In our new 1 acre pond I would like to raise the water level 1" by putting a small block on the over flow. This would be approximately 27,000 gallons of water. Is there anything I should be aware of that I could mess up?

I wouldn't sweat 1" or even 3". The only thing is by blocking off part of the overflow pipe you will be reducing it's total volume capacity in case of a large rain. 10"-12" dia pipe?

If you have an emergency overflow area, then I really wouldn't lose any sleep over it. If the pipe is the only overflow, then I might give it some more thought if I've seen the pipe at capacity before.

Did you mean 1 ' ? One foot or one inch?

My overflow pipe is 12". My water shed area is way too small for a 1 acre pond so I'm not too worried about emergency water. I do have an emergency overflow but I suspect it will never get used. I filled the pond with the help of a stream at the lower end of the property that I pumped up.

1"

I agree with ESSHUP. I raised one of my ponds by 6-7 inches a few years ago. It is still about 18 inches below the emergency overflow. It has given my pond several more years of life without having to rework it.

You likely will not even reduce the flow where your pipe looks to be almost horizontal. A horizontal pipe unless it has head pressure from being completely covered a ways by water will not flow full. There will always be an air gap at the top at the outlet. So cutting down the inlet at the bottom edge by a small amount likely would not even affect flow. If the pipe were slanted down and expected to go into siphon mode at some point, then the restriction at the bottom of the inlet might come into play and restrict flow a small amount. But as long as there is an air gap at the top of the pipe at the outlet, I can't see where 1" at the bottom at the inlet would ever make a difference absent significant head pressure.

I raised my pond level above design by 3".

The important factors are:

that the dam is structurally sound enough to hold the extra pressure, which is should be or you are in trouble should the water ever get to emergency overflow height.

That there is sufficient height of the dam that there is no possibility that water will overflow the top of the dam (which has to do with the size of the watershed in relation to the surface area of BOW or in other words the surge capacity of the pond)

That the emergency overflow can handle any excess water flow that the overflow pipe can not (related to watershed size and width of emergency overflow).

As long as you have plenty of capacity to get rid of excess water and have a rather small watershed in relation to pond size and do not have huge rain events I would not worry about raising the pond an inch or two or even a little more.

My emergency overflow was designed to be a foot above full pool with an 8" overflow pipe. In other words when the water got somewhat above 8" full pool the overflow pipe would enter siphon mode and increase its flow rate (it is slanted downward so can get significant increase flow from siphon - horizontal pipes don't have gravity to put them into siphon). Then if the overflow pipe could not handle the flow when water got 1' above full pool or in other words 3" above my pipe the emergency overflow would come into play. Now the way it stands, once I'm above the 8" overflow the emergency spillway will come into play so likely my overflow pipe will never again enter siphon mode. I've had one rain event that brought water level just right at the edge of the emergency spillway. That was 12" of rain in less than 24 hours. My pond also has a very small watershed in relation to the size of the pond. Which is a good thing in normal rainfall years and not so good when droughts come along.

One way I have thought of raising a pond level and making it variable (but don't know how well this would actually work because have never tried it) is to put a 90 degree elbow on the overflow pipe so it could be rotated to the desired water level inlet height. This might change the water flow characteristics of the overflow pipe and give a real boni-fied engineer a heart attack though so I'm not recommending it. Would also probably need to be a smooth PCV type pipe. Not sure if you can get elbows for corrugated pipe.

Right now my old pond has a rip-rap earthen spillway. If I get energetic this summer and build another pond right next to it, I plan on taking some of the extra clay excavation and after cleaning out the rip-rap and getting a solid base plugging this spillway up and putting in a pipe overflow with an emergency spillway further down at the end of the dam. If I do this, am going to raise the water level another foot. I have plenty of dam height for the watershed this pond encompasses.

Thanks for all of this info, I raised it 3" based on this. Now all I need is the rain!

ToddM,

I am curious, why did you want to raise the pond level 3 inches?

Many reasons. Dock is too high off the water being one, and having too small of a watershed area I will be able to keep my level up higher in the dry times.

I think snrub hit it on the head. I raised mine 6" over design looking at all the factors snrub laid out and also held a short on-site meeting with my dirt guy and SWCD contact. I think the 2 most important points to consider is dam width and emergency spillway size.

Don't know if it is possible but you could always remove the block before a large storm or you are hitting capacity.

I would not worry about pressure, flow or anything else when raising an otherwise solid dam, an inch. If flow were a concern, cut a slight slant on the inlet of the overflow pipe so you have more open area than a squared off end.

One inch of water will add a whopping .036 PSI to the pressure on the dam.

We just raised ours by adding a concrete spillway 8 inches above the old one . our levee and runoff is fine we just wanted to add a few more inches for drought .not sure how it will work but with possible storms next few days we will soon know

Yeesh! You must be in a hollar where the mountains suck all the moisture out of the clouds before they get to you.

We are saturated in the north eastern part of the state. I think my ponds have been above full pool for about two-and-a-half years. And -- it has been raining for the last two days, with more rain forecast for tomorrow and the next day. I spent about 40 hours on my tractor keeping the driveway clear of snow this past winter. We got 18 inches of snow starting in October, and got more last weekend.

I just hope my frogs and fish don't drown. So far, even my ramps haven't shown their beautiful leaves.

Ken

Yes Ken, we are at full pool also but I need water now since I just blocked the spillway yesterday. Well wouldn't you know it, overnight we got plenty of rain to fully fill us up to the new level. The overflow pipe is now partially submerged, but the pond looks much fuller. I'll put up another photo tonight of the new level.

Stocked it today with LMB, RE, BG, CC, FHM and one grass carp. Installed the airator and added a half quart of blue dye.