Chamber storage overflow device

[JDeWick]

Can the catch basin of an underground chamber system be used as the overflow (primary outlet) of the chamber system?
We designed a simple low volume stormwater detention system using the HydroCAD Chamber Wizard. It's 24" pipe and stone in well drained soils and holds the entire volume of the design storm with the help of exfiltration. The primary overflow/outlet device is the catch basin feeding the chambers. Someone is asking if we need another outlet device. I don't think so, but want hear if there is a problem with it and if there are other recommendations.

 

[KaBone]

Your catch basin might be in low point. So you have water trying to enter, but uh-oh, there’s no more room, so where will the water try to go next? How much flooding will there be before it finds another route? If that’s a problem you might need another outlet.

 

[JDeWick]

KaBone,
Thanks for your input. The rim of the catch basin is higher than the storage system.

 

[KaBone]

I figured the rim of the catch basin would be at grade level. Is the surrounding grade higher all around? Then your CB is in a sump and the area will flood bc the underground chamber is full. If the surface has a slope to it and the CB is there to intercept some of the flow, then when the chamber is full the entire flow heads downstream. If the chamber being full causes adverse conditions in either case then you probably need another outlet.
I don’t know what your design storm criteria is, but my jurisdiction says the system has to handle the 50yr storm without adverse affects. Meaning if your system in my jurisdiction can handle the 50yr, then you wouldn’t need another outlet.

 

[JDeWick]

KaBone,
Good thoughts. As it turns out our criterion is the 50-yr storm as well. It does hold all water generated by the 50-yr storm.