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item Bingner, Ronald - Ron

Submitted to: Federal Interagency Hydrologic Modeling Conference
Publication Type: Proceedings
Publication Acceptance Date: 7/28/2002
Publication Date: 7/28/2002
Citation: Yuan, Y., Bingner, R.L. 2002. Subsurface flow component development for AnnAGNPS [CD-ROM]. Proceedings of the 2002 Second Federal Interagency Hydrologic Modeling Conference, Las Vegas, NV, July 28-August 1, 2002. 11 pp.

Interpretive Summary: Groundwater can be a significant means of moving pollutants into streams and lakes. Understanding the processes that produces groundwater can lead to better evaluations of best management practices on agricultural watersheds. The incorporation of practices that can facilitate the removal of water from the soil or reduce groundwater pollution into a watershed simulation model provides a significant tool for watershed management. By tracking the movement of water and pollutants from the surface to the groundwater using a watershed model, sources of pollution can be identified and targeted for implementation of alternative practices. Technology is described in this study that can be used to provide the link between surface and subsurface pollutants leaving agricultural fields and the pollutant loadings downstream in the rivers of a watershed. This technology is important to local, state, and federal watershed management planners who are required to determine the impact non-point source pollution from agricultural watersheds has on the impairment of rivers and streams.

Technical Abstract: The Annualized Agricultural Non-Point Source Pollutant Loading model (AnnAGNPS) is a watershed scale, continuous simulation, daily time step model. It is currently utilized in many locations of the U.S. by EPA, NRCS and others to estimate the impact of BMPs on non-point source pollution. The model has many unique and powerful features, but until recently, did not include the simulation of subsurface flow processes such as tile subsurface drainage, subsurface lateral flow, and groundwater flow. However, this flow can be significant in areas with soils having high hydraulic conductivities in surface layers and an impermeable or semi-permeable layer at shallow depths. In addition, when simulating the effects of riparian buffer strips, the simulation of these flow conditions is very important. Subsurface lateral flow, including a tile subsurface drainage feature, was incorporated into AnnAGNPS and discussed in this paper. Subsurface lateral flow was determined using Darcy's equation. Users have several options available within AnnAGNPS to determine the impact of tile subsurface drainage based on the availability of information on the system. Subsurface lateral flow is assumed to only occur when soil becomes saturated. The impact of subsurface lateral flow on total runoff depends on the rainfall amount, soil properties and the drainage systems.