A Spatial Analysis of Dispersion Mechanisms in the Hydrological Response Using a Spatially Distributed Travel Time Model

Abstract

Various dispersion mechanisms are known to link the spatial heterogeneity of the basin morphology and flow dynamics to the hydrologic response. Recent studies have conducted spatial analysis of the kinematic and geomorphological dispersion coefficients that characterize these mechanisms, as well as identified the influence of hillslopes, channels, and runoff production on their values. Nevertheless, an explicit and distributed dynamic representation of the travel times has not been used for this purpose. This study quantifies dispersion mechanisms by calculating spatially distributed flood wave travel times and hillslope and channel velocities, with a spatially distributed kinematic-wave based model that explicitly accounts for the path heterogeneity, the dynamics of upstream flow contributions, and the nonlinear dependence on runoff intensity. Hence, the role of these factors and their influence on the dispersion mechanisms across different scales is studied in detail. Using different runoff intensities, the scaling of the dispersion mechanism coefficients according to the contributing areas within the Quintero Creek basin and two of its sub-basins (in central Chile) is obtained. These scaling relationships are compared against those previously reported in the literature, which were obtained with approaches that simplify the treatment of travel times. Both basin-specific and more general factors manifesting in the behavior of the dispersion mechanisms are found. Dispersion coefficients increase with area, and the role of the hillslope-channel transition is controlled by runoff intensity, affecting the relative contribution of the dispersion mechanisms to the total dispersion at different spatial scales.