People, Land and Water at the
Headwaters of the
Rappahannock River Basin

3 What factors can we use to assess the health and protection of our watersheds?

The quality of water in the streams is a reflection of the health of the surrounding watershed.  Nearly every subwatershed in the County drains to one of four river segments that have been designated as “impaired” by the Virginia Department of Environmental Quality. The water in those river segments has exceeded Federal standards for levels of certain bacteria.  High bacteria levels are an indicator of other types of contamination such as nutrients and sediments. However, subwatersheds vary in the extent to which they contribute to contamination of streams.

Many factors contribute to the health and protection of watersheds – from the ways in which individual landowners use and manage their lands, to naturally-occurring topography, soils, and vegetation, to public policies and other legal and regulatory tools.  The following are the six factors we used to assess and compare the extent to which subwatersheds within and adjacent to this County are “protected”, within the context of the larger natural and human and policy factors.

3.1 Shenandoah National Park (SNP)

The SNP provides permanent Federal government protection of 31,700 forested acres within the county’s land area – about 18.5 percent.  This provides the highest level of protection available to land in this county, both in terms of legal protection and forest land cover.  See Map 2: Percent of Land in Shenandoah National Park.

3.2 Conservation Easements

Easements help to protect against subdivision of land parcels and the fragmentation of forest land that typically results from subdivision. Over 19 percent of privately owned land in the County is under permanent conservation easement with the Virginia Outdoors Foundation. Subwatersheds in the County vary in terms of the percentage of land in easement. Several local organizations, including the County government, Rappahannock County Conservation Alliance (RCCA), the Krebser Fund, and Piedmont Environmental Council (PEC), have proactive programs to encourage conservation and farmland preservation through easement donation and purchase of development rights.  See Map 3: Percentage of Land in VOF Easement.

3.3 Land Cover

“Land cover” is a way of categorizing what is covering the land. Land cover dramatically affects what happens to raindrops when they hit the earth.  Major categories include: water; developed (e.g asphalt, buildings); barren (e.g bare soil, forest clearcuts); forested upland; shrubland; non-natural woody (e.g. vineyards); herbaceous upland (e.g. upland grasses); planted/cultivated (e.g. pasture, hay, lawns); wetlands.[8] Nearly 69 percent of the County’s land cover is deciduous, mixed, or coniferous forest.  Pasture, hay, and crops account for nearly 30 percent of land cover, and less than one percent of land cover is “developed” low density residential or commercial.  We used the National Land Cover Database[9] to assess land cover, in combination with aerial photos.  See Map 4: National Land Cover Data and Map 5: Percentage of Land in Forest Cover.

3.4 Forested Stream Buffers.

Scientific research has shown that the vegetation in a 100-foot buffer area along the streams serves many important functions for protecting the quality of surface water and groundwater, recharging groundwater, and providing a corridor of habitat protection for wildlife.[10] According to the Rappahannock Tributary Strategy, “The 100-foot buffer area … is deemed to achieve at least 75 percent reduction of sediments and a 40 percent reduction of nutrients.”  This is especially the case in Rappahannock County, where we have many miles of small streams, which are more vulnerable than larger rivers downstream from us. According to a recent review of the scientific literature on the subject of riparian buffers, “Substantial evidence exists to emphasize the importance of maintaining riparian zones in upstream headwaters or backwaters regions, which can be areas of high nitrogen removal.  For a 10th order stream[11], up to 90% of the cumulative stream length consists of ephemeral, first, and second order streams (NRC 2002). Thus, the largest proportion of annual stream nutrient load enters watersheds from the headwaters where the capacity to remove nitrogen is great, while less additional nitrogen processing occurs in the main channels of higher order streams “(Richardson et al. 2004, Bernot and Dodds 2005).[12]

County-wide, 62 percent of the 100-foot stream buffer area is forested. Among the 26 subwatersheds in the County, the percentage of 100-foot riparian buffer area that is forested ranges from 26 percent in White Walnut Run to 99 percent in the Upper North Fork.  We used the NLCD to quantify stream buffer vegetation, in combination with aerial photos and field observations.  See Map 6: Stream Buffer Vegetation, and Map 7: Percentage of Stream Buffer Area Forested.  Also see maps 25, 31 and 39 for stream buffer vegetation in White Walnut Run, Lower Rush, and Upper Battle Run.

3.5 Zoning

Overall for the County, more than 97 percent of the land area is zoned Agricultural or Conservation Zone. These zones protect against intensive development, allowing for a maximum of one new dwelling per 25 acres. Map 8 shows the zoning for the County and Map 9 shows the percentage of each subwatershed’s area that is zoned Conservation or Agricultural.

3.6 Erodible Soils on Non-forested Land

Using the Official Soil Survey for Rappahannock County by the Natural Resource Conservation Service (NRCS), we assessed a subwatershed’s vulnerability to erosion by a combination of soil type, slope and land cover.  In the Soil Survey interpretive tables the Erosion Factor called “Kw,” estimates erosion based on the texture (with rock fragments) of the soil type.  Then we looked at the slope classes of the soil map. Soils on steeper slopes have greater potential for erosion. A GIS layer was created combining the Kw factor, the slope classes along with the vegetative cover of the county, producing an erodibility potential map. Since forested areas represent the best management to protect the land from erosion, the maps focus on land cover other than forests. See maps 10 and 11 for the results of the erodibility analysis.