Erosion is the movement of soil through wind, water, or gravity. Most local erosion occurs because of water, and is a natural process in the Tualatin River watershed because streams are constantly changing. A healthy stream has access to its floodplain, native and diverse plants covering its banks, healthy and connected wetlands, and natural formations, such as meanders or fallen trees. These formations slow water down and reduce erosion.
Managing Erosion
Depending on the extent of the erosion, it can be reduced by slowing the water and holding the soil with plants. This can be accomplished by removing invasive plants that generally have shallow root structures, and planting diverse, deep-rooted native plants that are adapted to our local conditions along streams and out into the floodplain. In addition, allowing wood, branches, or rocks to stay in the stream lets them slow the water; and allowing beaver dams to form will naturally slow water and capture the sediment.
Only a professional can determine what can be done to stop or slow severe erosion, but if you are near a stream and see erosion, consider these factors:
Plants: Is there a wide strip of healthy native grasses, shrubs, and trees with different root depths bordering the stream, or is it bare dirt, lawn, or other impervious surface next to the stream? If there’s nothing to hold the soil down at multiple depths, erosion will happen faster.
Slope: Does the stream bank gradually slope down to the water, or is it a steep drop, with visible tree roots exposed? Is water moving under the stream bank? If so, more erosion is likely to occur. Contact a professional about options.
