Cosumnes River Provides Model for Floodplain Restoration in California

News Deeply –

With California’s surface drought over, the state can prioritize investing in groundwater recharge and floodplain restoration to help fight one of its biggest lingering problems: groundwater overdraft. As it does so, the relatively unknown Cosumnes River watershed has emerged as a model.

Roughly half of the groundwater basins in California’s Central Valley are critically overdrafted, including the San Joaquin Valley basin to the south of the Cosumnes. Though groundwater levels in the Cosumnes basin have also appreciably declined since the 1950s, cutting edge research at the Cosumnes River Preserve, a 50,000-plus acre public-private partnership in the eastern Sacramento-San Joaquin Delta, has shown that floodplain restoration can substantially recharge groundwater as well as provide habitat and improve fish migration.

Preliminary results from an ongoing University of California Water study on the Cosumnes River suggests that breaching levees to allow small- and medium-sized floods to inundate agricultural fields could triple the recharge provided by irrigation. This is welcome news as California figures out how to make the state’s surface and groundwater systems more sustainable and have more multi-beneficial uses for humans and wildlife.

Facing diminishing groundwater levels, the state passed the Sustainable Groundwater Management Act (SGMA) in 2014 to work toward long-term groundwater sustainability. That same year, voters approved the Water Quality, Supply and Infrastructure Improvement Act (also called Proposition 1) to provide $7.5 billion for water-related infrastructure projects. Groundwater supplies roughly 30 percent of water deliveries in the state, and that amount skyrockets in droughts, such as the recent record-breaking one. California’s dependence on groundwater for agricultural and municipal use has caused an immense statewide overdraft averaging over 1 million acre-feet per year. This is partly due to the vast majority of Central Valley rivers being dammed and leveed, which shrinks the river’s floodplain and consequently reduces groundwater recharge.

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