First post - Glad to have found this forum.

We have owned 30 acres in the Ozarks and have been dreaming of a private pond. Had some difficulty finding a local pond builder but have now found someone we trust to give us a quote.

We are close to pulling the trigger on roughly one acre pond, 10 foot deep pond. Loamy silt soil but have dug several core samples and good usable clay a few feet down. Pond would be excavated with a lower dam as it would be damming a dry creek that occasionally has running water during heavy rain.

My main concern that I have talked with the builder about is that the area has a large watershed of 150 acres. Builder insisted that a concrete spillway and larger diameter drainage pipe are necessary. Concrete added some cost but not unreasonable. Also, the creek does move a good amount of gravel when runoff water moves through it.

So my questions are basically (1) how much runoff is too much (i.e. 150 acres) and (2) does anyone have similar issues with gravel/silt backfilling pond?

Thanks for input.

He's right 150 acres is a lot. You could probably use a siphon system without concreting the dam.

You would need to install some sort of bypass system for times of heavy flow. During heavy storms the flow into the pond should be very limited.

For a one acre pond in the Ozarks, about 10 acres of watershed is all that is needed. 150 acres will definitely wash out your dam within a few years, or at least fill your pond with silt.

My neighbor has 1.5, 4, and 7 acre ponds in a chain on about a 400 acre watershed by the time it reaches the lower end, and has had major washout and silting problems that simply cannot be fixed without spending many many thousands of dollars.

I can tell you that an oversized watershed can be worrisome. My 1/4 acre pond has about 25 acres of watershed, maybe 10 times what it should. When I had it renovated last year I intentionally added extra freeboard to the dam so that it can fill up more so than most ponds before going over the emergency spillway (read low spot on the end of the dam). This allows the water to build up more before topping the dam. I also have a 15 inch drain pipe that I have seen 1 foot under water as the pond was trying to overfill. Before the pond was renovated it had a 20 inch drain pipe and overflowed the dam once every couple years. No damage occurred however and the pond was 40 plus years old so it had been doing this off and on for while without compromising the dam. A lot of luck was involved, I'm sure. The pond was originally 10 foot deep and before renovation it was only 2 foot deep...it had 8 foot of silt in it that had to be removed. I would guess that the old pond was too shallow for fish to survive many winters by the time it was 20 years old.

I am not encouraging you to build this pond with an oversized watershed, as my pond already existed when we bought the place and is actually used to slow the water down before it reaches the front yard.

High amounts of incoming water can also cause temperature turnovers, rapid silting, and fast PH/water quality swings which can be hard on fish populations.

All that said, I would not intentionally build a pond with too much watershed. Like John says...look into diverting some of that watershed.

I suggest walking into the local NRCS office and see if they will design your pond for you. Mine did, even came out with transits and took measurements and flagged it. They will either give you data on primary and emergency spillway requirements, pipe size, elevations, etc or perhaps they will say don't do it due to the watershed being ~10x larger than recommended. Its at no cost to you. However not all Missouri counties have the ability, or they may be backlogged with work.

That's some good advise right there! Missouri has some of the best conservation departments in the country.

Thanks guys for the responses. I think you validated my concerns. I cannot picture a bypass/diversion of the watershed. Will have the conversation with MDC and the builder to see if they have suggestions.

Look into installing a siphon.

If you are determined to build it, look into building a sediment pond of about 1/4 acre above the main pond in the watershed. It would not have to be built to standards to hold water long term; only for a few days, like a detention pond for flood control. It would catch the bulk of the sediment, plus slow the inflow.