Stormwater Recharge Planning
Sonoma County’s weather is characterized by rainy winters, followed by long, dry summers. During large winter storms, creeks and streams are often overwhelmed and can cause flooding in local communities. In contrast, dry summers—and increasingly frequent droughts— can place strain on both surface water and groundwater supplies. This Mediterranean pattern is becoming increasingly pronounced as our climate changes, but it also provides an opportunity.
Across California, water managers are rethinking how we handle stormwater. Instead of viewing it solely as a flood risk, we are beginning to see stormwater as a valuable resource that can help replenish our groundwater basins and improve long-term water reliability. By slowing, spreading, and sinking stormwater into the ground through recharge basins, open spaces, and natural waterways, we can use high-flow events to increase groundwater levels within the aquifer, enhance baseflows to interconnected surface water, and help support sensitive beneficial users.
With SGMA Implementation grant funds, the Petaluma Valley GSA has taken steps to build on stormwater recharge projects identified in the Southern Sonoma County Stormwater Resources Plan and further planning toward broader implementation of Stormwater Capture and Recharge projects.
In 2024 and 2025, the GSA and a consultant team led by Bachand & Associates began planning for three pilot projects on sites yet to be determined:
- Stream Restoration to Reconnect Streams to Shallow Groundwater: Pilot will construct beaver dam analogs (essentially human made beaver dams) in a stream to slow flows and widen stream area, increase stream to aquifer connectivity, and reduce losses from shallow aquifer to surface water.
- Upland Vineyard Cover Cropping and Compost Applications to Increase Groundwater Storage: Pilot will study best management practices for vineyards to increase groundwater storage, such as using a crop cover mix that will have elevated groundwater benefits and high-rate compost application.
- Upland Swales on Contours to Increase Groundwater Storage on Upland Pasture and Rangeland: Pilot will construct swales (shallow depressions) on slopes in pastures to slow water as it travels downhill.
Stormwater recharge is an integrated and voluntary resource management strategy that takes collaboration with landowners, farmers, scientists, and water managers to create a successful project. The pilot projects are designed to answer practical questions such as: How quickly does water soak into the ground, and what factors — like soil type and cover crops — affect that rate? The pilots hope to lay the groundwork for future projects by figuring out what it takes to run programs like these, from working with willing landowners to managing the day-to-day logistics.
Staff will use what they’ve learned from these pilots to estimate the costs and potential benefits of expanding on-farm and other stormwater recharge to a larger scale. This is an important step toward building a more resilient local water supply.
Read more about the pilot plans and ongoing efforts here.
