Article reposted courtesy of The Watershed Alliance of Adams County
The word stormwater may create images of swollen rivers and flooded streets, but this term actually describes any amount of rainwater or melted snow that runs off from a developed or natural land area. A potential flood may be the most obvious reason to be concerned about stormwater, but even small amounts of stormwater impact our water quality. When water flows across a surface, it carries with it any substance that is on that surface, from dirt on your roof to the oil spot on your driveway to litter and pet waste on the street. These substances can pollute your drinking water, ruin your favorite fishing hole, or spoil your summer vacation at the beach or lake.
Highly developed areas generally have a greater amount of stormwater runoff than rural areas due to a higher percentage of impervious surfaces. Impervious surfaces do not absorb water. Roofs, roads, sidewalks, and parking lots are examples of impervious surfaces. Increased runoff can also occur in areas where the soil is compacted, vegetation is absent, or existing plants have shallow roots, such as sports fields and the lawn surrounding a home or business.
Agricultural and construction sites are also susceptible to increased amounts of runoff when plowing or excavating creates large areas of bare soil. The washing away of soil is called erosion. On a farm, erosion reduces the productivity of the land and carries away the residues of pesticides, herbicides, and fertilizers which may have been applied to previous crops. In a construction zone, erosion can transport pollutants from machinery, construction materials, or remnants from previous land uses. A large amount of sediment, or soil particles in water, creates muddy streams and rivers which are unhealthy for humans and wildlife. When the soil eventually settles to the bottom of a water body, the pollutants may settle with it, potentially contaminating the water body for many years.
The destination of a drop of water after it reaches the ground depends upon several factors. One of these factors is the surface of the land, also known as topography. Since water flows by gravity, stormwater runoff will make its way downhill to the lowest point in the landscape. Usually, this low point contains a body of water such as a wetland, stream, or pond/lake. The entire area of land which drains to a certain low point is called a watershed. The quality of the water in a watershed will depend upon all the ways the land is currently or was previously used throughout the entire watershed. Since small watersheds often drain into larger watersheds, activities happening hundreds of miles away may also impact water quality in a certain area. The Chesapeake Bay, which has a 64,000-square-mile watershed, is a good example.
The type and structure of the rocks and soil which make up the earth under our feet also determines the amount of water which is either absorbed or runs off. When precipitation can be absorbed where it falls, not only is the amount of runoff reduced but water quality and water supply are improved. These improvements are the result of trees, vegetation, soil, and spaces between the underlying rock acting as filters to remove some of the pollutants which rain and snow pick up from both the air and the ground. The absorption of water into the ground also provides water storage, and thus helps maintain our water supply.
Healthy communities require high quality water in adequate amounts. After a mostly dry summer and fall, Adams County remains in a moderate drought status. Although Pennsylvania is fortunate to be a water rich state, changing rainfall patterns means that an awareness of how to keep the precipitation we receive so that is available for us to use is important. In the next couple of months, this column will share ideas for reducing the amount of water that is lost to run off and increasing the amount that can be captured to meet our water needs.
Karen Kaslow
Watershed Alliance of Adams County Board Member
Master Watershed Steward Coordinator, Penn State Extension
