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Hydrocad - Bypass Flows

Hydrocad - Bypass Flows

Hydrocad - Bypass Flows

I am modelling a detention basin, but only the Q1 and Q2 flows enter the tank, all other storm events (eg Q5, Q10, Q20, Q50 and Q100) go overland and discharge directly into the creek. This would mean that the Q1 and Q2 needs to be stored longer to acount for the higher storm events.
Is there anyway to input this senario into the Hydrocad program?


RE: Hydrocad - Bypass Flows

What is the physical mechanism that makes the larger flows go overland and into the creek?

Assuming it's an overflow of some type, you would use an overflow device and set the routing to secondary.  This will let you route that portion of the flow to the creek.

Peter Smart
HydroCAD Software

RE: Hydrocad - Bypass Flows


Where we are proposing the detention basin is slightly higher than the rest of the site, we can discharge the pipes (which are design for Q1 and Q2 flows) into the basin but not the overland flows, these flows will discharge into the creek.
The reason for proposing the detention basin in this slightly higher area is due to site constraints.



RE: Hydrocad - Bypass Flows

Sorry, I still don't understand the "switching" mechanism that is implied by your original post.  When you say "only the Q1 and Q2 flows enter the tank", what prevents the other flows from entering the tank?

I assume everything enters the tank until it fills up?  If this is the case, you can use an overflow device to route the excess.

On the other hand, if the overland flow always goes to the creek, just route it there to begin with.

If you have further questions, a sketch would be helpful.

Peter Smart
HydroCAD Software

RE: Hydrocad - Bypass Flows

After looking at your attachment, I wouldn't use a "user defined outlet" in 1P.  I'd just enter whatever culvert geometry you want into 1P and have a ditch or what-have-you as a secondary outlet routed to R2.  Let the model determine how much goes where, and you adjust the size and elevation of your pipes to produce the sort of flows you're looking for at different events.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: Hydrocad - Bypass Flows

You should be able to use the zero-storage pond with a culvert outlet routed to primary (for the Q1 and Q2 flows) and perhaps a second (larger) culvert for the bypass routed to secondary.  Model what you will actually plan to build and let the software do the split.  As beej67 said, use the actual device geometry.  You don't need a special outlet.

Remember there will always be some flow through the "stormwater pipes", even in the larger events.  The exact flow will be a function of the pipe parameters and the headwater generated at the flow splitter.

This is a very common diversion scenario, and doesn't require anything special on your part other than using the primary/secondary device routing.


Peter Smart
HydroCAD Software

RE: Hydrocad - Bypass Flows

Hello psmart and beej76.
I made the changes and it seems to work.
Thanks for your help.

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