When you first posted about your situation, I hadn't really considered my own situation as relevant. But after you've added more details, I see my situation is not that far off.
The main source of water for my pond is a horizontal inlet pipe in the upward pool side of a dam on a medium sized creek; the inlet pipe is perpendicular to the dam. The creek varies from 15-25' in width, 4' to less than a foot depth. The dam is made of sandbags, rubber & plastic sheets, and 2'x4' concrete patio slabs. Rebar is used for reinforcement.
The level of my pond is directly related to my creek dam holding water. The dam is basically 2.5' high meaning that if I had a total breach of my dam, I would loose 2.5" of water in my pond. When the dam is good, that's basically full pool for me, except in super high water situations; in these cases, when the creek runs high, it can run 4-5' above my dam. At those times, my pond will be 4-5' high above normal.
At any rate, many times a year, my dam gets breached, but not the full height. Bur more important, the water always finds a way under, and we haven't found a way to fix that. When we find an underwater leak, we try and plug it up with sandbags, or rock-filled bags, and rubber sheeting. That holds for a while, but then ends up leaking around all the blockage we crammed in. Sometimes it holds for days or weeks if there's no heavy downpours.
We do fill sandbags and re-do parts of the dam every year, sometimes twice a year. It's always the same parts of the dam that go, even when high water situations have water raging 4-5' high over the dam, and it's usually only a section of the top row of sandbags that get's pushed out.
The good part for me is that even with total breach of my dam, my pond still would have a max depth of 12' feet or so. So if I choose to neglect the dam for a season, it's not a huge loss.
When I was a kid, if there was a creek, I'd be damming it up. I guess I'm still doing that.
I'm also looking for any input on DIY creek damming technique.
