Overcoming source limitations in drainage delineation by combining the streams of toposheet and DEM in river morphometric studies

Abstract

This paper suggests an approach that combines the drainages of DEM and toposheets, by matching streams (number and length) and spatial coincidence, the critical aspects of such operations, for overcoming source limitation in river morphometric studies. We illustrate the approach taking Gaurang, a Himalayan river basin, as an example where the toposheets for the uppermost part is inaccessible. Stream matching in terms of number and length is controlled by a method of automatic stream generation from downscaled DEM and flow accumulated rasters. Stream estimated by this method are tested, verified and finally applied to the portion of the basin where the data is unavailable. The other critical aspect- spatial coincidence is controlled by commonly used method of GCPs. In the present case, use of the nodal points of the major tributaries generated from DEM as GCPs for georeferencing of toposheets have restricted the positional mismatch to much less than a pixel. With the consent of both the aspects i.e. stream matching and spatial coincidence, the DEM generated stream is considered to combine with the stream of toposheets to get the drainage of entire basin.