The Groundwater Banking Solution for California - Mission Agua Cadiz
Learn what groundwater banking is, and why it’s a good strategy for addressing California’s water needs.]
Cadiz, groundwater, groundwater banking, water strategy, California water
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The Groundwater Banking Solution for California

The Groundwater Banking Solution for California

California’s water infrastructure was designed to provide protection from the fluctuations between wet and dry years that characterize its climate. Over the last century, engineers built a sprawling network of reservoirs and canals to store and deliver a consistent, reliable supply of water throughout the state.

However, this infrastructure is not always capable of providing an adequate supply of water to the state’s growing population. During droughts, California’s primary infrastructure projects – the Central Valley Project (CVP), State Water Project (SWP) and Colorado River Aqueduct (CRA) – reduce water deliveries to districts throughout the state, putting a strain on residents, farms, and businesses.  Climate change and the failure to address infrastructure challenges in the Sacramento / San Joaquin Delta are creating a critical situation where finding suitable storage is imperative – especially south of the Delta.

Simply building more dams and reservoirs would boost the state’s capacity to store and deliver water, but groundwater banking is an innovative strategy offering the added benefits of less surface disturbance, reduced losses attributable to evaporation, and a reduced carbon footprint.  It is a solution being adopted by many districts across the state.

What is groundwater banking?

Banking water during wet years provides water districts with a cushion of protection during droughts. It also conserves any unused water, rather than letting it run out to the sea or be lost to evaporation.

Groundwater banking or, aquifer storage, is a process that stores water naturally in underground basins or aquifers, rather than in open-air reservoirs above ground. The stored water creates a bank of supply from which withdrawals can be made through a well in future dry years. It’s as simple as adding money to a savings account to build a rainy-day fund.

Many districts across California and other Western states already use groundwater banking. During a wet year, excess runoff and imported water from the SWP, CVP, and other delivery systems is diverted into shallow ponds, spreading basins or wetlands. The water seeps into the ground, eventually reaching the aquifer. Water can also be injected directly into the aquifer through wells.

According to the Public Policy Institute of California (PPIC), California’s groundwater basins can store three times as much water as the state’s dams in a cost-effective manner. PPIC also expects groundwater banking will become more important to the state’s water supply as the climate warms and shrinks the mountain snowpack further augmenting the need to storage in California.

California has 517 groundwater basins across the State. Stanford’s Water in the West institute estimates that the capacity of underground water storage in California, is at least 20 times greater than that of the state’s reservoirs and lakes. However, there is a lack of conveyance to bring surplus water into storage and return it in dry years.  Environmental Defense Fund, Sustainable Conservation and other non-governmental organizations have noted that the pressure to improve management of groundwater in accordance with the Sustainable Groundwater Management Act of 2014 has created the opportunity to expand recharge basins and banking particularly in agricultural areas.


This chart appears in Recharge: Groundwater’s Second Act


Why consider groundwater banking?

Storage of water in California and the West has historically been principally obtained through the construction and operation of  dams and surface reservoirs.  As the need for additional storage to accommodate changing hydrology has increased, California has largely retreated from the construction of dams as the primary water supply strategy in California due to cost and environmental concerns. The last major dam built in Northern California was New Melones Dam in Calaveras County, in 1979, with a capacity of 2.4 million acre-feet.  In 2003, the Metropolitan Water District built Diamond Valley Lake, an off-stream surface storage facility which holds 800,000 acre-feet at a cost of over $2 billion. The combination of the current environmental regulatory framework and limited public funding for large infrastructure projects without state and federal subsidies have made it extremely difficult to construct dams.

 Groundwater banking offers a number of benefits, including minimal surface disruption, no interference with beneficial uses of surface water and little to no evaporation.  For example, the Colorado River’s largest reservoirs Lake Mead and Lake Powell lose as much as 500 billion gallons of water to evaporation annually – that’s five times more water than the city of Denver uses in one year.  In California, there are limited studies on the total amount of water that evaporates from reservoirs and open-air water infrastructure. The CA Department of Water Resources once estimated that California’s reservoirs and ponds generally lose 1 to 2 meters of water to evaporation every year. On a summer day, a reservoir or pond might lose about 9,000 gallons per acre of water surface.

Climate change requires California to make investments in water supply reliability. Groundwater banking has the advantage over other supply options of being effective in a variety of settings and typically in a cost-effective manner. Delta protection is requiring those agencies exporting water from the Delta to make investments in reducing their reliance on exports – and this will require storage.  Meanwhile,  the Delta Conveyance program to improve reliability of Bay-Delta supplies for southern California carries a price-tag of more than $15B in its current formulation.  The feasibility of design, building and financing that project is presently under intense scrutiny and without storage to regulate deliveries, it likely faces tough sledding.  Desalination, although fiercely resisted by environmentalists in some locations, has been successfully permitted in San Diego and Santa Barbara at price points of $2,150 and $3,150 per acre-foot respectively. Comparatively, groundwater storage provides a less costly, less impactful option that offers added flexibility that is beneficial to local communities, especially for banks that can convert surplus water into reliable supply for communities in need. Recently theMunicipal Water District of Orange County evaluated supply augmentation projects available to its service area and all options were conservatively valued at more than $1000/acre-foot.

How The Cadiz Water Project Will Boost California’s water Storage System

Located on privately owned land in the Mojave Desert, the Cadiz Water Project area overlays a massive aquifer with federally protected headwaters. Scientists estimate that this aquifer contains more than 20 million acre-feet of water, rivaling Lake Mead—the largest reservoir in the US.  —. Groundwater that is not used for farming at Cadiz slowly flows to hyper-saline dry lakes, where it turns salty and evaporates.  By better managing this aquifer system which has been farmed since the late 1980s without any adverse environmental impacts, the Cadiz Water Project would augment supply and storage capacity in Southern California.

In Phase 1, the Cadiz Water Project will capture an average of 50,000 acre-feet of fresh water annually that would have otherwise been lost to evaporation.  This conserved water will be delivered to communities across Southern California via a pipeline. Phase 1 also offers up to 150,000 acre-feet of carry-over storage (water stored by preventing loss of fresh water to high-salinity and evaporation).The Project will operate under a groundwater management plan that has been approved by San Bernardino County.

In Phase 2, the Cadiz Water Project will provide new storage space for banking imported surplus water in wet years. The project will be accessible by two pipelines connecting to Southern California’s main sources of imported water supplies. The first would be a pipeline to be constructed wholly within a 43-mile railroad right of way and interconnect with the Colorado River Aqueduct (“CRA”).  The second will utilize an existing 30” steel pipeline to move water northwest through San Bernardino, Los Angeles and Kern Counties.  As a result, participating water agencies could bank excess water from the Colorado River Aqueduct, the State Water Project, and potentially the Los Angeles Aqueduct in Cadiz’s underground basin for future dry years.  The Cadiz area has an estimated 1 million acre-feet of imported storage capacity.

Once implemented, the Cadiz Water Project would be the only large groundwater bank adjacent to the Colorado River Aqueduct and have the ability to directly interconnect with the State Water Project and other northern California sources of supply.

The Project offers:

  • Minimal loses in recharge, migration or uncontrolled pumping;
  • Highly porous clays and silts support high infiltration rates, and ease of management and recovery;
  • Very low TDS;
  • Spreading and in-lieu storage;
  • Two conveyance inputs and outputs connecting the State;
  • Judicially validated groundwater management plan;
  • No overlying land competition and protected headwaters.

Cadiz has the flexibility to be integrated into a variety of portfolios while maintaining overlying farming and fully protecting the environment and ensuring sustainability.  Groundwater banking will continue to be an optimal solution to manage California’s rapidly changing water supply and demand , Cadiz is well-positioned to help.


Successful Groundwater Banking Projects

Here’s a look at three prominent groundwater banking programs that are already operational.

  • Chino Basin Bank – The Chino Basin lies at the intersection of eastern Los Angeles County, south western San Bernardino County and western Riverside County. It is subject to a Court adjudicated management plan that authorizes storage of both local and imported water for the principal benefit of the $2 billion economy that is dependent upon reliable water.  Chino Basin has a court-approved process that facilitates storage, transfers and withdrawal on an expedited basis that has enabled the successful banking and storage of nearly 600,000 acre-feet of water.  The bank has been able to benefit from improvements in water recycling and the construction and maintenance of extensive groundwater recharge basins that capture and store local and imported water through collaborative spreading agreements carried out among the County of San Bernardino Flood Control, the Inland Empire Utilities Agency and the Chino Basin Watermaster.  Of the supply presently held in the basin, more than 80% is reserved for public and private local needs with the balance being accessed by the Metropolitan Water District of Southern California, the region’s primary water wholesaler.  Although the bank operates within a largely developed and ever urbanizing area it has exceeded all expectations and is now evaluating methods to safely increase the quantity of water held in storage up to 800,000 acre-feet.


  • Semitropic Water Bank – Perhaps the largest capacity held by any water banking system in the world, the Semitropic Groundwater Storage Bank offers six major water agencies a place to store excess water in wet years. Participating agencies include the Metropolitan Water District of Southern California, the Santa Clara Valley Water District, the San Diego County Water Authority, as well as private parties that hold water in storage directly or through the cooperation of water districts that store water on their behalf. The bank has a design capacity of around 1.65 million acre-feet—about the same capacity of Lake Berryessa, one of the State’s largest reservoirs. In a dry year, when the SWP is only able to deliver half the water it has contracted to provide to water agencies, Semitropic can provide 356,500 acre-feet of water to supplement their supplies. Semitropic has a developed share structure for participating agencies, with participants generally funding long-term shares of reserved capacity in the bank.


  • Kern Water Bank – The Kern Water Bank was created in 1995 to provide a more reliable supply of water for farmers, residents, and businesses in the San Joaquin Valley, especially during dry years, when water imports from the Central Valley Project and the State Water Project aren’t enough to satisfy demand. During wet years, surplus water flows into shallow ponds, where it slowly percolates underground, recharging aquifers. As an added benefit, flooding these shallow ponds has created a seasonal wetland habitat for more than 40 species of native and migrating birds. The Kern Water Bank has successfully operated for more than 20 years and as of October 2017,  the Kern Water Bank reported that it has recharged 2.6 million acre-feet of water and recovered over 1.5 million acre-feet of water from storage during operations.


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