Demonstrating Road Improvements in the Napa River Watershed
The Napa County Resource Conservation District (NCRCD) and it's technical consultant, Pacific Watershed Associates Inc. (PWA), implemented road related erosion control and erosion prevention treatments along approximately 5.17 mi of road in two subwatersheds of the Napa River basin: Sulphur Creek and Carneros Creek. The work plan addressed treatment sites previously assessed as having high or high-moderate treatment immediacies, as well as all lengths of hydrologically connected road. The completed work in the Carneros and Sulphur Creek subwatersheds represents the first two phases of a three-phase sediment reduction and watershed restoration project being undertaken by the NCRCD for the Napa River basin.
In the Sulphur Creek subwatershed, PWA supervised upgrading treatments along approximately 3.85 mi of road on 4 private landownerships. The work was completed between August and October 2010. A total of 32 sites were treated, including 29 stream crossings, 2 ditch relief culverts, and 1 landslide.
In the Carneros Creek subwatershed, sediment reduction treatments were completed between August and November 2009 along approximately 1.32 mi of road on 3 different landownerships. A total of 14 sites were treated to reduce erosion and sediment delivery: 12 sites were upgraded (11 stream crossings and 1 ditch relief culvert), and 2 stream crossings were decommissioned.
PWA estimates that treating the 46 sites and 5.17 mi of road reaches in the two subwatersheds will substantially diminish the delivery of coarse and fine sediment to the stream system, including approximately 3,465 yd3 of sediment projected to originate from episodic erosion at individual sites, and approximately 4,045 yd3 of fine sediment estimated to originate from the chronic erosion of road, ditch, and cutbank surfaces during the next decade alone.
The successful completion of this project represents important progress in reducing road related erosion and sediment delivery to Carneros and Sulphur Creeks, and establishing long-term improvements in water quality in local streams as well as in the Napa River.