Watershed delineation are all derived from the basic premise that water flows downhill, and in so doing it will follow the path with the largest gradient (steepest slope). In a DEM grid structure, there exist at most 8 cells adjacent to each individual grid cell.(Cells on the grid boundary are not bounded on all sides) Accordingly, water in one cell travels in 1 out of at most 8 different directions in order to enter the next downstream cell. This concept is referred to as the 8-direction pour point model.