Pond Boss Forums INTRO Questions & Observations seepage through dam

We drained a small pond and spent months rebuilding the dam with an excellent overflow system etc. the dam is about 10' across on top and about 20'+ across on the bottom. everything was well compacted. all red clay. we filled the pond (about 5'6" deep) and water seeped through to the other side. it started about 1' up and followed the high water line across about 1/3of the dam. got bad enough for the water to run at the bottom. we drained it again. now what do we do? what did we do wrong? i have already spent more than i can afford! please help!!!!

Carol,
Give as much info as you can.
You say small pond .. how small
Who built the dam?
Was it leaking before you drained the pond?
How was it compacted?
Was the clay mixed with good soil?
What is the pitch of the dam, sounds like 1 X 1.
Give the guys on here enough info & they'll help all they can.

Thank you!! The pond is about 225' diam. The dam is about a 45degree pitch. My husband (who is a perfectionist) did it. We got 150 yards of red clay (same as what we have all over our land) in 20 yard increments which he compacted by spreading and running the cat over it about a million times.....plus the delivery trucks drove over it also. There was some water on the other side of the old dam but didn't appear serious and we figured it was just natural seepage from underground. Hope that's enough info. If not I'll try to give more.

Carol--You might research bentonite, a colloidal clay which swells to many times its original bulk when saturated, and which when the pond is dry can be laid down in a fairly thick layer and then permeates/expands into gaps. A starting point, without cost information, is at http://msucares.com/wildfish/fisheries/farmpond/problems/leak3.html I'm afraid that a large batch of bentonite will not be extremely cheap, but I don't know the cost factor. Because it sounds like you've ended up with a porous dam, bentonite might be a worthwhile solution.

If the dam truly was well-compacted, a concern (especially because there may have been leakage before you started) might be that there is a layer of rock which is not sealed off and which is allowing water to leach over--or under--it. This wouldn't be a happy situation. However, because the seepage started (as I understand your posts) near the top of the dam, it seems like compaction may have been imperfect.

Another issue, but one which seems inconsistent with seepage near the water line, is whether the dam was dug with a keyway which goes well below the level of the water, with the clay built up in layers from the bottom. You don't say how deep the foot of the dam is, which is an important issue; for example, our pond is 12' deep in the center, and the keyway (a long trench which forms the foot of the dam) was dug 20' deep, so that in order to get around the clay the water would have to somehow migrate down many feet to get around a solid, and compacted, wall of clay. After the keyway was dug, including going through a bedrock layer so that there was no leach possibility, the clay was built up about 18" at a time and compacted layer by layer, which you guys, did, but with a sheepsfoot compactor, which is sort of a steamrooler with large steel cleats on it, and is more likely to do a solid compaction than a bulldozer.

You don't say how wide the dam is from water to slope (as opposed to from end to end).

If I were you, I would find someone local with knowledge of your soil conditions. I would start with the county extension service, which doesn't have a profit motive to color the advice, but would also consult with a local pond builder.

Thank you. It's getting late where you live but I'm going to take a picture and try to post it on here - it would be worth a thousand words since I'm not so good at explaining things. What you said makes a lot of sense but it is too late to dig down since the dam is already built. Will check in again tomorrow.

Carol--looking forward to the picture. I wasn't clear about the bentonite; it is a substance which you actually just spread on the inside of the pond and till in while the water level is low, and then it swells up when the pond fills, so you could do it immediately if you are willing to shell out for it. It's fairly widely available from online sources, if there's nobody in your area who sells it. However, I don't know that it's right for your situation and so would still urge some local knowledge.

I will definately go to the extension service. Bentonite is worth a try but sure would like to discover the source of the leak without digging up the dam! Your help (and this site) are wonderful!! Hope you can see the picture......

oh oh can't get it on here - you can see it on:
http:www.msnusers.com/MyWebDocuments I think. It will be under LEAK. (the spot in the middle of the dam is just my dog).

Carol,

Please explain where the leak is again. I'm sorry but I'm having trouble following, it started 1' up from what .. the bottom?
How long did it hold water before leaking? Or did it star imeadiatly?
Is 5'6" the depth of water @ the dam? So with say 2' of freeboard the dam would be 7'6" high?
Sorry for so many questions but it helps since we aren't there.
Was there a stream running through/under it? Or does it just fill from run off?
BTW I couldn't get to the pic from that address.

Ok, I see from your other post there is a seasonal stream. As Island said you should have dug a core trench under the dam. Esp. with the rocks & sand from a stream under it. The core trench is dug down until you hit good clay soil and then filled with clay/soil mix.
If this is the problem & since your dam is so steep perhaps you could remove the front of the dam dig the core trench & fill back in with a good mix of clay soil.
This may not be your problem, & bentonite may solve your problem. Cecil Baird in one of his post on bentonite says he bought it in bulk on the cheap. I'll see if I can find that post.

Found .. it here it is:
Cecil Baird1
Lunker
Member # 245

Member Rated:
posted March 10, 2004 10:36 PM
--------------------------------------------------------------------------------
Mark,

I don't know what the problem is but I had no problem talking to the company representative and they sent me an information packet. However I decided not to go with the product because it clogs the gills of fish if they are present, and this particular pond could have a subterrainean connection to my trout pond which is full of trout.

The pond in question is just a small holding pond 25 X 30 and I was able to seal it with 10 bags of sodium bentonite available at a local feed store. In this case the "sprinkle method" worked well. However I later had to drain the pond and that brook the seal. Still seepage is not that high and I will add 10 more bags of sodium bentonite at $5.00 per bag to seal it again.

--------------------
Cecil D. Baird

And here is the link to the thread:
http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=2;t=000044

Hi, yes the dam is about 7' 8" high. Water is about 5'6 deep over most of the pond. The leak started about 1 or 2 feet from the bottom of the dam and was about 1 foot across (just a wet spot). Then as we filled the pond the wet spot spread up, down, sideways with the rise of the water. you could try that picture again if you want at www.msnusers.com/mywebdocuments - I think it was locked and I unlocked it. I am going to town and talk to the ext. service but think you are right about digging a trench and packing in clay (maybe mixed with bentonite) in the trench. You have all been very helpful. Will let you know what happens.

Hi all you nice, and smart guys. I'm learning more about ponds than I ever wanted to know!! Went to the extension service and they said our local "red clay" is not clay but silt! The pond has about a foot of water in the bottom when "empty" so we can't dig there. We are thinking of digging a trench down the middle of the dam to about 2' below the bottom level of the drain/overflow pipes and fill it with clay/bentonite or pond liner plastic. Think that would work? I have no idea where to buy clay???
I read in one of the postings that ponds are constant $$$$$. Looks like this is true! Was anyone able to pull up the picture?

Hmmm--Sounds like you and Mr. Perfectionist have a little talking to do, Carol! Haven't seen the picture yet--refuse to get an MSN Passport or whatever it is. As to the foot of water in the bottom, a 2" trash pump from your local rental store will make almost-immediate work of it, so that's not an obstacle to doing it right.

As I understand your proposal, it is to trench vertically through the, ummm, silt and put in pond liner, oriented vertically, and then refill the trench.

First, I think it will be impossible to trench in a soggy dam and keep things intact. Sounds dangerous to me, and likely to collapse. Heavy equipment + shiftable land = very scary.

I'm no hydrologist but it seems to me that the rubber sheet will do nothing about the problem on the pond side, and the dam on that side will wash away fairly quickly, leaving you with a rubber sheet holding back about, oh, 200,000 gallons of water from another few feet of now-weakened red silt. Add the Oregon rains (or do you live in the east?), not to mention what if your stream takes on an unusual (say, 10-20 year rain event) flood and dumps all that water into your pond in an hour or so), and the waterward side of your dam will be undriveable--if not gone--over time. My guess is the whole dam will be gone.

The clay-filled trench, while it seems it might have a higher likelihood of success if only because it adds heft, will still permit the pondward side of the silten dam to wash out, meaning that you have about 2-3' of clay holding back that same amount of water. Now, my experience with clay is that water will wet it at least a foot or 18" from water's edge. I don't feel too good about that one, either.

I don't know enough about bentonite to know if it would seal whatever red silt is, but it seems like your dam is making like a sponge and I'd be really antsy about not addressing the structural issue.

Two thoughts. Most important, IMHO, is now that now you've got the free advice from the extension services get an opinion from the most experienced local pond builder you can find; I'd ask at a really well-established landscaper, if the extension folks won't give you a name. At least then you'll know. The last thing you want to do is spend the summer digging a trench and having the whole thing go fubar.

The other is that you might look into a liner--not for a slot in the dam, but for the pond. The do make them in huge sizes, and a 50' square liner is about $1000. that would certainly give instant gratification and save a big ol' headache. It would also allow you to maintain both clear water and koi, which tend to stir up the mud in farm ponds like mine.

Interesting problem, I hope you keep the board posted!!

I thought our plan made sense. Now what you say makes more sense! There don't seem to be any pond builders around here - it appears that everyone just digs a hole. We will definately do much more research on this and post what we come up with. Thanks

I better clarify some things (I'm learning). Without the picture you couldn't tell. Our pond is filled with a seasonal creek, a spring, and runoff from mountains on 2 sides. We put in a 7" and a 12" verticle pipe that stand 5'8" and 5'10" high. They go horizontal about a foot below the bottom of the pond floor, under the dam to a liner and rock filled field that leads to a creak. They extend about 20' beyond the bottom of the dam. Therefore, the water level should be consistant within 2". There is no leak around the overflow pipes. The 7" pipe also has a drain which we have used twice and it all works perfectly. Also, mr. perfectionist was going to put the trench 10'deep on the pond side of the top of the dam so the only thing would be the slope from the top of the dam into the pond. It seems like there would be no reason for it to go anywhere since the water pressure would be constant. Does that make sense? I will still talk to a local pond expert but the only one I've found sells liners so that's what he pushes. It is too big for a liner and the way it fills, all the water would go under it anyway. This is becoming a (stressful) joke!!

Problem solved!!!!! Just to let everyone who helped me so much, our leak is gone. We dug a 2' X 10' trench with a rented backhoe parallel with the dam on the left center of the top of the dam. About 8' down water started running in from a weak spot in the original drainage ditch that we had dug to empty it. We dug out that area to the pond and went 2' lower. Filled it with a mixture of red clay and bentonite and tamped it real good. The leak stopped. Then we poured more bentonite in the pond along the dam bottom and up a few feet on the side of the dam. We have started refilling and are above the original leak and the far side of the dam is dry as a bone after a few days. By the way, we got bagged bentonite from a farm feed store and it was less than $6.00 per 50lb bag. I didn't think that was too bad. We got some good advise from you nice people and decided next time we will do more research BEFORE we start something we're not knowlegeble about! Thanks again.

Glad to hear it! Good job!

Carol--

I was hoping you'd report back, but missed your post until today. What a happy ending--great work!! Did you get to drive the backhoe?

--Rick