When the Solution is the Problem
Throughout history, people have built in the floodplains of streams and then tried to keep them from flooding or changing shape. Traditional engineering practices are designed to prevent flooding and erosion by lining streams with concrete and building reservoirs and levees. A major problem with these structural techniques is that they replace dynamic living streams with concrete ditches devoid of life. In addition, these projects require extensive maintenance and are very expensive to install and repair. Concrete channels collect sediment along the bottom and need to be dredged. Natural banks downstream from engineered banks often erode because water deflected off the hard, engineered surfaces hits softer, natural surfaces with more force.
Stream Restoration vs. Enhancement
Stream restoration means returning an ecosystem to a close approximation of its condition prior to disturbance. Ecological restoration may no longer be possible or desirable. Landscape changes in the watershed may no longer support previous conditions, especially in areas where land-uses and infrastructure such as roads, buildings, and water-control structures have been built. Nevertheless, stream conditions can be enhanced through structural and non-structural techniques.
Structural enhancement involves recreating the shape of the stream bank and often includes adding materials such as rock to harden the bank. Riprap and/or large boulders are used to anchor the toe (the bottom of the bank), redirect erosive flows away from the portion of the bank, or armor the entire bank. In-stream work involves placing structures within the stream to help re-create fish habitat such as pools and riffles. Non-structural work includes incorporating conservation measures to minimize the effects of land use, such as prescribed grazing or planting riparian vegetation. These types of enhancement projects can help to improve or protect an ecosystem. Maintenance and monitoring are important components of successful stream enhancement.
In many situations, a stream will be able to recover and develop a more natural appearance and structure on its own if disturbances are removed. Therefore, changing land-use practices or protecting land along stream corridors might be enough to see a stream on the road to self-recovery. This approach, however, could take a hundred years or longer for the stream to stabilize, making a combination of structural and non-structural techniques more desirable.
A Handbook for Stream Enhancement and Stewardship
A basic resource that will help individuals, groups, organizations, companies, communities, and others plan and carry out environmentally sound, cost-effective stream corridor assessment, enhancement, and stewardship programs. This resource provides a solid foundation by which volunteers may become informed observers, advocates, and organizers of stream enhancement programs and participants in their implementation. Available through McDonald and Woodward Publishing Company, 800-233-8787, www.mwpubco.com/conservation.htm