Evaluation of Sediment Load Reduction by Natural Riparian Vegetation in the Goodwin Creek Watershed

Abstract

Abstract. Natural riparian vegetation can contribute to edge-of-field filtering of nonpoint-source (NPS) pollutants and function as a conservation structure. The challenge resides in quantifying the performance of riparian vegetation. In this study, the impact of natural and constructed riparian vegetation in reducing sediment loads was evaluated at field and watershed scales in the Goodwin Creek experimental watershed using the Annualized Agriculture Non-Point Source (AnnAGNPS) watershed pollutant model. Detailed characterization of actual natural riparian vegetation was performed with the AGNPS-Buffer GIS tool (AGBUF), and the results were integrated with the AnnAGNPS model to estimate suspended sediment concentrations at the edges of fields and at the watershed outlet. The specific objectives focused on natural vegetation characterization, quantification of sediment trapping efficiency (TE), and comparison of sediment loads of different particle sizes under contrasting alternative scenarios with varying buffer widths and concentrated flow path (CFP) assumptions. Simulation results indicated that the potential of natural riparian vegetation to reduce sediment yield differed for clay, silt, and sand particle sizes. Evaluation of the simulation describing actual conditions but with varying CFP assumptions indicated improved agreement with the observed values when an increasing number of CFPs was considered. Simulation results demonstrated the importance of maintenance to prevent CFPs, as comparisons of simulations containing constructed buffer alternatives suggested that narrower well-maintained buffers can be as efficient as wider buffers containing CFPs and have the potential to remove less land from production. Keywords: AnnAGNPS, Buffer trapping efficiency, Integrated field and watershed scales, Natural riparian buffers, Watershed modeling.