Rebuilding a pond

Question
We have a pond in the yard that is naturally fed, and drains out thru a pipe that was probably added 50 + years ago. When the water is right to the top of the pipe it flows into it nicely and I can se it going out of the other end. However when the water rises above the pipe and is higher than the opening it seems to slow down and then overflows out the back.
Is this a vacuum effect happening, or do you think the pipe is semi- clogged and just can't handle it, thus backing up?
Also, can you suggest a book for me to look at before I have the pond rebuilt...liner, underlay, etc..

Thanks in advance for your time and expertise.

Rob

Answer
I would think it is either a semi clog or the pipe is too small  in diameter to accomodate the flow. How big is the pond and how big is the pipe? As far as a reference book knowing your situation the only I would think is search the
Web until you find your answer. I appears you have a very unique but greatly envious dilemna. Without seeing it I would think it is the size of the pipe in relation to the water flow. If it backs up that much the flow should keep the pipe clear.

               KEEP PONDING & KEEP IN TOUCH
                      Leigh