Rainman ,
Thank you for the reply.
The issue I have is it appears to be leaking in a corner and at the 3rd 8" board.
One thing I neglected to mention is the dam is a county dirt road. They were given the ROW, but had to maintain the discharge pipe up to the box. About 30 yrs ago the discharge pipe was replaced by the county its located in and they built a coffer dam directly in front of box and it covers the bottom 3 ft of the box. All this was none of my doing, Ive had it aprox 25 yrs. It was handed down to me from a family member. I can go to a larger diameter pipe but, can't find the proper information to base a reasonable determination on the correct size. I've got to do something in the next couple of weeks or I may lose everything in the pond .
Another issue is I've had someone tamper with the spillway before. I think it was a guy I had prosecuted for trespassing and fishing w/o permission , but can't prove it. The locks were cut and several boards were pulled and tossed in the water, which is why I would like to do a standpipe to prevent this from happening again.