Tennessee Valley Authority Economic Development
Sustainable Development Guide
Section 4: Conservation of Natural Areas
Design principles
Create a vegetated buffer system along perennial streams
Use native plants for the buffer system
Enhance forests and other natural vegetated areas
Avoid discharging untreated storm water into sensitive areas
Create a vegetated buffer zone along perennial streams
A water quality buffer zone is a strip of undisturbed native vegetation, either original or reestablished, bordering a stream or river, pond, lake, wetland, or seep. It is very important to water quality, stream integrity, and wildlife habitat. It protects the physical and ecological integrity of water bodies from surrounding upland activities and can protect the stream bank from erosion. A buffer zone is most effective when storm water flows into and through it as a shallow sheet, rather than through concentrated channels or gullies.
Forest cover amplifies the benefits of buffered streams. Those benefits include:
- Reduction of watershed imperviousness. An average buffer width of 100 feet reduces watershed imperviousness by 5 percent. Buffers discourage excessive storm drain enclosures and channel hardening. They prevent increases in runoff from impervious cover and subsequent erosion and overflow of headwater streams.
- More room for best practices. Where topography, floodplain limits, and groundwater limits allow, buffers provide more room between developed areas and streams for the placement of best practice modifications, like storm-water ponds. They also improve septic system performance. Even a modest buffer provides space and access for future stream restoration, bank stabilization, or reforestation.
- Flood control. Property too close to a stream may experience flooding, standing water, and bank erosion. Other, more expensive flood controls are not necessary if a buffer includes the 100-year floodplain. Stream “right-of-way” allows for lateral movement, and most stream channels shift or widen over time. A buffer protects both the stream and nearby properties.
- Protection from stream-bank erosion. Tree roots consolidate floodplain and stream-bank soils, reducing the potential for severe soil erosion. Avoiding construction activity on steep slopes along a stream is the best way to prevent such erosion.
- Community enhancement. Buffers can be attractive amenities that add to property values. They provide the foundation for greenways, and such connected open space allows pedestrians and bikes to move efficiently through a community.
- Removal of water pollutants. When properly placed, buffers remove pollutants and control flows from developed areas. When properly designed, they can provide effective pollutant removal for development located within 150 feet of the buffer boundary. A forest canopy prevents further stream warming in developed watersheds.
- Protection of wetlands. Stream buffers can protect wetlands frequently found near streams.
- Improved habitat. Buffers provide food and habitat for wildlife. Leaf litter is the base food source for many stream ecosystems, and forests provide woody debris that creates cover and habitat structure for aquatic insects and fish. Riparian corridors preserve important terrestrial habitat, including forest cover. They are important transition zones, rich in species. A mile of stream buffer can provide 25 to 40 acres of habitat. Unbroken stream buffers provide “highways” for migrations of plant and animal populations. Buffers also provide essential habitat for amphibians, which require both aquatic and terrestrial habitats to complete their life cycle. Buffers maintain the base flow of streams.
Small headwater streams are very important to protect since they comprise 75 percent of many watersheds. Communities establish stream buffers to regulate development within the floodplain and to protect water quality.
Schueler identified three zones in a stream buffer. Each zone can be managed to accomplish different functions and objectives. (1)
A minimum buffer width to maintain water quality and habitat commonly ranges from 75 to 100 feet. Buffers narrower than 35 feet cannot sustain aquatic resources; widths of 35 to 100 feet are needed under most circumstances. Buffer widths toward the lower end of the range support some of the physical and biological needs of the stream ecosystem, especially on small streams. Those at the upper end of the range are most likely to protect the physical, chemical, and biological characteristics of the aquatic resource.
The optimal buffer width depends on its intended purpose. (2)
Buffers should incorporate sensitive landscape features such as floodplains and wetlands. Including the entire floodplain width is desirable, but often difficult. Storm-water ponds and buffer infiltration areas can be incorporated in buffer areas, but take care not to locate such practices too close to a stream. For example, a treatment pond intended to control a 10-year event will not be effective if it is flooded by the stream every two years. Flooding may increase the maintenance required to remove sediment. High or seasonally high groundwater may exclude several practices, as may local floodplain regulations.
Refer to the following document for more information about these best practices:
Environmental Protection Agency Post-Construction Storm Water Management
Use native plants for the buffer system
The type of vegetation in a buffer is important to its function. Both grass and forest buffers can reduce nutrients and sediments from surface runoff and nitrates from subsurface flows. Forested buffers have high rates of nitrogen removal. Soil and hydrological conditions also affect the performance of buffer zones. (3)
To preserve buffers for a project:
- Designate the buffer on clearing and grading plans. .
- Inform the contractor about the extent of the protected area during a preconstruction meeting. Inspect and maintain the buffer according to an agreed-upon schedule during construction. Require a maintenance bond to ensure the repair of any damage that occurs during construction.
- Annually monitor and report on the condition of buffers, open space, and other storm-water infrastructure. .
- Include allowable uses and management activities, such as the removal of dead trees, in long-term maintenance plans.
TVA’s Riparian Restoration web site, which includes a Native Plant Selector, helps owners of stream-bank or shoreline property plan landscaping that enhances their property and protects water resources.
Limit forest clearing
Site fingerprinting, or footprinting, carefully limits the clearing of vegetation and disturbance of soil to a set distance around proposed structures and improvements. It restricts clearing to the minimum area required for building footprints, construction access, and safety setbacks. (4) Through onsite preconstruction meetings, contractors can be informed of what to preserve and mark with fences or flags. The preserved natural areas of vegetation retain all of their hydrologic functions and can be integrated into a storm-water management system. This approach reduces the construction costs associated with clearing, and because the runoff volume is lower, storm-water management costs are also reduced. (5)
Enhance forests and other natural vegetated areas
Natural vegetation can become an important part of a storm-water management system. Trees and other types of vegetation evapo-transpire at least 40 percent of rainfall. The forest duff layer absorbs large amounts of runoff, releasing it slowly to the streams through shallow groundwater flow. (6) Mature vegetation is also an efficient water quality buffer. Identify and preserve the highest-quality forest stands prior to development. Where possible leave mature trees. (7)
Planting additional vegetation, clustering trees, and promoting the use of native species can enhance forests and other vegetated areas.
Native plants are beneficial because they
- Require less water and have deeper root systems
- Create a more stable landscape and require less fertilizer
- Are drought tolerant
- Emit carbon dioxide and control ozone
- Control temperature
- Reduce storm-water flows
- Reduce erosion
- Have lower maintenance costs
- Are better adapted to climate changes and pests. (8)
Refer to the following document for more information about these best practices:
Environmental Protection Agency Post-Construction Storm Water Management
Avoid discharging unmanaged storm water into sensitive areas
Site design is key to solving storm-water treatment problems. New outfalls should not discharge untreated storm water into jurisdictional wetlands, sole-source aquifers, or other sensitive areas. Aquifers are a key underground source of drinking-water supply in many communities. Develop a pollution prevention plan for all sites during the design phase. (9)