Precision Design for Improving Buffers and Water Quality
Precision agriculture techniques can be applied at field margins to improve performance of water quality protection practices. Effectiveness of vegetative buffers, conventionally designed to have uniform width along field margins and riparian areas, is limited by spatially non-uniform runoff from fields. Effectiveness can be improved by placing relatively wider buffer at locations where loads are greater. Forest Service scientists developed a GIS tool that accounts for non-uniform flow and produces variable-width designs that are more-effective. The design model was developed by simulation modeling using the Vegetative Filter Strip Model (VFSMOD-W) to produce relationships between pollutant trapping efficiency and buffer area ratio. These relationships were synthesized into a family of equations which divide the full range of possible relationships into fairly even increments. To apply the model, one equation is selected that best describes a given field situation based on slope, soil texture, field cover management, and pollutant type. This equation is used to determine the buffer area ratio that would produce a desired level of trapping efficiency and it would be applied to the contributing area to each segment of field margin. This equation also can be used in reverse to estimate the performance of existing or hypothetical buffers. The model was adapted for use in a GIS tool, called AgBufferBuilder, which employs an aerial orthophoto to define the field margin, a DEM grid to segment the field margin and to determine contributing areas and slopes to each one, and a digital soil survey for corresponding soil texture. The photo is used again to map the resulting buffer on the ground. A validation study showed close agreement between measured performance of filter strips in central Iowa and estimates provided by both the manual model and its GIS adaptation. Case studies using the GIS tool showed that precision design could double the effectiveness of buffers over traditional constant-width designs. Through terrain analysis, the GIS tool produces designs that can substantially improve the water quality performance of vegetative buffers.
|GIS tool, documentation, user's manual, and practice data sets||(external web site)|