

Cost Estimate:

N/A

 

General Counsel Review:  N/A

Committee Recommendation:  N/A

CEQA Compliance:  N/A

 

SUMMARY:  Since 1995, storage capacity in California American Water’s (CAW’s) reservoirs on the Carmel River, i.e., Los Padres and San Clemente, has decreased by more than 50% or 1,500 acre-feet (AF).  Currently, there is no usable storage capacity in San Clemente Reservoir and less than 1,200 AF of usable storage capacity in Los Padres Reservoir.  This decrease in storage capacity significantly limits the amount of surface water that can be stored during the high-flow season for release during the low-flow season.  These releases are necessary to maintain streamflow in the Carmel River below Los Padres and San Clemente Dams and recharge the Carmel Valley Alluvial Aquifer.  Presently, more than 50% of the streamflow in the Carmel River below Los Padres Dam is due to the release of stored water from Los Padres Reservoir[1].

 

The storage capacity in Los Padres Reservoir can be increased in three ways: (1) raise the height of Los Padres Dam and/or spillway, (2) dredge the sediments from Los Padres Reservoir, or (3) some combination of raising the dam and dredging the reservoir.  Director Bower has requested that the Board prioritize coordination with CAW on increasing the height of Los Padres Dam to increase storage capacity.  As explained in Exhibit 18-A, by raising Los Padres Dam 10 feet, storage capacity would be increased by approximately 680 AF.  Similarly, by raising Los Padres Dam 20 feet, storage capacity would be increased by almost 1,560 AF.  Director Brower’s request is consistent with Mitigation Measure AR-2 in the Phase 1 ASR Project EIR that requires the District to cooperate with CAW in developing a project to “maintain, recover, or increase storage in Los Padres Reservoir”.   

 

RECOMMENDATION:  District staff recommends that the Board approve Director Brower’s request to prioritize coordination with CAW on increasing storage capacity in Los Padres Reservoir by increasing the height of Los Padres Dam.  In addition, staff recommends that the coordination with CAW include consideration of increasing storage capacity in Los Padres Reservoir by dredging the reservoir, consistent with CAW’s request before the California Public Utilities Commission (CPUC) for funds to conduct a Dredging Feasibility Study at Los Padres Reservoir in 2009.  This request is described in Exhibit 18-A.  Lastly, staff should be directed to provide a status report to the Board on coordination efforts with CAW, the National Marine Fisheries Service (NMFS), the California Department of Fish and Game (CDFG), and the California Department of Water Resources’ Division of Safety of Dams (DSOD) by June 30, 2009.  The report should include a summary of progress made by CAW on their proposed Dredging Feasibility Study and recommendations for further actions.      

 

BACKGROUND:  At the February 28, 2008 Board meeting, the Board approved a request by Director Brower to direct staff to prepare a report regarding the feasibility of increasing the height of CAW’s existing Los Padres Dam in the upper Carmel River Basin. This report, which reviewed the procedure and timeline for conducting a feasibility study of increasing the storage capacity of Los Padres Reservoir by increasing the height of the dam, dredging the reservoir, or some combination, was prepared by the District Engineer and presented at the Board’s April 21, 2008 meeting.  At that time, the Board directed staff to confer with CAW regarding the feasibility and methods that could be used to raise the height of Los Padres Dam and investigate costs and possible funding sources.  In addition, staff was directed to contact the NMFS and the CDFG regarding potential modifications to Los Padres Dam and Reservoir.  Lastly, staff was directed to prepare a report that provides estimates of the amount of storage capacity that would be available in Los Padres Reservoir at varying elevations, if the dam was raised.  Staff has discussed the possibility of raising Los Padres Dam and dredging Los Padres Reservoir with representatives from CAW, NMFS, and CDFG. 

 

On August 4, 2008, staff submitted a memorandum to the Board that provided estimates of the amount of storage capacity that would be available in Los Padres Reservoir if the dam was raised 20 feet, i.e., from the existing spillway elevation of 1,040 feet to elevation 1,060 feet (Exhibit 18-A).  As noted in the memorandum, the estimated storage values for Los Padres Reservoir were taken from the original elevation-area-capacity curve that was developed in 1947.  As noted in the memorandum, for each foot that Los Padres Dam is raised between elevation 1,040 feet and elevation 1,050 feet, storage capacity would be increased by approximately 68 AF.  Accordingly, by raising Los Padres Dam 10 feet, storage capacity would be increased by approximately 680 AF.  Similarly, for each foot that Los Padres Dam is raised between elevation 1,050 feet and elevation 1,060 feet, storage capacity would be increased by approximately 88 AF.  Therefore, by raising Los Padres Dam 20 feet, storage capacity would be increased by a total of approximately 1,560 AF (680 AF + 880 AF = 1,560 AF).  The memorandum also provided an estimate of the amount of storage capacity in Los Padres Reservoir that could be recovered by dredging.  Specifically, based on CAW’s 1998 estimate of storage capacity (1,569 AF), if Los Padres Reservoir was dredged to its original capacity (3,070 AF), approximately 1,500 AF of additional storage would be available for release.  Altogether, if the dam was raised 20 feet and the reservoir was dredged to its original capacity, more than 3,000 AF of water would be available for release during the low-flow season.

 

Lastly, as referenced in the memorandum (Exhibit 18-A), CAW has applied to the CPUC for funds to conduct a Dredging Feasibility Study at Los Padres Reservoir.  As requested, the study would cost $200,000 and would begin January 2009 and be completed by December 2009.  The study will include investigation of dredging, transportation, and disposal methods and associated costs.       

 

IMPACT ON STAFF/RESOURCES:  The coordination effort outlined in this staff report would involve time by the General Manager and Planning and Engineering Division staff. 

 

EXHIBITS

18-A                Memorandum from Darby Fuerst to MPWMD Board of Directors regarding Increases in Los Padres Reservoir Storage Capacity for Selected Elevations, dated August 4, 2008

 

U:\staff\word\boardpacket\2008\2008boardpackets\20081020\ActionItems\18\item18.doc


[1] On October 1, 2008, District staff measured 2.7 cubic feet per second (cfs) of flow into Los Padres Reservoir and 5.5 cfs of flow out of Los Padres Reservoir.  The difference, 2.8 cfs, is attributable to the release of stored water in the reservoir.