A NEW METHOD FOR THE DETERMINATION OF FLOW DIRECTIONS AND UPSLOPE AREAS IN GRID DIGITAL ELEVATION MODELS

A new procedure for the representation of flow directions and calculat ion of upslope areas using rectangular grid digital elevation models i s presented. The procedure is based on representing flow direction as a single angle taken as the steepest downward slope on the eight trian gular facets centered at each grid point. Upslope area is then calcula ted by proportioning flow between two downslope pixels according to ho w close this flow direction is to the direct angle to the downslope pi xel. This procedure offers improvements over prior procedures that hav e restricted flow to eight possible directions (introducing grid bias) or proportioned flow according to slope (introducing unrealistic disp ersion). The new procedure is more robust than prior procedures based on fitting local planes while retaining a simple grid based structure. Detailed algorithms are presented and results are demonstrated throug h test examples and application to digital elevation data sets.