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gisgrass

What does the result of r.hazard.flood show?

I am using the GRASS GIS software to research where a potential site could be for a new recycling centre.

I have used the command r.hazard.flood to analyse where potential areas are likely to flood. This command will return 2 data layers in the software one called flood and one called mti as the documentation outlines from the below.

From the documentation:

Usage:
 r.hazard.flood.py map=elevation flood=flood mti=MTI
[--overwrite]
   [--help] [--verbose] [--quiet] [--ui]
Parameters:
    map   Name of elevation raster map
  flood   Name of output flood raster map
    mti   Name of output MTI raster map

Can someone explain the results of mti so I can understand what I am looking at? My assumption is that within mti the lighter yellow areas are those more prone to the risk of flooding. Is this correct?

Output layer mti: What the MTI data layer looks like

Solution

  • According to the documentation of r.hazard.flood, the method is based on a formula described in Di Leo M., Manfreda S., Fiorentino M., An automated procedure for the detection of flood prone areas: r.hazard.flood, Geomatics Workbooks n.10, 2011. (See page 83.)

    The formula used to find MTI is this:

    MTI = log(((acc+1)*cellsize)^n/tan(slope + 0.001))

    The variable acc is flow accumulation, and is higher the more flow is on a particular cell. Therefore, MTI increases the more a cell is exposed to rainfall. So, a higher MTI corresponds to a higher flood risk.

    The paper also says

    The higher values (in red) detect the presence of a lake within the area.

    ...which confirms that high MTI means high risk.

    According to the legend in your example, the yellow areas have higher MTI, and are therefore at higher risk.