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Central Napa River Assessment Project
The Napa County RCD received funding from the California Department of Fish and Game in 2002 to carry out the second phase of a three-phase watershed study covering the entire Napa River basin. The geographic scope of this project covered the Napa River basin from Bell Creek to Soda Creek. This study was intended to assess the quality and quantity of available aquatic habitat, specifically relating to salmonid life history requirements, and identify key areas for restoration, improvement, or preservation.
Extensive field surveys were conducted in the mainstem Napa River and the following nine tributaries: Bale Slough, Bell Creek, Canon Creek (tributary to Bell Creek), Conn Creek, Montgomery Creek (tributary to Dry Creek), Rector Creek, Soda Creek, Wing Canyon Creek (tributary to Dry Creek), and York Creek. Sufficient landowner access was not granted for Bear Creek, Campbell Creek, or Segassia Creek. In the ten streams with sufficient landowner access, we conducted habitat surveys, snorkel fish counts, gravel permeability, water quality monitoring, continuous temperature monitoring, stream flow monitoring. Salmon surveys were conducted in the mainstem Napa River in 2004.
Habitat survey results showed an overall lack of suitable summer rearing habitat for juvenile salmonids, due primarily to lack of perennial stream flow and poor water quality conditions during critical warm months. Continuous temperature monitoring results documented multiple sites with excessively warm summer water temperatures, especially in the mainstem Napa River. Tributaries with sufficient flow, canopy densities, and groundwater influence (York, Segassia, Canon, Soda) maintained favorably cool water temperatures during the hot summer period. Several reaches with high quality salmonid habitat were identified in the following tributaries: York Creek, Wing Canyon Creek, and relatively short stretches of Bell Creek and Soda Creek.
The Napa River offers minimal spawning and rearing habitat for steelhead as indicated by the low abundances of juveniles observed in the mainstem. However, the river does appear to provide spawning habitat for Chinook salmon. In 2003 and 2004, significant numbers of Chinook salmon were observed spawning in the mainstem and several of the larger tributaries. In 2004, we conducted spawner surveys, redd surveys, and carcass counts along the river. Results of these efforts documented over 100 live spawning Chinook salmon and 62 redds in a 3.6 mile reach of the Napa River near Rutherford. Coded wire tag analysis from one hatchery marked carcass was recovered and determined to be a 2002 Spring-run Chinook from the Feather River hatchery. Given the relative scarcity of available data on Chinook salmon in the basin, it is not clear what percentage of the observed run was of hatchery origin or wild Napa River stock.
A total of 135 potential restoration opportunities have been identified, mapped, and ranked according to their relative importance and cost. These restoration sites include 67 sites with exotic vegetation, 47 bank erosion areas, five migration barriers, eight riparian canopy sites, four sites with elevated water temperatures, and one potential site for immediate woody debris placement. Within the surveyed reaches, stream bank erosion was most prevalent followed by lack of riparian canopy, presence of migration barriers, and lack of rearing habitat. Restoration priorities for each of the ten surveyed streams are available from the Napa County RCD as separate documents, and are subject to landowner confidentiality agreements.
