Upper Napa River Watershed Road Assessment

Unpaved roads can have unanticipated effects upon the watersheds in which they are found because they often concentrate runoff, increase erosion, and can potentially deliver excess into streams. These effects can negatively impact aquatic habitat; however, it is possible to mitigate their influence with the implementation of certain storm-proofing techniques. This was the goal of a project in 2014-2016 to assess potential impact of road-related sediment delivery in the Upper Napa River watershed. The Assessment of roughly 85.5 miles of road identified over 21,725 cubic yards of sediment from entering the stream system over the next 2 decades.

Quick facts:

  • Significance: Paved and unpaved roads owned by County and private owners were assessed for their contribution of sediment to the stream system. Road-related sediment delivery contributes significantly to degradation of aquatic habitat and water quality. Assessment includes treatment prescriptions as well as prioritization of treatments according to ecological impact and treatment costs
  • Where: Ritchey Creek, Mill Creek, York Creek, Sulphur Creek, and Bale Slough subwatersheds
  • Results: 332 sites and approximately 37.4 mi of road/avenue surfaces were identified as having potential to deliver sediment to stream systems. This assessment identified treatments at 300 sites which could prevent approximately 10,000 yd3 of sediment delivery. Further, we found that treating 34.4 mi of connected road/avenue lengths could prevent approximately 12,000 yd3 of fine sediment from delivering to the stream system over the next decade. 
  • Funds: California Department of Fish and Wildlife, County of Napa, Napa County RCD
  • Partners: RCD & Pacific Watershed Associates