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WSU-led model: groundwater levels projected to decline across much of eastern Washington
Summary
WSU and Ecology presenters warned that groundwater levels across Eastern Washington are likely to fall under business-as-usual and compounding scenarios, with deepest basalt aquifers most at risk; a regional program (Odessa Groundwater Replacement Program) could offset decades of decline in some places, researchers said.
Sasha McLarty, principal investigator for the Washington State University research team, told attendees that model simulations show groundwater levels “will continue to decline across most of Eastern Washington” if recharge and pumping practices remain unchanged.
The groundwater module compared four scenarios. Under business-as-usual—current pumping and recharge—the model produces broad declines in water levels, particularly in the deepest basalt layers. In a “compounding” scenario (a 15% increase in pumping combined with a 15% decrease in recharge) declines are more severe and widespread. A compensatory scenario (15% increased pumping but matched by 15% increased recharge) produces localized improvements, mostly in shallower layers, but the deepest basalts still show substantial declines in most model runs.
McLarty flagged model limitations: model estimates of recharge are likely overestimated in some areas (notably parts of the Wanapum and Grande Ronde layers), and deep aquifer recharge is negligible across much of the central basin. “A model is just a simplified representation of the real world,” she said, urging readers to treat outputs as scenario-based evidence rather than precise predictions.
The team also simulated the Odessa Groundwater Replacement Program (described in the presentation as AWGWARP), in which some groundwater users are switched to surface water. Implementing the program within the modeled boundary produced widespread simulated increases in water levels and, in the Grande Ronde, had the potential to offset as much as about 30 years of decline in the modeled scenarios.
Researchers emphasized uncertainty in recharge estimates, pumping rates, and geologic controls on groundwater movement and urged that model outputs be used to guide further monitoring, targeted recharge studies (including isotope age dating), and policy choices about managed recharge and demand reduction. The team said further work will relate modeled water-level changes to metrics such as available saturated thickness in follow-up analyses.
