I have a small sediment pool before my pond. Glad I did it even tho it was a spur of the moment decision., but as always, you see thing that could be better after it's done. I don't have the area like you to run a valley to one side for major rainfalls. I really like that ability.
One thing that I would consider in your scenario is having a shut off in the pipe from the sediment pond to the main pond. Reason being is that if you get a heavy rainfall that brings suspended soils with it, it will pour into the main pond and turn the water brown for a week or so. With the shutoff valve, if you see that happening, you would have the option to stop it, open it back up once the big event is cleared up.
