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Thread: Dam problem

  1. #1
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    Dam problem

    During the last rainy season our dam broke down. It is at the bottom of a hill and the water flow can be some time quite strong. Below is the picture today after it collapsed, leaving a passage around 2 m deep and 3m wide




    Closer look :





    I want to fix it before the new rainy season but I wanted to check a few details first. The backhoe operator quotes me 1,300 Baht / hour but insists on a full 8 hours job or he's not interested to do the job. There is no problem for that, there is a number of things I'd like to be done, but we don't agree on the number of hours for this specific job. I say no more than 4 hours (including digging the pond to make it bigger), but he said he needs more. Any opinion ?
    The things we regret most is the things we didn't do

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    Then there is the cement work. And the choice between a simple spillover dam or something more sophisticated like the following






    My wife saw that dam in a temple nearby and really want this style. Any opinion in favor on one or the other solution ?

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    digging the pond bigger can be as long as a piece of string

    it all depends on how deep and what profile etc

    just let him get on with it; as long as you are around and he keeps working, no problem


    that last pic looks good, it would stop erosion of the edges quite well
    I have reported your post

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    Agree with that, but there is a couple of jobs I would like him to do. Then I need to book the other people for the cement job.
    The other problem is those people seem to be very busy, so if at the end of the day he hasn't finished and I haven't book him for the next day, I may have to wait for the next dry season before seeing him again.

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    We used to fit syphon spillways to small dams .
    Simple to make and trouble free in operation.

    Cant insert a Word Draw drawing but for a simple sketch can PM it or email if you want






  6. #6
    Have you got any cheese Thetyim's Avatar
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    Quote Originally Posted by DrAndy
    it all depends on how deep and what profile etc
    Also depends how big the pond is.
    Without giving the size I fail to see how anyone can answer the question

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    The pond is not that big, around 30m in diameter, but the problem is not there. It's in the middle of a steep slope, so the current is very strong during heavy monsoon rain. The water then fall in a bigger pond 5 m lower.

    For the dimension of the dam, you can judge from the picture, around 4 m width, 2 to 2.5 m deep.
    Last edited by Perota; 25-02-2009 at 02:35 PM. Reason: Add additional information

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    Guest Member S Landreth's Avatar
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    Pity it costs so much to rent a hoe and operator. The job looks like it wouldn’t take any longer than ˝ hour to complete with a combination.

    The spill way your wife took a picture of is nice, but costly (for your small pond). If you were to purchase an inlet and some corrugated pipe, you might be able to protect the earthen dam from breaking again. However I do not know the amount of water that could possibly flow into the pond during a down pour????????

    If you go the easy way,.inlet and corrugated pipe,…..just have the contractor set the top of the inlet (in the pond) to the height you want the water level in the pond to be at, during rainy season. Run the pipe from the inlet to a place where the overflow/run off of water can be accepted (under/through your diked off area),…like a ditch that flows away from any ones property. You don’t want to create a problem with you neighbors, with the/your water overflow.

    A cheaper way to construct a spill way would be to set a 20 foot section of pipe through the dike. Set the pipe at the elevation you want to water to spill over into a safe area. Make sure you get the contractor to extend the pipe far enough away from the embankment so it will not erode the embankment/earthen dam once the water starts flowing.

    With the information you provided,..a 36 inch pipe should be fine. Maybe??????? We/I still don’t know how much water can flow into the pond area, during your rainy season.

    If you had the pipe when the guy shows up with the hoe,…………the entire job shouldn’t take any longer than a ˝ day to complete. Have the contractor tamp/compact the material/soil around the pipe and when he is filling the break.

    I always think corrugated pipe (steel or aluminum) because that is what I usually use, but that can be expensive. You can use a good plastic pipe also. You might not need a whole section of 20 feet either,……………..I don’t know how wide the earthen dam is, but your pipe should extend into the pond and extend out of the earthen dam far enough that it doesn’t erode the soil, when the water starts to flow.

    The hoe operator/owner should know where you can get the pipe.
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    Drawings sent by email - totally f*cked up trying to insert it in a posting !

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    Quote Originally Posted by S Landreth View Post
    Pity it costs so much to rent a hoe and operator. The job looks like it wouldn’t take any longer than ˝ hour to complete with a combination.

    The spill way your wife took a picture of is nice, but costly (for your small pond). If you were to purchase an inlet and some corrugated pipe, you might be able to protect the earthen dam from breaking again. However I do not know the amount of water that could possibly flow into the pond during a down pour????????

    The pond has been "man made" in the bed of a river that collect the water from the surrounding lands. The amount of water can be quite high when it's raining hard. On the positive side it never dries up and the level is almost the same at the beginning and the end of the dry season. But the river dries up, in case you wonder why we need a dam.

    If you go the easy way,.inlet and corrugated pipe,…..just have the contractor set the top of the inlet (in the pond) to the height you want the water level in the pond to be at, during rainy season. Run the pipe from the inlet to a place where the overflow/run off of water can be accepted (under/through your diked off area),…like a ditch that flows away from any ones property. You don’t want to create a problem with you neighbors, with the/your water overflow.

    A cheaper way to construct a spill way would be to set a 20 foot section of pipe through the dike. Set the pipe at the elevation you want to water to spill over into a safe area. Make sure you get the contractor to extend the pipe far enough away from the embankment so it will not erode the embankment/earthen dam once the water starts flowing.

    The problem is we will need to have the pipe above ground With a wall to protect them, like in the above design, we can have the pipe buried but at the same time keep a high level of water. Or we go for the spillover model.

    With the information you provided,..a 36 inch pipe should be fine. Maybe??????? We/I still don’t know how much water can flow into the pond area, during your rainy season.

    So far we will go for two parallel pipes, should be 30" each

    If you had the pipe when the guy shows up with the hoe,…………the entire job shouldn’t take any longer than a ˝ day to complete. Have the contractor tamp/compact the material/soil around the pipe and when he is filling the break.

    That the reason the backhoe operator gives us for such a long working time, Because of the heavy water flow, the soil need to be properly compacted, and it takes time ... While I agree with part of his explanation, I have some doubt on the time really needed

    I always think corrugated pipe (steel or aluminum) because that is what I usually use, but that can be expensive. You can use a good plastic pipe also. You might not need a whole section of 20 feet either,……………..I don’t know how wide the earthen dam is, but your pipe should extend into the pond and extend out of the earthen dam far enough that it doesn’t erode the soil, when the water starts to flow.

    We will probably use concrete pipes, no special reason beside the fact that what they usually use in our area.

    The hoe operator/owner should know where you can get the pipe.
    One of my main problem is also to estimate the price of the concrete work. If I listen to them, it will cost as much to cover a dam with concrete than to built a house. The previous dam collapsed because of the poor concrete job. It didn't help that our dam was on the way of our neighbor 's cows but this problem is now solved. Any advise regarding cement ? I've really no experience in this matter

    By the way Happyman, I never received your drawing

  11. #11
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    you can't just dump a load of cement on top of the earth and hope it will last

    you have to make the soil firm, sink some retaining bars (maybe drive in 10mm bar at lest 1 metre deep at around 15/20 cms apart, in both directions), then create the form with lots of bars inside, then pour your nice strong concrete mix in

    don't forget to put your pipes in first

    make it like a proper supporting beam

  12. #12
    Guest Member S Landreth's Avatar
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    This doesn’t seem to be the little pond/dike problem you first described.

    I would do one of two things.

    The first and cheapest way (if you don’t have to rebuild that often). Construct the spill way like I described with the 20 foot section of plastic pipe through the embankment. If the dike blows out it will not cost much to repair. I don’t know how often the earthen dam will blow out due to high water (heavy rains/down pours).

    Keep the pipe (or two runs of pipe running parallel with one another) at a high water elevation if you want to keep a lot of water in the pond.

    Purchase plastic pipe if you are able to,…………….because you might be able to reuse it if the earthen dam breaks around the pipe (if it doesn’t break around the pipe,.better for you, just fill in again). If you place sections of concrete pipe through the embankment and the water erodes the fill around the pipe, it might move the concrete pipe and you might have to reset the entire line. If it’s plastic pipe,…..just pick it up and place it back into the excavated line,………tamp/fill and you are good to go until the next break. A year? Two years? Ten years???????? I don’t know.

    You can control where the next erosion will occur,….just keep the height of the dike a little lower than the rest of the dike in an area away from the pipe line. Preferably this low area on the dike should be placed where the contractor can reach it easily when they come back to rebuild/refill.

    The next option,….hire an engineering firm to design a spill way. Maybe a double pipe system with sand cement rip-rap (in bags), with a weir.

    I don’t think building the double pipe system with sand cement rip-rap bags will cost anywhere close to what a new home would cost (but then I don’t know what type of home your guys are talking about, when they are comparing).

    After you get a set of prints from the engineer,.you can ask contractors for an estimate or price to complete the project. Ask the contractor to also give you a price for the cheap spill way I explained above.

    Now you have to think (Cost Benefit Analysis),………………how often will I have to rebuild the cheap system vs. building an expensive system, one time (maybe).

  13. #13
    Member corvettelover's Avatar
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    how about a pile of lovely rocks dumped in the hole with cement on top and some 2 foot plastic pvc as a spillway thai workers are cheaper than a backhoe

  14. #14
    Member tuktukdriver's Avatar
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    Quote Originally Posted by Perota View Post
    Then there is the cement work. And the choice between a simple spillover dam or something more sophisticated like the following






    My wife saw that dam in a temple nearby and really want this style. Any opinion in favor on one or the other solution ?
    Why not a poor man's version? Get some corrugated metal pipe, maybe 1/2 meter in diameter, set 2 of them in some rock, then cover with dirt.

  15. #15
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    The second one is overkill....the first one is all you need and still may be overkill for the size you described...all depends on the flow really......if strong and fast, then build accordingly.

    As for the backhow.....we just hired a large excavator for 5500b for the day, so your rate seems awfully high for a bankhoe......think he is having a lend of ya.
    I like poisoning my neighbours dogs till they die cos I'm a cnut

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