Restoration

Stream systems normally function within natural ranges of temperature, sediment, flow, and other characteristics in dynamic equilibrium. When the system is pushed beyond these normal ranges, it may require intervention to help restore dynamic equilibrium. Restoration efforts help a system recover to a self-sustaining dynamic equilibrium. Restoration efforts should be designed to allow reestablishment of natural system fluctuations.

A wide variety of stream system conditions may necessitate restoration efforts (FISRWG 1998):

• stream aggradataion
• stream degradation
• streambank erosion
• impaired aquatic habitat
• impaired terrestrial habitat
• increased peak flood elevation
• increased bank failure
• lower water table levels
• impaired water quality
• altered hydrology
• loss of gene pool of native species
• decrease of species diversity

Stream system restoration projects can be designed to accomplish a single goal (i.e., restore fish habitat) or to restore ecological functioning of the entire ecosystem. Several factors should be considered in the design stages of a restoration project. First, the decision needs to be made whether the goal of the effort is to address the root cause or causes of the stream degradation or to treat the symptoms. The scale of the effort also needs to be clearly defined: is this project aimed at a particular reach of stream, or is it planned to encompass an entire watershed? Finally, costs, long-term management, roles and responsibilities, land access, and local, state, and federal statutes should be carefully discussed and documented. Large projects typically require expertise in soils, biology, plant sciences, landscape architecture, geology, engineering, and hydrology to be represented. The Stream Corridor Restoration manual, produced by the Federal Interagency Stream Restoration Working Group, provides detailed recommendations for planning, organizing, and undertaking a stream corridor restoration project (see link at bottom of page).

Stream Restoration Methods

Stream Channel

Severely degraded streams may require reconstruction of a stream channel, involving reengineering stream dimensions including width, depth, cross-sectional shape, slope, alignment, and sinuosity. Projects of this nature are complex and costly, requiring many measurements and calculations to ensure the reconstructed system will function as desired. Other stream channels may reflect natural flow and flooding regimes, but may require bank restoration efforts to slow excessive erosion to a rate more appropriate for the system.

Stream Banks

Stream bank stabilization techniques can encompass a wide variety of materials, including concrete, rock, and gravel; logs, brush, grass, and tree plantings; and geotextile materials. Geotextile materials are natural or synthetic fabrics which reinforce and protect soils. The methods and materials selected for stream bank stabilization must be resistant to erosion during high flow periods, but must also minimize environmental impact and be cost-effective. Some of the most commonly implemented techniques are briefly described below. Often, several of these methods will be used together as part of a restoration plan.

Bank Shaping and Planting In this approach, vertical banks are reshaped to a stable slope and stabilized by reestablishing vegetation. This tactic is appropriate under moderately erosive conditions and may need to be supplemented with stronger materials to tolerate highly erosive conditions.
Live Woody Plant Cuttings Stakes of woody plants that readily sprout, such as willows, can be driven into the ground to provide erosion resistance and to stake other materials. As the plants’ roots and branches grow, erosion resistance and wildlife habitat are enhanced. This method is inexpensive and performs best under conditions where the soil is frequently wet.
Riprap This commonly implemented approach consists of a layer of rocks or stones along the stream bank slope. Though riprap has long-term durability, it should be used with plantings to ensure regeneration of stream bank vegetation.
Vegetated Geogrids Vegetated geogrids are alternating layers of live plantings and compacted soil. Geotextile materials are used to stabilize soil. This method can be very effective at restoring a stream bank to a natural state but can be expensive.
In-stream Techniques
Boulder Clusters Clusters of boulders in the stream channel create riffles, slow stream velocity, increase dissolved oxygen in the stream, and enhance in-stream habitat.
Leaving Debris in Place Felled trees, brush, and logs slow the speed of the stream, dissipates the stream’s erosive capacity, and creates fish habitat.
Small Dams, Weirs, or Sills Logs or boulders placed across the stream channel slow stream velocity and create habitat. These structures can be used to slow the movement of sediment downstream, as sediment will be trapped behind the structures.

All images courtesy of Stream Corridor Restoration: Principles, Processes, and Practices, 10/98, by the Federal Interagency Stream Restoration Working Group (FISRWG).

For Further Reading

A comprehensive treatment of the steps involved in planning, executing, monitoring, and maintaining a stream restoration project is provided in the Stream Corridor Restoration manual.

A series of 21 Ohio Stream Management Guide fact sheets provide helpful information.