An integrated algorithm for depression filling and assignment of drainage directions over flat surfaces in digital elevation models

Abstract

Depression filling and assignment of drainage directions over flat surfaces, two of the common requirements of digital terrain analysis and other related hydrological work, are usually considered as stand-alone steps. This paper presents an integrated algorithm and its pseudocode combining the two steps to increase the efficiency of the overall process. We have developed a Chain Code Matrix to take advantage of the process sequence in the depression filling, which points the drainage direction of cells on flat surfaces towards the lowest potential outlet. Therefore, to improve the drainage direction assignment on flat surfaces, the Chain Code Matrix can be used to guide the calculation of the gradient directly from higher towards lower terrain on flat surfaces instead of applying iterative searching. This avoids finding flat surfaces through the drainage direction calculation in the Digital Elevation Model, which is inevitable in the existing methods. We used the Digital Elevation Models of ten Chinese provinces from the Shuttle Radar Topography Mission data to validate the results and compare the speeds. The experiments show that the integrated algorithm provides the same result for depression filling and drainage directions on flat surfaces as the previous algorithms, but is more efficient.