Estimating surface flow over digital elevation models using a new improved form-based algorithm

This paper discusses new improvements of a form-based algorithm, which is used to estimate flow distribution over a continuous surface. In the new form- based algorithm (IFBFD), cells in a DEM are classified into five different classes. The classes are Peaks, Complicated, Sinks, Flats and Undisturbed cells. The method of how to estimate the flow distribution from each cell depends on its class. Estimating the flow distribution over flat area cells and sinks is done in an innovative way. The flow over a flat area can be either flow-out or flow-in. Flow-out occurs when one or more cells on the flat area border has an elevation lower than the flat area cells. The flat area is classified as 'flow-in' when all cells on the border of flat area have elevations higher than the flat area cells. The result is that the flow will be converged in the center of the flat area, and that cells will have no outflow (sink). Additionally, a culvert function is added to the new algorithm to enable the user to deal with man-made flow barriers like roads and railway lines. The new culvert function breaches the barrier and connects the flow between two defined points on both sides of it. The new algorithm is tested using the number of mathematical surfaces, as well as on a real DEM derived from LIDAR data. The results of comparing our new algorithm with some well-known algorithm used in most GIS programs shows that the IFBFD algorithm produces more realistic results than other algorithms. Tests show the capability of the new IFBFD algorithm to deal with different terrain types, flat areas and sinks, making it suitable for simulating the real flow distribution over any DEM without the need to e.g. fill sinks. Moreover, the IFBFD algorithm produces a convincing result when deriving the drainage network.