Volume-Based Runoff Coefficients for Urban Catchments

The rational method is derived as a special case of kinematic wave flow. The definition of runoff coefficient is expanded from the peak-based to volume-based ratio between runoff hydrograph and rainfall hyetograph. The new method presented in this paper provides a dimensionless approach to derive the runoff coefficients for the conventional two-flow drainage system and the low-impact cascading drainage systems. The key factors for the determination of runoff coefficients were identified as the ratios of depression loss and infiltration amount to the design rainfall depth. Although this method provides theoretical values for runoff coefficients, field data or computer simulation are always helpful for further validation.