Wet Pond Modeling

[TBENGINEERING]

Looking for some feedback on how to model this drawing. The wetpond has a permanent pool elevation that is based on impervious area conveying to the pond. The permanent pool elevation is set based on that volume, any additional runoff will then overtop the bench and flow into the underdrain gravel bench area to a raised structure that will handle larger storm events. Which steps would I take to model this. I understand the outfall pipe from the structure will be the primary outlet, but the benched underdrain portion with the invert below the bench elevation is causing me issues. These elevations are from a different project, just attached for a visual.

Thanks,

 

[psmart]

Not sure exactly what "issues" you're trying to address.

Normally you would set the starting elevation to the permanent pool. But your underdrain will cause the level to draw down, correct? So it's no longer a permanent pool. If you want to maintain the initial WSE you would need to eliminate the underdrain, or add a base flow to balance out the underdrain.

 

[TBENGINEERING]

Not sure exactly what "issues" you're trying to address.

Normally you would set the starting elevation to the permanent pool. But your underdrain will cause the level to draw down, correct? So it's no longer a permanent pool. If you want to maintain the initial WSE you would need to eliminate the underdrain, or add a base flow to balance out the underdrain.

I am trying to layout the outlet devices and which devices to use. The permanent pool is constant at the bench elevation, which in this drawing is set at "Elev D", only volume over this elevation will be directed into the underdrain gravel trench. The underdrain will not allow draw down below this elevation. Modeling the underdrain pipe and gravel trench is what I'm mostly having issues on routing and classifying. I currently have:
1. Outfall Culvert (primary)
2. Raised Structure directed towards primary 2->1
3. Broad Crested Rectangular Weir (modeled for bench), 3->4 (is this routed as secondary?)
4. Gravel Trench (how do you model this?) 4->5
5. Underdrain Pipe (how do you model this) (5->1) ties back into the raised structure.

Thanks,

 

[psmart]

When configuring any outlet setup, start at the final device and work backwards towards the pond storage. For example:

Device#1=Culvert outlet from riser structure, routing=Primary
Device#2=Orifice at top of riser, Routing=Device#1
Device#3=Orifice in side of riser, Routing=Device#1
Device#4=Culvert from trench to riser, Routing=Device#1
Device#5=Horizontal orifice at top of trench, Routing=Device#4

Then check your stage-discharge curve. Flow should begin at the top of the trench, increasing more abruptly at each opening in the riser.

For further details see www.hydrocad.net/pond1.htm

 

[TBENGINEERING]

When configuring any outlet setup, start at the final device and work backwards towards the pond storage. For example:

Device#1=Culvert outlet from riser structure, routing=Primary
Device#2=Orifice at top of riser, Routing=Device#1
Device#3=Orifice in side of riser, Routing=Device#1
Device#4=Culvert from trench to riser, Routing=Device#1
Device#5=Horizontal orifice at top of trench, Routing=Device#4

Then check your stage-discharge curve. Flow should begin at the top of the trench, increasing more abruptly at each opening in the riser.

For further details see www.hydrocad.net/pond1.htm

Can you model a perforated pipe? I've read a few different threads that it can be difficult. Also, modeling a gravel trench that contains the perforated pipe, there were different opinions on the limiting factor as far as infiltration either being the open graded stone or perforation in the pipes. Do you have any tips on this? I don't have hydraulic conductivity data on the stone, I know the perforated pipe data can be found online.

 

[psmart]

I suspect that the pipe diameter will become the limiting factor before the perforations or flow rate through the gravel. Otherwise you could use an exfiltration outlet and/or orifice array in front of the culvert.

 

[carlosbenjamin]

Looking for some feedback on how to model this drawing. The wetpond has a permanent pool elevation that is based on impervious area conveying to the pond. The permanent pool elevation is set based on that volume, any additional runoff will then overtop the bench and flow into the underdrain gravel bench area to a raised structure that will handle larger storm events. Which steps would I take to model this. I understand the outfall pipe from the structure will be the primary outlet, but the benched underdrain portion with the invert below the bench elevation is causing me issues. These elevations are from a different project, just attached for a visual.

Thanks,


View attachment 4718

You’ll want to model it in stages—first, set the permanent pool as a storage node with a defined elevation. Then, create a weir or overflow for when water overtops the bench. For the underdrain, you might need to use an orifice or low-permeability outlet below the bench to simulate slow drainage. Make sure your routing accounts for both normal and extreme flow conditions. What software are you using?

 

[TBENGINEERING]

You’ll want to model it in stages—first, set the permanent pool as a storage node with a defined elevation. Then, create a weir or overflow for when water overtops the bench. For the underdrain, you might need to use an orifice or low-permeability outlet below the bench to simulate slow drainage. Make sure your routing accounts for both normal and extreme flow conditions. What software are you using?

I am using HydroCAD

1. Culvert (outfall pipe out of raised structure)
2. Orifice/Grate (raised structure)
3. Culvert (6" Perforated pipe embedded in bench)
4. Orifice/Grate (Bench)