Erosion around inlet.

[bsmith1972]

I'm looking at a area around a curb inlet in a private parking lot. The soil around one side of the inlet is eroding and starting to cave in. Is this due to a bad pipe connection to the inlet. The pipe in this area is corrugated HDPE.

What would be the best solution....dig and re-grout the pipe...install a concrete collar?


Also the pipe outlets into a pond via a earthen ditch. A fence was installed next to the outlet pipe and the ditch is eroding. There is all types of debris in there from previous jigga-rigging to keep the ditch from eroding. Would the best solution here be to extend the pipe past the fence area and install a end treatment to the pipe. I was thinking about riprapping the ditch. The ditch is pretty steep...would it be a good idea to flatten it out to like 0.3% and have stepdowns.

Just trying to bounce some ideas around and see what you guys think.

 

[Ryb01]

The cheapest solution would probably to excavate and re-grout the pipe. This could solve the problem or....

An option would be to install a core and seal type system from the structure to the corrugated HDPE. Your best bet would be to contact your local pipe manufacturer to get a coupler that best suits your needs. This would essentially produce a water tight seal from structure to pipe.

It would also help to bed the connection with clear stone to aid in additional drainage.

There are a number of options for providing erosion protection for channel sections and outlets. HEC-15 woud be a good reference for designing flexible linings (rip rap) and also HEC-14 would be a good reference for energy dissipation at outlets. Both references can be found at the following website;

http://www.fhwa.dot.gov/engineering/

The cheapest solution would probably be to construct a plunge pool at the outlet.

Extending the pipe past the fence line, land permitting would provide a few benefits by protecting and maintaing the outlet and protecting the fencing from caving in.

Also consider your soil conditions in the area, sandy soils would require more design considerations than clay type soils.

Hope this helps.

 

[bsmith1972]

The only thing about a plunge pool is mosquitos and west nile.

 

[ALBUD1962]

If your outlet ditch is greater than 1% and you have significant flows into the pond, I would consider several ways to dissipate the energy. A simple one may be to extend the pipe add a manhole and have a significant step up from the manhole invert to the inflow pipe. Lay the pipe leaving the manhole at shallow slope. Another variation of this layout would be to have two pipes leaving the manhole at 90 degrees to the inflow pipe, add 90 degree elbows and then daylight to two small headwalls or end sections. This effectively splits the flows and hence reduces the velocity. The 90 degree bends provide energy loss as well.
NRCS also has a rock chute spreadsheet which I have used to assist in design short steep sections of channel.

ftp://ftp-fc.sc.egov.usda.gov/OH/pub/engineering/Design_Spreadsheets/Rock_Chute.xls

Al Budinsky
Skelly and Loy
Harrisburg, Pa