Napa County Flood Control and Town of Yountville Complete Hopper Creek Steelhead Fish-Passage Restoration

Fisheries biologists with the Napa County Flood Control and Water Conservation District and Town of Yountville Public Works completed in-channel construction on Friday morning for the Hopper Creek Fish-Passage and Riparian Shade Project, removing a seventy-year-old concrete pipeline apron that impeded migrating steelhead trout between the Napa River mainstem and upper Oak Knoll spawning gravels. Situated just west of Highway 29 and the Napa Valley Vine Trail crossing in Yountville, the three-foot vertical concrete drop previously blocked adult winter-run steelhead during moderate rainfall years while trapping juvenile smolts in warm downstream pools each spring. Over the dry autumn work window, heavy-equipment crews replaced the barrier with a 180-foot series of engineered basalt boulder step-pools and deep resting alcoves that mimic natural mountain riffles.

Hydrologic modeling conducted with the Napa County Resource Conservation District confirmed that the gently sloped rock ramp maintains passable water depths at flows ranging from 4 cubic feet per second up to a 100-year flood event, simultaneously protecting the underlying municipal water main with buried steel casing. Along both banks of the restored reach, conservation corps crews planted 320 native white alders, California buckeyes, valley oaks, and wild rose shrubs irrigated by temporary drip lines until roots reach the water table.

Once mature, the streamside tree canopy will lower summer water temperatures by up to 4 degrees Fahrenheit along the Yountville corridor while stabilizing silt banks that border adjacent organically farmed vineyards. Automated acoustic Doppler streamflow and dissolved-oxygen sensors mounted at the Finnell Road bridge will stream real-time watershed telemetry to county flood engineers throughout the upcoming winter rainy season.

The $940,000 restoration was funded through a California Department of Fish and Wildlife Proposition 1 Watershed Restoration grant matched by Napa County Measure A flood-protection funds. Residents can view live Hopper Creek stream gauges and volunteer tree-planting Saturdays on the Napa County Resource Conservation District Portal.