pipe slope

[johnhan76]

The last pipe in my proposed storm sewer network discharges into a detention pond. The pipe is 75' long, at a slope of 18% and discharges into the pond at a velocity of 8 fps. IS this too steep to construct? Will erosion be a problem? Would I be better off making a deep manhole and entering the pond at gentler slope? I can not lift the outlet end of the pipe because of HGL concerns. Thanks for the help.

 

[SiPaul]

I had a similar thread about RCP on a steep slope. That was at 42%. I think that 18% is steep but with velocities below 20 fps (using rcp) and not expecting too much sediment you should be ok. The pipe data/deisgn codes should provide maximum velocities for abrasion.

The anchoring requirements may depend on the type of soil. The geotech for the pond may be able to provide information on this. Although, at 18% I don't think that should be a big major concern.

Will this pipe have an anti-seep collar? That would provide some anchorage as well.