Different physical structures may be used in stream restoration in order to provide channel stability and in order to provide habitat and other beneficial functions. Some of the typical structures that are used are revetments made of gabions or riprap and woody debris. Each type of structure has benefits and costs that should be considered before installation and some are more appropriate in certain situations than others.
Gabion revetments are used to control stream bank erosion. Gabions are stone filled wire baskets that are placed along stream banks. The typical size of a basked is 3 feet wide by 3 feet tall and the length can vary. They are effective for protecting submerged portions of stream banks. They can be used when the slope cannot be cut back due to buildings or roads. Gabions are freeze and thaw resistant and may not require heavy equipment for installation but they are susceptible to deterioration and can be labor intensive to install (The Ohio Department of Natural Resources).
Riprap revetments can also be used to stabilize stream banks. A riprap revetment is comprised of rocks of varying size and shape placed to protect a stream bank. The rough surface of the rocks allows them to fit together, protecting the bank. The variance in the size and shape of the rocks allows the revetment to absorb the impact of water instead of deflecting the flow of water, which could cause erosion. Riprap revetments may be expensive to put in place and may require heavy machinery to place the rock. Once in place the revetment will provide long term bank protection with relatively low maintenance (The Ohio Department of Natural Resources).
Live fascines can also be used to stabilize banks. The long bundles of live woody vegetation can be buried in a stream bank in shallow trenches. The plant bundles sprout and develop a root system, holding the banks in place. Live fascines are most often used on longer slopes (The Ohio Department of Natural Resources).
Another example of a type of structure used is an energy dissipater. An energy dissipater is any device created to protect the area downstream from erosion by reducing the velocity of the flow. An effectively designed energy dissipater will restore the flow downstream of the dissipater to a condition that is close to the natural flow regime. There are two broad categories of energy dissipaters, those that cause a hydraulic jump and those that are considered to be impact basins (Tennessee Department of Transportation, 2010).
There are many other structures and techniques that are used in the field of stream restoration. The use of riprap is a common technique and there are examples of its use locally in San Diego. Additional structures may serve other purposes such as directing flow or providing habitat. Woody debris, for example can provide habitat to many animals. Root wads from trees provide excellent hiding areas for juvenile fish. The stream restoration design and stated objectives will...