Working with Agriculture to Recharge California’s Groundwater Supplies

Current rates of groundwater pumping are far from sustainable, as we’re using much more than is naturally replenished. As a result, California is facing serious overdraft issues – including land subsidence and the intrusion of seawater into groundwater basins close to our coastline. This effectively jeopardizes our food supply, drinking water and groundwater storage capacity that could serve as a much-needed buffer during future droughts.

California has one of the most robust agricultural economies in the U.S. and supplies 50% of the fruits and vegetables that the nation consumes. Most agriculture in California requires irrigation and farming uses more than 75% of the state’s developed water supply.

Groundwater Overdraft in the Kings River Basin

The Kings River provides water for much of the farming in the Tulare basin region, located at the southern end of California’s San Joaquin Valley. Today, the lower Kings River basin, like much of California’s Central Valley, faces both water supply and water quality issues.

Because groundwater offers greater reliability and accessibility than does surface water from the Kings River, farmers opt to use groundwater to irrigate crops, even when surface water is available. Groundwater in the Kings River basin is pumped at an average rate of 125,000 to 150,000 acre-feet per year above its sustainable yield. This overdraft amount equates to about 10% of the basin’s overall average annual surface water usage.

Groundwater overdraft has ironically been compounded by the widespread adoption of water conservation technologies. As farmers switch to drip and micro-sprinkler irrigation, they rely more on groundwater and forego irrigation using river water, which previously helped recharge the aquifers. This has resulted in groundwater that’s more difficult to access – with some farmers having to drill wells to depths of over 200 feet. That’s up to 30 feet deeper compared to a decade ago.

Many irrigation districts have been addressing the overdraft problem by buying sandy farmland and excavating to create basins to capture and infiltrate floodwater from the river when available. But despite these efforts and natural recharge processes, groundwater pumping exceeds the rate of replenishment

Partnering with Local Farmers to Boost Groundwater

Sustainable Conservation aims to expand the rate of groundwater recharge beyond the limits of dedicated recharge basins by encouraging farmers to apply available floodwater on their active farmland in ways that do not compromise crop production. Sustainable Conservation is partnering with the Kings River Conservation District to promote the capture of additional floodwater from the Kings River for on-farm groundwater recharge.

Maximizing the capture of flood flows during wet years replenishes groundwater supplies for use during dry years, while also reducing downstream flood risk. Our goal is to capture an additional 25,000 acre-feet of otherwise unused flood flows from the Kings River during wet years. That’s as much water as it takes to fill about 12,500 Olympic-sized swimming pools.

Terranova Ranch Pilot Project

flooded-vineyards_terranova

In the high-water year of 2011, Fresno County farmer Don Cameron of Terranova Ranch tested the application of seasonal floodwater from the nearby Kings River onto active cropland (wine grapes) to help recharge the underlying aquifer. A significant amount of groundwater was captured without affecting crop yields.

Sustainable Conservation has been involved in the Kings River basin since 2011 via our work on a Terranova Ranch groundwater recharge pilot project. The project evaluated the benefits of capturing winter and spring floodwaters from the lower Kings River. That water was spread across farmland to increase recharge to the most severely depleted part of the Kings River basin groundwater aquifer.

Three feet of water per acre on 1,000 acres was successfully captured without affecting crop yields. This equates to flooding an area the size of 756 football fields and filling each field with water approximately three feet deep.

It also generated considerable interest from numerous farmers and downstream municipalities looking for flood safety benefits. We are working with farmers on adjacent farms to scale the project to 16,000 acres. We are also reaching out to irrigation districts across the broader Kings River region and in adjacent counties to encourage on-farm recharge as an affordable strategy to increase flood water capture and groundwater recharge.

Evaluating the Benefits of On-Farm Recharge

Irrigation districts remain concerned about applying floodwater on farmland that contains nitrates from fertilizer, because drinking water in rural communities has been degraded as a result of historic dairy waste, fertilizers and traditional irrigation practices.

In response, we are conducting a study with University of California researchers and hydrology consultants to evaluate the expected dilution effect of floodwater capture on farmland to determine appropriate methods for applying floodwater to avoid putting farmers at risk for non-compliance with water quality regulations. This study, combined with our work evaluating the comparative economic costs of on-farm recharge versus traditional dedicated recharge basins, will greatly assist water managers and farmers with deciding how best to achieve a sustainable groundwater supply.

Partnership with the Almond Board of California

In 2015, we entered into partnership with the Almond Board of California.

This partnership marks the first concerted effort to increase groundwater recharge on almond farmland, and launches just as California is entering a much-anticipated El Niño year, which could bring an exceptionally wet winter.

For more than 20 years, the Almond Board has funded several research projects to understand water movement in the soil, and preserve and improve groundwater quality and, through nearly 100 innovative Almond Board-funded research projects since 1994, California almond growers have incorporated state-of-the-art, research-proven irrigation practices that reduced the amount of water needed to grow each pound of almonds by 33 percent.

As part of this partnership, Sustainable Conservation and a team of UC researchers and other specialists will model and determine how floodwater can be best applied on almond orchards to protect and improve groundwater quality. As the research progresses, we, along with UC Davis, will present findings to the public, groundwater management agencies, industry experts and farmers to help drive the development of best practices to promote groundwater sustainability in almond orchards throughout California’s Central Valley.

About this partnership, our Executive Director, Ashley Boren, states, “Both the Almond Board and Sustainable Conservation believe that a healthy environment and farming sector can only be achieved through collaboration and uniting around common goals. California’s record drought and its crippling effects felt in every corner of the state call for bold alliances in delivering a sustainable water future.”

Impact

California farmers in 2016 expressed great interest in our on-farm groundwater recharge efforts:

  • 130 demonstration sites representing 10 crops on nearly 15,000 acres throughout the San Joaquin Valley

Highlights

Partners

Almond Board of California

Lawrence Berkeley National Laboratory

TerraNova Ranch

University of California, Davis

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