222 N Havana
Spokane WA 99202
C181 SOIL EROSION
New building and development causes significant site damage, often resulting in soil erosion. Eroded
soil causes many problems for homeowners and public facilities. Soil erosion carries away valuable
topsoil containing critical nutrients, as well as excess fertilizers and pesticides. This traveling soil
eventually reaches rivers and lakes. In addition, eroded soil clogs storm water facilities such as sewers,
infiltration swales and drywells. The siltation of these facilities by eroded soil costs taxpayers tens of
thousands of dollars in additional maintenance.
The susceptibility of soil to erosion depends on: Soil cover
- Its presence and form. Soil types
- Sandy and silty soils are the most erosion-prone. Slope of the land
- Moderate to steeply sloping areas are most likely to erode.
Soil erosion around homesites, particularly new ones, can have serious consequences. However, it can
be prevented in a number of convenient and potentially attractive ways. The first step is to identify the
source of the water causing the damage. Redirect the water coming from gutter downspouts away from
slopes with splashblocks. Place the splashblocks so that water is directed into an area where it is
allowed to slowly dissipate into a shrub border or gravel area.
Slowing the flow of water allows it to soak into the soil rather than rushing over the surface. Disguise
splashblocks and gravel areas with groundcovers or other vegetation. The plants will benefit from the
additional water and will eventually cover the gravel.
Directing water from downspouts or other sources can provide interesting opportunities for landscaping.
One way to control water is by installing area drains connected to pipes to move the water to
underground sumps/drywells or areas that can handle the flow of water without damage. Always strive
to control water on your property rather than sending it onto someone else’s.
Cooperating Agencies: Washington State University, U.S. Department of Agriculture, and Spokane County.
WSU Extension programs and policies are consistent with federal and state laws and regulation on
nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation.
Evidence of noncompliance may be reported through your local Extension office.
Another way is to construct a dry stream. Fill a low swale with 1-3 inch diameter washed river rock for
directing storm water to plants or areas that need more water. Slope the swale away from foundations or
basements to areas that can handle the runoff.
To minimize erosion on a steep slope it is best to create terraces. Make terraces by leveling out the soil
every 2 feet of elevation change. Terraces hold the water, reduce its velocity and give plants a better
chance to establish a roothold. Planting groundcovers and drought tolerant plants in the terraces protects
the slope while not requiring additional water after establishment.
Bare soil exposed to rain is a primary cause of erosion. Replant vegetation as soon as possible where
practical. Choose plant materials that are suited for the site. County extension offices and conservation
districts can help you make these choices. Straw, grass clippings, wood chips and commercial erosion
control materials are good surface mulches and will reduce the amount of erosion that occurs. One
distributor of commercial erosion control materials such as woven fabrics, plastic or straw is AM
Leonard, Inc. Call 1-800-543-8955 for a catalog. Other companies are listed in the telephone directory
under "Erosion Control." Straw is available locally from farmers (look for classified ads in the
newspapers) or some farm and seed supply stores.
In summary, the key points are: control the source, protect the soil, redirect water flow on slopes, and
revegetate bare soil with the right plants. Preventing erosion will prevent damage to landscaping,
property and storm water facilities.
Compiled by Mike Terrell. For more information, contact Master Gardeners at (509) 477-2181.
Revised January 2005