On Friday morning, stakeholders in local water issues got an overview of the Sustainable Groundwater Management Act and its implications at the Lockeford Plant Materials Center.
Farmers, water managers, high school students and others turned out for the crash course in local groundwater, hosted by the Lower Mokelumne River Watershed Stewardship Steering Committee.
Once they got a background in the shrinking East San Joaquin Groundwater Basin, surface and groundwater rights, and the legal and political challenges of getting 17 separate agencies to work together on a single groundwater plan, presenters offered up some possible paths forward.
The biggest focus was on recharge.
As cities, farming operations and other users pull water from underground, the groundwater table shrinks.
In the past, water from winter rainstorms and the snowpack that flooded the state’s low ground every spring helped to recharge that groundwater.
The increasing use of dams and reservoirs to control flooding — while beneficial to the people who live in areas that could be devastated by flooding — is one of a few factors short-circuiting that natural process.
“We have millions of acres of agricultural land in California, and we focus on keeping floodwaters away from them,” said Dr. Toby O’Geen of the UC Cooperative Extension.
Instead, water managers and growers should come up with ways to direct those waters to groundwater recharge, he said.
Fewer and more intense winter storms and smaller snowpacks in recent years have also cut the amount of water naturally flowing back into the ground, said Joe Choperena, project director of the Central Valley Groundwater Recharge project operated by Sustainable Conservation.
“One of the current challenges is really just adjusting to climate change,” he said.
So along with other restoration programs, the nonprofit Sustainable Conservation is working with farmers and agencies around the Central Valley to try and fill in that gap left by nature.
Right now, they’re seeing how groundwater recharge projects might be used on private land, including a farm owner south of Fresno, a vineyard just off the Mokelumne River near Lodi, UC Davis, CSU Fresno, the Department of Water Resources and several others.
The first recharge project was the one south of Fresno, in the Lower Kings River groundwater basin. The farmer there initially started pumping water onto his farmland to protect his levee when water levels in the river got dangerously high.
“We evaluated this technique in 2011 and it was very effective,” Choperena said.
Since then, they’ve worked with several other growers to figure out when and how farm fields can be used for recharge without damaging perennial crops like grapes, almonds and walnuts.
They found that flood irrigation in post harvest fields is not only effective at helping to restore groundwater, it’s also cheaper than most dedicated recharge basins. Recharging through over-irrigating or irrigating dormant fields costs about $40 to $107 per acre-foot of water, he said, versus $124 per acre-foot for a recharge basin.
The main cost relies on how much infrastructure farmers already have for flood irrigation, and the transport of surface water to their property.
That said, recharge on farm sites isn’t ideal.
“Flooding permanent crops is not the first location that people should be looking at,” Choperena said.
Non-cropland is the best place for a recharge project, followed by non-active cropland. While flooding fields of trees and grapes during the non-growing season seems to do little damage in most cases, it’s still risky to the crops.
That said, one 4-acre walnut orchard off the Tuolumne River was unexpectedly flooded during the torrential rains of early 2017.
“It was underwater from January to April,” Choperena said.
Only six of the 360 trees needed to be replaced, but the trees did produce a much smaller amount than usual that year. The orchard is still producing, though it’s crop was still below normal last year, he said.
And while flood irrigation can benefit groundwater tables during the wet season, when there’s plenty of surface water to go around, during dry years the state might want farmers to stick with conservation methods like drip irrigation or sprinklers.
Sustainable Conservation does have one tip for farmers who want to give it a try (and who have the permits to do so): alternative flooding. This allows the roots to “breathe” between irrigation sessions and keeps the soil from becoming as saturated, while still providing enough water that some seeps down into the groundwater table.
“If possible, have berms for your plants and trees to reduce direct exposure to water,” he added.
O’Geen has been working on recharge from another angle: the soil.
As he and his colleagues studied which cropping systems were best suited for capturing excess flood water, they discovered that California’s patchwork of soil types could drastically affect how well that water soaked into the groundwater table.
Floodwaters also have different effects on soil health depending on the type of soil, O’Geen said.
“There’s an incredible amount of soil diversity in California,” he said.
Sandy, permeable soils are great for groundwater recharge projects. But other soils can have cemented layers, claypans and hardpans that block water from reaching the groundwater table quickly.
“As you can imagine, those are not ideally suited for groundwater recharge,” O’Geen said.
So his team set out to evaluate soil throughout the state, based on soil surveys, current crops and data from Google Earth.
The Soil Agricultural Groundwater Banking Index gives soil in each area two ratings on a scale from Very Poor to Excellent, one for if it had been deep tilled — breaking up those cemented layers — or not. The ratings indicate whether each location would be a good site for recharge or not.
The tool takes into account deep percolation, chemical limitations such as fertilizer use, topography, surface condition and more.
O’Geen provided two examples from the Lodi area.
One site, on the Mokelumne River alluvial fan, is made up of Tokay soils. It’s a sandy soil without cemented layers, and the team’s SAGBI tool rates it at 92 if unmodified and 93 if modified by deep tilling — both considered “Excellent.”
“It’s really a fine candidate for this practice,” O’Geen said.
A second location, in the red area of the tool’s map, has a rating of 12, or Very Poor. However, with deep tillage to break up cemented layers, the site’s San Joaquin soil type can still be great for recharge. If modified, this site would jump to a score of 72, or Good.
Other types of soil, like Jacktone, are really not improved by deep tilling, O’Geen said.
How recharge might affect crops and whether they have the right soil are just two of the issues growers need to consider before moving ahead on a project.
One of the biggest challenges to getting recharge projects off the ground? The California State Water Resources Control Board doesn’t consider recharge alone to be a beneficial water use, attorney Jennifer Spaletta said.
That means that even during years where there is plenty of surface water to go around from the Mokelumne River, most of the water right holders cannot store that water for recharge purposes. At least, not without specific permitting.
The North San Joaquin Water Conservation District has the right to use water for recharge, Spaletta said, meaning members of that district can work with recharge projects, provided they get the proper permits. But other Mokelumne River users will need to go through some red tape before they can take on recharge projects.
“Water rights and temporary permits are required in order to do recharge,” she said. “Every location is really site-specific, and your district knows best.”