An Efficient Variant of the Garbrechnt and Martz Algorithm for Calculating Flow Directions Over Flat Surfaces in Raster Digital Elevation Models

The flow direction calculation over flat surfaces in a digital elevation model (DEM) is vital for hydrological analysis. The Garbrecht and Martz (G&M) algorithm is a widely used algorithm to obtain correct hydrological flow patterns over flat surfaces. In this study, we propose an efficient variant over the fastest variant of the G&M algorithm. The proposed variant introduces three improvements and significantly reduces redundant computation. For all tested DEMs, the running time of our proposed variant is 26% to 49% shorter than that of the fastest variant. The proposed variant can be used to obtain correct hydrological flow patterns over flat surfaces with less time.