Establishment of Riparian Buffers
Riparian buffers provide various important stream functions.
- Leaves that fall into the water are a food source for aquatic animals.
- Branches and roots provide shelter for in-stream organisms.
- Overhead leaf cover shades water and keeps it cool, improving fish habitat.
- Roots hold stream banks in place and prevent erosion.
- Vegetation slows water velocity, thereby reducing runoff-induced erosion and also allowing particulates to settle out.
- Soils and root systems filter nutrients and pollutants from runoff (especially from agriculture and residential areas) before they reach reach surface waters (Haberstock, 2000).
Riparian buffers also serve to filter water by forcing it to decelerate. As non-point source pollutants are difficult to regulate and control, it is critical to provide rivers with a defense against runoff contaminants.
Riparian buffers should be established along rivers; the width should be determined based on the criteria detailed below.
The width of the buffer depends on many factors, especially the slope of the land (steeper slopes require wider buffers, since steeper slopes allow water to flow faster and water's ability to carry sediments increases exponentially with volume (Chapman, 1996), the permeability of the soil (less permeable soils require wider buffers because water takes longer to infiltrate), and the presence of overland water sources--like intermittent streams or gullies-which can render small buffers ineffective (Haberstock, 2000). The type of vegetation-such as wooded or ground level vegetation can influence buffer efficacy (Haberstock, 2000). Buffer width is measured from the floodplain edge (Haberstock, 2000). Haberstock also notes that wetlands in these areas should be preserved, because they serve to fix nitrogen and retain contaminants and sediments; the issue of wetlands preservation is detailed on another page. Ideally, a consult should be taken to determine the ideal width for an area.
However, if it is not economically feasible to establish a buffer of the recommended width, it is still beneficial to establish a riparian buffer of a smaller width. Studies have found that buffers of 20 feet of native grasses can remove up to 90% of nutrients and 80% of sediments in agricultural areas (Lutz). Furthermore, a riparian buffer does not mean that no human activity or industry can take place in these zones; for example, selective logging can take place if best-management practices are followed (for example, see pages 5-21 of this document) and some agricultural activities such as growing nut trees can easily serve as a buffer and a source of income.
Riparian buffers also are significant because they offer a potential check against the effects of increased precipitation and runoff predicted by some models of climate change (IPCC). Overhead leaf canopy mechanically slows water velocity as it falls, thereby reducing the eroding capacity of the water and the ability of it to carry other particulates.
Regulations should be established to preserve existing riparian corridors. Funds should also be made available to establish new buffers in problematic areas and to reestablish destroyed buffers.