Global Mapper v25.0

Watershed Analysis - Interference from Road

 Hi, I'm new to the forum and have only been using Global Mapper for a few months. I'm using GM version 18.2 (I have also tried it on v17.2).

I'm trying to do a watershed analysis of a mountainous area. Both intuitively and using the legend for the atlas shader, I know that one large river at the base of the mountains is the low point in the topography. However, when I run the analysis, the watershed area features end at a small highway that lies between the slopes and the river. New watershed features begin on the other side of the highway. This seems incorrect to me. I've tried creating a line feature along the river and checking "create watershed areas showing drainage to selected lines", but nothing has fixed the problem.

Any suggestions would be helpful :). Thanks!



  • Mykle
    Mykle Global Mapper User Trusted User
    Look at your elevation data.  Possibly by running a line down the drainage, across the highway, and to the river.  Then look at the profile of that line.  You can also shade the elevation data, looking at the character of the surface near the highway.  I suspect that the area around the highway is relatively flat, the highway could be running on fill, berms may exist nearby, any of which could create elevation surfaces that do NOT flow smoothly to the river. 

    As a result, you can describe the character of your elevation data and the effects upon the watershed creation. 

    There may not be much that you can do with the elevation data, if it does not run smoothly to the river.  If your elevation data is editable, you may have options.