Draining most of the parking lot lake, 08/21/2017

Please see the video uploaded just after this,    • Two grown men having fun in a parking-lot ...   , which will show us in the parking lot before we did this. It will answer a lot of the questions posed below.
Note that this is not the pharmacy parking lot. It belongs to a bank.
We had to visit the pharmacy just east of this. Housemate pointed out that the parking lot was a lake! He then inquired if I wanted to wade in it, and I said I would.
After he got back from the pharmacy, he joined me. (He does not go barefoot all the time as I do; though he does enjoy doing it under the right circumstances.)
We waded around for about five minutes (the vid upped after this), and as he was ready to leave, he found a pile of leaves and began moving them with his feet.
There was a drain under them, and it began sucking the water down!
I quickly turned the camera back on to record this.
When I shut it off, the only part of the lake that was left was where the pavement dropped below the level of that drain; the other drains were plugged by something other than leaves.
At 2:15, the rotation changed direction and you can hear the sucking sounds as the water drains. He feels the suction at 3:13.
At 4:00, he clears some of the leaves but just throws them back upstream! I tell him they will return, and you can see that. I had to laugh. He gets the idea at 5:27, and I remark, “Don’t move the same leaves twice.” I note at 6:23 that the water level is almost down to “surface” though “pavement” would have been a better choice. We then leave the whirlpool for a couple minutes, starting at 7:21, and I point out how much water has disappeared by showing the high-water marks on the pavement and curb. In addition, he shows on his leg how much the depth has decreased at that grate (7:59). There is a drastic difference in the water level at the end compared to what it was at the beginning (as shown by my feet over the grate)!