GlS ) tool for precision design and performance assessment of filter strips

Spatially nonuniform runoif reduces the water qua1iry perfortnance of constant-width filter strips. A geographic inlormation system (Gls)-based tool was developed and tested that ernploys terrain analysis to account lor spatially nonuniform runoffand produce more ellbctive filter strip designs.The computer program,AgBufTerBuilder, runs with ATcGIS versions 10.0 and 10.1 (Esri,Redlands,California) and uses digital elevation models to identify detailed spatial patterns of overland runoff to field margins.The tool then sizes filter dimensions according to those patterns using bufTer area ratio relationships.The resulting design is larger along se€intents where more runoff flows and smaller along segments where runoff is less and delivers a constantlevel of trapping etlciency around the field margin for sediment and sediment-bound pollutants. The tool also can estimate trapping elficiency of existing filter strips or hypothetical configurations. In a validation test, estimates of sediment trapping efEciency using the tool's assessment function compared closely to measurements taken on large field plots in central Iowa. Using AgButlbrBuilder, designs developed for a sample of fie1ds in the midwestern United States were estimated to trap nearly double the sediment, on average, during a design storm than constant-width conligurations having equivalent total filter area.AgBuflerBuilder can be used to bolster environmental perlormance of lilter strips where runoffis spatially nonuniform.The AgButTerBuilder tooi is publicly available on the websites htrp:/ /www2.ca.uky.edu/BuflerBuilder and http://nac.un1.edu/too1s/ AgButTerBuilder.