REPORT: Fresno State report details how Shallow Subsurface Artificial Groundwater Recharge can recharge clean water to aquifers

New technique allows recharge to occur under existing crops at 100% efficiency

To address declining groundwater levels throughout the State, the legislature in 2014 enacted the Sustainable Groundwater Management Act, which required groundwater users in medium and high-priority basins to form Groundwater Sustainability Agencies and develop plans to bring their basins into balance within 20 years.

Several tools are available to accomplish SGMA’s goal.  These include reducing groundwater use through fallowing agricultural land and agricultural and urban water conservation, and adding water to the aquifer through groundwater recharge.  Groundwater recharge methodologies include recharge basins, flood-managed aquifer recharge (FloodMAR), and shallow subsurface artificial groundwater recharge (SSAGR).  A new report from Fresno State’s California Water Institute focuses on SSAGR and how it compares to traditional recharge basins.

A general Shallow Subsurface Artificial Groundwater Recharge (SSAGR) system consists of a surface water source, a connection from the canal to a pump wet well, a lift pump, a flow meter, a delivery pipeline, a standpipe, and a distribution pipeline consisting of solid wall header pipes and perforated recharge pipe.

Simply put, recharge water from the canal is conveyed to a pump through a connecting pipeline and is lifted into a standpipe, where it is distributed to three perforated system pipelines buried in the subsurface.  (Refer to the report for a more thorough technical description of the system.)

During the study, the system accomplished over 1200 hours of recharge during June, July, and August of 2022, with 100% of the applied water recharged to the aquifer.  Moisture probe data indicated the recharge water was not retained in the vadose zone (the layer between the bottom of the root zone and groundwater table) but moved downward and horizontally.

The report notes several benefits to SSAGR compared to a traditional recharge basin.  While the recharge basin can handle more water at a time than an SSAGR system due to its size, the total amount of water is not recharged due to surface evaporation.  A recharge basin can lose significant water due to evaporation if recharge occurs during the summer months, reducing the basin’s recharge efficiency to 94%.

SSAGR systems are less expensive to construct and operate underneath existing crops or drip irrigation systems, so they don’t require taking land out of production.  Recharge is possible during irrigation season, and even concurrently if the pump capacity is large enough.  Researchers also noted that SSAGR systems are far enough below the root zone that legacy pesticides, fertilizers, and herbicides would not be mobilized by the recharge water and transported to the groundwater.

Click here to read/download the report.

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