State, tribal and county teams present Clear Lake Hitch hydrology study and model under development

Consultants from Okconor Environmental and representatives of the State Water Resources Control Board presented an integrated hydrologic study to the Lake County Board of Supervisors on April 7 that aims to assess habitat for the Clear Lake hitch and the effects of surface and groundwater use on stream flows in Big Valley.

Study leaders described field data gathering — streamflow gauging, groundwater elevation monitoring, seepage runs, pump tests and fish‑passage observations — and explained a physically distributed, MIKE SHE model being built on a roughly 1.6‑acre grid. The model simulates precipitation, evapotranspiration, runoff, soil moisture, groundwater and stream interactions at daily (hourly for streamflow) time steps. The current implementation covers 2015–2025, a period chosen to include recent dry and wet years for sensitivity testing.

Consultants said the model will help prioritize stream reaches for restoration, evaluate cumulative land‑use and groundwater‑use effects on instream flows during the Clear Lake hitch spring spawning season, and assess effectiveness of potential water‑management strategies under wet and dry climate conditions. The team is coordinating with tribal partners and CDFW and has assembled diverse data sources including lidar‑derived topography, well completion reports, aerial geophysical (AEM) surveys and various gauge networks.

Public commenters representing the Big Valley Band of Pomo Indians offered monitoring data collected since 2018, including pressure‑transducer records and rescue counts for stranded hitch (the tribe reported the rescue of tens of thousands of hitch over recent drought years). Conservation partners and community members urged the county to use the study to identify actionable near‑term protections where management can improve spawning connectivity.

Next steps: consultants expect model completion and calibration in the near term and scenario analysis through the summer and fall; final study products and recommendations are anticipated roughly a year out, with follow‑up meetings planned between agencies, tribes and the board.

Why it matters: Lake County and tribal leaders emphasized that better science on surface–groundwater interactions is needed to target conservation and management actions for an endangered‑sensitive fish — and to weigh the effects of groundwater pumping and land‑use choices on spring stream flows.