THE ASSIGNMENT OF DRAINAGE DIRECTION OVER FLAT SURFACES IN RASTER DIGITAL ELEVATION MODELS

Drainage direction assignment over Bat surfaces in raster Digital Elev ation Models (DEM) has been a stubborn problem for DEM processing meth ods. A new approach that improves upon current methods of Bat surface treatment is presented, The approach is based on the recognition that in natural landscapes drainage is generally away from higher and towar ds lower terrain, To produce such a drainage, DEM elevations of a flat surface are modified to impose two gradients: one away from higher te rrain, and one towards lower terrain. Subsequent processing of the DEM produces a drainage pattern over the flat surface that is topographic ally consistent and exhibits Row convergence properties, The proposed approach is not restricted by the shape of the flat surface, the numbe r of outlets on its edge, or the complexity of the surrounding topogra phy. A comparison with the drainage pattern of an established method t hat displays the 'parallel flow' problem shows significant improvement s in producing realistic drainage patterns. The proposed approach exte nds automated DEM processing to digital landscapes for which existing methods cannot provide adequate flow directions over flat surfaces to conduct a drainage analysis. The necessary algorithmic details for imp lementation of the approach are provided. (C) 1997 Elsevier Science B. V.