Hydro v5.1 parameter "Annual Average Flow" default and range issues

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Hydro v5.1 parameter "Annual Average Flow" default and range issues

Post by rcoville » Thu Jul 27, 2017 11:33 am

There are multiple Hydro v5 issues revolving around the parameter q0 (listed in the GUI as 'Annual Average Flow of Project Area') having its default value and range calculated incorrectly by the software. We're converting from Annual Average Flow (m^3/s) in the GUI to specific discharge (m/hr) and specific discharge is the value saved in the param.dat file as parameter "q0" which the model uses in its algorithms.

Because v5 is calculating the default and range of q0 and Annual Average Flow incorrectly, sometimes calculating it by hand is necessary, and the equations to do so are below. This has been corrected in v6. Most projects are unaffected by this, as most erroneous default values for this parameter are corrected in model spin-up as precipitation is processed through the project area. If project results have baseflow making up over 90% of total flow, then this issue is likely affecting overall results, and this parameter will need to be corrected.

To go from raw observed USGS streamflow (ft^3/s) to processed Qobs.dat aka specific discharge aka parameter q0 (m/hr):

Raw(ft^3/s) * 0.0283(m^3/ft^3) * 3600(s/hr) / Watershed-Area(m^2) = Specific Discharge (m/hr)

To go from processed Qobs.dat aka specific discharge aka parameter q0 (m/hr) to GUI 'Annual Average Flow':

Parameter-q0(m/hr) * Watershed-Area(m^2) / 3600(s/hr) = GUI 'Annual Average Flow' (m^3/s)

When problems are encountered with the default Annual Average Flow generated by the GUI, take the default q0 value of 0.000016 and plug the project area into that second equation to get a better Annual Average Flow to enter in Step 3. If the result of that second equation is above or below the range Hydro is accepting for that parameter in the troubled project, then use the closest acceptable value. That method resolves most problems related to this parameter.
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