Pond Boss Forums POND CONSTRUCTION Building a dam Dam vs sides ?

I have been reading everything I can on here, and purchased three books to date, but the one thing I still have yet to understand is this.

If the area I am thinking about building a 5 acre pond is a natural bowl, with a natural wetland excape (below the surface I suspect) Do I still build a dam with a core, or just remove the top soil, process soils and add additional clay?

I see pictures of ponds in "Perfect Pond Want One?" where it appears the whole side is a "dam" too, I really hope I don't need to do that into each hill.

Nutty,
Your description sounds pretty much like what I had to start with. If it has a decent watershed, you are blessed. It can take a long time to find this kind of topography, particularly with the pondsite completely captured within your property boundaries.
I have not perused PPWO? yet, so I can't relate to your findings therein. The one thing I want to define further, tho, is your statement about a "natural wetland escape". It sounds as if you say that the area where a dam would be constructed is currently a wetland or marshy zone. If this is correct, does it actually hold water or are we talking minimal retention only when it rains...then it dissipates and runs off further downstream?
Either way, getting back to our potentially similar pond projects, I had the same 5 ac bowl that ran off and out one end in a small, narrow creek that only had water when it rained. This runoff ran between two opposing hills about 30 feet high, 350' apart near the tops. It was ideal for placement of a dam to cork up the bowl. We cored it. In fact, the forum developed a pretty lengthy and informative thread on this thread . Looking back, we might very well have gotten away without a core; our clay content was that good. My contractor always cored his ponds and the PB support crew gave me no reason to not go ahead and do it. We did. Yeah, it cost a little more, but I'll never say "what if". Plus, it gave me a look at what is down there, directly below the most important engineering feature of the pond.

Well, yes and no, none of this is wetland. The "lowest" side is still 15' above the lowest part of my Y shaped "bowl". What I mean by a natural excape is there is a wetland on my neighbors property which is lower and directly inline then my lowest side, so I assume the water actually ends up piping down there.

My soils are about 15 to 20% clay, with a fair amount of sand, (combination soil) not the best for pond building but there is water everywhere too. The stuff will hold water if compacted well. But this area does NOT currently hold water. Also, there is a huge commercial sand pit about 1.5 miles away, and if I can get them to give me a fair price, plan on hauling in some good clay soil they have ran into in areas to process with my soils. (When I actually start digging I may have some of these areas as well, but don't plan on doing alot of digging, other then for fish structure reasons).

Right now my plan is to construct a dam on the lowest area so I can have a structured outlet, and raise the water level maybe 3 ft. But really wouldn't need to if I would just let the water eventually overflow this side. This assumes I can seal the sides and bottom of my bowl so it eventually holds water.

I am still working against nature, as my lowest part of the natural ground level of my bowl is about the top of the water level of lake my property borders about 400 to 600 ft away from where I would like to build this pond. This will create a couple hill building sites with water on both sides of the house. And several more with views of pond, lake, and two small pond/wetlands (that I may or maynot improve).

OH and thanks for the link. Very good read!

One other related question, that came to mind after reading your link.

Do most people remove all topsoil from the whole site?

We did. I don't think it does your dam any good wrt compaction and sealing, and it's too valuable to let disappear. We made four topsoil piles; one got spread over the completed dam, one went for improving upstream landscaping, one I am pulling topsoil off as needed for whatever, and one is in reserve.

Yep, quite a few hurdles to not only understand, but overcome.
That's gonna be a lot of clay if you have to create a 5 acre x 2' thick clay liner. Then we add the dam mass, which will also be homogeneous, contiguous with the pond liner. All this, and the fear of leaks. Man, Nutty...does any of this dream have something to do with your handle?
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Have you shot elevations between the existing lake and your low spot water level? I would be VERY curious to see if they are, indeed, the same elevation. If they are, you already know where I'm going with this. The next ? is does the lake level fluctuate much. Is it possible that your pond is more of a drag-line excavation project?
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Have you actually taken soil samples from different areas of the pondsite? What is your soils assessment based on?
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I had a whole bunch of topsoil within my 5 ac natural bowl. I thought I had the hot set-up all laid out. I ran ads in the paper for Free topsoil; U-haul; 5000+ Cu yds avail and had quite a few inquiries. Most of the inquiries were for a t/l or two, but there were 3 or 4 that wanted all that I had. These verbal deals were cut in February, to be executed in the next couple of months, after the thaw. Well, after the thaw, all the equipment that these jokers expected to use to haul free TS was being used to make bigger bux on real jobs. Ultimately, nobody came thru and I wound up leaving the vast portion of the site TS in the bottom of the pond. Yes, alot of it was used for the peripheral "above water" zones, but most of it is underwater right now. When you do the math, to excavate 5000 cu yds over the 3 acre zone that most of it was located in, the couple/three feet of additional depth was not going to make-break my project. I sure wasn't going to pay somebody to haul it away.

No I guess I don't know where you are going, are you saying that I will be unable to hold water above this level and will need to dig it all out. No have not actually shot the elevations, just stood on the hill and looked down both sides and they appear very close. The lake does not fluctuate much, is high right now, as every lake is, we are getting rain after rain.

I have dug down through the topsoil and taken samples. I have not dug far down though. These samples when compressed in a coffee can with many holes in the bottom held water like a bucket for days. When I place soil in a mason jar half full of water and mix it well and let it settle the line on top is about 20%, which is the clay percentage that the web soil survey says too.

I am not thinking 2ft of soil brought in, more like 6" over the top of the compacted existing soil. (top soil removed)

nah, sorry....more like the possibility that the lake and your low spot are both at water table elevation. If this was the case, you may not have any other options than to accept it as your normal pool depth and start digging down to create your pond. At this point, tho, I must admit my inexperience with this geologic hydrology stuff and relent to the wisdom of others within this forum that can guide you further and straighter. When you noted pourous soils, the close proximity of a very large body of water, and the similarity of the water levels within both entities, my water table wheels started turnin'.
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Regarding the soils, once again we need others with more experience to chime in. I did not need to lay in a clay liner or do any patching, but others within this forum have and the golden rule seems to be 24" thick. If you intend to process imported high % clay to process/mix with your questionable soils, I need to step back one step with you and ask some of the dirt guys about the practicality of that (particularly considering the size of the area)