Editing a digital elevation model to achieve a correct stream network: an application to Kalu-Ganga River in Sri Lanka

Abstract

Modelling a watershed accurately is an important step in water management. Geographic Information Systems (GIS) together with mathematical models have made modelling watersheds an easy task. Digital Elevation Model (DEM) ts a primary data set necessary to model a watershed. DEMs developed using many methods and DEMs are developed from remotely sensed data are the cheapest. Some of them are freely available on-line. In modelling watersheds, it is a common practice to delineate the stream network from a DEM. Matching of the delineated stream network with the natural stream network will depend on the accuracy of the DEM. Some hydrologic models contain built-in functions to edit DEMs to overcome this problem. Hydrologic model, HEC GeoHMS, contains such a function to edit DEM as required by the user. To edit the DEM it is necessary to have the exact stream network to compare with the delineated network. In this work, Kaluganga River stream network was delineated using a DEM available freely on-line and it was compared with the natural stream network of Kalu-ganga River digitized from 1:50,000 maps produced by the Department of Survey. Then the DEM was edited using the HEC GeoHMS model to achieve the desired stream network.