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Lake Oroville Dam

Water Reliability

Focusing on the long-term needs for the Tri-Valley

How does water get to Zone 7?

Zone 7’s Total Water Supply is made of three major sources:

Imported surface water:

The majority of our water, approximately 70% is imported into the Tri-Valley through the State Water Project. Our water begins its journey in the Sierra Nevada where melted snow makes its way into Lake Oroville, one of the largest reservoirs in the state. After being released through the Lake Oroville Dam, water flows along Feather River, into the Sacramento River and to the California Delta. From there water is pumped into the South Bay Aqueduct where it travels another 40 miles into the Tri-Valley. Most of this imported surface water is used as needed and a small amount is sent to storage.

Local water:

Our local water supply is made up of groundwater, rainfall into our local reservoir at Lake Del Valle, and other sources such as recycled water. Our groundwater basin provides approximately 10% of our water in an average year. This is our water “savings account” used to supplement our imported water supplies as needed. Rainfall goes directly into the Del Valle Reservoir or through drainage basins to recharge the Livermore Valley Groundwater Basin. We also use some of our imported water to recharge the basin, when it is available.

Stored water:

Stored or “banked” water is an exchange system we have with our neighbors. Zone 7 has “storage space” in San Luis Reservoir through the State Water Project and in Kern County’s Semitropic and Cawelo water banking systems. When we need to “cash-out” our banked water, we take the additional water from our imported State Water Project sources, reducing the amount in our downstream bank accounts.

Water Reliability Project Updates

Los Vaqueros Reservoir Expansion

up to 20,000 acre-feet of water storage

Zone 7 continued to invest in the Los Vaqueros Reservoir Expansion Project. The project seeks to expand the existing reservoir to a capacity of up to 275,000 acre-feet. This project is located in Contra Costa County and will serve as a local storage facility that will increase water supply reliability in the Bay Area. This year, the project made advancements in environmental planning, design and engineering, and securing funding. If this project were online during a critically dry year like this year, Zone 7 would have more operational flexibility and more water available from storage to supplement low supplies.

Sites Reservoir

10,000 acre-feet of new water supply and storage per year for Zone 7

Zone 7 continued to invest in the Sites Reservoir Project. The project seeks to construct an off-stream reservoir in Glenn and Colusa Counties, providing up to 1.5 million acre-feet of storage. The Sites Reservoir will capture excess flood flows from the Sacramento River without damming a river or stream. The project would provide new water supply, new storage capability, and ecosystem benefits – all of which are important factors for protection against climate change. This year, the project made advancements in environmental planning, evaluating the “right-sized” project, and refining cost estimates. If this project were online during a critically dry year like this year, nearly one million acre-feet of additional water would be available to project participants.

Significant Achievements in Water Reliability

2020 Urban Water Management Plan

Every 5 years, Zone 7 completes an Urban Water Management Plan (UWMP). The UWMP describes the availability and reliability of Zone 7’s water supplies and current and projected water use. The UWMP lays out supply and demand projections for the next 20 years under normal and drought conditions, and thus serves as an important long-term planning tool for Zone 7 and a means of communicating to the public. 

2020 Tri-Valley Municipal and Industrial Water Demand Study

Zone 7 completed the 2020 Tri-Valley Municipal and Industrial Water Demand Study (Demand Study) to better plan for long-term reliability for the Tri-Valley region. The Demand Study was a regional effort and included close collaboration with Zone 7’s retailers. A land-use based tool for projecting municipal and industrial water demands at buildout was developed to support the Demand Study. Zone 7 will use this tool to continue updating the region’s water demand projections as we move closer to buildout, which will inform investments in water supplies and infrastructure.

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Water Quality

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Flood Protection