We tried overflow pipes 4 times and finaly ripped it out for a rock spillway best thing I ever did.
I now have stable water levels. muscrats don't dig around the pipes. Don't have to deal with leaks around the pipe anymore. The field rock was free. I have a huge watershed in the early part of the spring and it handles the water well. Spillway is about 6 foot wide

"If people concentrated on the really important things in life, there'd be a shortage of fishing poles." Doug Larson