By Bob Johnson, Ag Alert
Watsonville-area farmers who rely on well water to produce berries and vegetables are continuing to progress on their long-term goal of reduced depletion of underground water through a combination of conservation and new sources.
The Pajaro Valley got a head start on meeting requirements the Sustainable Groundwater Management Act will require more widely, because overdrafted underground water was causing seawater intrusion that made some wells too salty.
“We have been increasing water deliveries and reducing pumping,” said Brian Lockwood, general manager and hydrologist at the Pajaro Valley Water Management Agency. “The Sustainable Groundwater Management Act requires high priority, critically overdrafted basins like the Pajaro Valley to achieve sustainability by 2040. We do a lot of the things SGMA calls for, but we were doing them long before the law was enacted.”
The three-county agency that oversees water policy in the basin was created in 1984, and began developing and implementing programs to reduce seawater intrusion near the coast in the 1990s.
Because the Pajaro Valley is not served by deliveries from state or federal water projects, the district has had to develop additional local water sources.
Lockwood and University of California, Santa Cruz, hydrology professor Andrew Fisher discussed past and current efforts to preserve the underground water used to irrigate 28,000 acres of crops during the Fertilizer Research and Education Program Online Nutrient Management Program.
The district has maps dating back to 1951 showing the boundaries of seawater intrusion, which happens when pumping drops the underground water serving the coastal district to below sea level. Levels in the aquifer drop below sea level during droughts and the peak spring and summer season, and rise above sea level with recharge during wet years and the winter rainy season.
“It was determined we needed to reduce groundwater extraction in the coastal area while maintaining agriculture,” Lockwood said. “We have done that with our recycled water facility and the Harkins Slough recharge facility.”
The recycled water facility receives 4,000 acre-feet a year from Watsonville homes and businesses, treats it to a level that is safe for crop use and delivers it to coastal farms through a 21-mile network of pipes.
The Harkins Slough project moves water leaving the wetland to an area where it can move down through the soil to replenish the underground basin.
“The water recycling facility has been producing more water each year; it is now up to 7% of the district total water use,” Lockwood said. “If we didn’t take the water from Harkins Slough, it would run down to the Monterey Bay, mix with seawater and be of no use to us.”
These new sources of water, combined with conservation efforts by farmers, have been enough to reduce pumping from 50,000 acre-feet in 2008 to less than 40,000 acre-feet in 2019, and have kept the underground water table above sea level in average rainfall years.
The goal, Lockwood said, is to improve the balance between pumping and recharge by an additional 12,000 acre-feet of water a year. That would be accomplished through further efficiency efforts and increased supply from expanding current projects and reimbursing farmers for efforts to use stormwater runoff to recharge the underground aquifer.
Fisher said one aspect of climate change could be an increase in the amount of water that comes during high-intensity storms.
“More rain is falling during intense storms, and we don’t capture as much,” he said. “We are trying to map where managed recharge might be possible.”
Fisher is a co-founder of the Recharge Initiative, which will reimburse farmers for the value of runoff water that is captured and diverted to ground where it will seep down and recharge the aquifer.
One of the recharge projects already set up is at the Bokaria-Drobac Ranch, which has a goal of putting 100 acre-feet of water a year back into the aquifer during storms. Another recharge project started in 2019 at the 1,300-acre Kelly-Thompson Ranch.
Fisher said he is looking throughout the Pajaro Valley for sites that have plentiful runoff during storms and soil structure that makes for recharge.
“We think intermediate-sized projects offer the best opportunity for economic collection of stormwater leading to managed recharge,” he said. “Our goal is to have many projects that add up to 1,000 acre-feet of recharge.”
The recharge projects have the added benefit of improving water quality, because the addition of clean water reduces nitrate concentrations in the underground aquifer.
“Recharge benefits water quality,” Lockwood said. “When we can’t recharge, we see nitrate levels spike.”
The next step in the Recharge Initiative will be to find economical ways to further reduce nitrates by treating the runoff water before it travels down to the underground aquifer.
“We are looking at running the water through carbon-rich amendments in the recharge area, like almond shells, wood chips, biochar or rice hulls,” Fisher said.
“One of the things we have been working on is improving water quality as it is recharging,” he said. “Managed aquifer recharge with stormwater can benefit groundwater resources; it can also benefit water quality.”
