TMDL Products: Numeric targets for habitat attributes and related sediment loading based on regionwide effort.
Source Analysis and Allocation:
The potential significant sources include: shallow landslides, deep seated landslides, agricultural activities (viticulture and cattle grazing), road building and maintenance, urban development, streambank failure and streambed degradation.
Some sediment load and streamflow data are available in the Napa River watershed .
Preliminary investigation of streambank degradation was conducted as part of the U.S. Army Corps of Engineers Flood Management Plan (1991)
Erosion Control Plans for new viticulture operations installed since 1991 are on file with the Napa County Planning Department. The County has contracted with a consultant to review these plans and produce estimates of the extent and acreage of new vineyard development. However, this analysis will not include estimates of vineyard erosion.
USGS has one operating gauging station on the Napa River and several historical stations. Currently, the Napa County RCD is working with Professor Luna Leopold (Emeritus, UCB) to implement a citizen monitoring program for rainfall and runoff.
No local sediment budget studies are known. Some regional sediment budget data (Lehre, 1982; Reneau, 1988) and regional sedimentation data (USDA, 1975; Brown and Jackson, 1973; Larsen and Sidle, 1980) are available. These data will assist in developing the sediment budgets, however they are insufficient for distinguishing major sediment sources and rates in the Napa River Watershed to a level of accuracy needed for management and regulatory decisions.
Conduct detailed land use and ecological historical analysis leading to the development of a historical reference state model for the Napa River Watershed;
Conduct rapid sediment budgets: a) type and location of the major natural and management-related sources of sediment; b) approximate amount of sediment contributed by each type of source; c) grain-size distribution of sediment contributed from each source; d) the approximate volume and grain sizes of sediment in storage along streams; and e) the approximate transport rate of sediment through stream channels. This will be done using intensive (field evaluation) and extensive ( i.e., aerial photos, GIS/DTM based shallow landslide modeling) methods;
Develop and use a calibrated erosion control model to evaluate different land use scenarios and BMP effectiveness, with an emphasis on vineyards;
Develop Hydrologic Budget to determine if hydrologic changes in watershed are affecting streambank and streambed stability (this information will also be used in subsequent nutrient TMDL);
Conduct Riparian Zone Analysis and modeling to determine affect of riparian zone on stream habitat and water quality;
Synthesize results of watershed analysis to establish linkages between management practices, sediment production and delivery, and instream habitat conditions needed for healthy populations of steelhead and other target species, and water supply. Establishing these linkages will rely in part, on data developed for the proposed regionwide numeric targets study. Once the source analysis and numeric targets have been developed, there will be a scientific basis for development of an allocation of responsibility.
Review existing potential BMPs and develop additional BMPs for each source category, as necessary, to obtain numeric targets. GIS/DTM, reference state and erosion control models developed in above tasks will be used to explore the likely effects of different management scenarios.