Lag times and spatially distributed unit hydrograph model for flood studies

The first part of this research is an investigation of hydrologic lag times. Lag time is an essential input to the most common synthetic unit-hydrograph models. In this study, the lag times of 19 rural watersheds in Kansas were determined from rainfall and streamflow data by calibration of Snyder's unit hydrograph model. The peak coefficient in Snyder's model was also calibrated. The lag times of 12 urban and developing watersheds in the Kansas City area were determined from gaging data by model calibration. Digital datasets and Geographic Information Systems were used to estimate watershed characteristics and urbanization indices. Based on these data, two sets of regional equations were developed for estimating lag times from watershed characteristics. One set of equation is applicable to rural watersheds in Kansas, and the other set is applicable to urban and developing watersheds in the Kansas City area.; The second part of this research is an investigation of a spatially distributed unit hydrograph model. The ModClark model (Peters and Easton, 1997) is an adaptation of Clark's unit hydrograph technique to accommodate gridded NEXRAD precipitation data. Two features were added to the ModClark model: a spatially distributed loss model and a spatially distributed velocity field. A new formula to calculate the spatially distributed velocity field was derived. Maps of spatially distributed runoff curve numbers for Kansas and Oklahoma were developed. The improved ModClark model was applied to 25 storm events on six watersheds. The calibration results are excellent. Two global parameters, the time of concentration and the storage coefficient, were calibrated for each event. Based on the calibration results, two equations to estimate the time of concentration and the storage coefficient were developed. This model and the equations for the two parameters were applied to simulate four storm events on two watersheds. The results are satisfactory.