A calibrated rational method for flood discharge estimation for larger watersheds

The estimation of flood discharges for rural, unregulated streams is important for proper design of bridges and culverts in Kansas. This study develops a calibrated rational method to estimate flood discharges for drainage areas in Kansas up to 30 mi2.; Rational method runoff coefficients for six different recurrence intervals were calculated for watersheds in Kansas with at least 20 years of record. A regression analysis of physical and climatic watershed characteristics resulted in equations to predict the runoff coefficient in a calibrated rational method. Application of the equations resulted in lower standard errors of prediction and calculated biases than the USGS regional flood frequency equations.; Quality control and regression analyses were applied to an updated data set and final equations were developed to predict the runoff coefficients. A sensitivity analysis showed no particular limitations in the application of the calibrated rational method in Kansas.