ArcAPEX Modeling of Optimum Widths and Placement of Grass and Agroforestry Buffers to Reduce Runoff and Sediment Transport In Claypan Watersheds.

Existence of a claypan layer in soils at depths ranging from 4 to 37 cm restricts vertical water movement and has contributed significantly to high rates of runoff, sediment transport, and other non-point source loadings from croplands in watersheds.  The deposition of these pollutants in rivers, streams and lakes is a major environmental concern.  A field study evaluating grass and agroforestry buffers in two small corn (Zea mays)-soybean (Glycine max) watersheds over a period of 19 years showed significant reductions in runoff, sediment, and nutrient loadings compared to a control watershed.  The present study was conducted to model these watersheds using ArcAPEX (ArcGIS-based Agricultural Policy Environmental eXtender) model in order to find the optimum buffer widths and placement for the watersheds to reduce runoff and sediment. The calibrated and validated model was used to simulate the watersheds with varying combinations of buffer widths and placements with trees and grass only buffers.  An increase in buffer widths was found to decrease runoff and sediments and placement of buffers at lower slopes had more effect than at higher slopes.