Streamside Erosion

Hundreds of creeks, streams, and rivers form the network which drains the Puget Sound basin. All urban streams, and many rural ones, receive runoff from lawns, fields, highways or parking lots. Sediments from eroding streambanks and changes in land use can smother aquatic life, clog fish gills, and cut off needed light to underwater plants. How we manage the land around the streams and creeks in our neighborhood helps determine the quality and quantity of water flowing in the Sound.

Streamside areas are important to life in and around the stream. Trees and low bushes shade the stream and help maintain water temperatures that are suitable for fish while protecting streambanks from erosion. Streams are dynamic systems. Erosion and siltation are natural processes which can’t be totally eliminated, nor should they be, but large scale removal of natural ground covers does impose an unnecessarily heavy risk of excessive erosion and siltation.

Tiny ditches belong to water networks that provide critical spawning and rearing grounds for salmon, trout, and other aquatic life. They also provide a constant supply of water to larger downstream livers, lakes and the Puget Sound.

We can all play a role in minimizing streambank erosion by taking a few simple steps to improve stream quality. The most important control measure is to make sure your stream is surrounded by plenty of trees. As much as possible, leave stream banks and channels in their natural, unaltered condition. Trees and shrubs are important to both the stability of the streambank and to the health of the stream itself. Trees should not be cleared away, their roots are nature’s best purifying system, removing nutrients and excessive sediments harmful to stream and Sound ecology.

Before you plant trees on the banks of your neighborhood creek, call the Department of Fisheries habitat office at (206) 753- 6550 for information. Any work done within the ordinary high-water line requires a hydraulic permit from the Department of Fisheries and/or the Department of Wildlife (206) 753-3318.

When clearing land near a stream, leave a vegetation buffer strip along the stream. The width of the strip depends on the slope of the land and the existing vegetation. Your local soil conservation district can provide you with assistance on your site.

Watering and feeding areas for farm animals and horses should be kept away from streams. Because trampling by livestock increases the potential for streambank erosion, fencing or hedges should be used to restrict livestock movement. Fencing and hedges can also be used to restrict vehicle or foot traffic.

Remove trash, litter, and obstructions from your streambed. On the other hand, leaning trees, large snags, and other obstructions on the streambank may help stabilize the bank and benefit fish habitat. As with tree planting within the high-water mark, a Hydraulic Project Approval permit must be obtained before removing obstructions.

In cases where streambank erosion is severe, vegetation alone will not be adequate and structural measures may be required. Streambank restoration requires the assistance of a trained professional. Contact your local soil conservation district office for guidance before attempting any structural work to protect your streambank. In your planning, recognize that streams can be expected to naturally shift their banks, sometimes gradually, sometimes abruptly.

Waterfront Erosion Control