The assignment of drainage direction over flat surfaces in raster digital elevation models

Drainage direction assignment over Bat surfaces in raster Digital Elevation Models (DEM) has been a stubborn problem for DEM processing methods. 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 towards lower terrain, To produce such a drainage, DEM elevations of a flat surface are modified to impose two gradients: one away from higher terrain, and one towards lower terrain. Subsequent processing of the DEM produces a drainage pattern over the flat surface that is topographically consistent and exhibits Row convergence properties, The proposed approach is not restricted by the shape of the flat surface, the number of outlets on its edge, or the complexity of the surrounding topography. A comparison with the drainage pattern of an established method that displays the 'parallel flow' problem shows significant improvements in producing realistic drainage patterns. The proposed approach extends 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 implementation of the approach are provided. (C) 1997 Elsevier Science B.V.