Spatially distributed hydrological modelling in the Illinois river drainage area, Arkansas, using SWAT.

This study aims to calibrate and validate hydrological processes on a long-term continuous basis at a total of seven monitoring gauges, including the drainage outlet of the Illinois River Drainage Area in Arkansas (IRDAA). The study watershed is also of interstate concern for the EPA owing to a lawsuit filed by the State of Oklahoma citing human health risks resulting from the application of poultry litter as a fertilizer source on pasture lands in the watershed. The results demonstrate that spatially distributed model simulations helped in understanding hydrological processes across sub-watersheds within the IRDAA. The model calibration and validation were carried out for total flow and its constituents: surface flow and base flow. The calibration procedure for hydrology involved a fairly rigorous, 10-year (January 1996-December 2005) statistical and graphical (not presented) comparison of measured and simulated total, base and surface flows. Subsequently, the model was validated using 3 years (January 2006-December 2008) of measured data at the same gauges. This study showed that multi-site calibration and validation provide a means to gain more confidence in the model's predictive abilities at the outlet and at other spatially distributed locations within the watershed. The case study included in this chapter suggests that the SWAT model is a useful tool for conducting spatially varied hydrological evaluation of large watersheds.