Location: Water Quality and Ecology Research
Title: AnnAGNPS GIS framework for characterizing riparian buffer effects on sediment loads from watershed systems Authors
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 22, 2014
Publication Date: N/A
Interpretive Summary: The effectiveness of riparian buffers to filter sediment from water flowing through vegetation is reduced when water flows too fast. Current technology to evaluate buffers is limited to lumping flow paths through buffers into a single flow path and effectiveness. Technology describing the impact of buffers on sediment moving with each flow pathway has been developed for use with existing topographic and vegetative data and integrated into USDA watershed conservation management technology. Buffers that were 5 meters to 40 meters wide were shown to be up to 72% to 100% effective in trapping sediment. The ability of buffers to trap sediment was significantly reduced to only 3% effective when gullies passed through the buffers. Utilizing improved riparian buffer technology provides action agencies with critical information and management tools necessary to assess the ability of riparian buffers to reduce sediment loads entering downstream wetlands, rivers or lakes for the development of effective management plans within watershed systems.
Technical Abstract: Understanding all watershed systems and their interactions is a complex, but critical, undertaking when developing practices designed to reduce topsoil loss and chemical/nutrient transport from agricultural fields. The presence of riparian buffer vegetation in agricultural landscapes can modify the characteristics of overland flow between the origin in upland agricultural fields and downstream water bodies such as streams, ponds, and lakes; most often the presence of such vegetative cover reduces flow velocity, in turn promoting sediment deposition and nutrient filtering. Watershed simulation tools, such as the USDA-Annualized Agricultural Non-Point Source (AnnAGNPS) pollution model, contains the necessary components to account for efficacy of vegetation in reducing sediment and chemical loads; however, these tools typically require detailed information for each riparian buffer zone throughout the watershed describing the location, width, vegetation type, topography, and possible presence of concentrated flow paths through the riparian buffer zone. Research was conducted to develop GIS-based technology designed to spatially characterize riparian buffers and estimate buffer efficiency in reducing sediment loads in a semi-automated fashion at watershed scale. The methodology combines modeling technology at different scales, individual concentrated flow paths passing through the riparian zone and at watershed scales. At the concentrated flow path scale, vegetative filter strip models can be applied to estimate the sediment trapping efficiency for each individual flow path, which are aggregated based on the watershed subdivision and used in the determination of the overall impact of the riparian vegetation at the watershed scale. This GIS-based technology is combined with AnnAGNPS to demonstrate the effect of riparian vegetation on sediment loadings from sheet and rill and ephemeral gully sources. The AnnAGNPS riparian buffer component represents an important step in understanding and accounting for the effect of riparian vegetation, existing and/or managed, in reducing sediment loads at the watershed scale. Additionally, this component provides watershed conservation managers the necessary tools to characterize and evaluate existing and proposed implementation practices by providing the means to generate information describing the integrated effects of riparian buffers, at multiple scales and, consequently, offering information for targeted action to mitigate non-point source pollution resulting for a better utilization of watershed resources.