Unit Hydrograph Editor - Initial Abstraction Depth

Hi All,

As you all should know, about the Unit Hydrograph Editor - Initial Abstraction Depth, one can read:

«Select this tab to provide parameters that describe how rainfall will be reduced by any initial abstraction depth available (i.e., interception and depression storage) before it is processed through the unit hydrographs defined for a specific month of the year. Different initial abstraction parameters can be assigned to each of the three unit hydrograph responses. These parameters are:
Dmax: the maximum depth of initial abstraction available (in rain depth units)
Drec: the rate at which any utilized initial abstraction is made available again (in rain depth units per day)
Do: the amount of initial abstraction that has already been utilized at the start of the simulation (in rain depth units).»

Unfortunately, the manual does not specify support characteristic values​​, neither examples to serve as references for user apply.
Does anyone know a procedure for calculating the 3 parameters, with example and influence in results?
Thanks in advance,

Valter Albino

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  • Good question, I will answer more over the weekend but they are sensitive, the SSOAP download page has some more information 




    Note: The initial abstraction in the three RDII UH’s vary between 0 storage and maximum storage (Dmax). The speed of storage recovery is governed by the parameter Drec. You can see the sensitivity of this parameter in this graph of the UH Storage.


    • Bob Dickinson,

      Thank for your answer.

      And how should be determined the 3 parameters?

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