| Two methods of simulating streamflow for a tile drained watershed were compared using the Soil and Water Assessment Tool (SWAT). The SCS curve number method (CN) was compared to the Green-Ampt Mein-Larson (GAML) method on the Vermillion River Watershed (VRW). The VRW is a 579 mi2 watershed located in the "Tile Belt" of Central Illinois, and is a headwater stream to the Mississippi River Basin. The overall objective of this study was to determine if the SWAT model could adequately simulate the hydrology of an agricultural watershed with intensive subsurface drainage. The model was run on a daily basis during the period of 1970--1988 and model output under the two scenarios was compared to observed flow data. Both model approaches produced similar results with r2 and Nash Sutcliffe efficiency values of 0.72 and 0.53, respectively. The analysis suggested that both methods worked equally well for the tile drained watershed and that while the watershed is drained, it still primarily acts from a water balance standpoint as a watershed with no subsurface drainage. For this example it was determined that modeling with more complex input data such as hourly rainfall is not necessary and that daily weather inputs can be used with equal results. |
