Taking Eroding Property Lines to the Bank: Creek Bank Stabilization Approaches
January 9th, 2008 by bruce_richmondIf a creek is eroding your property, what you do to stabilize the banks can have significant unintended consequenses to your property and others downstream.
Some typical guidelines for bank stabilization approaches include:
- Do not reduce the width of the creek, as this will almost certainly cause erosion both in the bed and downstream.
- Do not reduce the length of the creek (by straightening a bend for example). This action will steepen the bed profile, increasing erosion locally, and on the next bend downstream.
- Where possible, combine grading activities to flatten bank angle and use a mixture of biotechnical methods such as brush mats and willow planting.
- Where rock is required, place rock (mechanically or by hand) rather than by dumping. Dumped rock generally forms an unsustainably steep angle, which eventually collapses and rolls rock into the creek.
- Limit the upper vertical extent of placed rock for structural and erosion protection requirements on the bank slope to maximize plantable areas. Key rock into the bed several feet to prevent undercutting.
- Utilize rock sizes based on calculations of flow force and resistance.
- Integrate native trees such as willow and alder with the engineered rock bank protection.
- Integrate native trees such as willow and alder with the engineered rock bank protection. Integrated planting has several benefits:
- Roots anchor the soil beneath the rock, providing a living support system that increases the strength of the bank protection over time
- Vegetation slows water velocities, reducing erosion both at the bank and downstream, and
- Trees provide shaded cover for the creek, improving habitat conditions.
These “conceptual restoration approaches” come directly from Portola Valley’s Citizens’ Guide to Creek-Side Property Protection. The guide was created as a tool for the Town and its residents to use in guiding design, permitting, and construction of bank stabilization and revegetation efforts along Corte Madera Creek.
I know that Palo Alto and Menlo Park are looking to this an other guides for stabilizing the banks of San Francisquito Creek. It will not surprise me if other local like-minded towns (Woodside, Los Altos Hills, and Los Gatos, at least) move in this direction, too, if they can get it through the creeky legislative system. (Sorry, I had to work that in somewhere.)
