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 deriva tion of channel networks and the quantitative description of the geomo rphic characteristics of basins. A common method of channel network ex traction from DEM data is based on the specification of a threshold ar ea (A(t)) that is the minimum support area required to drain to a poin t for a channel to form. Usually, an arbitrary constant threshold area value is chosen for channel network extraction. In this study the eff ects of threshold area selection, both on the morphometric and scaling properties (such as drainage density, total channel length, Horton la ws and fractal dimension) of a channel network and the associated hydr ological response function are analysed. The response is obtained foll owing the geomorphological instantaneous unit hydrograph theory. Two d ifferent probabilistic models are used. They both relate the character istic response function of the basin to its DEM data derived networks: one is derived assuming a Strahler stream ordering system and the oth er is obtained by averaging a flow equation with respect to the networ k structure (described by the width function). Applications are shown for three mountainous basins in the Italian Alps. A sensitivity analys is is performed to study the influence of the variability of morphomet ric properties, with respect to A(t), on the hydrological response obt ained. It is shown that the model based on the width function is able to reduce the effects of this variability on the simulated response. ( C) 1997 by John Wiley & Sons, Ltd.