USE OF DIGITAL ELEVATION MODEL DATA FOR THE DERIVATION OF THE GEOMORPHOLOGICAL INSTANTANEOUS UNIT HYDROGRAPH

The use of digital elevation models (DEMs) allows the automatic derivation of channel networks and the quantitative description of the geomorphic characteristics of basins. A common method of channel network extraction from DEM data is based on the specification of a threshold area (At ) that is the minimum support area required to drain to a point for a channel to form. Usually, an arbitrary constant threshold area value is chosen for channel network extraction. In this study the effects of threshold area selection, both on the morphometric and scaling properties (such as drainage density, total channel length, Horton laws and fractal dimension) of a channel network and the associated hydrological response function are analysed. The response is obtained following the geomorphological instantaneous unit hydrograph theory. Two different probabilistic models are used. They both relate the characteristic response function of the basin to its DEM data derived networks: one is derived assuming a Strahler stream ordering system and the other is obtained by averaging a flow equation with respect to the network structure (described by the width function). Applications are shown for three mountainous basins in the Italian Alps. A sensitivity analysis is performed to study the influence of the variability of morphometric properties, with respect to At, on the hydrological response obtained. It is shown that the model based on the width function is able to reduce the effects of this variability on the simulated response. © 1997 by John Wiley & Sons, Ltd.