Catch Basin

[lizgr]

I see that most standards state to slope the inside of a catch basin at 1:12 (8.33%) minimum towards the outlet pipe. Has anyone seen a deviation from this?

 

[msquared48]

Are you talking about a catch basin for stormwater, as in a
Type 1 which is small, (18" square or so) or a Manhole that is anywhere from 48" to 72" in diameter, or a precast concrete vault?

In general, for storm, the bottom slopes will be flat for the small CB's and Manholes. However, for sanitary sewers, although the minimum line slope is at 0.5%, the bottom side slopes perpendicular to the trench within the Manhole are greater. Is this the slope you are referring to?

Mike McCann
MMC Engineering

 

[lizgr]

It's a 28' Curb Opening Catch Basin for Storm Water. The slope i am referring to is the bottom of the Catch Basin Towards the outlet pipe.

 

[bank]

Down in these parts, the City's standard details call for 1:2 slope from the back of the inlet to the outlet pipe.

 

[gbam]

lizgr - yes, I have seen sediment/trash traps at the bottom of inlets, typically 6 inches to 18 inches below pipe invert. However, there would be a requirement for maintanence if this scenaripo is used. Many agencies do not have the funding for this and prefer the bottoms be sloped.

 

[beej67]

I've seen it vary widely. In Georgia the practice is typically a two tenths drop for sanitary and match crowns for storm. (so flat if your pipes are the same size in as out) In southern Florida where all flow is by differential head, they often want a sump and baffle in each structure.

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

http://www.campbellcivil.com

 

[cvg]

they are all slope and varies from 6 inches from front to back, 12H:1V, 20H:1V, and 4H:1V. there seems to be no consistent standard except to slope to drain.