Digital watershed modelling (DWM) is an important component of the hydro-geomorphological analyse, hence is required in modern hydrological simulation. The separate fields that quantitatively deals with the DWM and other terrain parameters is called Geomorphometry. For most hydrological modelling, DWM is a first steps. Since topography is the first controlling factor in the water flow, hydrologists have to understand and incorporate the topographic information in model development. In this section, I briefly describe the topographic characteristics, more specifically the hydrogeomorphology, of the large river basin, Upper Blue Nile. I used uDig Spatial Toolbox (uST) for this purpose. It starts from the acquiring the DEM to the sophisticated channel and HRU coding and numbering. There are many online DEM sources, some of these are:- http://earthexplorer.usgs.gov
This DEM can be imported to the GIS system. The imparting process varies according to the GIS software we use. In uDig GIS, once you have set processing region, as required by the spatial toolbox, its really easy. It is possible to import (1) as right click -> import ascii or tiff file, then add the DEM data downloaded, or (2) it is possible to drag and drop the DEM to the map layer or map view section.
Then thanks to the uDig GIS tools specialised to hydro-geomorphological analyse, spatial toolbox, one of those tools can be selected, assign the input and the output, run the tools. Here, the geomorphological setting of Upper Blue Nile basin is analysed.
The DEM is processed for the usual routine steps for hydrological conditioning i.e flowdir, accumulation area (Tca), subbasin extraction and channel ordering. Here I have the maps of the sub basin extracted from UBN basin and the channel coding in the automatic procedures of uST.
d. Pfafstteter ordering
e. Similarly the subbasin extraction can be done using the netNumbering tool to extract raster DEM, and extract into shapefile using the BasinShape tool of uST, and in this case, the screenshow cast is :