Aquifer Recharge Efforts Ramp Up During Rainy Season

El Niño and new state laws create a storm of aquifer activity in California
Aquifer Recharge Efforts Ramp Up During Rainy Season
UC Davis hydrologist Helen Dahlke stands in a Modesto, California, almond orchard in an experiment she is leading to recharge the aquifer by flooding farmland in the winter.

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While it’s not apparent just yet whether this winter’s rainfall will bring closure to California’s historic drought, it is clear that the state’s underground water concerns will linger on. According to the San Jose Mercury News, water has been removed from aquifers faster than nature can refill them for decades, and the state has deemed 21 groundwater basins “critically overdrafted.”

There are consequences that go hand in hand with the overpumping of groundwater. Last summer, for example, sections of the San Joaquin Valley collapsed by 2 inches per month – endangering roads, pipelines and canal linings – and on the coastal regions, seawater intrusion has transformed groundwater into unusable brine.

Experimentation underway
As the last of the Western states to regulate groundwater, it took California’s most brutal drought ever to force the Legislature’s hand. But the 2014 law requiring water agencies to refill the state’s aquifers led to a crucial problem, according to the Mercury News report. Many local officials weren’t quite sure how to go about that process.

The influx of winter rainfall has the creative juices flowing, however, and it appears that the mandate – in conjunction with this change of weather – has helped generate new experiments. Farmers in Modesto flooded an almond orchard using the city’s stormwater, for example, and water managers in the Fresno area have more than 20 new groundwater recharge projects in the works.

Because they began monitoring a percolation basin just as the drought began back in 2011, UC Santa Cruz hydrologist Andy Fisher and his team have a head start on the explosion of activity now underway. With Fisher’s assistance, the owners of the property and the company farming the land built ditches to capture runoff before it rushes off.

Those ditches direct the water into a sediment-settling pond, and a culvert funnels it into a 2-acre infiltration basin. Afterward, the water drains through sandy soil to restore the aquifer. Pressure sensors track the flow, and a rain gauge monitors precipitation levels. There’s also a camera that takes a picture every few minutes to ensure the accuracy of the measurements, noted Sarah Beganskas, a Ph.D. candidate in hydrology who assists Fisher.

The researchers have learned that the type of rainfall has an effect on the amount of water collected by basins. Rain has time to soak back into the soil and filter down to the aquifer during light showers but rushes into rivers and the ocean during heavier storms (unless a stormwater collections system is in place to collect it).

Small projects, big potential reach
Recharging groundwater supplies using surface water is far from a fresh idea. For example, the Santa Clara Valley Water District maintains 99 percolation ponds, district spokesman Marty Grimes told the Mercury News.

When groundwater overdraft led to roughly 13 feet of land subsidence in parts of San Jose between 1915 and 1965, the district replenished the aquifer below, and since then the groundwater level has rebounded.

The Santa Clara Valley district’s percolation basins are fed partly by the state and federal water projects. The Pajaro Valley and its nearby basins, on the other hand, depend on alternative sources such as recycled wastewater or stormwater runoff.

Fisher and Beganskas are working on other percolation ponds in the Pajaro Valley and estimate that the valley could support about a dozen sites like the one they’re observing. Together, the sites could supply roughly 10 percent of the annual groundwater deficit in that region.

The reach of their project – and others like it – could extend even further, however. The knowledge and data gleaned could potentially be used to implement similar methods throughout the state and beyond, UC Davis Groundwater Hydrologist Thomas Harter told the Mercury News, as long as local conditions are taken into account.

Source: San Jose Mercury News


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