CHANNEL NETWORK DERIVATION FROM DIGITAL ELEVATION MODELS - AN EVALUATION OF OPEN SOURCE APPROACHES
The use of the coarse resolution ASTER and SRTM elevation model is very common for many purpose in hydrological research, a standard procedure is for instance the extraction of river channels. However, depressions in the elevation models resulting from vegetation cover or just from noise in the data cause challenges for the flow routing algorithms used for the channel derivation. There are two common methods to handle this: filling the sinks and creating a depressionless elevation model or applying a least cost path approach routing through the unmodified DEM. In this study we take the catchment of the Naryn River in Kyrgyzstan as an example and compare these two methods using the two widely used open source GIS systems SAGA and GRASS. The statistical comparison with a digitized reference stream shows that the least cost path approach implemented in GRASS GIS gives significant smaller distances of the computed to the digitized stream. Furthermore the derivation from the SRTM elevation model is closer to the reference as the one from ASTER. In summary, we suggest GRASS GIS in combination with the SRTM elevation model for the analysis of large scale watersheds.