Abstract: Drainage networks are usually digitized from the existing
topographic maps using GIS. Unfortunately, this method is expensive and time
consuming. But, nowadays, automatic extraction of drainage network from Digital
Elevation Model (DEM) with the help of GIS has become possible and used for
hydrological studies. DEM consists of a sampled array of elevations for a
number of ground positions at regularly spaced intervals. It is a storehouse of
a variety of hydrological information along with terrain characteristics and
valuable in groundwater system analysis. In this paper, the contour maps with
20 m vertical intervals were digitized to create DEM data and drainage networks
were extracted from DEM. Further, a comparative study of simulated drainage
networks extracted from DEM using GIS-based Arc Hydro model is carried out and
the drainage digitized from surveyed topographic maps for identifying
infiltration zones in an urban watershed, upper Bagmati which covers the whole
Kathmandu valley. It has been verified that the automatic drainage extracted
technique from DEM is an efficient and cost-effective method in comparison to
manual digitization. Hence, thus obtained drainage networks may be very useful
for environmental studies, watershed management, and storm water and
groundwater system analysis.
Keywords: Automatic extraction, groundwater, Kathmandu, GIS, DEM, infiltration zone
