Clogging in detention pond outfall

[fujikate]

When designing the outfall structure for a large detention pond should I take clogging into account?

 

[TerryScan]

Typically, this is part of the function of an emergency spillway. Calcs for spillway capacity often assume the principle spillway is clogged.

 

[cvg]

i would recommend that if you have a grate / trashrack on the outlet you should assume up to 50% clogged.

 

[bltseattle]

You asked if you should take clogging into account.

Take clogging into account by designing the facility to trap sediment and flotables upstream of the outlet structure rather than in the pipe/orifice/weir/restrictor that forms the hydraulic control for the facility. In many cases you can use a submerged pipe or orifice upstream of the restrictor that will trap flotables at the water surface, and provide a sump for sediment. In a few cases I've seen a floating boom used to trap flotables; this makes sense if the restrictor is an open-channel device like a weir or flume.

With these clog-prevention design elements included, I would not include clogging when performing hydraulic calculations to size the flow restrictor, so long as an overflow is provided as noted by Terryscan.