Riparian: How Riparian Corridors Protect Water Quality
The riparian corridor affects more than the visible stream channel. Riparian corridors improve both ground and surface water quality. The existence of adequate vegetated corridor widths slows the drainage of water and regulates the water flow, allowing for a more symbiotic relationship between the creek level, the water table and plants and animals.

As a stream meanders through the riparian area, it exchanges water with and provides water for underground storage. If a stream were to be straightened, deepened or "improved" with concrete and culverts, surface water would flow directly into larger waterways without the opportunity to exchange with and replenish underground sources, and the water table would fall. Drought is potentially more frequent with straightened rivers and streams, because as the water table falls, the sub-surface water is too low for moisture to reach plant roots. In this scenario, there is no filtering of nutrients under the surface, and the change in the riparian ecology can have significant affects on flora and fauna populations and diversity.

Underground water flows into and out of every open stream channel. This exchange between river and sub-surface water contributes minerals and organic matter to flowing streams. It is commonly held that the river or stream is at the "bottom" of the underground flow of water. Yet closer investigation shows that the water level of a river is essentially the same as the level of the water table. This interaction is commonly referred to as the sub-surface ground water interface with the stream.

Depending on the type of soil and the position of the water table with respect to the stream, a stream could be "gaining" or "losing." A gaining stream occurs where the soil is moist and is lower than the water table. This type of stream is continually fed by ground water, which brings nutrients and organic matter to the stream and the surrounding roots of trees even during a drought. In contrast, a losing stream is typical of arid areas and is much higher than the water table. Water flows out of the channel down into the water table. For either type of stream, the natural exchange of stream water and ground water brings valuable nutrients to the water and helps to control the flow patterns of the stream such as reducing extreme low flows and flood peaks, to which aquatic species are not adapted. The riparian corridor serves as an area of storage for surface water and an area of recharge for the ground water that will ultimately feed our streams.

Various studies have proposed minimum widths for riparian corridors designed with water quality in mind. While Wenger (1999) recommended a minimum of 30 feet for the elimination of most sediments from streams, Newbold (1980) believed only a buffer strip of 30 meters (90 feet) or wider would adequately filter the effects of logging on the macroinvertebrate population in his study.

There have been many proposals for describing the ideal riparian buffer width for blanket legislation. Some have used the meander width over time as a proper amount for protection (streamway concept). Others take the flood plain itself as the correct width to protect a riparian corridor. One thing remains clear throughout: most of the research speaks of the need for individual assessments of nutrients, vegetation types, gradients and sediment to find the proper riparian boundary between a waterway and agricultural land, roads, or parking lots (Spackman and Hughes 1995).
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