Pond Boss Forums POND CONSTRUCTION Building a dam Serious TROUBLE!!!!

It would be NICE to know that it is just springs under the dam...

Here is another thought that makse me suspisous. The second lake we built here 6 months ago, by the same contractor. Does not have this problem. This lake sole purpose in life is to rais its water level high enough to flow over into the big lake and hopefully fill it up. As a result I have this little 2 acre pond, (has no fish in it). But from the same senario, if you go down the creek channel form it, it is BONE dry!! Its like this dam has completely seald off the water. Why has this other creek channel have water in it?

big_pond, do you still have water flowing into the main lake?

I think you had mentioned in the past that the lake had filled to a certain level and never filled up higher than that? Is that true?

Your right, it did fill up to a certain point and then stop. Actually I just measured it on line with terra server. They have the most recent 2005 photos which show my lake and alow me to measure it. The lake back then was about 5.5 acres. It had filled to this point with all the rain we had in the winter of 2005. Now it has dropped about 3 feet since then. Mind you about a 1.5 fot of it was dropped this summer.

This past spring I decided to divert a near by stream into this lake. I esentially built if you would, a 2 acre pond on this near by stream, that filled up durin this drought. Now there IS more water flowing into the big lake. It has been doing this for about a month now.

So is there a level that the pond will not come up above?

If so (and bear in mind that I have zero pond building experience), might the potential leak be related to that elevation.

To rule out that possibility, could you stop any more inflow into the lake? Then see where it levels off at; also take into account evaporation and any rainfall.

So if you're loosing an inch a day due to evaporation (when theres no rainfall), but the pond is not loosing any more water than that, then it's holding water; thus meaning the leak is somewhere above that point????

Big_Pond, have you carefully scanned the banks for sand or gravel strata at the water line? A pond that big has about a half mile of bank, and there is alot of places for it to hide.

No I have not really done that YET...but what I can tell the whole bottom is clay. We had the wole pond rimed out and while we were riming it we never noticed any silt or sand or anything like that. It was mostly all clay..

Have forgot about you Sunil, just don't quit know how to answer that question.

I am SURE its not an obvious leak. It has to do with a combination of a spring under the dam and water working its way into the spring system under the dam from the lake. this would be my guess...

I would guess that if the leak is under the current water level and you removed any water inflow, the pond would continue to loose water until the water level fell below the actual leak.

Again, this is just my logic, without any experience base.

BigPond, price yourself a two foot clay liner. You will fix your pond with this.

Have you priced it? I would like to know how much. You likely could get away with the area above your pool, or maybe drain it a couple feet below.

Good luck.

You know, thats a REALLY good question right there!! One thing that concerns me is I would be covering up springs.....
I also thought about just filling in the deep areas of the pond..In other words just make the lake around 15 to 20 feet deep instead of 30 feet.

without diverted creek, how much land drains into your big pond? big_pond

do you have link to 2005 sat pic?

It is on terraserver.com

http://www.terraserver.com/imagery/image...r_id=380&t=&OL=

Click the left most part of the page and it will pop up right in the middel of your screen.

Big Pond,
If it is leaking my guess is also that water is working into the spring system and it could be at any elevation. I would guess that the elevation the water stays at is how high the water has to go to find an escape in the ridges your dam is tied into.
Then the water flows underground around the dam and core then on down to the low point behind your dam where it surfaces.

Big_Pond

I have been away from the computer for a day or so.

Wow, lots of good comments.
The perforated pipe you describe towards the backside of the dam is in fact a toe drain. These are a very good idea, especially for ponds with proposed higher head pressures like yours. They are very similar to a sewer drain----------only they operate in reverse. Instead of letting water out they collect any water that makes its way through the dam and safely channels it to an opening on the backside of the dam. If this toe drain were not installed and water did make its way through the fill, the result would be a saturated back slope of the dam. NOT GOOD! Once a dams back slope becomes “water logged”, it may begin to slip and erode severely. Remember, most dams fail from the backside. (Some seepage can be expected and not to worry) You might add also animal damage, tree roots and severe storm events to the list of culprits.

A leak of 15 – 20 gpm does not surprise me at all on a structure of this size and height.
I just hope you have the inflow and watershed to overcome the losses?


Toe drain installation in our HSB/YP pond.
Outlet from toe drain pipe is NOT perforated.


Perforated longitudinal toe drain w/ tee.


Ed

Yeah this is about right. It looks just about like this. slightly different configuration but the Idea is the same and they are there for the same purposes of relieving water that might have slipped through.
You are right my REAL fear is that I don't have enough coming in to over come the pond's losses. I am just not quit sure of how to attack this proble if in deed it is a problem. I was hoping to dig a new core accross the back but these toe drains would have to be removed first then reinstalled.

Or I can just drain the wohle thing and fill in the deep areas and make the lake on 20 feet instead of 30 feet.
Just not sure of what to do right now.

Hey big...sorry for all your concerns. Don't get in too big a hurry to do anything just yet. You say you're in a drought condition and have only lost 1.5 feet this summer? We're in (just a bit below, actually) normal conditions and I've lost that much from my little 1.7 acre pond. We've had plenty of rain for crops, but no real runoff this year.

Could that not be the actual problem? 20 gpm inflow? I've done some calculations that show I'd lose (on an average summer day) about 25% of that just in evaporation. You should see quite a bit more from your pond...maybe you just need to see what an average year will do for you...whatever that is. And, if we ever see another one....

Matt I think that is what I am going to do. just see what happens. Besides it look like it could be even MORE harder to build a lake in this state now. I might have to some how make what I have work.

BP sorry to hear your continued trouble. You are gettign some good advice form what I saw. Not my area of expertise that is for sure. If you need some fish, you got my number. thanks

Ed,
Excellent photos depicting the toe drain work...almost looks like we use the same photographer.
Is the toe drain trench filled with gravel, kinda like a reverse septic field (or more accurately, like a french drain)? Also, it looks like your toe drain is located at the base, likely a number of feet behind the centerline (or core, if required)of the dam....correct?
V interesting...new for me. My reaction would have been that if there is enough anticipated seepage to warrant a toe drain, there may be reason to re-consider the construction engineering and integrity of the dam...or the entire project. It seems kinda creepy to think that one would see a constant trickle/flow out of toe drain embedded in an earthen dam holding back a substantial mass of water. How is it's need calculated?...and...how is it's performance predicted?

Brettski,

I should have known there would be some tough questions.

Toe drains are generally located downstream from the dam centerline about 60% of the distance to the downstream toe. Not being an engineer I am not sure why that distance is warranted?
The perforated pipe is enveloped in compacted gravel (47B fine grade to be exact, which reminds me of good concrete gravel). Yep, I said compacted, if its not it will settle and leave a possible void in the structure.

Interesting question; “why consider building a structure when you know it will leak?”

Actually not every situation or dam building site has the luxury of having optimum building materials (good clays) near the site. A good example would be Merrit Reservoir located near Valentine, Nebraska. This is a Bureau of Rec structure built many years ago from almost pure beach sand. Does it leak? YES. Is it a controlled leak? YES. Is it a safe structure? Very Safe. Why was it built? Same reason most structures are built…. irrigation, elec. power, flood abatement, sediment retention, recreation, fish and wildlife, etc.

Sooooooo why build a dam from less than ideal material? Because you want a pond!
If you want it bad enough---go for it. Just follow the rules, specifications, safety, design; and remember that if it has a controlled leak that exceeds the inflow, you don’t have a pond--------- you have expensive pasture!

To answer your question as to when a toe drain is needed? Again, good question for an engineer. Rule of thumb in Wyobraska, if you have a perennial stream and a permanent pool (pond) that exceeds 10 ft. in depth, you may want to consider a safety valve (toe drain). Hope I didn’t muddy the water too much.

Ed

I was mindlessly watching the tube the other day, and the show was discussing the Hoover Damn.

One of the site personnel was being interviewed, and he said that he believed that the very center of the damn's concrete was still probably not even cured and hardened yet, and that it was probably still soft. He added that such a situation probably helped with the damn's integrity allowing it some flexibility.

They also showed how the damn springs leaks down in the tunnels. When that happens, they create/drill conduits to efficiently drain the water as opposed to trying to "patch" the leak.

Ed,
Thanks for the tune-up on Toe Drain -101. We likely encroached on the advanced course; my advantage.
Now, back to big_pond....
Would these engineering decisions and construction practice provide any clues to what may be going on with his dam? The decision to install the toe drain might indicate fore-knowledge of potential compromise, whether it be in the dam soils or active springs within the damsite. Are they a clue, or is focus an over-reaction? Big_pond noted the toe drain activity: What is the guesstimated volume? History and frequency of flow? Is this a clue to hydrolic activity within the dam mass (and perhaps the entire site)?

Hmmm--- Any clues as to what is going on in Big_Ponds dam?

Guessing and speculation on my part.

1. Equipment used in construction included; Track hoe, dozer and two dump trucks.
Was adequate soil compaction achieved using this combination of equipment?
Again I am guessing but was dirt brought to the site with dump trucks and spread and compacted using the dozer? There has been a lot of discussion on this site regarding the use of a dozer for compaction. I believe adequate compaction can be achieved by using a dozer if lifts are kept less than 6 inches, adequate soil moisture is maintained and the dam is a low head structure. (20 - 30 ft. is not a low head structure IMHO.)
If you can take a shovel and push it into the dam fill------you do NOT have adequate compaction. Digging a hole 8 inches deep with a shovel in a properly compacted dam fill, should be very difficult.
Mother Nature generally deposits our soils at 70 – 80% compaction in a natural environment. A 627 Cat scraper fully loaded weighs in at about 120,000 lbs. That’s a lot of weight distributed on 4 tires. At proper soil moisture content and 9 inch maximum lifts a 95% compaction can be achieved with one pass.

2. Was quality assurance employed throughout the entire work process?
In other words, did the landowner and contractor assure that proper moisture and compaction were employed each day? At the beginning of each day soils can dry out on the dam fill. So was there a good contact from previous days work to the next days work. (No dry seams.)

3. Core trench?
Core trench was probably plenty deep on this project (10 ft. I think)
Was water present in the core and pumped out?
Were side slopes of the core trench sloped at least 1:1. Vertical slopes are not stable and will not accept compaction when core is re-filled. This is a very important step and should not be short changed.

4. Situations beyond landowners control?
Perfect soils for dam construction are not always available throughout the entire process.
Water seeping through the existing upstream banks and exiting downstream.
Un-foreseen gravel and sand layers just under the excavated area.

A personal note on possible over-reaction? If this structure at 25 ft. of pool height is only loosing 20 gpm from seepage……I would be tickled!

Hope I didn’t step on any toes.

Ed

My experience is somewhat limited, but every pond leak I have seen, every single one, has that same rust colored residue present. Further, I have never seen a natural spring or any other source of ground water produce that same signature. This knowledge is how I distinguish between a pond leak and a natural non-pond source of water. In a pond leak, the water filters down through the dam and/or material...in a natural source of water, it is pushed up from below. Thus the difference...or at least my theory on the difference.

I don't claim this applies to anyone but myself and the area I am familiar with. I offer the comment only in hopes it adds to the discussion.