I have a large flood control lake (60 acres). It has a large fluctuation of water several times a year. Usually only 5 foot or less over full pool. This last rain it is up 10 to 11 feet. My question is the in coming water is it replacing the bottom water or the top water in the lake? Or does it mix in with all the lake water? I would assume the incoming water is full of oxygen.
What fish will fallow the water out of the lake. I have put in CC,BG, RBG,WA,WP,BCP, LB and grass carp. Fish that made their own way in are BH, common Carp and GSF. Am I just chasing a dream by putting these fish in and they just wash out and go with the water. Catch rates are very low but I know I stocked way less fish than what I needed , do to cost ($5000. so fare).

I recently tested the DO level of rain runoff coming into my pond and found it to be 7ppm, pretty good considering my pond water DO level was a little low at 5ppm.

My take on what happens to the water inflow with respect to what it pushes out has most everything to do with temperatures of the inflow AND the lake waters. Cooler water sinks until it gets colder than 39 degrees F. Assuming that you do not have inflow colder than 39 degrees F andf your inflow is on the opposite side from the overflow...Cooler inflow would mostly push out the upper layer of your lake water...cooler water enters and sinks causing the upper layer at the overflow to exit. If the inflow is warm, it would not sink and most likely travel across the lake's surface and exit itself. There will be some mixing due to the turbulence and potential temp differences, but, in general, the above should be mostly what is happening.

Disclaimer: I do not have actual experience with the matter...just my book learning coming out. I am more curious about what effects massive inflow could have on turning a BOW over unfavorably...my little BOW has extreme inflow events on occasion.

As far as fish going over the spillway: Young fish seem to be more prone to that. I have heard that carp are more prone too. I stocked about 600 panfish in my 1/4 acre pond and have only found 3 HBG that have escaped to the yard/downstream ditch over the course of two seasons. I'm sure their were more, but surely not many more.

It would of been nice to know what the water temp. was before the rain. I new it was on the colder side do to the past 2 rains where it came up only 1 to 2 feet. Grand kids were swimming and did not stay in very long do to the cold water.
My thoughts on the water temp affecting the incoming water were the same as yours. But as the water was coming up I had to go out in the water to reattach a paddle boat that only had a 5 foot rope tied to it. The water was very cold by the bank, but by the time I was shoulder deep in the water the lower water seemed warmer than the water next to bank. I may have just gotten used to the water temp but as I walked out it seemed colder at the bank.
I have caught carp, bass and wipers below the dam, both were 10 to 12 inches long. Just wondering if all of the fish I stocked left the lake with the high water, or just a few of the fish.
Thanks for the insight of your pond.