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calibrating the freshwater model for Z

Hi all,
If I have a watershed from the National hydrography data set do I ned to use delineateIT do calibrate my model for Z ?


  • jdouglassjdouglass Administrator, NatCap Staff
    DelineateIt is used to delineate watersheds from point geometries (representing outflow points) and a filled DEM.

    Another helper tool included with InVEST is RouteDEM, which exposes the routing functionality used by the various hydrologically-routed InVEST models and allows you to experiment with the Threshold Flow Accumulation parameter in order to find a value that will best represent your stream network.

    Does that help?
  • the water yield for the subwatershed used in calibration comes up as 4% different from the 50 year average measured stream flow . .  that seems OK to me. The difficulty is that the calculated yield is significantly larger that reported regional production.
  • jdouglassjdouglass Administrator, NatCap Staff
    Interesting!  I'm a bit out of my depth on why this might be ... maybe @swolny or someone else can weigh in?
  • swolnyswolny Member, NatCap Staff
    Hi @hildegaardl -

    Is the watershed being used to define the catchment draining into the point where you have observed data? If so, if you feel that the NHD watershed is the proper catchment, then I'd say use it if you're working with Annual Water Yield. If you were working with a model with a DEM (like SDR, NDR or Seasonal Water Yield) then it would be important to generate a watershed using the same DEM as you use as input to the model. 

    I don't quite understand what you mean by "the calculated yield is significantly larger that reported regional production" so it's hard for me to comment on that. Does this mean that the subwatershed results look ok, but the larger watershed (the whole area that the model was run on) water yield is significantly larger than reported once you apply the calibration from the sub-watershed? 

    ~ Stacie
  • New data set
    The water yield model keeps telling me that my data sets don't over lap and the most recent error 'NoneType" object has no atribute'GetLayer'
    Can you suggest anything ? these data sets worked together 6 months ago
  • My revised question. 
    I ran the water yield model last summer for a very large watershed. I got it to run. When I compared the results to the water yield published by the local water utility the water yield model output was significantly higher. I found a couple of stream gauges in the watershed and decided to compare Water Yield model outputs to the stream gauge Q's. The first stream gauge is almost at the bottom of the watershed . .  the "pour point". The stream gauge calculation result is much larger than the utility reported production but almost an order of magnitude smaller than the original Water Yield calculations.
    Hm.m.m.m so I decided to try all of the original files with a subset of the watershed that empties into another stream gauge. When I tried to run the water yield model with the truncated watershed, it rebelled. telling me that my data sets don't overlap  . . what do you think is going on ?
  • jdouglassjdouglass Administrator, NatCap Staff
    It's hard to say exactly why the datasets won't overlap, but this can be caused by two projections that don't match exactly, which could be harder to visualize in a GIS as well.

    Hope this helps, and sorry for the delay!
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