COMPARISON OF DEPRESSION REMOVAL METHODS IMPLEMENTED IN OPEN-SOURCE SOFTWARE

Abstract

Modern tools for hydrological analysis are based on data derived from DEM. Hydrological methods that create a stream network by overland flow simulation require removing depression (pit or sink) on DEM first. Depression occurs when a cell or group of cells is surrounded by adjacent cells at higher altitudes. Even though their removal creates an incorrect DEM, it is common practice to remove all topographic depressions (real, artificial, or combined) not to interrupt the creation of stream networks. There are two basic methods of depression removal: the filling method and the carving or breaching. Combined methods contain good characteristics of both procedures. GIS software includes a depression removal algorithm within its hydrological analysis module. The paper investigates which methods are implemented within individual open-source software SAGA and GRASS. A comparison of DEM before and after depression removal for each method is given. The methods were tested on a DEM, resolution 5x5 meter for a hilly area intersected by a significant number of watercourses.