The Application of a Mathematical Model to Extrapolate Study Results to Other Locations

Environmental models are used to simulate or reproduce real world conditions and how those conditions change due to varying input. Modeling enhances our ability to extrapolate results from intensively-studied test sites to other potential use sites. These models are used by industry and governmental organizations alike to support scientific analyses.

Input will vary based on the model being used and conditions the modeler would like to simulate, but it can include changes in land use, land management techniques, weather data, etc. The model ArcSWAT 2009 is being used to simulate conditions at the Maryland sites and to show how the incorporation of BMPs (i.e., adding compost to the soil and using a lawn seed mixture containing microclover) affects runoff.

Specifically, ArcSWAT is currently being used to model runoff characteristics from the Clarksville, Maryland test and control sites. ArcSWAT is an interface between Esri’s ArcGIS Geographic Information System and the SWAT model (Soil and Water Assessment Tool) developed by Dr. Jeff Arnold of the USDA Agricultural Research Service. SWAT is a physically-based model, which means it relies on soil, elevation, land use, and weather data to simulate water and sediment movement as well as nutrient cycling within a watershed. Therefore, it allows one to examine how various management methods affect runoff. Subbasins of the watershed are divided into hydrologic response units (HRUs), which are areas of similar elevation, land use, and soil data. Ultimately, the model simulates loadings from each HRU to the stream on a daily, monthly, or annual time step.

The Clarksville test and control sites’ watersheds have been delineated using ArcSWAT. We are currently working on refining input variables in order to accurately simulate water, sediment, and nutrient movement at each site. Once the input is complete we will be able to run the model and compare the modeled results with the results of the on-going monitoring. Ultimately, when the model is appropriately calibrated, the results will be extrapolated to other sites throughout the Chesapeake Bay watershed.