Simulation of runoff in agricultural watersheds with tile drains using an extended TOPMODEL

A physically based model was used to simulate runoff in agricultural waters heds with tile drainage systems. The TOPMODEL, which is based on the detail ed topographical information provided by a digital elevation model (DEM), w as modified for this simulation study. Nine possible flow generation scenar ios were used in the development of the model. The model can identify the p ortions of the hydrograph resulting from tile flow subsurface flow and surf ace runoff. The performance of the model was tested through a calibration, sensitivity analysis and validation process. The simulated hydrologic respo nse was designed to produce several components of the outflow hydrograph wh ich were associated with the various possible flow generation scenarios. Th e results of this simulation study show that the model describes the physic al system well and provides a better insight into the hillslope hydrology o f agricultural watersheds with subsurface drainage systems.