Hi,
I want to download and Process DEM of a Dam watershed. I know only the latitude and longitude of Dam site. I am using this website to get DEM http://srtm.csi.cgiar.org/SELECTION/inputCoord.asp. Kindly guide me among data file and mask file which file I should process to get DEM. What is the format of DEM file ? Moreover guide me how to locate sub-basins,Meteorological and Hydro-logical Gauging stations within the catchment and outside but nearby the catchment on the DEM.
You need to know rough area that drains to that dam site (Watershed). This will be the extent of your DEM download. This extent might involve selection of several tiles for the watershed. You can mosaic tiles to create a continuous DEM layer. It is easy to process this in ArcGIS.
My expertise is not GIS, but I use it alot. From your question, I detect you may not have delineated a watershed boundary before. I would suggest for anyone, even modeler, do it by hand the old fashioned way a few times. I have done it by hand so many times, the boundaries on topographic maps are easy to pick up, and will give you appreciation of what flow accumulation modeling and boundary determination can and cannot do. The dam is your hydrologic outlet (low point), and in delineating, you go from dam perpenducular to contours on both sides of the dam to the ridge, then follow the highest ridge that defines water flowing into or out of your watershed. Your line will intersect top of ridge or mountain, continue through saddles between the highest points. Doing this by hand may be slow at first, but it is an exercise for understanding. Infrequently, you may find generally small mistakes in modeling boundaries, that may force a closer look at the stereo pairs as topographic maps are seldom perfect. We have a researchgate paper from 2015 discussing improved delineation of coastal hydrologic units and streams. I doubt it will address the GIS process detail you want, but may suggest how difficult this can be in relatively flat terrain with standard topographic map DEMs. LiDAR DEMs are much better at defining detail -- also 2007 paper discusses other applications for using LiDAR in gully and channel delineation.
You could get the ASTER Data (30 m) directly from NASA website:
http://reverb.echo.nasa.gov/reverb/
You can select the area around your dam based on the coordinates you have. The file should be TIF (image). A software such as RiverTool or TNTMip is required in order to process and delineate the streams.
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