Creeks in urban and suburban areas often suffer from extensive erosion due to the torrents of water that pour off paved surfaces, rooftops and compacted soil when it rains. Nothing can be done about the sources of water from off-site, but a stream bank can be reinforced to prevent further erosion. In addition, all water draining to the creek from on-site has to do so without adding to the problem.
Rip-rap are small, inexpensive boulders that can be spread along stream banks to keep them from eroding. They typically range from 4 to 12 inches in size and are effective as a quick fix if erosion is beginning, though they have low aesthetic value. Rip-rap are also useful where pipes from gutters or other drainage systems on the property outlet into a creek. An apron of rip-rap created around the end of such a pipe dissipates the velocity of water exiting the pipe reducing its erosive potential.
Gabions are wire cages filled with rip-rap and used as informal retaining walls to stabilize stream banks. They are built in roughly the proportions of a cinder block but are much larger; heavy-wire fencing knit with steel cable contains the rocks. Gabions are typically about 2 feet tall and deep and 4 feet wide. Just like a block wall, they can be built in courses with each row offset from the one below. A flat base needs to be excavated for the first row along the edge of a creek. Gabion walls can be built by any motivated homeowner, but they are a very laborious process.
In nature, vegetation prevents a stream bank from eroding. Once erosion begins, however, plants need extra help to become re-established. After rip-rap or gabions have been installed, the area can be planted with locally adapted riparian species. They may include ornamental trees such as weeping willow, also called Babylon weeping willow (Salix babylonica), and river birch (Betula nigra), which are hardy in U.S. Department of Agriculture (USDA) plant hardiness zones 6 through 8 and 4 through 9, respectively. Moisture-loving ground-covers, such as river oats (Chasmanthium latifolium) and swamp lily (Crinum americanum), can be used to populate the understory and conceal the rocks' jagged appearance. River oats is hardy in USDA zones 3 through 8, and swamp lily is hardy in USDA zones 7 through 11.
Regulatory Considerations and Professional Help
Any work in a stream bed or riparian area typically requires a permit from local authorities. The area's office of the state environmental protection division is a good place to check. Depending on the work's complexity and the creek's size, there may be such stringent engineering requirements that the work is not feasible without the help of a specialized contractor. Plans may need to be drawn up by an engineer or landscape architect and submitted for approval before any work can begin. The USDA's National Resources Conservation Service, which has regional offices in every part of the country, however, provides free technical support for erosion-control work.
- University of Nebraska-Lincoln Extension: Bioengineering for Hillslope, Streambank and Lakeshore Erosion Control
- Penn State Extension: Controlling Erosion Damage on Streambanks
- Missouri Botanical Garden: Salix Babylonica
- North Carolina State University: Trees -- Betula Nigra
- Walters Gardens Inc.: Chasmanthium Latifolium
- University of Florida IFAS Extension: Crinum Americanum
- Photo Credit Photos.com/Photos.com/Getty Images