Groundwater: The crucial challenge

(Ed’s Note: The following is part of a series on California water issues from experts convened by the UC Davis Policy Institute for Energy, Environment and the Economy).

California’s single most urgent water policy priority is preserving our groundwater supply.

In normal years, groundwater provides one-third of our state’s urban and agricultural water. In dry years, it provides up to nearly two-thirds.

As the severe drought has brought new awareness of the importance of our groundwater safety net, California leaders have made significant public policy changes. They include the California Sustainable Groundwater Management Act of 2014; 2015 laws that streamline groundwater-dispute resolution; and new requirements under the state Porter-Cologne Water Quality Control Act of 1969.

Research showed last winter that setting back levees on the Cosumnes River raised the water table in just one storm.

While these new standards are a good foundation, the real work has just begun. Changing behavior will be particularly challenging for the agricultural community, which uses 80 percent of the groundwater extracted but has never been asked to so actively manage and protect the resource.

More than ever before, researchers and the agricultural community need to work together to learn how to simultaneously grow crops, protect groundwater quality, and refill underground basins with clean water.

So how do you recharge a depleted aquifer? It starts at the surface with healthy soils, which move water well and keep agrichemicals away from groundwater. Where soils are degraded, adding compost or cover crops can raise soil carbon and improve soil structure and microbial diversity.

Another step is to identify the best areas for water to percolate through to underground basins. A new mapping tool, the Soil Agricultural Groundwater Banking Index, shows the most promising recharge sites. Roughly 28 percent of California farmland could likely accommodate deliberate flooding in the winter with little risk of crop damage or groundwater contamination. Early agricultural recharge tests in wine grapes, alfalfa, and pistachios are promising.

Another recharge strategy: removing some levees or rebuilding them farther from riverbanks. Research showed last winter that setting back levees on the Cosumnes River raised the water table in just one storm. Flood risk dropped, and baby fish and crops in the new floodplain benefited.

Efficient use of fertilizer and healthy soils are also key. Excess fertilizers and pesticides not used by crops can leach into groundwater. Early tests are focusing on crops that require less fertilizer, such as alfalfa and grapes. Fertilizer-hungry crops can be replaced with crops that fix nitrogen, or otherwise protect groundwater quality.

We also need new systems in addition to the monitoring-well networks we now rely on to identify contaminant plumes from point sources.  New approaches include combining well samples and soil analyses with grower data about the chemicals used and about farming practices.

Then there’s the issue of managing data. Governments collect data on stream flows, snowpack, rainfall, water temperatures, wells, water tables, water taken out of surface streams and water put back. Soon, more than 25,000 farmers on 7.5 million irrigated acres in the Central Valley and on the Central Coast will begin reporting farm nutrient management plans. But other important pieces of information are largely missing, such as frequent updates of land use and land fallowing data, which are currently done by the Department of Water Resources every seven to 10 years.

Some solutions to our water supply problems may be right under our feet.

Future Groundwater Sustainability Agencies will also need data on irrigation practices to estimate water demand, evapotranspiration, and the amount of groundwater pumped to irrigate crops. Data already being collected in some locations will need to be collected at many more locations and more often. The data will need to be knitted together into models that allow us to assess which are the most effective groundwater sustainability tools. Universities are helping the state decide how to learn from all this information. The information technology industry can help, too.

A long-term investment in teaching, learning, outreach and education is key to engage the broad range of agencies and stakeholders in the process of protecting groundwater resources.

Can we afford to make these changes? We can’t afford not to. Some solutions to our water supply problems may be right under our feet, through understanding soil and integrating soil management with groundwater policies.
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Ed’s Note: Thomas Harter is a Cooperative Extension Specialist for the University of California Agricultural and Natural Resources. Kate Scow is a professor of Soil Science and Microbial Ecology, and director of the Russell Ranch Sustainable Agricultural Facility. Helen Dahlke is an assistant professor of Integrated Hydrologic Sciences. Toby O’Geen is a Cooperative Extension Soil Resource Specialist. All are in the Department of Land, Air and Water Resources at the University of California, Davis.