Introduction to Groundwater Recharge

The Central Valley is one of the most productive agricultural regions in the United States. Growers and communities, however, are faced with a future of declining groundwater quality, quantity, and availability during drought, due to overdraft. In areas where soil conditions are suitable and excess water is available, ground water recharge represents one of the most cost-effective methods to increase storage, thereby ensuring water supply and improving water quality. 

How Groundwater Recharge Works

The vadose zone — which extends from the soil’s surface to the groundwater table or saturated zone — controls water movement and affects recharge rates. Sandy loam, loamy sand, and sandy soil textures are generally preferred for recharge due to higher infiltration rates compared to silt and clay. Unique layers in the subsurface such as heavier soils and clay layers (e.g., Corcoran clay) affect the time and place where the recharge water will arrive at the groundwater table. Recharge can also be directed underneath heavier surface soils to more permeable subsurface layers.

Methods of Groundwater Recharge

• Surface Application to Orchards: On-farm recharge (OFR) is the application of surface water above crop demand in agricultural fields such as almond orchards using existing or supplemental irrigation infrastructure, for the purpose of recharging the aquifer. One major advantage of OFR is that per acre-foot recharged, it can provide a less expensive, more distributed method than construction of new large dedicated recharge basins. While it can raise concerns around impacts to crop health and yield due to saturated soils in the root zone and excess humidity, recharge method, design, and operation can be used to avoid exceeding crop tolerance. 
• Below-Surface: Conducting subsurface groundwater recharge using reverse tile drains was first introduced to the San Joaquin Valley in 2017. Conventional tile drain systems are installed to drain water out of the soil in fields with a high-water table to avoid anoxic conditions that are harmful to crops. The adaptation of reverse tile drains instead applies excess water below the root zone into areas with overdrafted aquifers for the single purpose of recharge. 
• Basins or Water Conveyance Structures: In addition to OFR and its distributed systems, large-scale specialized recharge basins – reliant on centralized Infrastructure – provide options for Districts and GSAs. Growers may also identify portions of their parcel that are better for recharge and take advantage of existing conveyance and distribution systems, leading to development of targeted, smaller on-farm basins. 

Is Recharge a Good Fit for Your Operation?

To determine whether a recharge project is a potential fit for a given operation and if so which method, growers should begin by answering these four questions.

• Do I have access to surface water for recharge?
• Is my orchard soil suitable for recharge?
• What recharge methods are available?
• What orchard management changes are necessary to perform recharge?

Producers can ensure recharge programs are in place at their local GSA and water agencies and directly participate through On-Farm Recharge, subsurface recharge systems or basins. As growers evaluate their property’s potential as a recharge site, they must engage with their local Groundwater Sustainability Agency (GSA) and District, to coordinate and support efforts to maximize recharge.

Learn more about groundwater recharge and if the practice is right for your operation below. 

Additional Resources from Sustainable Conservation

• OFR Methods Manual
• OFR Case Studies
• Central Valley GW Recharge Incentives & Strategies
• District Recharge Program Guidance 
• OFR Guidance Sheet 

Groundwater Quality (GWQ) 

• Protecting GWQ While Practicing OFR: English and Spanish
• Management Considerations for Protecting GWQ Under AgMAR
• Protecting GWQ While Replenishing Aquifers: English and Spanish