For your friends pond I assume the cement over flow is the emergency spillway?
If so, the cement should be checked out to be sure it will be able to handle all the water the current metal pipe used to handle plus an extreme rain or snow melt events.

I’ve not repaired a pipe like this but after seeing some of the methods they do scare me a little.
One thought is to install a plastic pipe inside the metal pipe and pour cement in between the two pipes. But having a valve in the mix will prevent this so called fix.

Another thought is to just fill the pipe with cement to eliminate the overflow. Question here is how big of diameter is the pipe and the total length down and out is the current pipe to figure out how much cement is needed. Plug up the outlet and call in a pumper truck.

Make sure in any case that where the pipe going the dam is sealed again, even if cemented in and not in use the outside diameter can allow water to seep out which that leak will get bigger over time. Find some local clay and place it around the pipe on the water side of the dam, about a foot thick or more, sort of like a patch. If no clay can be found check out the Pond Seal page for the audio, http://www.whatpond.com/pondseal/ Or send us an email with the pipe diameter, location and we’ll figure out how much is needed and costs.

I would still add a new overflow pipe instead of using the emergency spill way for the water to leave the pond. Over time there is a lot of water flow leaving the pond and if the spillway is not built large enough or strong enough it will be the next potential leak point, possible erosion which could become a dam failure. It doesn’t have to go to the bottom of the pond but at least down below the frost line 3′ minimum depth.

Hope this helps?
Be careful and caution anyone downstream.

Darrell Rhoades