As California enters its winter rain season, state and local water agencies are preparing to capture and store stormwater for use during drier months and potential future droughts.
Water managers use the winter season to collect, move, and store runoff to support water supplies through the summer and fall. After approximately three weeks of dry conditions across much of the state, reservoirs currently have available capacity to manage incoming storm flows. Lake Oroville, the largest reservoir in the State Water Project, is at 54 percent capacity, leaving space to capture additional runoff while also supporting flood management operations.
State officials say California is taking steps to maximize water capture during wet periods while expanding long-term storage options. These efforts include surface storage, groundwater recharge, and infrastructure improvements intended to address more frequent weather extremes.
Stormwater-capture projects implemented by local agencies have already contributed to water supplies. In November, storms in the Los Angeles region generated billions of gallons of captured stormwater, according to state data. That volume is estimated to be sufficient to supply tens of thousands of households, with additional capacity expected as new projects are completed.
Expanding water storage and groundwater recharge
The state is continuing flood diversion and groundwater recharge efforts launched in 2023. California has partnered with 14 local agencies in the Sacramento and San Joaquin regions to divert flood flows and prepare land for groundwater recharge. Preparations include the deployment of 20 large-capacity pumps and clearing more than 650 acres of land to allow floodwaters to be directed into underground aquifers. The effort builds on a 2023 executive order authorizing flood flow diversions for flood risk reduction and groundwater recharge.
Along the Sacramento River Basin, the Big Notch fish passage project is operational. The project is designed to improve fish migration conditions for endangered winter-run Chinook salmon while supporting State Water Project operations. The effort is part of broader infrastructure upgrades intended to balance environmental protection and water supply reliability.
In August, the state committed an additional $219 million to the Sites Reservoir project. When completed, Sites Reservoir is designed to store up to 1.5 million acre-feet of water captured from the Sacramento River during wet periods for use during dry seasons. The project is intended to improve long-term water reliability amid climate variability.
Local efforts contribute to statewide supply
Beyond surface storage, California continues to expand groundwater recharge initiatives. The California Department of Water Resources reports that groundwater conditions have improved in recent years due to increased precipitation and coordinated efforts to capture high flows during winter storms. These efforts include expanding recharge basins, improving groundwater monitoring, and coordinating among local agencies to reduce pumping.
State officials say the combined investments are intended to improve California’s ability to store water when it is available and manage supplies during extended dry periods.
