Hydrologic Response Using Rescaled Width Function for Ungauged Basins

The issue of constructing Synthetic Unit Hydrographs for ungauged basins is addressed in which only the Unit Hydrograph for a gauged basin in the region is known, but data for its derivation are not available. This is a common situation in urgent hydrological studies. Within this framework the approach of Width Function Instantaneous Unit Hydrograph (WFIUH) or, else, Rescaled Width Function (RWF) is adopted in the form of drainage density weighted RWF or ddRWF, which takes into consideration the heterogeneity of both the earth relief and drainage density of the hydrographic network. New features are introduced in the method which regard the estimation of flow velocity in channels using a novel regionalization procedure and, second, the extraction of hydrographic network from a Digital Elevation Model (DEM) in an automatic and objective manner using topographic maps. The proposed methodology is applied to six drainage basins in Greece, in one of which a Unit Hydrograph derived from observed rainfall and runoff data is available, whereas the remaining five basins are ungauged. Results showed that the median value of relative error for time-to-peak and peak discharge of the basin Unit Hydrographs is about 12% and 17% respectively compared to values from regional relationships. Also, the proposed method for extracting the hydrographic network generally produced satisfactory results with the median value of relative errors in time-to-peak and peak discharge (with respect to an existing method) equal to about 0% and 12%, respectively. Sensitivity and uncertainty of results are also investigated.