TMDL Studies
North River Watershed
The approved TMDL final report is available for download at the DEQ website.
The North River watershed (VAV-B16R, VAV-B17R, VAV-B23R, 523,298 acres) is located in Rockingham and Augusta Counties, Virginia, encompassing the cities of Harrisonburg and Staunton (See figure below). North River flows east, merges with South River, and discharges into the South Fork of the Shenandoah River (USGS Hydrologic Unit Code 02070005). The South Fork of the Shenandoah River joins with the North Fork of the Shenandoah River to form the Shenandoah River; the Shenandoah River flows into the Potomac River; the Potomac River discharges into the Chesapeake Bay. The North River watershed includes the Beaver Creek watershed. Water quality samples collected at three stations in the North River watershed during the 2004 assessment period violated the instantaneous water quality standard for bacteria 29, 33, and 37% of the time.
Location of the North River Watershed.
There are sixteen small (1,000 gpd) and two larger point sources permitted to discharge bacteria in the North River watershed; however, the majority of the bacteria load originates from nonpoint sources. The nonpoint sources of bacteria are mainly agricultural and include land-applied animal waste and manure deposited on pastures by livestock. A significant bacteria load comes from cattle and wildlife directly depositing feces in streams. Forested area is the largest land use in the watershed at 49% of the total watershed area, followed by pasture at 43%.
The HSPF model was used to model hydrology and water quality. The hydrology component of the model was calibrated to one flow gage located midway through the model; the water quality portion of the model was calibrated to three monitoring stations located throughout the watershed. The HSPF model was then used to generate allocation scenarios for North River.
Contributions from various sources in the North River watershed were represented in HSPF to establish the existing conditions for a representative 5-year period that included both low and high-flow conditions. Meteorological data from 1988-1992 were paired with bacterial loading and land use data for existing conditions to establish this baseline scenario. Results of the calibrated HSPF model predict that an estimated 91% of the E. coli in the mean daily E. coli concentration at the watershed outlet currently comes from areas covered by a previously developed TMDL. Of the remaining 9% of the mean daily E. coli concentration, 51% comes from upland contributions of cattle, wildlife, humans, and pets; 23% from wildlife directly depositing in the streams; 19% from cattle directly depositing in the stream; 5% from interflow and groundwater; and 3% from straight pipes directly discharging in the stream. Simulated bacteria concentrations exceeded the calendar-month geometric mean water quality standard 63% of the time at the watershed outlet.
A stressor analysis was also completed for North River to change its impairment category. Analysis of the available data showed that, in similar fashion to the bacteria TMDL, most of the benthic stressors were coming from watersheds for which benthic TMDLs had already been completed. We put together a document that supported the reclassification of North River from category 5A, impaired and requiring a TMDL, to category 4A, impaired but not needing a TMDL because a TMDL to address the pollution is already in place.
