I should have said this in the very beginning but, my pond is really a kind of "impoundment" of a perpetual stream so, there is not really any time (except during the worst of the drought) that water doesn't run out of my pond. I'm guessing that is why they put in the shutter system.
Though, it could be said that my drain box is kinda like a gigantic standpipe if I block off the opening by putting up all the shutters and letting water pour in over the top. But, that would leave practically no safety margin other than the spillway and water would be within a couple of feet of overtopping my dam. I don't think I would ever do that.
The other 2 factors (which we control rather religiously) are: beavers constantly trying to build in front of the shutters; and all that floating timber - tons of it - that tries to float it's way into the box. We keep all of that stuff cleared out - at least once per week.
And that explains, in large part, why this question is so interesting to me. I have to protect my dam! If I were to lose the dam, I can neither afford to rebuild it nor could I ever get a permit for it.
