Digital landscape parameterization for hydrologieal applications

Abstract Several advances in automated landscape parameterization from DEMs for hydrologieal applications are presented. The parameterization procedures address the treatment of depressions and flat surfaces in the DEM, the indexing of channel links in raster generated drainage networks, the sequencing of channel links for forward-marching flow routing schemes, and the parameterization of Wooding-type sub-catchments. The advances result in improved drainage definition and in a more accurate network and subcatchment parameterization. INTRODUCTION Automated drainage identification, watershed segmentation and catchment parameterization from raster Digital Elevation Models (DEM) is emerging as an attractive source of topographically derived data for semi-distributed hydrologieal modelling (Wolock & McCabe, 1995; Wolock & Price, 1994). However, existing DEM data extraction procedures have limitations and are sometimes based on simplistic assumptions that can lead to inaccuracies (Tribe, 1992; Martz & Garbrecht, 1995 ; Quinn et al., 1991). This paper presents several advances in DEM data extraction procedures that are based on the D-8 method (Fairchild & Leymarie, 1991) and the downslope flow routing concept. The described advances are incorporated into the comprehensive topographic parameterization model TOPAZ (Garbrecht & Martz, 1995) which processes digital landscapes to produce topographic data that is generally needed for water resources, hydraulic and hydrologieal applications. TREATMENT OF DEPRESSIONS A fundamental problem in the determination of surface drainage over digital landscapes is the occurrence of depressions in the DEM. Drainage paths entering a depression cannot advance by the simple D-8 flow routing method beyond the lowest point of the depression. This problem has traditionally been solved by assuming that depressions are spurious (Freeman, 1991) and systematically raising the elevation of all cells within the depression to the level of its lowest outlet, thereby replacing the depression with a flat surface (Jenson & Domingue, 1988; Martz & Garbrecht, 1992). However, spurious