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Multiple Basin Outlets

Multiple Basin Outlets

Multiple Basin Outlets

Scenario I'm dealing with:

I have a wet sed basin with an outlet control structure. the OCS has an internal weir wall, overflow grate, and discharges via 36" pipe. The discharge out of the 36" pipe is causing some erosion concerns on an adjacent golf course. The city is wanting another discharge pipe routed underground through the golf course to remove some overland flow. How would you model that? I currently have the internal weir and overflow grate routed to the 36" pipe. How would you also model the additional outlet pipe that will connect to the OCS?

I have tried modeling the pond with the weir and overflow grate as the primary outlets routed to a separate pond node with the 36" and added outlet pipe as primary and secondary outlets. This is causing some invalid results. Would I need to use a Link node somehow?



RE: Multiple Basin Outlets

Sounds like you're on the right track, and you just need to fine-tune the model.

Since your are splitting the flow after the grate and weir, you would need to use a separate zero-storage "pond" to model the water surface elevation after the weir. Then you can have your two outlet pipes, one routed to primary and the other to secondary.

Since the lower "pond" will probably create a tailwater for the weir, you will also need to change to DSI routing. The warning messages will alert you to this situation.

Peter Smart
HydroCAD Software

RE: Multiple Basin Outlets

I have it modeled exactly as you described. My error occurs when I run the 100-year event as the outlet pipes will then be the controlling outlet device, not the weir wall and overflow grate. So the zero-volume "Pond" node that my dual outlet pipes are in is peaking above the HWL of the main basin node causing the peak discharge to exceed reality.

RE: Multiple Basin Outlets

Check your warning messages. Click each message for details and solutions. If you still have questions please post your HydroCAD file.

Peter Smart
HydroCAD Software

RE: Multiple Basin Outlets

I found a different method to complete this. I created a hydrograph of the lowest discharge value at each specified head of the new discharge pipe and the weir structure. I took this hydrograph and added it as it's own outlet on the OCS. Results look correct and expected. Thanks for you help though!

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