Pond Boss Forums GENERAL QUESTIONS Help Leaking overflow standpipe in 1 acre pond

Being a cheep skate as my wife describes me I always look for the easiest and cheapest way first. Then do it right. But my thoughts would be buy a larger culvert and set on top. Get a trash pump with a 3/4 or 1 inch ridged pipe on it's exit side and use water pressure to dig out the dirt between the two pipes. Hopefully with 4 to 6 inches of space between pipes. When you believe you are deep enough go an extra couple feet. Then put some thing on top, you can use a bobcat or some other heavy equipment to push it down some more to hold the water out for a while. Fill with concrete on the bottom for 10 to 12 inches. Hopefully it would hold water from coming in, then fill with bentonite or if it fills with water, pump water out and fill with more concrete. Your picture shows a lot of holes in your pipe. So my guess would be your pipe was a cheaper product that was used from the start. It will just keep getting more holes.
OR put new pipe on the inside if it would not cut down size to much for your drainage area.
You could plug your drain and put in a syphon type drain, would not have to dig all the way to the bottom of your pond that way. Probably the best choice. But if you would cut it out to the bottom you then could remove the muck on the bottom. See how it gets expensive. You have to love these money pits.