August 1996
A properly planted landscape is the best protection against erosion, a serious urban/suburban problem that has significant impact on water quality. Most of us don't think of soil as a pollutant. In fact, sediment deposited by storm runoff is a major source of surface water pollution. Urban runoff, including soil erosion, has been identified as the primary pollution source that must be controlled if the Chesapeake Bay is to survive. All of us in Virginia live in a watershed. If you have the responsibility for the management of any land, be it a small, urban, front yard or a hundred acres, you have the ability to reduce such nonpoint-source pollution by reducing soil erosion on your property.
Soil erosion occurs when soil particles are carried off by water or wind and deposited somewhere else, such as in a stream or at the bottom of a bay. Often soil particles are carried by runoff, water that does not soak into the ground, but instead flows over the surface and runs to another area, such as into storm drains, streams, or lakes. In addition to soil sediment, runoff can wash fertilizer and other pollutants along with it. Sediment makes up most of the pollutant carried by runoff, however, and most of the phosphate and pesticides entering Virginia's waters are attached to these soil particles. Erosion in the home landscape also creates unsightly bare areas and deposits mud and dust on driveways and walkways that is then tracked into the house.
Erosion begins when rain or irrigation water loosens soil particles. When there is too much water to soak into the soil, it fills surface depressions and begins to flow. With enough speed, this surface runoff carries away the loosened soil. Runoff from roofs and paved areas can contribute to erosion by directing large amounts of water in a short time period to nearby areas that are unable to absorb it quickly enough.
To reduce erosion, the soil surface must be protected from rain. For example, plant cover, such as that provided by a well-maintained lawn or other groundcover, or a combination of mulch and plants, such as trees with mulch covering any bare soil below, will effectively protect the soil surface from rain. Plant roots also help reduce erosion by holding soil in place. In some cases,it will also be necessary to control or redirect runoff or take other measures to effectively control erosion.
Bare soil is the most obvious source of erosion. By mulching or planting bare soil areas, erosion can be reduced. For example, consider seeding your vegetable plot with a cover crop, such as winter rye or hairy vetch for the winter. Promptly seed any bare patches in your lawn and mulch around trees and shrubs. Other more subtle indications that erosion is occurring on your property include tree roots, small stones, or rocks becoming exposed; small rills or gullies beginning to show; soil splashes on windows and outside walls; stream channels widening or deepening; or sediment collecting in low areas or on pavement.
Practicing good landscaping techniques will help protect water quality and give you the added benefit of healthier plants and a more attractive yard. Your Virginia Cooperative Extension agent can provide you with information on landscaping techniques that reduce erosion and protect the environment.
(Prepared by Susan Day, Research Associate, Consumer Horticulture, Virginia Tech, Blacksburg, VA 24061-0327.)