A Proven, Effective Water Storage System
The Semitropic Groundwater Bank is California’s largest and most established groundwater banking program. Located in the southern San Joaquin Valley, the Bank uses the underlying groundwater aquifer to store groundwater during periods when supplies are available and recovers that water when it is needed most.
Groundwater banking allows California to take advantage of the natural variability of its water supply—capturing surface water in wet years, storing it underground, and making it available during dry years and extended droughts.
For Semitropic Water Storage District, groundwater banking also complements the District’s longstanding mission of maintaining a reliable water supply for agriculture while providing important water-supply benefits to communities throughout California.
How Groundwater Banking Works
The concept is straightforward:
Capture in Wet Years
Store Underground
Recover in Dry Years
During wet hydrologic conditions, water that is available for export from the Sacramento–San Joaquin Delta can be conveyed south through the State Water Project and California Aqueduct to Semitropic.
Once delivered to the District, that surface water can be stored through a combination of in-lieu recharge and direct groundwater recharge. With in-lieu recharge, surface water is delivered to agricultural users who would otherwise pump groundwater. The groundwater that remains in the basin becomes stored water available to the banking program.
Direct recharge facilities provide another means of placing available surface water into groundwater storage.
During dry periods, stored surface water can be recovered through wells and conveyed through District facilities for delivery to banking partners or used as part of coordinated water-supply operations. This ability to shift water from periods of abundance to periods of shortage is what makes groundwater banking an important component of California’s water infrastructure.
A Strategic Location for California Water Banking
Semitropic’s location is particularly well suited for groundwater banking.
The District is located in Kern County in the southern San Joaquin Valley, adjacent to one of California’s most productive agricultural regions and near the California Aqueduct, the backbone of the State Water Project.
The proximity of the Semitropic Groundwater Bank to the California Aqueduct allows water to be easily conveyed to and from the groundwater bank. As a result, stored surface water beneath the Districts agricultural lands can provide reliability benefits to water users hundreds of miles away.
A Statewide Water Resiliency Asset
The Semitropic Groundwater Bank demonstrates how agricultural water infrastructure can provide benefits extending well beyond the boundaries of an individual water district. Semitropic’s banking partnerships support water agencies serving communities throughout California, from the Bay Area to Southern California.
During wet periods, the Bank provides an opportunity to place available surface water into underground storage rather than relying exclusively on reservoirs or current-year deliveries. During droughts and other periods of limited water supply, previously stored surface water can be recovered to help banking partners maintain water deliveries.
This provides an important form of long-term water-supply insurance and reduces dependence on the hydrology of any single year.
Groundwater banking is particularly valuable as California experiences increasingly variable hydrologic conditions characterized by both extreme wet periods and extended droughts.
Storage on the Scale of a Major California Reservoir
1.6 Million Acre-Feet
The Semitropic Groundwater Bank has approximately 1.6 million acre-feet of total storage capacity, providing the ability to capture and carry significant quantities of surface water from wet periods into future dry years.
800,000 Acre-Feet
On average, approximately 800,000 acre-feet of water is held in storage for the District’s banking partners. To put that volume in perspective, 800,000 acre-feet is equivalent to more than 80 percent of the total storage capacity of Folsom Lake, one of California’s major surface reservoirs.
1.6x Folsom Lake
The Bank’s full 1.6 million acre-feet of storage capacity is approximately 1.6 times the capacity of Folsom Lake and is also greater than the individual storage capacities of several other major California reservoirs, including Pine Flat Lake, New Bullards Bar Reservoir, and Lake McClure.
Less Evaporation More Reliability
Unlike a surface reservoir, Semitropic stores this water underground, where evaporation losses are minimized and the groundwater basin itself provides the storage space. This large underground reserve provides banking partners with the ability to store abundant surface water supplies and recover it during droughts and other periods of water shortage.
Agriculture Makes the Bank Possible
Agriculture is fundamental to the operation of the Semitropic Groundwater Bank.
Semitropic was originally formed to improve water reliability for agricultural lands that historically depended heavily on groundwater. The introduction of imported surface water allowed the District to reduce groundwater pumping and improve groundwater conditions.
The same agricultural water-delivery system subsequently provided the foundation for large-scale groundwater banking. During periods when surface water is plentiful, delivering that water to farms instead of pumping groundwater creates in-lieu groundwater recharge. During periods when stored surface water must be recovered, Semitropic’s extensive well and conveyance infrastructure allows banked surface water to be recovered and managed across a large geographic area.
This relationship between agriculture, groundwater management and statewide water reliability is one of the defining characteristics of the Semitropic Groundwater Bank.
Decades of Groundwater Banking Experience
Semitropic began developing its groundwater banking program in the early 1990s as California water agencies looked for additional ways to store surplus surface water available in wet periods for use in dry periods. Over the following decades, the District developed partnerships with major California water agencies and expanded the facilities necessary to recharge, store, recover and convey critical surface water supplies.
The District subsequently began development of its Stored Water Recovery Unit (SWRU) projects to expand and strengthen recovery capabilities and improve the reliability of stored-water deliveries.
Today, groundwater banking is integrated with Semitropic’s broader responsibility for sustainable groundwater management. Under California’s Sustainable Groundwater Management Act (SGMA), Semitropic continues to manage groundwater conditions while balancing the needs of agriculture, groundwater sustainability and long-term water banking.
Preparing California for the Next Wet Year
California’s water challenge is not simply a lack of water. Increasingly, the challenge is having the infrastructure and operational flexibility necessary to capture water when it is available and preserve it for when it is needed.
Large wet-year flows can occur for relatively short periods. When regulatory requirements, Delta conditions and conveyance capacity allow water to be exported, groundwater banks provide an opportunity to convert those temporary supplies into long-term water reserves. The Semitropic Groundwater Bank provides that capability.
By combining groundwater storage, agricultural water management and access to the California Aqueduct, Semitropic can help California:
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Capture available water during wet periods.
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Store water underground for future use.
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Reduce evaporation losses associated with surface storage.
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Provide additional reliability during droughts.
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Support sustainable groundwater management.
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Maintain productive agricultural lands and communities.
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Improve the resilience of California’s interconnected water system.