Spatially Distributed Sheet, Rill, and Ephemeral Gully Erosion

Ephemeral gully erosion seriously degrades agricultural soils, but few conservation planning tools adequately account for this form of erosion. To address this deficiency, this paper describes a spatially distributed adaptation of version 2 of the Revised Universal Soil Loss Equation and a new ephemeral gully erosion estimator. The modeled results were compared to runoff and sediment yield measured from 1975 to 1991 on a 6.3-ha instrumented watershed near Treynor, Iowa, managed with conventional tillage corn and containing a grassed waterway. Using a 3-m rectangular grid, this investigation determined surface drainage patterns and delineated concentrated flow channels where contributing areas exceeded 600m2. Computed gully evolution based on soil properties, runoff, and sediment transport contributed approximately one-fourth of the total erosion, with the rest contributed by sheet and rill erosion. More than half of the eroded sediment was deposited within the grassed waterway. Without local calibration, simulated runoff of 67mmyear-1 was 34% larger than the observed 50mmyear-1, and simulated sediment yield of 17.5Mgha-1year-1 was 20% larger than the measured 14.6Mgha-1year-1.