Regression equations with HydroCAD 1

[DuckEngineer]

I have a project that involves a dam with a 130 square mile watershed. Part of the project is to de-water the impoundment. I am trying to model what happens when a storm event hits during these draw downs (empty unit, partially full, full). I have my stage-storage table, a user-defined outlet of flow vs. depth (based on HEC-RAS), and regression flows at my point of interest. The regression flows use 24 hour precipitation values as a part of the formula, so I think applying an SCS 24 hour type 2 distribution is appropriate for my incoming events. Is there a way in HydroCAD to take the SCS hydrograph, apply the known peak flow (from regression), and let HydroCAD fill in the limbs of the hydrograph for routing purposes?

 

[psmart]

You could manually adjust the CN value until you get the desired peak flow. Or you could enter a complete runoff hydrograph using a link.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[DuckEngineer]

Thanks for the quick reply! Is there an exportable hydrograph within HydroCAD that would have percentage of total flow vs. time, so that I could just apply my known peak multiplier to the Y axis?

 

[psmart]

Every hydrograph is different, so you should probably define your own curve. However, there's a sample file called LinkTest1.HCE that you can load into a link to get you started. The curve has a peak flow of 10CFS. Use the discharge multiplier to adjust the peak to the desired value.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[beej67]

I wouldn't say I prefer the method Peter suggests, of monkeying with your CN until you get the right peak flow, but I will admit to having done it before to get inputs for unsteady HEC-RAS models. Just be careful when you're doing it, since there are many factors that influence hydrograph shape other than just CN. Tc, for instance. It would be of some value after calibrating your inflow hydrgraph to match the flows, to go back and compare your calibrated CN to the actual watershed CN. Major differences might indicate you need to tweak your Tc or your Ia.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com