Meredith - when we were digging the pond, my husband had them dig the shelves and then after the liner was in, he foamed the rocks standing up sideways so that they were a walled off shelf, but with small gaps to allow water to flow freely. So, essentially the water from the bog runs directly into the pond with the pea gravel aiding in the filtration process. We have pumps that dump into the bogs as well as plants that are planted into those areas.
I have pictures before the plant growth so you can see what I am referring to and a photo that was taken 2 weeks ago for comparison
Quite often when people are digging ponds, I have seen where they install plumbing into their bogs so that they have a permanent fixture for the water to filter through their bogs.
I have seen some beautifully planted bogs. The water celery took over my bogs - it is great for filtration, however, quite an invasive plant. If/When I do it again, I would not put in the water celery.
March
April/early May
July