Pipe Inverts in relation to ditch bottoms

[diggerman]

Is there any common rule of thumb with setting the elevation of a pipe invert (where the mitred end exists) with relation to the ditch bottom. I've heard many diferent schools of thought on this. Contractors appear to build the ditch bottoms slightly (approx. 2 tenths of a foot) lower than the end of the pipe invert. The problems we've been encountering is that this creates more of a sump than actually directing the water through the sidedrains. I've been told typically you want the ditch bottom slightly higher to actually force the water into the pipe creating somewhat of a "catch" for water to go in. Does anyone get my drift?

 

[diggerman]

Maybe I'm making this harder than it is. However these thigs do happen. We've had some heavy rains and water sat along the ditch nottoms for weeks at a time. Ground was so saturated already where the water wouldn't even perk into the ground.I guess that's a crash course in drainage 101!

 

[fattdad]

are you talking about a perforated pipe?

f-d

¡papá gordo ain’t no madre flaca!

 

[GoldDredger]

I like to see the ditch bottom to be slightly higher or even with the pipe invert, that way a sump isn't created with pooling water. Are you planning on constructing a headwall with your pipe? That will extend a bit of concrete away from the pipe invert. At the end of that construct a bit of 'turn down' concrete to block water going under the headwall.

Or, if not using a headwall, perhaps some rip rap outside of the invert extending away from the pipe a few feet. Or a gabion basket filled with rip rap if you are worried about water velocity carrying the rocks away.

I think what tends to happen is contractors don't really compact the disturbed earth outside of the pipe invert, then when it gets wet it settles and makes a bit of a sump.

 

[diggerman]

No headwall, just a long ditch bottom that runs underneath a few driveways. It ends into a local creek. But I think you've answered the question for me. I have heard the same...that typically either equal to or a bit higher than the invert. Even when we sodded the bottom it was still about 3-4 inches low. The contractor argues that is was per plan and it was to perform as a sump. Either way then, I think it was a poor design because the water litterally sat there for weeks until it turned green. Also, the elevation of the ditch bottom was close to water table. Anyways, the ditch (rougly 300 feet long) was regraded and brought up to a better elevation.

f-d...RCP no Corregated Metal Pipe. If it was CMP, would it be a different call?

 

[Drumchaser]

Te downstream FL of any pipe (RCP/CMP/Thermo) should always be a little below the ditchline or outfall FL.

If you have the reverse, scouring and washing usually occur.