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
Use alternatives to impervious paved surfaces for patios, walkways,
and driveways. Gravel, brick, stone, and decking are permeable
materials that allow water to infiltrate the soil.
Maintain a vegetated buffer zone between the creek bank and
your yard or sheds, patios and other structures on your property. A
robust buffer zone will decrease property loss and damage from
flooding and erosion. Check with the local building authority for
permits and information on legal setback zones.
Replant barren slopes on your property as quickly as possible.
Even areas that are not located next to the creek can increase the
sediment load to the creek. Don’t use tires, concrete rubble,
appliances, or other debris to cover these areas.
Divert roof runoff to open landscaped areas (away from the creek).
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:
Check your creek regularly, especially during storm events, and learn
to spot problems. Some sediment and foam is natural. Excessive
sediment or colored or oily foam indicate problems such as erosion
or pollution upstream.
Try to identify the cause of the trouble. If the source of a particular
problem occurs upstream, your restoration efforts may be defeated
unless that problem is addressed.
Consider least invasive options first; creeks are resilient and may not
need extensive (or expensive) restoration techniques.
Consider techniques that use living materials, such as willows and
native vegetation. Hard structures such as rock and concrete-lined
channels provide no fish or wildlife habitat and tend to increase the
flow speed.
Never use tires, concrete rubble, or appliances to repair erosion
problems. These items can be washed away by water and cause
further damage. These items may also contain materials that are toxic
to creek life.
Most creek repairs need to be engineered or designed. All creek
repair will require a Streambed Alteration Agreement from the
California Department of Fish and Game and permits from Alameda
County Public Works Agency, U.S. Army Corps of Engineers, and the
Regional Water Quality Control Board. Contact the Alameda
Countywide Clean Water Program or the Alameda County
Conservation Partnership (see Who Do I Call.
Source:Creek Care: A Guide for Residents in the San Lorenzo Creek Watershed (Alameda County Public Works Agency)
