Precision Design of Riparian Buffers for Improving Water Quality
Vegetative buffers, such as forested riparian buffers and grass filter strips, are a common practice on agricultural lands for improving stream water quality. These buffers have traditionally had a prescribed uniform width along field margins and streams. A GIS tool was developed to test the effectiveness of uniform-width designs compared to designs that account for uneven patterns of runoff flow that field terrain can create. The project had two parts: (1) development of a terrain-based buffer design and assessment model, and (2) adapting the model for use in a GIS.
The model concept is to size a buffer according to the size of field area that drains to it. If runoff is not uniformly distributed along the field margin, then the buffer width should vary accordingly, to maintain a high level of pollutant trapping. Mathematical relationships were developed that quantify pollutant trapping effectiveness as a function of the fraction of field drainage area that contains buffer, i.e., buffer area ratio.
The model was adapted for use in a GIS tool, called AgBufferBuilder, which employs a digital elevation model (DEM), to determine drainage areas to different segments of field margin. The mathematical relationships determine performance level of each segment of buffer based upon its buffer area ratio. The tool can also be used in reverse – to determine the buffer area ratio required of each segment to produce a desired level of performance.
Using AgBufferBuilder on a sample of agricultural fields in the Midwest U.S. it was determined that buffers designed by accounting for terrain were, on average, twice as effective as uniform-width buffer designs covering the same amount of area. Widespread use of this tool for designing vegetative buffers could greatly improve prospects for water quality improvement in agricultural landscapes. The AgBufferBuilder tool is currently being upgraded for compatibility with current versions of ArcGIS (ESRI, Redlands, CA) software. The current version of the AgBufferBuilder tool, user's manual, and documentation can be downloaded from the website http://nac.unl.edu/tools/AgBufferBuilder.htm.
|AgBufferBuilder: A geographic information system (GIS) tool for precision design and performance assessment of filter strips||(publication)|
Forest Service Partners