Event Based Efficiency of Grassed Waterways in Reducing Sediment Yield within an Agricultural Watershed

This research investigates the storm-event based efficiency of grassed waterways (GWWs) in reducing sediment yield via a calibrated Water Erosion Prediction Project (WEPP) Model. The study site is an agricultural Iowa watershed (2600 ha), namely the South Amana Watershed (SAW). Results of this study showed that the GWWs reduced sediment yield within the SAW 3.5–59% during the simulated storm events. Furthermore, a strong correlation between event-based rainfall totals and associated sediment yield reductions were observed. GWWs were found to be more efficient for smaller storm events. Finally, to investigate the effect of the drainage area size and the gradient of the surrounding landscape on the efficiency of GWWs, a small representative concave hillslope (15 ha) was also modeled with the calibrated WEPP. GWWs reduced sediment yield more efficiently when the contributing hillslopes had lower gradients. A threshold gradient of ∼3 % was observed beyond which the GWW efficiency was independent of the steepness of the surrounding topography. Overall, the GWW efficiency for the 15 ha drainage area was higher compared to the one for the SAW and ranged between 10–81%.