1. Interbasin Groundwater Modeling Shows Limited Connectivity Between Upper Valley/Forebay and Coastal Intrusion
The GSA completed significant modeling work funded by the Salinas Basin Water Alliance and Salinas Valley Water Coalition examining how pumping in one sub-basin affects others. The results demonstrated, in a hypothetical scenario where all pumping in a subbasin is turned off for the 1980–2022 period, that turning off all pumping in the Upper Valley would only reduce simulated seawater intrusion by approximately 380 acre-feet annually (about 4% of modeled intrusion), and turning off all Forebay pumping would reduce it by 420 acre-feet (also ~4%). Coalition consultant Dwight Smith characterized this as showing that Upper Valley and Forebay pumping has a relatively modest effect on seawater intrusion in the 180/400-Foot Aquifer, while other modeling results showed the East Side and 180/400 sub-basins are highly interconnected with significant groundwater exchange between them (a roughly 49,000 acre-foot change in net flow direction historically in the model).
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