Also, I am looking for the last dataset of, Major River Basin and stream network?
We are trying to update the boundary of Awash River Basin using 90m DEM. Since downstream of the basin is too flat it is difficult to delineate the basin and the subbasin.
It depends on your consider issues and how big your sub-basin you would like delineate.
Usually, subbasin are obtained by the drainage network obtained from a DEM, on the basis of steepest directions (it is an easy task to compute them). Of course, this can be done in a reliable way only if a topographic gradient, even small, exist. If this is not the case, you can obtain a perimeter of the basin just the same, after eliminating all the depressions and flat areas but, unfortunately, the perimeter that you will get probably will not be the “real” perimeter.
On the basis of my experience if the topographic gradient is too small to be represented by a 90 m DEM, I think the only way is by direct field survey of the local drainage network, if present.
Regards
Stick to the order of tributaries and the applicable distinctions (A Strahler / Baumgartner & Liebscher, et al.)
Use ASTER data. It is 30m but also be careful since ASTER on flatter areas can be problematic.
Dear Abebe Teklu,
If you feel the 90-m DEM is too coarse to have subbasin boundaries of your study watershed, you can try finer-resolution DEMs such as SRTM (if your watershed is not in US) or interpolating the 90-m DEM to 30-m or even 10-m DEM. You can find some information about interpolation methods in https://www.researchgate.net/publication/272524942_Interpolating_SRTM_Elevation_Data_to_Higher_Resolution_to_Improve_Hydrologic_Analysis.
Article Interpolating SRTM Elevation Data to Higher Resolution to Im...
You can use Softmap, which is available online and includes contours.