As you assess the water quality of local streams, you might find eroding stream banks, areas devoid of vegetation, deep and narrow stream channels, or wide and shallow channels. These are some of the characteristics of streams adjusting to changes in the watershed or within the stream channel. It is possible to remedy stream degradation, and volunteers can help streams to readjust to the changing landscape.
Effects of Disturbances on Streams
Healthy streams recover from disturbances quickly by changing shape to accommodate increased stream flow. Healthy streams have vegetated banks, meandering channels, and in-stream habitat such as riffles, runs, and pools. These streams maintain a state of equilibrium between the rate of sediment erosion and deposition. Where land is being or has been developed, however, water runs off with increased speed and volume because of paved surfaces, stormwater channels, and land disturbances in the watershed. The high, fast flows that result from runoff can erode banks, carry pollutants, and smother aquatic life with excess sediment. Streams without vegetation on the banks are even more susceptible to erosion and flooding. In heavily farmed areas, vegetation is often removed from the stream banks to make room for more cropland. When livestock are allowed to wade into streams, they also erode the banks and damage water quality.
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