Effect of channel network topology, basin segmentation and rainfall spatial distribution on the GIUH transfer function
Résumé
The hydrologic properties of the geomorphologic instantaneous Unit hydrograph (GIUH) are analysed as a function of the topological properties of the channel network and hillslopes, the hydraulic characteristics of flows (such as celerity and diffusivity), and the spatial distribution of effective rainfall. Applications were conducted on seven basins located in southern France. First, we study the effects of the spatial discretization of the catchment as a function of morphometric properties, such as the number of source points N, the total length of the channel network T and the mainstream length function M of the drained area S. Relationships are established between N(S), T(S) and M(S) and new descriptors are proposed and correlated with the hydrological properties of the GIUH. Results show that a subdivision of the basin into subcatchments determined by only two main nodes of the channel network is sufficient to identify the GIUH. Second, the sensitivity analysis shows that the GIUH is more sensitive to the channel topology and to the spatial distribution of rainfall when correlated with altitude than it is to the hydraulic properties of flow on hillslopes and in the channel. Numerical simulations enable one to compare the travel time on hillslopes and the travel time through the channel network as a function of the parameters of the GIUH, and to define constraints for basin segmentation in spatially distributed hydrological modelling