snrub,

A few years back, I was looking at a project similar to your pond, where the watershed would be carrying in a large silt load. My wife, said my only chance in hell of investing that much money was if she would have a "beautiful" lake.

My business went a little south before I made enough money to buy that land, but I sure did a lot of planning! I did plan a sediment settling pond much like yours.

My only design modification was to use a gravel-filled gabion basket for the water interchange between the settling pond and the main pond. I was going to put geo-fabric on the bottom and the "downstream" sidewall, and then fill it with the recommended size of gravel.

This system should allow a slow exchange of water from the settling pond to the main pond, but no exchange of fish or fry if you did want to try to manage the forage pond.

It has the added advantage of doubling as an emergency spillway for that 100-year rain event. If you had 2' of freeboard, and installed the top edge of a 20' long gabion basket 1' above normal pool, then you would have 20 square feet of outflow (equal to a 42" pipe).

If you had it perfectly level, it would go from a gushing waterfall to a trickle fairly quickly as your run-off water crested. Hopefully, there would only be a very short window for adventurous LMB to swim upstream.