"Buyer Beware" ... excavation of a pond
 

Hello,
One of the projects I'm researching is for the construction (excavation) of a small pond (approximately 30' x 30' and probably tear shaped). I've already had the legal aspects of this tended to and was told I do not need any type of a permit, that the soil in this area worked well for such a pond and where it would be dug would not interfere with rivers/streams/wild life, etc. Thus, all is good to go.

[The area has about a 10% slope ending in a natural trench from the water that has been flowing underground in that area for many years. I know the dam side would be on the low side of the excavation and would quite likely be rather high; thus would probably need to be sloped. It would, also, need piping thru it. The specifics of getting this dam built and the piping appropriately placed in that dam is part of what I'm researching. The trench that is already at the low end of the area will have a small "concrete" dam (about 5 ft long and about 3 ft high) wiill be about 30' - 40' from the dam; and it, too, will have a pipe thru it as well as an indentation at the top for any overflow. We have many nice rocks that can be placed wherever they are needed...3 chimneys that were torn down...and could be used to outline the trench, maybe even placed in slanted formation up the low side of the created dam (larger rock at the base and smaller toward the top).]

Now, I've spoken with several people around the area who do such work and I'm getting different information; thus, my inquiry here.

If you were having a small pond excavated on your place, what would you want to know before hiring someone to do it? What would you want to make sure that person did? Would any chemical/material/etc be needed to slow/stop leaks/seeping? Any informatin to help me get it done well would be appreciated.

The above statement causes me to think that you will have many high dollar problems keeping water in your pond. Underground water flow will require something to contain the water. Depending on the material that is there now, may require the use of a membrane.

Bentonite clay is used in some situations to make a semi impervious layer to retain water.

Your best advice will come from local folks. You might get on Google Earth and look for nearby farm ponds, then go asking questions of the owners.

I think you're getting way too elaborate. There was a pond constructed on one of our parcels that is very similar to your situation. You do not want a pipe through the pond. In our case the natural drainage trench was blocked when the dam was built.

On one end of the pond, preferably not in the dam, a spillway needs to be cut to avoid a heavy rainfall from dumping enough water and overtopping the dam. The dam will be higher. Talk to someone at your local NRCS office. They will have loads of info plus an engineer in the region that can look at your situation for free.

....................As test , I'd hire a backhoe too come in and dig a ditch , down too the same depth situated at the center of your pond where it would be located . Next I'd align the water runoff ditch with the test ditch and wait for it to fillUP . Then , you can see just how long OR , IF it is going to hold water . , fordy

Best resorce is going to be your local county soil management office. They know what will work best in your county with the type of soil and topography and will even come to your property and develop a workable plan for you at no cost. They can educate you and point you in the right direction even for the actual construction work.

Goat lady has it right. Get help from the experts. There are also programs that pay part of the cost.

No drainage pipe on ours, either.

I'd find a local guy who has build successful small ponds in the area...get some references...He should do some test holes first to see if the clay in your area will hold water. If the ground doesn't seem to be able to hold water, there is a substance called bentonite which you can use to "line the pond" with...look into it. Good luck.

Darren, we really don't want water running over the dam once it's constructed; nor do we want another trench created at the end of the dam for any run-off water. It is the piping thru the dam that we are thinking will work best as a spillway (more controllable and not disturbing to either the dam nor the areas surrounding the pond). Also, we have been told there use to be a very nice spring in that area...thus the deep trench; and we are hoping to keep that trench controlled as we're pretty sure this pond will be ever moving from the underground flow of water. If the pipe is placed correctly, there should not be pond water running "over" the top of the dam. As mentioned "in general terms", I've already spoken with the NRCS office and one of their engineers has already visited us and looked over the area. I have also spoken with what this engineer called a "soil expert" for this area and this person told me the soil around here nicely supports excavated dams because of its contents.

Fordy (and Goatlady), I've actually done that already (in part). I did not dig an entire trench; but we did dig down over 4 ft and watched to see how the water reacted in it. Also, when the dozer cleared that area of our property, it was during an extremely dry year and, as that huge dozer went over the area where the pond will be excavated, I actually saw the land on both sides of that dozer move like waves in an ocean. This tells me water is already being held there. I just don't know how deep it is.

I do so appreciate the help you have all given. I've contacted a few people who dig ponds. [One has already visited and told me he would do it for $3,500, which seems outrageous to me. Another didn't even inquire if I had appropriate permits, just told me he would be glad to dig it. Another (one who "did" ask about permits) will be visiting as soon as his calendar permits.]

I will do some research about this "Bentonite". I may be that I will need a roll of it handy.

LOL! Bentonite is a pure white clay that has the capacity to expand 10 times in density when wet and absolutely become impervious to water leakage. It's mined by the ton in Wyoming, bought by the bag, and spread like fertilizer in the bottom of a "dry" pond, then the water is "added." Totally nontoxic to animals, etc.

Bentonite is sold in 50 lb bags. It's a type of clay. I'm surprised you saw the "land move like waves". You are most likely correct in thinking water is trapped below. Especially since a dozer does not exert the same pressure on the ground as a truck would. That means you have a layer of soil below the ground that is saturated with water next to the bedrock. I saw the same thing during the construction of a new school.

The report from the soil borings clearly showed the saturated soil in the bore logs. That's the reason the school board decided to go with piling under the school. When the piles were bored, I picked up hand fulls of the soil as the auger drilled down to bedrock. When you squeezed the soil, water came out, not like squeezing a sponge, but still a surprising amount of water.

That's potentially a very unstable soil condition especially if the dam is built on top and the layer extends beyond the the downstream face of the dam. Do you have any springs below where you are planning to put the dam?

The school needed a water storage tank for the fire protection sprinkler system. That had to be built on a special foundation to avoid sinking since they did not put it on piles.

Is there any way you can post pictures of the site? I can do the same for our pond in the next few days so you get an idea of how the spillway was built. Our spillway is maybe 15' wide with a bottom about 8' below the top of the dam and extends out of the pond area without passing through the dam.

It was shaped to go around the dam and lets out below the dam. At a minimum it would be a good idea to pave your spillway with stone that's embedded into the dam if one's built. I'm not sure of the size of pipe or the numbers of pipes needed to keep water from over topping the dam. That will be determined by the amount of flow into the pond from the watershed in an extreme weather event such as a hurricane.

The NRCS should be able to calculate the runoff that will flow to the dam from the area of the watershed leading to it and the projected rainfall from a hurricane. That will be used to size either the spillway or the cross sectional area of the piping needed to avoid the dam from being washed out.

I'll post the pictures of our pond and dam within the next few days. I think the pond may be similar to what you want to build since it was constructed on a slope and is not that large, being much less than a quarter of an acre.

All ponds need a spillway or outlet, this is several feet below the dam crest so water will not overflow the dam in the event of a large inflow or the pipe becomes compromised and plugs. I have dug many "waterholes" for livestock and wildlife without a pipe. Pipe can be used 2 ways, layed so the bottom is at pond water level, thus exiting high on the bank of the pond, needing a spillway, or with a riser in the pond and pipe layed in the bottom to exit at ground level outside pond. Clay to seal the pond is best and cheapest. Bentonite is used if that doesn't seal, usually spread and worked into a few inches of clay material, a rototiller works good. I have never needed to use it. All vegetive matter needs removed for the entire dam base area and the "start" of the dam base needs keyed into the soil below. This key is a trench dug deep enough to set in stable soil, it keeps water from eroding the soil and starting a "leak". All soil is compacted and moisture is important so it will compact and seal. A sheepsfoot roller is used and may be vibratory.. Some soils can be wheel rolled....James

[QUOTE=motdaugrnds;5767424] It is the piping thru the dam that we are thinking will work best as a spillway (more controllable and not disturbing to either the dam nor the areas surrounding the pond). Also, we have been told there use to be a very nice spring in that area...thus the deep trench; and we are hoping to keep that trench controlled as we're pretty sure this pond will be ever moving from the underground flow of water. If the pipe is placed correctly, there should not be pond water running "over" the top of the dam. QUOTE]

In rereading this you are making it complicated. More controllable? Are you thinking of laying the outflow pipe in the bottom with some sort of valve? The spring.... Is it going to be in the bottom of the pond? Depending on pressure of the water exiting the spring, if not enough you will be plugging the spring, or, your water level will draw down to the spring level. The spring should be in the top 1/6th of the water level or, above and seep into the pond....James

You need to get the soil conservation folks out there before you spend a LOT of money and make rookie mistakes.

They've already had the Natural Resource Conservation Service (NRCS) out there. That's what the soil conservation agency is now named. Same agency, diiferent name.

Imho, if you don't have the right kind of soil (preferably clay), lining with bentonite is a non starter, as 50lb bags won't go very far.... the bentonite would cost more than the dam...

Can you make it bigger than 30'x30'? Personally I'd make it as large as I possibly could, and as deep as possible, to hold as much water as you can.... so in the drought years, your covered. My first pond I built (with a large tractor and front end loader) was around 30 x 60, 12' deep.... went dry in a drought year.... saved up and built one that'd handle four years of no rain. A lot easier building it bigger from the get go!

Personally, I'd be on site, during the excavation... just to make sure what I'd envisioned was happening. Also, for that kind of money per hour, I'm gonna watch. On my last pond/lake project (lasted several months) I actually knew the dozer operator, and mentioned one morning that his d7 'might' be low on fuel... he looked in the pit and saw where I'd piled dirt the evening before... I told him the blankety blank beavers were moving dirt... wink wink nod nod... I put in three extra hours on the dozer and hoes, after he shut down at 5 each evening... (at no cost to me!)...;)

Darren, that is exactly what we apparently have; because no matter how dry it gets, there is a large muddy spot in that area, though I don't know how deep it is. After reading your post, it becomes obvious to me we do "not" want to damage that bedrock now holding the water.

James, I'm thinking you're absolutely right. If we excavate a pond "below" the bedrock that water ("soil moving like waves") is sitting on, then we would not be taking a chance of plugging the spring. It could continue to flow, being caught in the pond; then continuing to run off down into the trench it already created.

Picture below shows area. The yellow dots is where the "wavy" land was seen. It doesn't look very wide; however, the width of our land straight across (from where I took the picture) to where the boundary line runs is about 80-90+ ft. Then, of course, going down the flow of the water (shown by white lines) is 100+ ft.

http://i114.photobucket.com/albums/n.../Pond/pond.jpg

Since the water running into this area is spring fed and has been since before we even bought the place, I have little doubt it will continue. Also, the "wavy" land showing up late August during one of our worst droughts seems to me to be another indication it will be ever-flowing.

As for the dam, itself. The professional who came out (as well as the soil expert I spoke with) suggested the dam at the pond have an over-flow pipe run thru it so water will "not" run "over" the dam itself. David is wanting this pipe to start out rather large, bringing it down in size to create some water pressure for some possible power that might help us get off the grid a bit.

The way I'm invisioning this now is 2-fold with the "wavy" area, of course, being "above" where the pond will be excavated and the depth of the pond being 6-8 ft under the top soil (or to where bedrock is discovered). The size would remain the same (about 30' x 30') because I want it at least 20 ft from the boundary fencing as well as from where I stood (near our drive) to take the picture.

Texican, David has experience with a backhoe and a dozer; however, I don't like the idea of a possible situation occurring with someone's machine that we might be held accountable for. I think you lucked out!

These are the pictures of the pond I mentioned. The dam was built on a slope. It intercepts the water from an estimated ten acre watershed. The pond is has the longest dimension running east west. The ground slopes up to the north and down to the south.

The spillway is on the east side of the pond. It is not part of the dam. It was dug out of a slightly sloping area on the east side. The spillway transitions to a swale that goes east then turns somewhat less than 180 degress to continue below the dam. It ends at a rough road that leads down to a creek.

The first picture below is looking northeast with the swale in the mid foreground and the dam beyond that. The top of the dam can be spotted by the high grass growing on it running right to left. in the middle of the picture and ending in the middle of the picture. The grass is allowed to grow to prevent Canada geese from settling in the area and provide habitat for a dragonfly study. The very light slightly green line running left to right is the middle of the swale to carry water from the spillway. Look for that line by starting at slightly above the base of the tree in the immediate foreground on the left.

http://i411.photobucket.com/albums/p...n/DSCF2284.jpg

The picture below is looking east to the end of the swale (valley) at the road just to the right of the small building in the picture. The dark object is in the swale.

http://i411.photobucket.com/albums/p...n/DSCF2285.jpg

The picture below shows the actual spillway looking south while standing north of the dam. The spillway is hard to pick out since it's only about three foot lower than the dam and about 15' wide. The two small trees close togther in the middle of the photo are at the center of the spillway. The larger shrub to the right is also in the spillway.

http://i411.photobucket.com/albums/p...n/DSCF2293.jpg

The picture below is looking east showing the dam to the right. The dam has the grass growing on the pondside.

http://i411.photobucket.com/albums/p...n/DSCF2288.jpg

The picture below is still looking east but showing more of the dam.

http://i411.photobucket.com/albums/p...n/DSCF2289.jpg

This picture show the pond looking northwest. The land to the west of the pond slopes upwards. That is the reason the spillway and swale were excavated on the east side.

http://i411.photobucket.com/albums/p...n/DSCF1833.jpg

Thanks for sharing Darren. I do hope I can learn to create a pond that is as healthy as yours looks.

First talk to you county extension agent. They can give you a contact you pay for through taxes to come out and advise you. There are even programs to help. But make sure you look at all the details in any agreement.

It's really not that healthy. There's an aquatic weed problem that I need to get after. I got a jon boat recently to start the weed yanking. Otherwise I'm concerned the dead vegetation will start affecting the fish.

If you're going to run the pipe through the dam, look into a collar to fit around the pipe/s that will help cutoff seepage through the dam alongside the pipe/s. I'd make sure there are no rocks near the pipe/s. If you're going to use bentonite, I'd mix it into the bedding and fill used around the pipe/s.

Thanks Darren. I appreciate that suggestion.