In my new 1/4 acre pond I am pulling the lawn irrigation from the pond and refilling via a 30 gpm well flowing through a large waterfall back into the pond. Typically the well runs 6-8 hours a day to replace the water that the sprinkler system has used. My goal is to keep Trout so in the hot summer months i may need to run the well more to keep the temp. down and the excess water will run out of the 10" overflow pipe. Here lies my question. My contractor placed the overflow pipe about 5-6 feet away from where the waterfall enters the pond when I am running to cool down pond how much of the cold water that is entering the pond is flowing right back out prior to cooling off the pond? Hopefully this makes sense.....

Thanks

Welcome to the forum! The question makes perfect sense. I don't have an answer for you, but I can tell you how to answer the question yourself.

Cold water sinks. So, theoretically, if the overflow is coming from the top water in the pond, it should be not mixing. BUT, here's how you check.

Measure the water temp where the waterfall goes into the pond.

Get a cheap wired indoor/outdoor thermometer to do that, and use the outside setting.

Measure the surface water temp in the pond opposite the waterfall.

Measure the outgoing water temp.

If that outgoing temp is more than a degree or 2 different from surfact pond temp on the opposite side, then there is mixing going on.

I would do the test esshup suggested, but take it a step further and measure areas surrounding your inflow on the surface.

You'll probably find that your well water is initially cooling down a rather large area, before it sinks like a rock!

My guess is you'll be loosing some cooling Btu's out your overflow if it is that close.