Pond Boss Forums Thread Like Summary - Raising water level?

I have an existing farm pond with a 15-inch green PVC outflow tube. The end of the pipe on the pond-side of the outflow pipe has been cut off so the bevel is gone. I have plenty of dam and would like to raise the water level about 18 inches. Any ideas on the best way to do this?

Update: My Agridrain inlet water-control box has been in service for 12 years now and it still works as it did originally except for a slight lowering of the upper PVC board due to beaver chewing... Beaver are now gone... It is located under my fixed dock which limits UV exposure, but thought that folks considering this might want to know.