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Study: Heavy Storms May Be Enough to Recharge Central Valley Groundwater

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Matt Weiser August 21, 2017  read full Water Deeply article here

California’s Sustainable Groundwater Management Act, passed in 2014, requires some 250 groundwater basins throughout the state to halt the overdraft in their aquifers. The big question for everyone is: Where will the water come from to do that?

It could come from “high-magnitude flows” – flooding events, essentially, that occur from just a handful of storms every winter. …A new UC Davis study …attempts to quantify these high flows… one of the first efforts to measure how much water might be available for groundwater recharge from these storm events, and the results are surprising.

…[the authors] estimate that 2.6 million acre-feet of water is available in an average year from these high-magnitude flows…based on real flows that have occurred. They also estimate this water is surplus to both existing water rights and to environmental flow requirements in the Sacramento-San Joaquin Delta…..this amount of water also nearly equals the average annual groundwater overdraft in the state’s Central Valley. This suggests these high-magnitude flows could be an important tool to recharge stressed aquifers. That is, if the water can be captured by groundwater banking projects, the flooding of farm fields and other means.

Within a few weeks, the results will be presented online in an interactive format at recharge.ucdavis.edu.

Water Deeply recently interviewed Kocis to learn more about her findings.see interview with the study’s authors here

Tiffany N Kocis and Helen E Dahlke. Availability of high-magnitude streamflow for groundwater banking in the Central Valley, California. 31 July 2017 Environmental Research Letters, Volume 12, Number 8

ABSTRACT: California’s climate is characterized by the largest precipitation and streamflow variability observed within the conterminous US. This, combined with chronic groundwater overdraft … creates the need to identify additional surface water sources available for groundwater recharge using methods such as agricultural groundwater banking, aquifer storage and recovery, and spreading basins. High-magnitude streamflow, i.e. flow above the 90th percentile, that exceeds environmental flow requirements and current surface water allocations under California water rights, could be a viable source of surface water for groundwater banking. Here, we present a comprehensive analysis of the magnitude, frequency, duration and timing of high-magnitude streamflow (HMF) for 93 stream gauges covering the Sacramento, San Joaquin and Tulare basins in California…The results suggest that there is sufficient unmanaged surface water physically available to mitigate long-term groundwater overdraft in the Central Valley.

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