Development and Application of Gully Erosion Components within the Usda Annagnps Watershed Model for Precision Conservation

A watershed scale assessment of the effect of conservation practices on the environment is critical when recommending conservation management practices to agricultural producers. The identification of all sources of sediment and subsequent tracking of the movement of sediment downstream is a necessary part of this assessment including the often overlooked contributions from gully erosion sources. Pollutant loading allocations established with comprehensive studies of all sediment sources will result in the precise placement of conservation practices to those locations that will have the most effective impact on reducing watershed sediment loads. The USDA Annualized Agricultural Nonpoint Source model (AnnAGNPS) was developed to perform watershed evaluations of conservation management plans that can be implemented to control all sources of sediment, including from gullies, and is a critical tool in watershed project planning. These enhancements include the development of ephemeral and classic gully components within AnnAGNPS and within geographic information system interface tools used to locate and parameterize gully information for use in the model. Many agricultural conservation practices have been implemented that impact gully erosion, such as conservation tillage, agricultural land conversion to CRP land, grassed waterways, and drop pipes, but there has not been an effective tool developed that can be used to evaluate these practices on controlling gully erosion within watershed systems. An analysis was performed within selected watersheds to demonstrate the applicability of utilizing AnnAGNPS to assess the contribution of gully erosion to a watershed’s total sediment load and the effectiveness of conservation practices designed to control gully erosion. Watershed model studies can provide critical information in a timely manner to action agencies, such as the USDA Natural Resources Conservation Service, when planning where to place effective conservation practices within a watershed.