Online extra: Questions and answers about Temperance Flat


Issue Date: June 21, 2017

Q: Once complete, how would the proposed Temperance Flat Dam and Reservoir operate? How would water be distributed and moved in and out of the project?

  • Temperance Flat Reservoir would be formed by a new dam constructed in the original San Joaquin River channel within Millerton Lake. The reservoir would extend approximately 18 miles to the downstream face of Kerckhoff Dam, and would be filled by San Joaquin River runoff from the Sierra Nevada. The operating plan would assure that existing delivery capabilities to Central Valley Project Friant Division contractors and obligations for downstream deliveries and river restoration are met before additional water supply would be stored.
  • Storage space in Temperance Flat Reservoir would be divided into accounts that would be purchased and managed by project investors. A water manager would monitor the amount of water in each account. Water would be put into storage accounts from reservoir inflow.
  • Water would be released from Temperance Flat Reservoir into Millerton Lake though a hydroelectric generation plant on the diversion tunnel between the reservoirs. Flood releases from Temperance Flat Reservoir would flow over a spillway on Temperance Flat Dam into Millerton Lake. Releases from Millerton Lake would continue to be made to the Friant-Kern and Madera canals and the San Joaquin River, through existing outlets, power facilities and the Friant Dam spillway.
  • Water would be withdrawn from storage accounts for release to the Friant-Kern and Madera canals or to the San Joaquin River for subsequent downstream diversion and delivery. Water delivered to Friant Division or other eastern San Joaquin Valley water users would help address groundwater sustainability objectives. Water released to the San Joaquin River would provide ecosystem and water quality benefits from Friant Dam to the point of diversion. The current operating plan considers diversions at Mendota Pool for Westside water users, and diversion at other downstream locations for delivery to wildlife refuges.

Q: What construction is necessary to complete Temperance Flat Dam and Reservoir?

  • Temperance Flat Dam would require construction of a diversion tunnel and cofferdams upstream and downstream of the dam site, and a diversion tunnel to convey water from the upper portion to the lower portion of Millerton Lake. Temperance Flat Dam would be a 660-foot-tall, roller-compacted concrete gravity arch dam with an integrated spillway. A hydroelectric power plant would be constructed at the discharge end of the diversion tunnel. Water would be released from Temperance Flat Reservoir into Millerton Lake through the diversion tunnel and power plant, and would generate hydroelectricity.
  • Temperance Flat Reservoir would inundate the generating facilities of the existing Kerckhoff hydroelectric power project, which would be decommissioned. Power generated by Temperance Flat would replace Kerckhoff generation to the extent possible, and remaining impacts to Pacific Gas & Electric Co. would be fulfilled through payments or other means.

Q: If Proposition 1 funding becomes available, when might construction begin? When might the project be completed?

  • The anticipated construction duration is from 2021 through 2027, but the start depends upon completion of the environmental review process, all the required permits, the real estate/right-of-way process and final contracts with project investors, including the state of California.

Q: How many agencies have signed the joint-powers agreement, and who are they?

  • The joint powers agency working in support of Temperance Flat enjoys wide representation within its 10 current members. In January 2016, boards of supervisors in five central San Joaquin Valley counties organized the San Joaquin Valley Water Infrastructure Authority, or SJVWIA. Tulare, Fresno, Kings, Madera and Merced counties are full SJVWIA members along with two cities: Orange Cove, representing all other Eastside cities in the five-county-region, and Avenal, representing all Westside cities in the five-county-region. Other full members are the San Joaquin River Exchange Contractors Water Authority and Table Mountain Rancheria, a San Joaquin River watershed Indian tribe. There is one public member.
  • Invitations have been extended to the Friant Water Authority and San Luis & Delta-Mendota Water Authority to join as full SJVWIA members. A letter of cooperation has been signed by the SJVWIA, Exchange Contractors, San Luis & Delta-Mendota Water Authority and Friant Water Authority, in which each agency has pledged to work together and accept membership on a project steering committee. The SJVWIA also has entered into a joint participation agreement with the U.S. Bureau of Reclamation.

Q: How would federal legislation affect the project's construction?

  • •The Water Infrastructure Improvements for the Nation Act, passed last year, and the Gaining Responsibility on Water Act of 2017, which remains before Congress, each contain provisions that would help the Temperance Flat project. Provisions in these bills would direct partnerships between the U.S. Interior secretary and joint-powers authorities, such as the SJVWIA, to focus on completing feasibility studies. They would also streamline the permit process and provide congressional authorization to build the project if it is determined to be feasible, along with establishing funding for construction.

Q: What would water from Temperance cost, and what is the latest benefit-cost ratio?

  • At this early stage in what is conceived as a complex and flexible water management system, it is not possible to determine an acre-foot cost of water. Too many factors remain to be determined, not the least of which would be the amount of state and federal funding ultimately made available as public-benefits investments.
  • Costs for such activities as regulatory work and permitting, completion of mandated federal and state environmental studies and findings, engineering and design, real estate and right-of-way acquisition, conducting and finalizing negotiations on other necessary agreements, studies of financing, and legal costs must all be determined along with estimates of actual project construction. Agreements must be reached and contracts developed with project investors. Only then will it be possible to achieve, with any confidence, meaningful estimates of overall project costs, possible water prices to project users and a benefit-cost ratio.
  • The value of water to users in the San Joaquin Valley and other parts of Central and Southern California has recently been demonstrated to be far greater than ever before as a result of dramatically short supplies. Recent record drought, coupled with regulatory curtailments on water supplies available south of the delta due to federal and state mandates and other actions, drove free-market water prices higher than ever experienced. Water became 10-20 times (or greater) more costly but still attracted willing buyers. Such a supply and demand factor is not likely to change within the San Joaquin Valley. Capture, storage and use of high-flow runoff water during big water years and major storms is now recognized widely to have a much higher value in order to satisfy vitally needed supply demands.

(Source: San Joaquin Valley Water Infrastructure Authority)

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