Canepole, if your spillway pipe is like a pipe that sticks out of the surface of the water, perpendicular to the water surface, then all you have to do is take a pipe (PVC) of larger diameter, and "sleeve" it over the actual stand pipe. Make sure the outer pipe is taller by a few feet than the original spillway pipe. The outer pipe should be at lease several inches greater in diameter than the original pipe.
Then you can take a metal shaft (like a dowell rod) and stick it through the outer pipe to serve as a stop to support the outer pipe; the rod will rest accross the top of the original pipe.
The outer pipe should be several feet higher than the original pipe at whatever your comfort level is for high water.
I may be over simplifying this.
I'm sure someone else will chime in.
