Open Throat Catch Basin Flow

[Builder604]

I need to calculate the flow (cfs) that an open throat catch basin can handle. Currently i have calculated it using a rectangular weir formula but im not sure that is 100% correct. q=3.33(L-.2h)h^(3/2). Any advice would be appreciated. Thanks.

 

[gbam]

If you don't have it already, download FHWA's Hydraulic Engineering Circular No.22 (HEC22). This is a great reference for inlet analysis. As to your specific question it depends on flow condition or whether it is on-grade or in a sag/sump condition. Also, I have never heard of an open throat catch basin. Is it the same as a curb opening catch basin? Do you have a sketch of this CB? Here is the link to FHWA:

http://www.fhwa.dot.gov/engineering/hydraulics/library_listing.cfm

 

[Builder604]

IT is basically a brick junction box with a slab top and on one side there is an opening 8" by 4'. you can see a drawing of it here Link
THank you for the reference i will check it out.

 

[cvg]

the detail does not appear to be installed in a street or along a gutter, so gutter flow is not an issue. The weir equation might be used until the water depth gets high enough then orifice flow. However, not sure where you got that form of the weir equation nor am I convinced that C=3.33

 

[psmart]

The equation appears to include adjustments for end contractions (-.2h)

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[gbam]

Intersting detail. I didnt think brick configurations were still used today. cvg is correct that the weir and orifice conditions should be evaluated once pond depth is high enough to determine controlling regime. Also the 3.33 coefficient seems high. I have tpically used cf=3.0 for smooth concrete inlets and Co=0.67 for orifice.

A note pertaining to HEC22, FHWA has had alot of testing conduicted on various inlets and etc... especially the hydraulic losses through access holes.

 

[beej67]

Read and learn HEC22. The time you spend reading and learning that will benefit you tenfold in your career.

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

http://www.campbellcivil.com