Wet winter aids groundwater replenishment


Issue Date: March 6, 2019
By Christine Souza

Heavy rains this winter will help replenish groundwater aquifers and benefit projects that use excess surface water to recharge groundwater basins. Water managers say such projects will be key to addressing California's groundwater woes.

At the California Department of Water Resources, planners focus on a voluntary strategy known as Flood-MAR, which stands for "managed aquifer recharge." The strategy combines floodwater operations and groundwater management in an effort to benefit working landscapes, and could also aid local groundwater agencies as they implement the state Sustainable Groundwater Management Act, which requires overdrafted groundwater basins to be in balance by the 2040s.

"With recent events, the focus is on flood risk reduction, which includes the use of levees and bypasses to keep floodwater off of land assets—such as agriculture—and get water out of the system quickly if there is nowhere to store it," DWR Supervising Engineer Jennifer Marr said. "Flood-MAR projects can help slow down flows and provide prime locations to divert floodwater to maximize recharge."

The Flood-MAR team, Marr said, envisions a future where flood agencies could contact local groundwater sustainability agencies before or during a storm, and obtain a list of landowners with prime recharge locations.

"In the future, all water rights, conveyance and other infrastructure (would be) in place and ready for the next event. Ideally, landowners would be compensated for the public benefits their Flood-MAR projects provide," Marr said.

DWR Supervising Engineer Jim Wieking said with SGMA and changes in the state's weather, it makes sense to connect management of surface water and groundwater.

"We're starting to get floodwater experts in the room with surface water managers and groundwater managers," he said. "Flood-MAR is saying: Maybe we can look at the potential for essentially irrigating fields in the wintertime and that would increase water into the aquifers in those areas."

Recharging groundwater has long been a priority of the Selma-based Consolidated Irrigation District, which serves farmers with water from the Kings River.

Consolidated Irrigation District General Manager Phil Desatoff said the district has been using floodwater to replenish groundwater since the 1870s, and started purchasing land for recharge purposes in 1921 when the district was officially formed.

"The district has been doing this slowly, but now with SGMA it becomes a major priority; we have to get this done," Desatoff said. "We're going to capture more of this floodwater and put it underground."

Located near the Kings River and with coarse soils that offer a favorable water-percolation rate, the district has 1,400 acres of ponds for groundwater recharge and plans to construct more.

During the wet winter of 2016-17, Desatoff said the district diverted an average 900 cubic feet per second or 1,800 acre-feet of floodwater per day for groundwater recharge, from January through September.

"That's 408,000 acre-feet of water that we were putting in the system," he said.

Consolidated Irrigation District formed the Central Kings Groundwater Sustainability Agency and intends to work with neighboring districts.

"We are going to be in balance, in fact we're almost in balance now," Desatoff said.

Helen Dahlke, a hydrology expert and professor with the University of California, Davis, Department of Land, Air and Water Resources, has been working with farmers, studying on-farm groundwater recharge locations and suitability for various crops.

"In many regions, we can definitely do more actively recharging our groundwater aquifers," said Dahlke, who currently has trials on alfalfa at the UC Kearney Agricultural Center. "It really depends on what region, how much surface water is available for recharge, what kind of sediment structure or hydrogeology we have underneath and whether it's suited for conveying large amounts quickly."

Despite abundant precipitation in recent weeks, she said the timing is not the best for studying impact of recharge on certain crops.

"We prefer on-farm recharge to happen in January and February, just because that is considered the dormancy season for most crops," Dahlke said. "With almond trees already blooming, often there is a greater risk of applying water on those crops."

She said recent precipitation has helped groundwater recharge overall, but there is "very little way of estimating how much it is helping."

"It's more or less impossible to account for all of the heterogeneity that we have in the landscape," Dahlke said.

DWR's Wieking said groundwater recharge is driven by precipitation and runoff, and precipitation also influences the amount of active recharge that can be applied. With the significant amount of precipitation this year, he said he believes much natural recharge is taking place and more water is available for farmers to take advantage of on-farm recharge.

The state tracks groundwater elevation trends through its California Statewide Groundwater Elevation Monitoring program.

"CASGEM information is updated annually and so there will be new updates after this water year," Wieking said. "Information collected from different wells is compiled so water managers can compare year to year. In terms of recharge for this year, we're ahead of average and so we're probably recharging more water to our groundwater basin than we do on average. In terms of knowing how we've done in a given year, you don't really find out until a couple of years down the line, usually."

Dahlke noted that after analyzing groundwater data following 2017, the wettest year on record for Northern California, "we could see in some wells the level rising 10, 20, and in extreme cases 30 feet, which is a lot—but measuring the water table does not tell us the volume of water that we have in the groundwater aquifer."

(Christine Souza is an assistant editor of Ag Alert. She may be contacted at csouza@cfbf.com.)

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