San Diego-Sweetwater intertie could boost local reservoir storage by 100,000 acre-feet of water
Posted by George J Janczyn on April 18, 2011
Since the end of California’s severe 1987-92 drought it has taken a 1993 Army Corps of Engineers reconnaissance study, U.S. Senate and House legislative support from Rep. Duncan Hunter (Sr.), Rep. Susan Davis, and Sen. Dianne Feinstein, a California Proposition 50 grant via the Integrated Regional Water Management Plan, and negotiations between Sweetwater Authority, the City of San Diego, and the U.S. Bureau of Reclamation — plus another major drought — just to reach this stage.
This stage is a proposal for a pre-feasibility study of a four-reservoir intertie between the City of San Diego and Sweetwater Authority systems.
The proposal will be presented today (Apr 18) at the Independent Rates Oversight Committee (IROC) [agenda] and Wednesday (April 20) at the Natural Resources and Culture Committee [agenda] where support will be sought in bringing it to the San Diego City Council. If full Council approval is obtained an agreement will then be executed by the City of San Diego, Sweetwater Authority, and the Bureau of Reclamation.
As described in a San Diego Integrated Regional Water Management document:
“Connecting the San Vicente, El Capitan, Loveland, and Murray Reservoirs would create an enhanced and integrated reservoir system to more efficiently use the reservoirs and increase accessibility to approximately 100,000 acre-feet of surface storage without creating new reservoirs or new storage capacity. The environmental effects of the future conveyance system would be minimal because each reservoir has been in place since the 1940s or earlier, and reservoir footprints would not increase. The Sweetwater Authority is serving as the lead agency for the regional intertie project.”
[Update: at the IROC presentation it was announced that the lead agency has been changed from Sweetwater to San Diego]
Since that report was written, of course, one reservoir footprint is increasing due to the San Vicente Dam Raise Project currently underway that will give it a more significant role within the potential intertie system.
As things are now, overall reservoir capacity is underutilized. To give one example, San Diego’s El Capitan reservoir (110,120 AF) is rarely full because its small imported water supply connection has very limited ability to supplement local runoff. An intertie connection would facilitate more optimal reservoir levels.
[I’ve since learned that another reason El Capitan water levels often appear to be low is that its catchment area produces the greatest amount of runoff of all the reservoirs in the San Diego area, so the city intentionally keeps water levels low there in order to capture the maximum amount of water during wet years and not lose any to spillway overflow].
Further south, Sweetwater’s Loveland Reservoir (25,225 AF) relies solely on watershed runoff which is usually not enough to keep it filled. An intertie would allow adding more water during drier times. On the rare occasions that very wet seasons such as we recently experienced result in spillway overflow, excess runoff at Loveland could be diverted to the larger El Capitan or San Vicente reservoirs instead of being lost.
San Diego’s much smaller Murray reservoir (4684 AF) was included because of its Alvarado Water Treatment Plant supplying a large part of the city.
The shared connections would permit more water overall to be stored in local reservoirs. That translates into increased reliability in the event of a cutoff of imported supplies due to disaster or other problem. The 1993 Army Corps of Engineers reconnaissance study of San Diego’s water supply (not available online*) also estimates that 23% of the total benefits from an intertie system would be from increased flood control.
Because an intertie system would be an immensely expensive and complicated undertaking, the pre-feasibility study would carry out “an appraisal investigation to determine the prudence of a full-scale feasibility study for the proposed intertie system” according to the Army Corps study.
(A subsequent Army Corps Executive Summary of Lessons Learned from the California Drought (1987-92) says one confirmed lesson is that “local and regional interconnections between water supply systems are effective and flexible options against severe water shortages.”)
If the pre-feasibility study recommends it, then a full feasibility study could be performed as a phase 2 project.
Funding for the pre-feasibility study will be shared between the U.S. Bureau of Reclamation ($344,332), state grant funding from Proposition 50 ($112,832), the City of San Diego ($171,500), and the Sweetwater Authority ($60,000) for a total of $688,664.
- San Diego County Water Supply Study / Prepared for U.S. Army Corps of Engineers … prepared by Gulf Engineers & Consultants, Inc., February 1993
- H.R. 4791: San Diego Water Storage and Efficiency Act of 2004 never got out of committee.
- H.R. 1190: San Diego Water Storage and Efficiency Act of 2005 passed the House but not the Senate.
- H.R. 1803: San Diego Water Storage and Efficiency Act of 2007 passed the House but not the Senate.
- State approves up to $25 million grants to benefit San Diego water reliability in 2008
- S. 22: Omnibus Public Land Management Act of 2009 passed the Senate but not the House.
- H.R. 146: Omnibus Public Land Management Act of 2009 became law (Sec. 9003 applies to the San Diego Intertie project).
* Thanks to Marguerite S. Strand, Assistant General Manager of Sweetwater Authority for allowing me to examine the Army Corps reconnaissance study and answering my questions.
This entry was posted on April 18, 2011 at 4:45 am and is filed under Environment, Sweetwater Authority, Water. Tagged: Reservoirs, San Diego four-reservoir intertie. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.