Applying a buffer to stream segments is a quick and easy method for approximating riparian extent.
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Buffering is a useful tool to quickly and easily approximate riparian extent by applying a buffer to a vector stream dataset, such as National Hydrology Dataset (NHD) streamline data. There are two types of buffers: simple and smart.
A simple buffer applies a constant buffer to all stream segments in the study area. This is the least exact approach, but might be suitable when complying with requirements to establish a default width for riparian areas in the absence of better scientific information.
Smart buffers offer a more sophisticated approach by varying the buffer width according to the size and nature of the stream. There are a variety of parameters that can be used to vary buffer width; however, Rosgen level and Strahler stream order are commonly used. Both of these parameters can be estimated directly from GIS data. A table or matrix is created with a buffer width for each Rosgen level-Strahler order combination. In general, the lower level/order combinations have relatively narrow floodplains and therefore the buffers that represent these features increase as the level/order combination increases. The width of the buffers is based on a generalized estimation of the riparian width by an individual familiar with the study area.
Buffer methods generate a set of polygons that delineate a fixed distance around each stream segment that can be used as a proxy for riparian mapping.
Evans, D.; Vanderzanden, D.; Lachowski, H. 2002. Stream Geomorphic Classification, Riparian Area Delineation, and Riparian Vegetation Cover Mapping on the Upper Middle Fork of the John Day River, Oregon. Rep. No. RSAC-31-RPT2. Salt Lake City, UT: U.S. Department of Agriculture Forest Service, Remote Sensing Applications Center. 21 p. This study mapped stream geomorphology and riparian vegetation on the Upper Middle Fork of the John Day River in Oregon. The study combined image interpretation and a smart buffering technique based on Rosgen level and Strahler stream order to map riparian areas and vegetation.
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