A distributed parameter model was developed to simulate the hydrologic response of a watershed. The model was written in Fortran 77 and was run on an IBM 3081-D mainframe. The model was designed to accept NEXRAD (Next Generation Weather Radar) hourly rainfall data when it becomes available in 1993. The model used the Green and Ampt method for infiltration, kinematic routing for overland flow and channel flow, and exponential decay relationships for interflow and baseflow from groundwater. A 4-kilometer by 4-kilometer grid size was used for the examples in the study which is approximately the size of one pixel of NEXRAD imagery. Each cell had one or more inflows from other neighboring cells, but it had one outflow to the adjacent cell in the down gradient direction. This process, from cell to cell, continued until the runoff reached the main channel. One calibration storm as well as two verification storms for the Tallapoosa River basin were simulated to evaluate the model's performance. Also, a series of sensitivity analysis runs were made to show the effects of different parameters on the outflow hydrographs. The model effectively simulated the runoff hydrographs at the outlet of the watershed. The model can also be used to simulate the effects of land use on runoff hydrographs. Impervious grid elements can be specified in the model to represent urbanization of the watershed. The Kalman filter was used to generate feedback from measured flow to update the state variables and the flow rates. The application of the Kalman filter was found to remarkably improve the accuracy of runoff hydrograph predictions.
展开▼
