robo2011, your example interests me for a few reasons. If do this design and I'm holding the pond at the lower level I might end up with a similar Alligator weed problem. The difference would be that I could close the lower siphon and during the wet season the weeds would be covered with 2 or 3 feet of additional water, killing them.
Then after holding the water at the high drain level for several months I might get the weed growing again. This time I could open the lower drain and leave the weeds high and dry.
I'm sure there would still be problems controlling aquatic weeds with this design, but I'm trying to get to a point where I can intelligently weigh the variables. One thing I'm fairly confident of at this time is that a gradual bank will be noticeably easier to maintain.
I appreciate all of your personal experiences very much.
