I am trying to build a sturdy end cap for a 18 inch galvanized steel culvert pipe corrugated..
The idea is to block off the flow in the pipe about 3/4 of the flow. The rest would spill over the top of the cap. I would want to use the outside ribs to secure the device and give it strength.
2 pieces would clamp on the pipe on the outside on either side and join together. Then a box would be constructed to carry out over the end of the pipe and a flat door/plate would slide down in a slot to block the water similar to an irrigation ditch gate that you see along a country road with a big screw handle on it.It doesnt need to be perfectly water tight.
Has anyone seen plans for building something like this?? I would make it out of high grade plywood and bolts and scrap 2 inch boards also...

 

If it's your culvert, can't you just raise it 1' and accomplish the same thing ?

And then you'd still have the added carrying capacity of the whole 18" unit if and when it's needed.

 

It cant be moved. the idea is to back up some water in the pipe so a smaller outlet pipe has more water over it