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differences between values in subwatershed and watershed having exactly geometry

tetidetetide Member
edited October 2018 in Freshwater Models
Hi, 

I would understant how it's possible that I have different values for wyield values when subwatershed and waterdhed have the same geometry and area, because is the headwater area of the basin (see attached file).

Thanks in advance


Post edited by tetide on

Comments

  • tetidetetide Member
    edited October 2018
    Hi again, I'm trying to validate the result I obtained and I realized there are some that I do not understand. I use version 3.4.4.
    I realized in the .shp and .csv outputs for subwatershed and watershed did not appear num_pixels and wyield_ha fields.

    Is the wyield_mn value mm/m2 instead of mm/pixel?

    My pixels are in 10x10m and if I would verify the mn value accepting wyield volume is correct, then the result was wrong.
    Example for one subwatershed:
    wyield_mn: 162.22
    wyield_vol: 1022170

    count pixels (calculated): 63224
    wyield_mn calculated mm/pixel (wyield_vol*1000(m3 to mm)/count): 16167.43587
    considering mm/m2 : 161.67

    I would appreciate your comments for continue with the correct option ;)

    Post edited by tetide on
  • swolnyswolny Member, NatCap Staff
    Hi @tetide -

    I don't see any attachments to your first post, don't know if it's still relevant for you or not.

    For the wyield_mn output in the subwatershed table, it is mean depth per pixel, so you should be able to calculate volume using the area of the subwatershed. I'm not sure how the model calculates the volume, but given your data, here are my calculations:

    162.22 mm/pixel = .16222 m/pixel 
    .16222 m/pixel * 100 m2/pixel area = 16.222 m3/pixel
    16.222 m3/pixel * 63224 pixels = 1025619 m3 total

    This is a bit different than the model output, but not too far, perhaps based on how the inputs are clipped or resampled within the model?

    ~ Stacie

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