Friends of San Lorenzo Creek

Creek Bank Erosion

Soil erosion is a natural process. Some sediment is needed to bring nutrients and mineral materials to aquatic ecosystems, but too much sediment causes problems. Sediment reduces the creek’s ability to carry flood waters by filling in the creek bed. It also fills pools, eliminates shelter and fish spawning habitat, and diminishes food supplies for fish and aquatic insects.

Erosion occurs on creek banks, roads, driveways, bare garden areas, or other areas where soil is not protected from the forces of irrigation water, rainfall, and gravity. When water flows over bare ground, the exposed soil moves downhill and often ends up in a creek.

Common causes of bank failure include over-watering lawns, removal of vegetation, and on-site or upstream alteration of the creek channel.

Minimizing Erosion

Repairing Streambank Erosion

Not all streambank erosion is harmful. Undercut banks and fallen trees provide important habitat for fish and other aquatic animals. Intervention may be necessary if the erosion threatens property, structures, or roads, or if it threatens prime riparian habitat. Consult an erosion expert, such as the Natural Resources Conservation Service to see if your erosion is severe.

Creek bank erosion that is extremely active should be monitored. Bare, vertical, and actively eroding banks are likely to need repair. Less severe problems may not require immediate attention, but treating a problem early may prevent costly fixes later.

Creek systems are complex. Stabilizing creek banks requires knowledge of the creek process and history of the site. When considering repairs:

Source: Creek Care: A Guide for Residents in the San Lorenzo Creek Watershed (Alameda County Public Works Agency)