Using 3 ft diameter HDPE pipe as a catch basin 2

[darthsoilsguy2]

A client bought a bunch 3ft diameter HDPE corrugated-out/smooth-interior pipe and a shop-fab 3ft elbow joint so they could build an HDPE catch basin and the discharge line that basically looks like an elbow. This was their idea before I came in and their goal was to intercept and divert runoff that crosses the property in a yard area. Permit authorities directed him to hire an engineer to issue a stormwater design. I told him I would look and see if I could find info that could support using the materials he already bought. If the materials weren't purchased and sitting there on-site already, we would just be building precast catch basin with a 24" pipe.... but here i am looking for a gigantic yard inlet detail for 3ft hdpe pipe and am striking out. I can punt on this idea and just use his 30" pipe and make them get a precast structure... but I figured I would throw a line out to the eng-tips crowd and see what bites.

 

[LittleInch]

Can you sketch this out and what is your issue a bit more?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[darthsoilsguy2]

the issue is there is an off-property railroad culvert uphill that dumps water on this property and causing deep gullies across the property as the soils are all sand deposits from the major river the property abuts. the goal is to intercept the culvert discharge runoff downhill from the railroad property and then pipe it across the property and send it to an armored ditch and armored apron at the river. They bought pipe based on this sketch that leaves a lot to the imagination for the inlet condition.

 

[btrueblood]

Is the water overtopping the retaining wall currently, in order to channel the propery? Or is the water undermining the retaining wall?

Either way, it seems the major problem in my mind is how to keep sediment and debris from clogging the inlet. A suitable trash cage around the inlet would be one suggestion I could make. Maybe something like these:

https://www.conteches.com/stormwater-management/treatment/stormrax

Past that, it's up to the property owner to properly maintain whatever gets installed (clearing mud out of the inlet and pipe periodically). The good thing is, there is no real vehicle traffic along that area if i'm interpreting the sketch correctly, so worrying about collapse of the hdpe basin due to ground pressure from trucks is not the worry?

 

[LittleInch]

Thats a whole heap better.

So how long is the retaining wall? What does this look like in plan view?

I would just lay perforated pipe in a french drain type affair and connect the pipes into the upstand of the vertical pipe and put a flange on the end so you can clean it out if you need to. Just drill holes in the pipe and insert the end of the drainage pipe and seal it off.

"leaves a lot to the imagination for the inlet condition" - called design....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[darthsoilsguy2]

the retaining wall doesn't exist yet either. that sketch was made by owner before they had to get an engineer involved. he was showing one to use as a backstop for the drop inlet. I was switching that out for an armored berm.

these comments have got me thinking about turning this thing into a detention structure, except not really for the purpose of detaining... keeping the 36" riser as an overflow with a trashrack like btrueblood linked to keep debris & people out, and (similar to littleinch) branching off to the side to receive a standard precast drop inlet with sump and 18" pipe with the DI grate 6" to 8" below the riser lip for all the normal flows.