Thanks for the replies and thoughts.

A few additional notes:
We have a total of 7 lakes using galvanized steel through pipes with some over 40 years old. Estimated life on such pipes is 40 years and the first point of failure is typically collapse of the down pipe where it enters the lake bottom and secondly rust through on the top of the through pipe, due to condensation, resulting in collapse. At this point the down pipes are looking OK. I suggested various plastic pipe solutions be considered along with the traditional galvanized steel to the engineer but he chose the galvanized steel and offered good reasoning. We recognize that at some point in the near future we will be replacing the old pipes when they fail. Hopefully, with enough time between failures to repair only one lake at a time. This new pipe should give us another 40 years on this lake.

The dam that failed did not fail due to the through pipe, in fact the through pipe was still in place after the water receded.

State water regulations for ponds of our type require they include a means of draining the lake. This essentially mandates a through pipe with a gate.

Keep your thoughts coming. Still need an answer to compaction under the through pipe.

Bo

If you don't care where you are you ain't lost. OMB