A FORTRAN-77 PROGRAM FOR PRELIMINARY EXTRACTION OF DRAINAGE NETWORKS BASED ON A DEM

Various authors have proposed methods for obtaining the automatic extr action of drainage networks from a Digital Elevation Model (DEM). That is an important aim to be achieved, in order to manage and process ge omorphological information in soil conservation studies. Attempts have shown that procedures only based on a DEM are able to solve the probl em but, in many situations, they require a post-processing step to int roduce a global view of the drainage network and connect the disjoined stream segments to an appropriate whole. The results of these approac hes depend on the DEM accuracy and the topographic features of the are a at hand. This paper presents a computer program based on the local i nvestigation of a DEM. A 3 x 3 mask is moved through the elevation mat rix starting each time from the relative maximum point until a pit or a border pixel are met. A linking and an upstream matrix are stored; f or each DEM's pixel, the first matrix represents the flow direction in one of the eight neighbors and the second one the number of upstreams . A threshold value on the upstreams permits a drainage network to be obtained ready for the post-processing step. Strahler's morphometric c lassification, lengths of selected segments, area of the relative basi ns and, finally, drainage density are the outputs for the user. The co mputer program was tested for an area in southern Italy. Theoretical a rguments, and experimentation performed by several authors, suggest th e use of Ordinary Kriging (OK) to ensure a better accuracy of the DEM.