A watershed is simply the area into which water is shed from the surrounding higher areas. You may consider the watershed area where you live to be the surrounding area that sheds water into a stream near you, or you may consider the larger watershed of a stream system that drains to a larger river.
Taking the larger view, the streams in the Elkins, Belington and Philippi areas drain into the Tygart Valley River, which drains into the Monongahela River at Fairmont. In other parts of West Virginia, streams drain into the Potomac River, which drains into the Chesapeake Bay. Our local, small watersheds are connected to larger watersheds and have a great impact on those larger regions. For example, the U.S. Environmental Protection Agency recently approved a Watershed Implementation Plan for Virginia, which established limits on levels of nitrogen, phosphorous and sediment in streams that are in the Chesapeake Bay watershed. The EPA did not approve West Virginia's Watershed Implementation Plan and is mandating specific measures to control these contaminants in West Virginia's streams that are within the Chesapeake Bay watershed.
How can the control of contaminants in West Virginia's streams have such a regional impact? The answer is that the contaminants have a cumulative impact: Small amounts of contaminants accumulate as the contaminated streams merge into larger streams or rivers, transporting the contaminants to these larger watershed regions. Concerning sediment as a cumulative contaminant, it is important to understand that as development increases, the result is an increase in surface runoff into streams. The resulting greater amount of water causes increased flow within the streams and rivers, with a heightened threat of flooding and with greater erosion of the stream banks. The greater erosion causes more and more sediment to be released into the streams and rivers, with the cumulative impact of too much sediment in the larger, receiving watershed. By this process, sediment becomes a contaminant because too much sediment smothers the stream life, degrading the streams so there is not enough food for fish and other organisms.
Surface runoff from rainfall varies according to the type of ground cover. Forested areas have the least amount of runoff because the trees intercept the rain, allowing it to gently fall to the ground such that a large percentage of the water is absorbed, recharging groundwater. Surface runoff is greater over grassed areas and gravel roads than in forests. The greatest amount of surface runoff is over paved roads and roofs. These areas are considered impervious, meaning that the water cannot penetrate them and simply flows over them.
The amount or discharge of surface water that flows into a stream or river within a particular watershed can be calculated. These calculations take into account the type of ground cover in order to determine how much rain may be absorbed into the ground and how much flows over the ground surface. The Center for Watershed Protection provides documents, used by the EPA, demonstrating that watersheds with 10 percent or greater impervious areas result in degradation to the watershed. This percentage provides a management tool for development.
In order to protect stream quality within a watershed, the developed areas within the watershed should not exceed 10 percent impervious areas. In the same way, surface runoff discharge from ground covers that are not impervious can be calculated to determine the amount of discharge that is equivalent to that of a 10 percent impervious area in the watershed. The 10 percent impervious area discharge can become a threshold amount for discharge to be used as a management tool to protect streams within specific watersheds.
Currently, the only measurement of discharge from developed areas into the watershed is controlled by the National Pollution Discharge Elimination System program, as required by the Clean Water Act, with authorization given to the West Virginia Department of Environmental Protection to issue permits. During construction activities, discharge of stormwater flow from the project area is calculated to determine the size of the drainage pipe that directs the water into a watershed. However, there is no requirement to evaluate the impact of this directed flow on the receiving stream. Directed discharge through the drainage pipe or through several drainage pipes into a single receiving stream will have greater impact on the stream that surface flow from the entire watershed.
The directed discharge will cause increased stream flow and stream bank erosion, resulting in more sediment polluting the stream. Sediment will continue to be a cumulative pollutant in all streams until there is a process for evaluating the impact of directed stormwater discharge into streams within specific watersheds. The management tools are available but are not being required for evaluation of negative, cumulative contamination impacts to our streams.
(Pamela C. Dodds is a local resident and is a registered professional geologist with expertise in hydrogeology. She has a bachelor's degree in geology and a doctoral degree in marine geology, as well as a Credential in ground water science. Dr. Dodds is also certified by the WVDNR as a Master Naturalist and participates as a stream monitor in the WVDEP's Save Our Streams program.)