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#41625 06/06/07 12:35 AM
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I have a 1 1/2 acre pond in southern iowa which is probly about 20 years old. I bought this property about 2 years ago. the pond is about 20 feet deep at dam end , surrounded by steep banks with well established trees and ground cover. One half of area below dam is all trees and brush, the other side is a grass area leading thru trees to road. This spring , on advice of a local friend, i put a elbow in the drain pipe on dam side with a 4 foot extention upward to fill pond up. With all the rain we have gotten this past 6 weeks, it has gone over the built in overflow 3 times now, on grassy area, and i have now noticed that the ground is very wet at the base of dam in that area about 10 feet across on the right side of dam. I thought at first it was from the over flow, but its in a different area than where the overflow goes. it is not drying out, but not getting worse. the pond does not appear to be going down any significant amount. Should i be concerned? i cut the pipe down 2 feet to lower the water level to see if that would help. the pond is probly at least 4 foot higher than is has ever been since i have owned the property. I have Any comments would be greatly appreciated.

#41626 06/06/07 05:53 AM
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Leaks, if they exist, are the most difficult culprit to identify and bring to justice. Facts are facts, so let's look at those first. In the 2 years that you owned the property, I assume that the water level was up to the original spillway level and never showed any signs of the wetness you now see...right? Now, with the 48" elevation, there is an area at the base of the dam that is not is the overflow zone that is wet...right? A few more questions. Is the area that is wet higher in elevation than the overflow run-off zone? We want to make sure that it's not just water migrating horizontally thru the soil from the over-flow run-off. If this new wet spot is indeed water migration thru the dam, my first inclination is that the new, elevated pond depth has put the water level above the clay core within the dam. Changing a pond's depth by 4' is alot. How far from the top of the dam is the new water level?
(edit, another thought/question)
You speak of substantial vegetation. Describe any trees/shrubs within 50 feet of the entire dam.

#41627 06/07/07 12:15 AM
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thanks for your reply, i just discovered this web site and its great. anyway, about the wet spot. its at base of dam on overflow side of dam, but the overflow area is probly at least 30 feet away. the end place of overflow is actually a bit lower, maybe 2 feet. the top of dam is about 20 feet above the base where leak is. also, the leak area, as well as area around both below and above are all well established grass and clover. /the overflow pipe, if thats correct name is in center of dam. the dam is about 200 feet across with the left 70 % below dam being all trees and brush, with of course a gully below pipe. the over flow side is on far right side and is designed to flow around end of right side of dam and the top and right 30% as well as below this 30% is the grass as stated before. its in the middle of the 30% at base where the wet spot is. before i cut pipe, the water level was within 30" of top of dam. thats why when i get these 2" rains, it overflows . I probley over explained this , but trying to give you a idea of structure of dam. I mow the top and all grass areas on dam and below, have been since i bought it , and have never had any wet areas until it filled up to top. i didnt intend to have it fill so high, but its been very wet this spring. the trees below dam are all well established pines, walnuts, etc with lots of brush below them. thanks again for any help

#41628 06/07/07 05:58 AM
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Good job painting the picture. I believe I have good mental snapshot of the dam, but a photo would be helpful.
If I read your presentation correctly, there are no trees or substantial shrubs growing ON the dam; just below it. I wanted to eliminate the possiblity that trees on the dam grew roots that provided a capillary route for the newly elevated water level. For now, let's move on.
I'm still a little confused, tho, on the spillway pipe. We need a little more detail there. Is it a simple horizontal pipe thru the dam that you elevated by attaching a 90 degree elbow to with a 48" riser pipe? What's the insided diameter? You state "before I cut pipe"; unsure where that's going...thought you added to it.
It sounds like you have a classic pond design with a principal spillway pipe and emergency overflow. As I read your explanation, you are saying that the emergency overflow at the far right of the dam has been functioning based on excessive rains recently. This is good, providing it is a very short-lived event until the rains and run-off subside and the principal spillway can catch up and handle the flow. The path of the emergency overflow runs right thru the area that is you concern for being wet...right? How are you certain that the area of concern is NOT a result of the passage of the emergency overflow? Let's try to eliminate this possibility.
There is good bit of info that pics would help to bring to light. I am still thinking that you have risen above the clay barrier within the dam with your new "normal pool". It will be v helpful to know the elevations of the original spillway pipe compared to the top of the dam and the new elevations.
Finally, and I know you guys are out there, kick it in. What am I missing here?

#41629 06/07/07 01:23 PM
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again thanks, i will get a pic or two to help. as far as pipe, yes, you have it right , i just put elbow on inlet and put a riser on it. i cut down riser to lower water level 2 days ago. am out of town now, so will check tomorrow when i get home as far as level of water. its a 4" pvc pipe. as far as spillway, the only thing there is is the pipe thru dam and overflow area which is lower than dam on right side. wet area i believe is far enough from overflow area , andsmall enough where it should be separate, but could be wrong. from what you have said, it think you may be right on water level now above clay base. thanks for help, i will check water level tomorrow, check wet spot, and get some pics. and may just remove elbow and riser totally to put back to original level where i didnt have this problem. i am guessing some here but i would say that the pipe inlet before modification was about 4 to 5 foot below top of dam. i say that because when i put in elbow and riser, the top of riser was probly less than a foot from top of dam if you drew a horizontal line from top to top of dam. i didnt think it would ever get this high, since i allowed a small gap between elbow and pipe, so it would still drain very slowly if it got high. but i was wrong i guess. again, thanks for help. i will get this issue solved , then i have some other questions on getting my fish populations balanced. another day though. thanks much

#41630 06/07/07 02:34 PM
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You are welcome, RRR07. I'm not sure that we nailed it, but based on your last post, it sure seems like it.
A 4" principal spillway pipe is tiny. Even if your pond was a sky pond (zero run-off; only the rain that hits it), at 1.5 acres I would be nervous with a 4" pipe. It will have difficulty handling any volume during a frog-strangler rain. If nothing else, a sparrow's nest could start a clog. The idea for that emergency spillway off to the right is exactly that...only used in emergencies. It should be a rare occurrence if you want to seriously consider it as your emergency. That being said, there are plenty of ponds out there that use a natural bank for a principal spillway, so I cannot say that your setup is necessarily inadequate. I'm just not used to it when a pipe (or trickle tube?) is also present.
WRT the height of the water compared to the dam. You need to get back to the old setup. If, in your estimate, you only had about 12" above the height of your 48" pipe extension, you were setting yourself up for eventual disaster. The time would come when it rained so hard, for even a short time span, that your emergency(natural) spillway would even totally fill with volume and the water would begin to overtop the dam along the very lowest points along it's length. The trickle goes to stream, goes to a hot knife thru butter. Disaster. You need the freeboard that existed before you added your riser. If you had about 48" above the pipe in the beginning, that would be sound pond construction. (as a a footnote, I am curious as to the height of your emergency spillway compared to the top of the dam. Also, how wide it is. If it is engineered to handle the correct flow, then the potential overtopping should not occur. It's all a math equation based on inflow and outflow)
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Finally, you may want a more on-site expert opinion about the entire package. It may be feasible to re-do the top of the dam by extending the clay core further up and deepening the entire pond. During this procedure, you will have the option to re-consider your spillway, should it need more engineering consideration.

#41631 06/10/07 10:01 PM
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I just want to say again how awesome this site is, wish i would have found years ago. And thanks so much for your input. I just got home this afternoon{sun}, and checked on pond. It has gone down i would say 2 1/2 feet since i cut riser down. the wet spot is still there, but i would assume that may take a bit too dry out assuming the problem is fixed and we get some dry weather. i will keep a close i on it. I will take some pics tomorrow and see if i can figure out how to put them here, that may help with any other suggestions. If i read your last post right, sounds like you suggest i remove elbow and riser totally and just let it fill and drain naturally according to rainfall. I do need to clarify a couple things, after rereading our posts. there are trees and brush below 70% of dam, but there are trees growing on the dam too in that area, mostly pine. I really should have made that clearer initially, sorry. the area where the wet spot is has no trees etc by it, its just grass and clover. the closet tree to it is probly 50 feet. i did look below dam in treed area and there are no similar wet spots there. So, i guess i am just going to wait and see if the wet spot drys out. Again, i will try and get some pics for you to show spillway, dam, etc. Thanks again!!!

#41632 06/11/07 05:51 AM
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RR07
I am by no means the resident expert on this forum for dam construction, but your situation presented a few basic fundamental no-no's that flew in the face of Pond -101. You're right; this site IS awesome. That's why I knew that if the seat of my pants started to rip as I neared the edge, one of the knowier (Gallus dictionary) posters would drag me (us) back to safety.
OK, back to the dam...
Trees on the dam continue in the No-No category. The roots of the tree can provide small highways for water to follow. This becomes worse if the roots die and decay. This would be one more good reason to drop the water level back where it started. It also might be a good reason to consider re-building the top of the dam sometime in the next couple of years. Don't hurry out there, though and start digging out the trees...yet. Post some pics and tell us about these trees; their types/size.

#41633 06/16/07 10:18 PM
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Just a quick update, pond is now back to its regular level, and wet spot is drying up nicely with all this hot weather. So you must have hit in right. i am still going to try and get some pics if i am ever home for more than 12 hours . lol thanks


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