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coastal vulnerability model, What is the threshold value of the erosion index

tjhop1123tjhop1123 Member
edited March 2016 in Marine Models

The coastal vulnerability model calculates a erosion index:

"In addition to mapping the exposure index, the model computes an erosion index ErI as: ErI = (RgeomorphologyRhabitatsRwaveexposure)^1/3"

However, the output erodible shoreline raster only has binary values. Erodible shoreline segments are given a value of 1 and non erodible segments are given a value of 0. These are not the actual ErI values but the user guide does not specify how the model takes the ErI value and classifies a segment as either erodible or not, Is there some sort of threshold ErI value that determines this?
Post edited by tjhop1123 on


  • Hello,
    I see that your area of interest (from a different post) is by the JCNEER...I am also working in that area and attempting to use the coastal vulnerability and nearshore waves and erosion models.
    I cannot tell from your user name if I have talked with you before, but if you would like to contact me you may at - I would be interested in talking further.
  • Hi,

    That's a great question, and I'm not sure of the answer.  I haven't worked very much with that output, and you're right - the user's guide description would suggest either a non-binary output, or that some threshold is being applied.

    I've reached out to the original model developer and I will let you know how he is treating the ErI.

    In the meantime however, you can easily compute the ErI using the equation provided in the user's guide and the ranks that the model spits out in the coastal_exposure.csv.  You can open the .csv in excel, recalculate the ErI using your raw data and then plot to points in ArcGIS (using the 'display x,y data' option and then exporting to a point shapefile).

    Stay tuned, I'll update you when I hear more.



  • Hi Jess

    Thank you for looking into it
  • Hi, 

    I followed up w/the model developer.  In short, the ErI never got implemented quite correctly.  The 1/0 as it is now is readying directly from the geomorphology layer with 1 being erodible shoreline (sandy/muddy) and 0 being non-erodible shoreline.  This is more simple than the user's guide and I would encourage you to calculate your own ErI using the ranks output from the CV model and the equation in the User's Guide.  Sorry for the inconsistency.

    If you have more questions about how to do this, I am happy to help.

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