Natural Resources & Sustainability

Watershed: More than an Event

by Adam Downing
November 2008

Without it we die. Too much and it can be destructive. Not enough of it and we struggle.

While water wars in the west are commonplace, the Eastern half of the United States has historically been a water utopia. Early Europeans spoke of the plentiful, clean, and available water. It has usually been this way in the mid-west and eastern United States, but it may not necessarily stay this way.

Increased populations, technologies, and higher per-capita demands have placed increased demands on water resources. If this increased demand, coupled with continued land-use changes, fighting over water may be the headlines of tomorrow. Watershed management can help us avoid this morose end.

According to “The Dictionary of Forestry” (Society of American Foresters, 1998), a watershed is “a region or land area drained by a single stream, river, or drainage network.” Every piece of land is part of a larger geographically defined area called a watershed. At the smallest unit, a watershed may drain into a small creek that sometimes has water and sometimes does not. This is an “intermittent stream”. In most cases, many intermittent streams empty into a perennial stream (containing water year around). This perennial stream would be a larger watershed unit. An even larger watershed would be drained by a river into which many perennial streams, and even more intermittent streams empty.

A watershed is simply an area that has one thing in common… the point to which it drains. An area within a given watershed may include parking lots, buildings, roads, sub-divisions, agricultural fields, forests or any other land use. The value of a watershed is directly related to land uses. As a rule of thumb, the more intensely a certain area is used, the more it limits the watershed’s ability to produce clean water. For example, water exiting a parking lot typically carries many pollutants left behind by automobiles. An agricultural field, depending on chosen management practices, may also contribute pollutants to waterways in the form of fertilizers (if over applied) or soil (if conventional tillage is practiced up to or near stream edges. Lawns are another serious source of water pollution resulting from over fertilization and little or no buffer left between a lawn and a creek. If these pollutants are close to a body of water, even a simple stream, water quality is diminished.

Diminished water quality costs us all. Municipalities collecting water from an unhealthy watershed are faced with costly processes to make water potable again. Fish and other aquatic organisms dependent on water (aquatic) habitats suffer also. As some of these natural ecosystem components are lost or damaged, the problem compounds.

Ecosystems dominated by natural habitats clean water as part of their natural processes. When these natural processes are lost or impaired, we are forced to make costly investments that would otherwise be provided free.

Forests are the most productive element of a watershed. A typical forest, hydrologically speaking, is a filter and a sponge. As rain falls on a forest, the leaf litter layer on the forest floor works to soak up the water, hold it in place so it doesn’t run off and slowly (maybe over the course of many days) release some of that water to recharge ground and surface water supplies. As this water is slowly released, soil particles, organisms and organic matter filters out most impurities. Water coming from forested watersheds is the cleanest water available, and this without any human inputs! Additionally, ground water and stream levels are more constant from a forested watershed. This also means the risk of catastrophic flooding downstream from heavily forested watershed is less.

While watersheds under the complete cover of forests are best for water quality and quantity, they are not always feasible, especially on the larger scale. However, some of the benefits forests provide over a whole watershed can be realized on a small but important part of the watershed as well.

“Riparian Buffers” – Th Hub of a Watershed

An important element of a healthy watershed lies next to the water. Certain plant communities are very effective at “buffering” the potential negatives of adjoining land uses. Some riparian areas are an abrupt change from a stream to a lawn or driveway. These are a liability in terms of water quality and even quantity.

Riparian buffers are riparian areas functioning to buffer water bodies from potential pollutants. Pollutants such as sediment or nutrients headed toward a body of water with an effective buffer in place are trapped and stored in plant tissue or absorbed onto soil particles or modified by soil organisms.

So what does a riparian buffer look like?

Most buffers are low maintenance areas, linear in shape and a certain width beyond water edge. There is some controversy as to what kind of vegetation community is best. Grass, shrubs and trees can all function as a buffer. In general, a mixture of these plant communities, much like a gradual edge for wildlife is good.

How wide a buffer should be is one of the first questions that needs to be asked. In many instances of small acreage owners, the width may be limited to space available. In general, the minimum width for a buffer is around 20 feet to meet bank stabilization, nutrient removal, flood control, and wildlife habitat goals. The wider the better, all the way up to 300 feet. Some of the factors in to consider is soil type and stream size. Finer soils and larger streams call for wider buffers. If you are not able to provide as wide a buffer as might be called for, remember that something is better than nothing.

In some cases, establishing a buffer involves nothing more than to stop mowing. In other cases, you may want to plant trees, shrubs and grasses native to the site. If you have cases of severe “cutting under” (i.e., where the stream is cutting under the bank causing stream bank collapse) it may be prudent to initially stabilize the bank with various materials and methods such as rock riprap or tree & shrub cuttings as live stakes.

In addition to keeping waters clean, forested buffers keep water cool. Cooler waters have higher oxygen contents, healthier macro-invertebrate populations and are more likely to support native fish populations as well. Natural riparian areas in the eastern United States are among the most productive biological systems in the world (Dickson and Warren 1994).

Most of these riparian areas are in the hands of private landowners. If you own land adjacent to water, not only do you hold a unique ecological area, but you also have an opportunity and responsibility to see that the riparian area is well vegetated with a variety of plants. For more information on riparian forest buffers, request the “Understanding the Science Behind Riparian Forest Buffers” series from your Virginia Cooperative Extension office or access them online at: http://www.ext.vt.edu/resources/ and clicking on the “Forestry, Fisheries & Wildlife” button.