A series of powerful storms have rocked California this winter, bringing record-breaking rainfall to Southern California and filling most of the state’s reservoirs nearly to capacity. This doesn’t mean that California’s water woes are completely over, however.
Groundwater, the water found underground in the cracks and pores in soil, sand, and rock, is the source of more than a third of California’s water supply. And according to the State Water Resources Board, despite this winter’s storms, groundwater in many areas of the state remains significantly depleted.
“Groundwater in the southern part of the Central Valley remains more than 10 million acre-feet below pre-drought levels,” writes Jay Lund, director of the Center for Watershed Sciences at UC Davis. Groundwater levels in some areas of the San Joaquin Valley, in particular, could take decades to recover.
The problems stemming from groundwater depletion go beyond water scarcity. Overpumping groundwater can cause the ground surface to sink in a phenomenon called land subsidence. In 2015, a NASA report showed that, due to excessive groundwater pumping, land in the San Joaquin valley was sinking fast – up to two inches per month.
Additionally, in coastal locations lower groundwater levels can allow seawater to creep inland. This process, called saltwater intrusion, can taint freshwater aquifers, making them unsuitable for human consumption or agricultural use.
So how can we fix California’s groundwater problem? Researchers and farmers may already have one solution.
Groundwater is stored in underground layers of permeable rock called aquifers. Wells can be drilled into these aquifers, and water can be pumped out. Sometimes, due to factors like drought or well overpumping, groundwater levels in aquifers can fall, giving rise to the problems that accompany groundwater depletion like water scarcity, land subsidence, and saltwater intrusion. Luckily, aquifers can be replenished, though slowly, through a process call groundwater recharge.
Groundwater recharge can occur both naturally and artificially. In natural recharge, rainwater, snowmelt, or streamflow soaks into the ground and into an underlying aquifer. Unfortunately, natural recharge is often not enough to prevent groundwater depletion, especially as wells are overpumped and paved, impervious surfaces in urban areas prevent rain and runoff from soaking into the ground.
Scientists, water planners, and farmers are now turning to artificial groundwater recharge to replenish California’s depleted aquifers. Through artificial recharge, surface water is purposefully moved into underlying aquifers for storage using methods – such as recharge ponds or even flooding fields – that allow water that might otherwise run off into an ocean or other large body of water to be captured so that it can slowly infiltrate into the underlying water basins.
This year, researchers and farmers are teaming up in the Central Valley to see just how effective artificial recharge can be. Helen Dahlke, a groundwater hydrologist at the University of California, Davis, is working with a number of farmers to flood their fields this winter. “We have test sites set up on almonds, pistachios and alfalfa, just to test how those crops tolerate water that we put on in the winter,” she told NPR. Their hope is that flooding fields will allow for groundwater recharge without harming crops.
If history is any indicator, the outlook is pretty good. For several years, Don Cameron, the general manager at Terranova Ranch, southwest of Fresno, California, has been flooding his vineyards every winter. The first year, Cameron flooded his fields with a large quantity water equalling three feet deep across 1,000 acres. His efforts were a success – the water soaked into the ground, and there was no harm done to his grapes.
“This is going to be the future for California,” Cameron told NPR. “If we don’t store the water during flood periods, we’re not going to make it through the droughts.”
Especially this winter, with its heavy rainfall and rivers flooding all over the state, artificial recharge seems like a good solution to California’s depleted aquifers. Scientists caution, however, that recharge isn’t a cure-all for California’s groundwater problems. According to Peter Gleick, a water expert and co-founder of the Pacific Institute, proactive groundwater recharge will need to be paired with stricter groundwater regulations and caps on groundwater use, especially for agricultural purposes. Groundwater recharge, it seems, will be just one of many solutions needed to ensure that California’s groundwater will be there when we most need it.