An Evaluation of Hydrological Pit Filling Methods in the Ekbatan Watersheds

Distributed hydrological models of sediment and runoff estimation for simulating the sedimentrunoff- precipitation processes in watershed surfaces require digital maps and some other information of the basin’s elevation. For example, the correct execution of erosion models which, according to the RULSE method, work in a distributed environment greatly depends on the quality of such information. The Digital Elevation Model (DEM), slop, flow direction and accumulative flow are considered as topographical derivations, a number of which can be extracted by standard Geographical Information Systems (GIS). According to the kind of interpolation method and DEM cell size, errors like digital holes and flat zones occur in the DEM. These errors usually cause some problems in the representation of the basin runoff and sediment delivery by hydrological and erosion models. In order to examine different methods of eliminatingDEM errors, three algorithms are compared in this paper, namely: D8, DE and combination D8 and DE. The parameters used in these algorithms are: length profiles of the main river, the basin’s accumulative flow, basin slope and comparison of built DEMs. The result shows that the algorithm in which the DE (Drainage Enforcement) takes place primarily and then the elimination of ditches in the conventional way executed by some GIS software systems is the most appropriate method. Conformity of the drainage with paper maps and also the removal of digital ditches is a way that the drainage directions in the DEM point correctly to the water channel, is the main adventage of this research.