A new method for the determination of flow directions and upslope areas in grid digital elevation models

TLDR

A new procedure for representing flow directions and calculating upslope areas in rectangular grid digital elevation models is presented. The method represents flow direction as the steepest downward angle on eight triangular facets and proportionally allocates upslope area between two downslope pixels based on the angle’s proximity to the direct downslope direction, with algorithms illustrated through test examples and DEM applications. The procedure outperforms earlier methods by eliminating grid bias from eight‑direction restrictions and avoiding unrealistic dispersion from slope‑based proportioning, while remaining more robust than plane‑fitting approaches.

Abstract

A new procedure for the representation of flow directions and calculation of upslope areas using rectangular grid digital elevation models is presented. The procedure is based on representing flow direction as a single angle taken as the steepest downward slope on the eight triangular facets centered at each grid point. Upslope area is then calculated by proportioning flow between two downslope pixels according to how close this flow direction is to the direct angle to the downslope pixel. This procedure offers improvements over prior procedures that have restricted flow to eight possible directions (introducing grid bia) or proportioned flow according to slope (introducing unrealistic dispersion). 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 through test examples and application to digital elevation data sets.