Global Mapper Pro

Streams and Watersheds

durga637
durga637 Global Mapper UserTrusted User
edited August 2012 in Elevation Data
Hi,
I am using 13.2 version prior to refering the below link.
"http://www.globalmapperforum.com/forums/elevation-data/8288-stream-drainage-area-top.html"

I am interested in streams and watershed of my area and used dem as source.
I tried the same previously and works fine. But after referring to above link, I downloaded the files and over write files in my installed folder and tried watershed option and got "no streams" and "gap watersheds". I mean some watersheds are missing. Attachment is for your reference.

I need to have streams and watershed.
Please let me know procedure to get streams and avoid getting blank watershed?
Please advise.

Thanks,
Prasad.
a1.jpg 395.1K

Comments

  • global_mapper
    global_mapper Administrator
    edited July 2012
    It seems to work fine for me, can you check the Vector Display tab of the Configuration dialog and make sure that you have turned off line display and that all types are checked in the line filter? Also are the areas that look to be missing actually missing or are they just the same as your background color? What does the underlying DEM surface look like?

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • durga637
    durga637 Global Mapper User Trusted User
    edited July 2012
    Hi Mike,
    I repeated the process and got streams and watersheds. Attachment is for our reference.
    I didn't change any default setting before or now but it works fine now.
    Thanks for your time.

    Is there any option to find drainage area of any chosen point along the stream ???
    for example, there is a 1km main stream and having sub-streams/branch streams upstream at 0.5km and 0.75km from down stream end. Both branches are 0.1km length. If I want to find drainage area at 10m interval points from downstream ends along the entire stream including branches. With this analysis, I can get get a point where I can get more drainage area and least drainage area etc....
    Thanks,
    Prasad.
    a2.jpg 404.2K
  • global_mapper
    global_mapper Administrator
    edited July 2012
    Prasad,

    If you first create the points that you are interested in drainage for, you can select those with the Digitizer Tool, then start the watershed operation. On the watershed options dialog there will be an option to find the area draining to each selected point. This option will create areas of everything that drains to each point.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • durga637
    durga637 Global Mapper User Trusted User
    edited July 2012
    Hi Mike,
    Yes we can do as you said , if I am specific to particular points/locations. But in my case I have streams... and I want to know at which location/point on the stream I will get maximum basin/watershed? I mean any point/location along the stream, I would like to know contribution of basin/watershed area. ie.,treating any point on the stream as outlet and getting corresponding basin/watershed area and the its volume. Volume I think we can get once we get area shape of particular point.
    Thanks,
    Prasad.
  • global_mapper
    global_mapper Administrator
    edited July 2012
    Prasad,

    You could basically do that by setting your stream threshold for the initial watershed creation to very low, like maybe 10 for the Stream Cell Count. This will give you a very large number of very short stream segments, each of which with inflow and outflow attributes, so you can easily track changes in outflow in very short segments.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • durga637
    durga637 Global Mapper User Trusted User
    edited July 2012
    Hi Mike,
    I calculated as you suggested and got watershed to each branch of the stream and corresponding drainage area.
    Here, I need some info on inflow and outflow attributes. What are those really mean and their units(not included in attributes)? How best we can use in our analysis?
    I hope it is not the runoff (Q m3/sec).

    Next I want to ask you on how to get drainage areas automatically of all points on the stream as shown in figure(c) of the attachment? I have many (thousands) points along the streams and their elevations but struck in getting drainage areas of those points as shown in figc. Please advise.
    Thanks,
    Prasad.
    b1.jpg
    b1.jpg 214.6K
  • global_mapper
    global_mapper Administrator
    edited July 2012
    The flow "units" are the number of cells draining into the beginning and end of stream. The size of each cell is determined by the sample spacing that you use to compute the watershed and defaults to the resolution of the input terrain data. So for example if each cell is 30m x 30m in size (900 m2), then an IN_FLOW of 500 would mean that 450,000 m2 of surface drains to the start of the stream. How much flow that equates to of course depends on the amount of water coming from each cell and other factors beyond what Global Mapper can compute.

    Once you have a bunch of points along your stream, such as by creating point features at the stream line endpoints using the Digitizer Tool, you can select those points with the Digitizer Tool, then run the watershed again, this time selecting to 'Create Watershed Areas Showing Drainage to Selected Point(s)'. This will create areas showing exactly what drains to each selected point.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • durga637
    durga637 Global Mapper User Trusted User
    edited July 2012
    Thanks Mike for your time and support.
  • durga637
    durga637 Global Mapper User Trusted User
    edited July 2012
    Hi Mike,
    I tried as you suggested and after calculating watershed it got hanged. I tried by repeating the process, both the times same result.Attached image is for our reference. Is there any limit of points selection in GM ? If not it should run and give result but it may take more time to process with out hanging. Please advise.
    Thanks,
    Prasad.b2.jpg
  • global_mapper
    global_mapper Administrator
    edited July 2012
    If you have a lot of points selected to create watershed areas from it may take quite a while to create all of the individual watershed areas. There is not progress shown for that as typically you would just select one or two points to create individual drainage areas for, so there isn't a progress bar. If you select a huge number of points like you have it will take a long time but no progress is shown, but it is working and will eventually finish. If you can reduce your point count at all that would speed thing up a lot.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • tom.luft
    tom.luft Global Mapper User
    edited August 2012
    Is there any possibility to calculate the watersheds and streams along a line? Approximating a line by points can be very frustrating and is far from exact (if you got long lines).
    Imagine you got a road and have to determine which areas are endagered most.
  • global_mapper
    global_mapper Administrator
    edited August 2012
    So what you would want is a way to select a line feature and calculate the watershed area that flows to any part of that line?

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • tom.luft
    tom.luft Global Mapper User
    edited August 2012
    So what you would want is a way to select a line feature and calculate the watershed area that flows to any part of that line?

    Yes, exactly.
  • global_mapper
    global_mapper Administrator
    edited August 2012
    Ok I've added this to the todo list (internal item 10763).

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • global_mapper
    global_mapper Administrator
    edited August 2012
    I have completed adding this new functionality. It will be in the v14 release, the first public betas of which should become available early next week.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • What are the units of the max flow generated in global mapper?
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