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Reservoirs

 The reservoirs operated by the Santa Clara Valley Water District are highly visible elements of our water supply and flood protection programs for Santa Clara County. Residents who drive by these reservoirs or use them for recreational purposes occasionally express curiosity or concern about their operations,environmental benefitssafety and water quality 

  • The Santa Clara Valley Water District operates 10 reservoirs in Santa Clara County.
  • The reservoirs have a total storage capacity of approximately 170,000 acre-feet. One acre-foot is enough water for two families of five for one year.
  • The reservoirs, which were constructed in the 1930s and 1950s for water conservation (not flood protection) catch storm runoff that otherwise would flow into San Francisco Bay.
  • The reservoirs also provide incidental flood protection by containing runoff early in the rainfall season, serve recreational needs, and benefit the environment by storing water to maintain flow in the creeks.
  • Current Reservoir levels

Water supply  
Water stored in district reservoirs provides 25 percent of Santa Clara County’s water supply. Reservoir operations are coordinated with imported Bay-Delta water received from the State Water Project and the federal Central Valley Project. Reservoir water can be treated at drinking water treatment plants or recharged into the local groundwater basins.

The management of stored water is adjusted as seasonal conditions change. Most stored water is released in the spring after the rainfall season and allowed to percolate into the underground aquifers, or it is sent to district treatment plants. Reservoirs typically fall to their lowest levels in the late fall, but rarely are empty. To protect fish habitat, minimum water levels have been established.

During the winter, in addition to overflow from the reservoirs when their capacity is exceeded, some water is released for percolation. When reservoirs fill early in the winter season, water may be released to provide more storage capacity for later-season storm runoff and to improve stream habitat. During a dry winter, releases are usually reduced to conserve the amount of stored water and to ensure habitat protection throughout the year. Guidelines for winter operations, which balance water conservation and the need to keep space available for runoff as winter progresses, are called “rule curves.”

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Flood protection  
While the reservoirs, except for Chesbro, were designed exclusively for water supply, they provide some flood protection. Because the outlets at these reservoirs are small, storage levels cannot be lowered rapidly. Releasing stored runoff for water supply during the summer results in low reservoir storage levels in the late fall. These lowered levels allow the reservoirs to catch runoff early in the rainfall season and help protect against flooding.

Reservoir operating rules include provisions to reduce the likelihood of flooding while having minimal impact on the water supply. If the reservoirs are nearly full before the rainfall season ends, some water can be released to create space to capture potential flood flow. This does not significantly reduce the probability of filling the reservoirs by the end of the season. Conditions for making a decision to release water vary throughout the winter. When reservoir levels are below the flood protection rule curve, no releases are made before a storm.

Chesbro Reservoir was designed as a multipurpose facility with a dedicated flood-storage level and an outlet that can significantly reduce storage in a short time. Chesbro Reservoir is kept only 60 percent full to provide a significant level of flood protection, as specified in the voter-approved bond act that funded its construction.

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Recreation  
Recreational activities at the reservoirs, such as swimming, boating or the use of personal watercraft, are managed by our partners, the Santa Clara County Parks and Recreation Department or the city of San Jose. Swimming at Almaden, Coyote, Anderson and Calero reservoirs is prohibited by the state Department of Health to protect the drinking water supply from potential bacteriological contamination. Storage levels in all reservoirs are kept above a designated minimum level for recreational use until the middle of October, if possible.

Environment  
Reservoirs are also generally operated to maintain the quality of wildlife habitats and provide good conditions for aquatic life. Except for extremely dry years, reservoirs are operated to keep the streams flowing to the bay year-round below the dams.
Minimum storage pools are also maintained in the reservoirs to provide for fish that live there. Reservoir guidelines have been expanded to provide suitable water flows and temperatures to benefit habitats. For example, at Uvas Reservoir in southern Santa Clara County, an agreement with the California Department of Fish and Game requires a continuous release of 20 cubic feet per second (cfs) in the winter and 10 cfs in the summer.

Dam safety  
Our dams fall under the jurisdiction of the state Department of Water Resources, Division of Safety of Dams. The dams are inspected twice each year and are continuously monitored for seepage and settling. Whenever we have a significant earthquake, water district inspection teams are immediately dispatched to each dam.

Reservoir/
Dam
Reservoir capacity (Acre-feet) Restricted capacity
(Acre-feet)
Restricted capacity
(%)
Reason for restriction Estimated average annual water supply impact
(acre-feet)
Anderson 90,373 61,810 68 Seismic stability concern 10,500
Coyote 23,244 12,382 53 Active fault movement (Calaveras fault) under dam 2,400
Almaden 1,586 1,472 93 Seismic stability concern 2,500
Calero 9,934 4,585 46 Seismic stability concern
Guadalupe 3,415 2,218 65 Seismic stability concern 800
Stevens Creek 3,138 No
restriction
N/A N/A N/A
Lexington 19,044 No
restriction
N/A N/A N/A
Chesbro 7,945 No
restriction
N/A N/A N/A
Uvas 9,835 No
restriction
N/A N/A N/A
Vasona 495 No
restriction
N/A N/A N/A
TOTALS 169,000 122,924     16,200

Water quality  
The water district's water laboratory routinely monitors water quality at the district's source water reservoirs, its water treatment plants, and at selected locations along the East / Snell and West drinking water pipelines. The lab conducts this monitoring pursuant to Title 22 of the California Code of Regulations under the direct oversight of the DHS. The Laboratory consistently meets all of the Title 22 monitoring requirements. In fact, the laboratory exceeds many of those requirements through increased monitoring frequencies and the use of state-of-the-art analytical technologies.

For more information about reservoir operations, contact James O'Brien at (408) 630-2443.

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