What You Need to Know about Groundwater Banking

What You Need to Know about Groundwater Banking

California’s water infrastructure was designed to provide protection from the fluctuations between wet and dry years that characterize its climate. Over the last 100 years, engineers have 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 delivering an adequate supply of water to the state’s growing population. During droughts, the Central Valley Project (CVP) and State Water Project (SWP) may reduce water deliveries to water management districts throughout the state, putting a strain on residents, farms, and businesses.

In addition, California is not capturing all the water it can. In an average year, around half of the rain and snow evaporates, is absorbed by plants, or flows out of the state into the ocean or saline lakes. While water must be left for the environment, there is still the potential to capture more for human use.

Although building more dams and reservoirs could boost the state’s capacity to store and deliver water, groundwater banking is also an innovative strategy with many benefits.


What is groundwater banking?

Groundwater banking or “aquifer storage” involves storing water in underground basins or aquifers, rather than in reservoirs above ground. The water creates a bank of supply from which “withdrawals” can be made via a well. It’s like adding money to a savings account to build a rainy-day fund.

Banking water during wet years provides water districts with a cushion of protection during droughts. In addition, it ensures that any unused water is conserved, rather than letting it run out to the sea.

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

There are several reasons why groundwater banking is an increasingly attractive strategy. For one, California’s groundwater basins can store three times as much water as the state’s dams, according to the Public Policy Institute of California. Building new dams and reservoirs is a massive undertaking, and groundwater banking can provide storage at a lower cost and without the problems associated with reservoirs, such as evaporation.

The PPIC referred to groundwater basins as “a cost-effective way to bank water for dry years” in a 2012 report and predicted that groundwater banking will become more important to the state’s water supply as the climate warms and shrinks the mountain snowpack.


Why are dams not enough?

California has largely backed away from the construction of massive dams as the primary water supply strategy in California due to both cost and environmental concerns. The last major dam built in Northern California was New Melones Dam in Calaveras County, in 1979. In 2003, the Metropolitan Water District built Diamond Valley Lake, which holds 800,000 acre-feet. In general, another limitation is that new environmental regulations have made it more difficult to construct dams, and changes to state and federal law have reduced the money available for big public infrastructure projects.


What are other reasons to consider groundwater banking?

Groundwater banking also eliminates a common concern associated with surface water storage: evaporation. Water naturally evaporates from any body of water exposed to sunlight, heat, and wind. In fact, Lake Mead and Lake Powell in Nevada lose as much as 500 billion gallons of water to evaporation each year. This amount is equal to one-tenth of the entire natural flow of the Colorado River Basin—at least five times as much water as the city of Denver, Colorado, uses in one year.

In California, there have been few efforts to precisely estimate the total amount of water that evaporates from reservoirs and the state’s other water infrastructure. The Department of Water Resources estimated in 1979 that California’s reservoirs and ponds 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. More recently, in 2015, students at the University of California, Davis, estimated that about 9,300 acre feet of water evaporate every day from the State Water Project’s 700 miles of canals.


Who uses groundwater banking?

Groundwater banks are becoming more common in California. Here’s a look at two prominent groundwater banking programs.

Semitropic Water Storage District – Perhaps the largest water banking system in the world, the Semitropic Groundwater Storage Bank gives 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, and others. The bank can store around 1.65 million acre-feet—about the same capacity of Lake Berryessa, one of the largest reservoirs in the state. 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 tide these agencies over. A groundwater monitoring committee helps oversee Semitropic’s operations.

Kern Water Bank – The Kern Water Bank was created 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.


How would the Cadiz Water Project benefit California’s water storage system?

Located on privately owned land in the Mojave Desert, the Cadiz Water Project area sits on top of a massive aquifer. Scientists estimate that this aquifer contains 20 million acre-feet of water, rivaling Lake Mead—the largest reservoir in the US—in capacity. Water from this aquifer slowly flows to shallow, hyper-saline “dry lakes,” where it evaporates.

In Phase 1, the Cadiz Water Project will annually capture 50,000 acre-feet of this water before it evaporates. A pipeline to the Colorado River Aqueduct will deliver this water to participating Southern California water districts. Phase 1 also offers up to 150,000 acre-feet of carry-over storage for participants so that in wet years they can hold water in Cadiz and instead deliver in future dry years.

Subject to strict limits, the project will operate under a groundwater management plan that has been approved by San Bernardino County. Over the course of the project’s 50-year span, no more than 5% of the aquifer can be pumped, and the water table cannot fall more than 80 feet below current levels.

In a second phase, 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. 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 total storage capacity at Cadiz is estimated to be 1,000,000 acre-feet, slightly smaller than Folsom Lake in Sacramento.

Once implemented, the Cadiz Water Project would be the only large groundwater bank off the Colorado River Aqueduct.


Add your name to the list of Cadiz Water Project Supporters: >>>