Global Mapper v26.0

Units of Max Flow

chanda
chanda
in Other Discussion
Dear All, Kindly assist with the units of the max flow as computed in global mapper. I have attached a screen shot of this. What would be the units of this.
Kind Regards

Answers

  • bmg_bob
    bmg_bob Global Mapper Programmer
    Hello,

    The flow is a count of the number of cells that flow in or out  of the stream. You could convert to a unit of area by multiplying by the area of a single cell (sample spacing X * sample spacing Y).  

    Cheers,
    Bob
  • chanda
    chanda
    Bob in the case of getting Max Flow as 1329 as per attached screen shot, kindly assist, what would the units be? is it in Cubic Meters per sec or what? That was the context of my question. Will appreciate feedback
  • bmg_bob
    bmg_bob Global Mapper Programmer
    chanda said:
    Bob in the case of getting Max Flow as 1329 as per attached screen shot, kindly assist, what would the units be? is it in Cubic Meters per sec or what? That was the context of my question. Will appreciate feedback
    Despite its name, flow is a count of the number of cells that drain into the stream.  It is not a measure of the volume of water moving along the stream bed.

    Cheers,
    Bob
  • chanda
    chanda
    bmg_bob said:
    chanda said:
    Bob in the case of getting Max Flow as 1329 as per attached screen shot, kindly assist, what would the units be? is it in Cubic Meters per sec or what? That was the context of my question. Will appreciate feedback
    Despite its name, flow is a count of the number of cells that drain into the stream.  It is not a measure of the volume of water moving along the stream bed.

    Cheers,
    Bob
    Hi Bob,
    would there be a way to generate a hydrological figure in terms of the flow in cubic meters per second from this? say precipitation multiply by catchment area by some factor of cell count, e.t.c?
  • Mykle
    Mykle Global Mapper User Trusted User
    Area and precipitation are certainly two of the factors in estimating streamflow.  The slope of the drainage, cross-section of the channel (at which you want a flow value), vegetation, and ground moisture are also factors.

    In my area, we would love to have an estimation of precipitation for a known watershed, possibly from weather radar.
    https://ams.confex.com/ams/pdfpapers/21960.pdf

    Our knowledge of current conditions would simply allow an estimation of drainage volume and timing.  We would not have any estimation of flow.  However the precipitation estimate would be much better than relying on a few rain gauges around the edge of the watershed, without any information about how much of the storm was inside your watershed or in a neighboring one while both cases will fill the rain gauge.

    So, Global Mapper can provide the area within a watershed.  An estimate of flow at the drainage point requires a lot more information, with several values being highly variable due to current conditions.  



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