HydroCAD Infiltration Cell Modeling
HydroCAD Infiltration Cell Modeling
(OP)
I have a storm water scenario I'm having trouble with. I have a wet pond, nwl with an 8" outlet at elevation 100. At 102, the pond overtops (weir flow) into an infiltration cell whose bottom is 101. So at elevation 102.1, my wet pond is 2.1' above the outlet and there is 1.1' of water in the infiltration basin. I have 27" horizontal orifice overflow at elevation 103. Let's just say my wet pond surface areas are as follows: 100=10000 sf, 101=11000 sf, 102=12000 sf, 103=20000 sf (wet+ area above infiltration), 104=22000 sf (wet+area above infiltration), 105=24000 sf (wet+area above infiltration). The infiltration cell areas are 101=5000 sf, 102=6000 sf.
How do I model this in HydroCAD?
Here's what I've tried: I used 2 ponds (1 wet, 1 infiltration). My wet pond had a primary orifice (8") at 100, a secondary outfall (weir) at 102, and another primary outfall (27" horiz. orifice) at 103. My infiltration pond only had exfiltration as an outlet because what doesn't exfiltrate will keep on filling up with the wet pond. However, when my infiltration pond filled up, I couldn't model it to go "back" into the wet pond as it was a circular reference.
So then I tried modeling it as one big pond. 100=10000 sf, 101=11000sf+5000sf, 102=18000sf, 103=20000sf, 104=22000sf, 105=24000sf. I had my 8" outlet at 100, my 27" outlet at 103, then exfiltration between elevations 100 and 102 and I used a discharge multiplier of 0.3333 (since the infilt pond was about 1/3 of the size of the whole pond system.) This at least 'worked' in the model but it didn't give me very high infiltration volumes so I question if that was the correct way to do it.
Does anyone know the 'right' way for a scenario like this? I know HydroCAD has provisions for embedded storage but I'm not sure if that is what this would be.
How do I model this in HydroCAD?
Here's what I've tried: I used 2 ponds (1 wet, 1 infiltration). My wet pond had a primary orifice (8") at 100, a secondary outfall (weir) at 102, and another primary outfall (27" horiz. orifice) at 103. My infiltration pond only had exfiltration as an outlet because what doesn't exfiltrate will keep on filling up with the wet pond. However, when my infiltration pond filled up, I couldn't model it to go "back" into the wet pond as it was a circular reference.
So then I tried modeling it as one big pond. 100=10000 sf, 101=11000sf+5000sf, 102=18000sf, 103=20000sf, 104=22000sf, 105=24000sf. I had my 8" outlet at 100, my 27" outlet at 103, then exfiltration between elevations 100 and 102 and I used a discharge multiplier of 0.3333 (since the infilt pond was about 1/3 of the size of the whole pond system.) This at least 'worked' in the model but it didn't give me very high infiltration volumes so I question if that was the correct way to do it.
Does anyone know the 'right' way for a scenario like this? I know HydroCAD has provisions for embedded storage but I'm not sure if that is what this would be.





RE: HydroCAD Infiltration Cell Modeling
Modeling as 1 vs 2 ponds depends on the relative volume of the areas. If the wet pond provides significant detention below the weir, you will need 2 ponds to properly simulate that effect. But if most of the volume is in the infiltration area, the storage of the wet pond may not have a significant effect on the hydrograph routing, and you may be able to use a simpler 1-pond solution.
As far as the exfiltration areas, rather than taking one-third of the exfiltration, just un-check the "allow exfiltration" box for the wet pond storage definition.
It's also important that you address any other warnings. Most problems (and their solution) are identified by warning messages. It's always the first thing I look at...
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
There is significant detention in the wet pond below 102 so in your second paragraph it sounds like I would want to model it as 2 ponds. And I realize it doesn't "go back" into the wet after filling the infilt but I wasn't sure how to describe that. Past 102 they need to fill up together and I just can't get it to do that. Thanks for the response!
I'm not sure about your 3rd paragraph. I want to have exfiltration in the infilt basin part of the pond so I think I need to allow that?
Thanks!
RE: HydroCAD Infiltration Cell Modeling
Your initial approach is reasonable, but you need to resolve each specific error or warning according to the details. (just click the message or Help button) Jumping to another approach is not helping you solve the problem.
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
RE: HydroCAD Infiltration Cell Modeling
Please review my previous link regarding weirs and the storage definition. Although this example deals with storage on only one side of the weir, describing storage on both sides is exactly the same.
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
RE: HydroCAD Infiltration Cell Modeling
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
RE: HydroCAD Infiltration Cell Modeling
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
RE: HydroCAD Infiltration Cell Modeling
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
RE: HydroCAD Infiltration Cell Modeling
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
RE: HydroCAD Infiltration Cell Modeling
In any case, DSI is the recommended routing procedure for your situation. For details please see www.hydrocad.net/dsi.htm
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
I believe this IS how you want to model this in HydroCAD. Two ponds with the "imaginary" wall between for storage calculations.
However, I think there IS the possibility you need to use Sim-Routing. During a larger storm event, if the storage rises above the connecting weir, and the "wet" side is discharging significantly quicker than the infiltration discharge, there will be a REVERSE FLOW from the infiltration node back to the "wet" node. This can only be accomplished with a sim-route. (see "Reverse Flows" in help and http://hydrocad.net/simroute.htm)
RE: HydroCAD Infiltration Cell Modeling
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
Moving forward - Dyn Stor Ind or Sim-Route...what's the best method?
RE: HydroCAD Infiltration Cell Modeling
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
(87) Warning: Pond 2P Oscillations may require Finer Routing or smaller dt
(80) Warning: Pond 3P Exceeded Pond 2P by 1.49' @ 21.43 hrs (0.00 cfs 2.299 af)
RE: HydroCAD Infiltration Cell Modeling
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
I remember one XPSWMM model on which I just couldn't solve the oscillation problem, and after about four hours of struggling with it, I discovered my design actually created a condition where the water sloshed back and forth. So in the end, I was modeling it properly, but the design created a sloshing condition.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: HydroCAD Infiltration Cell Modeling
I'd like to take a crack at this if you don't mind, and I think it would help us all get a better visualization.
I'm just curious, why is your infiltration basin downstream of the wet pond? Why not use the infiltration basin upstream, take care of the lower level storms, and then the wet pond handles the larger storm events.
RE: HydroCAD Infiltration Cell Modeling
The final solution was to model the infiltration volume as part of the wet pond's storage. Using a separate storage definition for the infiltration area, you can deselect the option to "allow exfiltration" in the wet pond volume definition.
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HydroCAD Infiltration Cell Modeling
As psmart says, we did resolve this. It's a strange design as the infiltration basin doesn't receive flow very often but a coworker had asked me if it could be modeled so I was just trying to figure out a way.
RE: HydroCAD Infiltration Cell Modeling
I was just curious as to the thought process. Glad you got this resolved.