County briefed on interbasin coordination analysis; two technical memos posted

County staff presented an update on an interbasin coordination analysis and modeling project, funded by grants and led by Butte County with consultant Montgomery Associates. The project analyzes how neighboring groundwater sustainability plans (GSPs) interact along river corridors and identifies differences in sustainable management criteria and data gaps.

Dr. Christina Buck described phase 1 work completed during Groundwater Sustainability Plan development and the ongoing phase 2 effort to evaluate plan implementation and border conditions. "We've been talking about interface and coordination really since Sustainable Groundwater Management Act came along in 2015," Buck said, noting that the project focuses on the North Sacramento River Corridor and the Feather River Corridor and that two technical memos are now available.

Buck highlighted that differences in measurable objectives and minimum thresholds between neighboring subbasins can be substantial — in one place water-level criteria differed by as much as about 60 feet between adjacent basins — and that Department of Water Resources (DWR) recommended corrective actions across groundwater levels, land subsidence and interconnected surface water in multiple plans. She said the third technical memo, on boundary flows and stream-aquifer interactions, is expected by late summer and that DWR review of periodic evaluations will raise interbasin coordination issues during upcoming plan reviews.

Staff also described parallel facilitation support from DWR and an upcoming webinar series covering the memos; a webinar on the Feather River Corridor results was scheduled the day after the meeting. Commissioners asked whether DWR will mediate differences between subbasins or leave reconciliation to local GSAs, and Buck said DWR has not been highly active in interbasin mediation to date but is expected to engage more as it reviews periodic evaluations.