Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2010
Publication Date: 11/5/2010
Citation: Dabney, S.M., Yoder, D.C., Vieira, D.A., Bingner, R.L. 2010. Enhancing RUSLE to include runoff-driven phenomena. Hydrological Processes. 25(9):1373-1390.
Interpretive Summary: The Revised Universal Soil Loss Equation version 2 (RUSLE2) is the most recent of a family of models proven to provide robust estimates of average annual soil erosion caused by rainfall from a wide range of land use, soil, and climatic conditions. The kind of erosion RUSLE2 estimates is called sheet and rill erosion and occurs from raindrop splash and runoff coalescence into small channels (rills) that occur randomly on the hillslope. RUSLE2 currently cannot estimate the erosion that occurs where surface runoff becomes concentrated within topographic swales within upland fields. Such erosion, called channel or ephemeral gully erosion, is considered by many to be a serious as a threat to soil resources and the environment as sheet and rill erosion. In this report we propose and evaluate a method of predicting a series of representative runoff events whose sizes, durations, and timing are estimated from RUSLE2 databases, and we link the results to a widely-used channel erosion model. Runoff predictions were evaluated against independent simulations and against a long-term rainfall and runoff measurements. Results suggest that the methods proposed allow RUSLE2 to define a representative series of runoff events and that ephemeral gully erosion may be the same order of magnitude as sheet and rill erosion. The new methods should improve conservation planning and the assessment of alternative management strategies on environmental quality. However, a larger database of measured long-term average runoff and ephemeral gully erosion rates is needed to improve and/or more fully validate the equations presented.
Technical Abstract: RUSLE2 is the most recent of the family of USLE/RUSLE/RUSLE2 models proven to provide robust estimates of average annual sheet and rill erosion from a wide range of land use, soil, and climatic conditions. Using methods of estimating time-varying runoff and the CREAMS process-based routines, RUSLE2’s capabilities have been extended to estimating sediment transport/deposition/delivery on the hillslope. However, because it is based on monthly climate information, RUSLE2 currently cannot estimate realistic channel erosion and transport phenomena, as these require knowledge of actual runoff rates, which must be based on a realistic storm sequence. In this report we propose and evaluate a method of predicting a series of representative runoff events whose sizes, durations, and timing are estimated from RUSLE2 databases. The methods are derived from analysis of 30-year simulations using a widely-accepted climate generator and runoff model. The method is validated against additional independent simulations not used in developing the index events, as well as against a long-term measured rainfall/runoff set. Comparison of measured monthly runoff with predicted patterns suggests that the procedures outlined may underestimate plot-scale runoff during periods of the year with greater than average rainfall intensity and a modification to improve predictions is presented. Use of the resulting set of representative storms is then illustrated with the channel erosion routines used in CREAMS to calculate ephemeral gully erosion, applying it to hypothetical 5 ha fields with silt loam soil cropped to cotton (Gossyipium hirsutum, L.) in Marshall County, MS, that are bisected with a potential ephemeral gully having channel slopes ranging from 0.5 to 5%. Hillslopes on both sides of the channel were modeled after the erosion plots at Holly Springs, MS, with 5% steepness and 22.1 m length, allowing hillslope predictions to be compared with observations. Results suggest that ephemeral gully erosion may be the same order of magnitude as sheet and rill erosion.