Clarification needed on HRU Impoundment Parameters — vol_dp_a and vol_dp_b

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Swetasree Nag

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Aug 15, 2025, 2:10:17 PMAug 15
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Hi,
Please give insight on the following matter.

While setting up HRU impoundments in SWAT+, I found limited documentation explaining each parameter, their units, and how they should be derived. One example is the vol_dp_a and vol_dp_b coefficients, which represent the volume–depth relationship using a power law:

Here:

  • = Storage volume (m³)

  • = Depth (m)

  • = Scaling coefficient (unit depends on exponent)

  • = Shape exponent (dimensionless)

Example from my study:

  • Volume =

  • Max depth =

Then:

This results in a large value (~8.94 million) with a unit of , which is very different from the default value of 1 suggested in some examples.

My questions to the community:

  1. Can SWAT+ handle such large, unit-bearing coefficients for vol_dp_a directly, or is it recommended to normalise these values?

  2. Is there a standard reference or default formulation for setting vol_dp_a and vol_dp_b when using actual measured volume–depth data?

  3. How do others ensure these parameters accurately reflect the storage–depth capacity without introducing scaling inconsistencies?

Any official documentation or user experience on this would be greatly appreciated.


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