Fairfax County is home to more than 750 miles of perennial streams, of which about 70% to 80% are in fair to very poor biological health. To address this, our Department of Public Works and Environmental Services regularly restores these streams to improve their water quality.
Why Is Stream Restoration Necessary?
Stream restorations are needed to improve water quality and to prevent runoff of pollutants into the Chesapeake Bay (Bay). The amount of nitrogen, phosphorous and sediments that can be present in the Bay is governed by the Environmental Protection Agency's Total Maximum Daily Load (TMDL) requirements.
Eroding stream banks are the major contributor of sediment to downstream waters and the Bay. Excess quantities of sediment are known to smother aquatic life in our streams and be a source of phosphorous, which contributes to algal blooms and dead zones in the Bay. Stabilizing streams reduces the overall amount of sediment in stormwater flows.
Raising the bed of the stream also allows storm flow to enter the floodplain, reducing volume, velocity, energy and channel erosion and allows sediment and pollutants to settle out before reaching the Bay.
Stream restorations are the most cost-effective technique to address the pollutants of concern for the Bay TMDL. It minimizes erosion and sediment loss, protects public infrastructure and enhances site ecology. It also helps reconnect streams to their floodplain where necessary and restores tributaries and outfalls. When streams become degraded and eroded, the surrounding trees along their banks that would normally keep the stream intact can become exposed and weakened, making them more likely to fall, which can lead to downcutting and widening.
How Stream Restorations Are Done
Fairfax County uses multiple methods to restore degraded stream channels. Like most localities in the mid-Atlantic, stream restorations here have often used Natural Channel Design to create a stable channel that can convey storm flows without eroding. This effectively reduces stream sediment and nutrients, and it requires little to no maintenance when well-constructed.
Stream restoration often requires construction activities that remove or damages trees and cause a lot of disturbance within riparian corridors. To minimize these impacts and improve the stream valley ecosystems, we have developed a number of methodologies that assess and restore natural resource functions:
- Inventory of vegetative communities at the start of a project to avoid impacts to good quality resources and design restorations to improve ecosystem functions.
- Careful design and implementation of restorations, including appropriate native plant species and inspections to make sure plants are of good quality and properly installed to maximize survival and performance.
- Control of non-native invasive plant species before, during and after restoration to provide optimal conditions for restoration plantings to thrive.
- Monitoring and maintenance of restoration sites for three years following planting to identify and control threats and take appropriate actions to ensure success.
What Happens After Streams Are Restored
Benefits after streams are restored are stability, pollution prevention and the opportunity to improve habitat for the biological community by installing native landscaping, floodplain wetlands and streambed and flow diversity. There also will be an improvement in the quality-of-life factors, such as infrastructure protection and flood mitigation.
Recent Stream Restoration Projects
- Scotts Run at Old Meadow Road Project, 3000 linear feet of stream restored.
- Old Courthouse Spring Branch Project, 4000 linear feet of stream restored.
- Crook Branch at Mantua Elementary School Project, 3900 linear feet of stream restored (video below).
For More Information
To learn more about stream restoration projects, visit the Stormwater Improvement Projects webpage.
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