Illogical sediment retention results

I was reviewing the output of my latest run of the SDR model and I noticed that the retention values were several orders of magnitude greater than the loss values. This of course makes no sense because export should equal loss minus retention. Right?

The model seemed to run smoothly, though, so perhaps this is just a decimal place issue with one of the final field calculations for the watersheds output shapefile.

Attached is the exported table of the watersheds output file. Is this a bug? What could possibly explain why the retention values are two orders of magnitude greater than the loss?

Note: the two sheets with the suffix "sdr1' are from what I think is the latest dev build (InVEST_dev148_3_1_x86), and the other two were results from v3.0


  • File Attachment...
  • PerrinePerrine Moderator, NatCap Staff
    Hi Sam, 

    I don't think it's a bug. If you're looking at the retention field in the .dbf, it is defined as the difference in the amount of sediment delivered by the current watershed and a hypothetical watershed where all land use types have been cleared to bare soil. 
    See User guide here for the definition, and there for more details.

    I hope this answers your question.
  • Thanks Perrine, you most certainly solved that for me... I just needed to read the latest documentation.

    I highly recommned closely reading the latest documentation for anyone who has also used the older Sediment Retention model (v3.0) because while it looks similar at a glance, there are a lot of new pieces to learn and study such as my experience with the retention output in this case.
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