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Just the FACTS

Groundwater Recharge

    • Groundwater recharge is an important water management practice in California.
      Recharge occurs when water seeps into the ground to replenish underground aquifers. Some recharge happens naturally when water flows into the ground from rivers and unlined canals or from the irrigation of crops and urban landscapes. In California, recharge is also done intentionally to restore groundwater levels and to store water for later use. In coastal areas, recharged water can also form a barrier that prevents salty ocean water from entering depleted aquifers. Groundwater recharge in dedicated ponds can also provide wetland habitat for migratory birds and other species. Active recharge is a longstanding practice in much of urban Southern California and parts of the Bay Area, Central Coast, and Central Valley. Recharge sources include surface water imported from other regions, local floodwaters, and recycled water.
    • A variety of methods are used to recharge aquifers.
      In some agricultural areas flood irrigation is the primary method of recharge. Some districts have invested in dedicated infrastructure, such as recharge basins or ponds for spreading water. Most recharge is done by agricultural and urban water suppliers on site, but recharge can also be done by partnering with groundwater banks. These are agencies in areas with good conditions for recharge that store water on behalf of both local and distant parties. Most banks are located in Kern County and Southern California. Banking requires formal accounting systems to keep track of balances, which decline during dry times as members withdraw water and increase during wet times as water is deposited back in.

Groundwater banking is an important tool for managing droughts

figure - Groundwater Banking Is an Important Tool for Managing Droughts

SOURCE: Updated from Hanak and Stryjewski. California’s Water Market, By the Numbers: Update 2012 (PPIC, 2012).

NOTES: “Taf” is thousands of acre-feet. The figure shows groundwater bank storage balances. For Kern County, storage is for more than 50 offsite parties in the San Joaquin Valley, Bay Area, and Southern California by the county’s nine largest banks: Antelope Valley Water Bank (WB), Arvin-Edison Water Storage District (WSD), Cawelo Water District (WD), Kern Delta WD, Kern WB, North Kern WSD, Rosedale-Rio Bravo WSD, Semitropic WSD, and West Kern WD. Some additional storage may be occurring for the entities themselves. Southern California banks store water for the Metropolitan Water District of Southern California (MWDSC) in the Mojave Basin, the Coachella Valley, and several of MWDSC’s member agency locations. Dry years are those classified as critical or dry for the Sacramento Valley.

    • Expanding recharge could help local water users bring their basins into balance …
      Groundwater is being overused in many parts of the state. The Sustainable Groundwater Management Act (SGMA), the state law requiring local water users to bring groundwater use to sustainable levels by the 2040s, has spurred widespread interest in expanding recharge. The practice is especially critical for the San Joaquin Valley, which has the state’s biggest imbalance between groundwater use and recharge. Replenishing valley aquifers will require capturing more water from large storms.

The San Joaquin Valley is ground zero for expanding recharge

figure - The San Joaquin Valley Is Ground Zero for Expanding Recharge

SOURCE: Updated from Hanak et al. Replenishing Groundwater in the San Joaquin Valley (PPIC, 2018).

NOTE: Panel A shows author estimates of the long-term groundwater deficit within the San Joaquin Valley (NW is northwest, NE is northeast, SW is southwest, SE is southeast, and KR is the Kern basin). Panel B shows UC Davis Soil Resource Lab estimates of the suitability of soils for recharge. The largest demands for recharge are in the southern part of the valley, which also contains many areas with suitable soils.

  • … and could also help address risks to water storage from the changing climate.
    The state’s groundwater basins have a much larger storage capacity than surface reservoirs, and are becoming more important as a drought reserve. More intense droughts increase pressures to draw down groundwater reserves. And warming winters have heightened interest in recharge as a strategy to help mitigate the loss of snowpack, which historically has accounted for up to a third of the state’s seasonal water storage. California will be able to store more water while managing growing flood risk if it manages surface and groundwater together to increase their combined potential. Enabling storage and conveyance facilities to work better together will require greater operational flexibility and more advanced weather forecasting.
  • Several barriers must be addressed to make the most of recharge in high-flow years.
    A key challenge to recharging more in wet years is inadequate conveyance for moving high flows to suitable recharge locations. A top priority is to improve the use of existing infrastructure (conveyance facilities, surface reservoirs, and recharge basins) and determine where additional investments are warranted—and where improved operations can make the system as a whole work better for recharge. The State Water Board also needs to develop a simple, rapid way to enable water users to capture water from large storms in the short time spans in which it is available. Finally, there is significant potential to increase active recharge on farmland if local agencies adopt better incentive systems and water accounting. Water managers and growers also need guidelines for on-farm recharge practices that protect water quality. These measures would not only allow more water to be captured for recharge, but would also help the state’s water grid better manage the higher winter and spring runoff that climate change is expected to bring.

 

Sources: Hanak et al. Managing California’s Water (PPIC, 2011); Mount et al. Managing Drought in a Changing Climate (PPIC, 2018); Hanak et al. Water and the Future of the San Joaquin Valley (PPIC, 2019).

Supported with funding from the S. D. Bechtel, Jr. Foundation.

Authors

Staffphoto JezdimirovicJelena Jezdimirovic
Research Associate
Photo of Gokce SencanGokce Sencan
Research Associate
Ellen HanakEllen Hanak
Vice President and Director of the Water Policy Center and Senior Fellow

PPIC WATER POLICY CENTER

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