Model Outlet Structure with Inlet Pipe Then Weir Then Outlet Pipe

[pcwpe]

What is the proper way to model an outlet structure that is designed with an inlet pipe from the pond then has a broad crested weir in the middle of the sructure and then on the oulet side has another outlet pipe. I have attached a sketch of the structure. I am questioning the proper routing since the water will be originally flowing into the 24" pipe then for low flows will go through the 6" orifice in the weir, then at higher flows overtop the weir and finally through the outlet pipe.

 

[psmart]

Unless the 24" inlet pipe will be a flow control point, the easiest solution is to omit it from the model and use this simplified outlet setup:

Device#1=48" outlet culvert, routing=Primary
Device#2=6" orifice, routing=Device#1
Device#3=weir, routing=Device#1

If you want to consider the effect of the 24" inlet pipe, you could use a custom weir/orifice to handle the flow split:

Device#1=48" outlet culvert, routing=Primary
Device#2=Custom weir/orifice, routing=Device#1
Device#3=24" inlet culvert, routing=Device#1


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[psmart]

A correction to my previous post:

If you want to consider the effect of the 24" inlet pipe, you could use a custom weir/orifice to handle the flow split:

Device#1=48" outlet culvert, routing=Primary
Device#2=Custom weir/orifice, routing=Device#1
Device#3=24" inlet culvert, routing=Device#2


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[psmart]

Another approach is to use two separate pond nodes:

Pond 1 = actual storage with 24" culvert outlet, routed to pond 2.

Pond 2 = zero-storage pond with the orifice/weir control structure and final culvert:

Device#1=48" outlet culvert, routing=Primary
Device#2=6" orifice, routing=Device#1
Device#3=weir, routing=Device#1

The solution requires a tailwater-sensitive routing procedure in order to handle the tailwater effects of pond 2 (the control structure) on pond 1 (the actual storage).

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[beej67]

Be careful with Peter's second solution. It's absolutely correct, but the tailwater issue can bork the model up. I've had many programs (including HydroCAD unfortunately) blow up when trying stuff like that, particularly if your downstream-most culvert starts to control half way through the storm.

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

http://www.campbellcivil.com

 

[psmart]

As always, watch your warnings messages, which will identify most routing problems.

Peter Smart
HydroCAD Software

http://www.hydrocad.net