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Erodibility K factor - SI units or US units?


the current documentation for the SDR says that the Erodibility factor should be in units of  

These are the SI units.

However, the InVEST 3.3.3 'Base Data' map appears to be in US units (range: 0.12 - 0.36), rather than SI units (usual range 0.02 to 0.06)

Values in US units are almost an order of magnitude higher than values in SI units.

Could you please confirm whether the documentation is correct? (and whether the 'Base Data' map is wrong?)

I'm scared this could have a huge effect on the estimated erosion potential - or would this be cancelled by other parts of the USLE also being in US units?

- Jessie


  • RichRich Administrator, NatCap Staff
    Hi Jessie, those sample data were created before my time.  And before the time of the SDR model.  I'd suspect that we carried over those data once and we didn't consider anything about it.  You are correct that the units of erodibility should be in SI units.
  • swolnyswolny Member, NatCap Staff
    Yes, Jessie, the sample data does have incorrect (US) units. Sorry, we really should update that. And you're correct that the conversion to use is 0.1317. An additional note: Please do not directly use the values in our sample data tables in your work. They are to be used as a sample only, for testing out the model. We no longer have a record of where the values came from, so no idea how accurate they are for your use.

    ~ Stacie
  • Thanks Rich and Stacey, 
    I'm relieved that I haven't been using the wrong units, I just had a terrible moment of doubt when I was going through the example and noticed the values in the example were so high.

    Yes, happy to use the sample data tables as samples only. 
    It can be hard to find locally relevant values, but knowing the exact source of information is definitely important.
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