Abstract

Spatially distributed travel time (SDTT) methods have been developed as an alternative to semidistributed and fully distributed methods for rainfall-runoff modeling. In these methods, the travel times of grid cells are summed along flow paths and then convoluted to generate the hydrograph at the outlet. One central aspect of SDTT models that remains partially addressed is the effect of upstream flow contributions and their dynamics on the calculated flood wave travel times. Some methods neglect upstream contributions, but these are known to produce incorrect representations of the hydrological response. Other methods assume static upstream contributions, but the reliability of this approximation is poorly understood. In this study, we develop a new travel time method that accounts for dynamic upstream contributions. We test our method in three synthetic basins generated with a landscape evolution model that allows explicit control of primary watershed characteristics. We evaluate the method's performance for different storms by comparing its response to that produced by a fully distributed kinematic wave model. Furthermore, the method is tested in a real basin. We also analyze the dynamic behavior of the upstream contribution and travel times within the synthetic basins. Results show that existing static upstream contribution approaches in SDTT models do not adequately reproduce the hydrographs from the fully distributed kinematic wave model nor the observed hydrograph of the real basin. The proposed method improves the reproduction of hydrograph peak flows and temporal variability. Furthermore, the instantaneous unit hydrographs produced by the new method exhibit more positive skewness than the static approximations.