Creating a Lake

[slowzuki]

Yes damning a creek is a difficult way to go as the spillway would be very critical. Usually a creek is fitted with a diversion to fill a pond or keep it topped up while the original creek remains to handle the torrents of water.

 

[have_blue]

Yes damning a creek is a difficult way to go as the spillway would be very critical. Usually a creek is fitted with a diversion to fill a pond or keep it topped up while the original creek remains to handle the torrents of water.

Very difficult indeed. It would take a very wide stone or concrete dam, as not even clay with thick grass would hold against a swollen creek. Plus, your fish could go bye bye.

 

[patrick_g]

Eddie, The pressure at any given depth is equal in all directions and the slope of the dam doesn't work the way you reconveyed the comments you heard. There are a lot of folks who can build a dam and lake that don't understand the physics. Bumble bees aren't aerodymanicists but they fly.

Earthen dams are "gravity dams" and require enough dirt in the air to provide enough weight to keep the submerged dirt held firmly in place. A slope as you suggest is a good practice, just not quite for the reason you were told. Bottom line is if the lake is what you want and the dam holds under all conditions of stress/overflow it doesn't matter why it works just that it does work. I have 10 ponds noiw and plans for some more but most are under 2-3 acres.

Pat

 

[Jarrett]

.....I’m posting a topo of my site to show the magnitude of this project.....

LOL, I noticed the contour lines on your topo show elevations in the 600's or more. The contour lines in my area are anywhere from 5 to 30 or so.

 

[bailey_trey]

Hey guys,

I've talked to the gas company and they are going to walk the site tomorrow. They are going to see if it is 'economically' sound to build the dam. The guy looked at my topo of the area and acts interested. He was talking about building an earth dam 200 to 250 yds long that would be 25 foot high at the highest point! The resulting lake would be 30 to 50 acres in size when full. That's a big project. Of course, I'm already excited and it will probably never happen. But I'm keeping my fingers crossed.

slowzuki and have_blue,

You guys are so right about building across a creek. I'm in the opposition situation as Eddie. He's pumping water 24/7 to fill his lake; one big rain in my area would likely fill my lake to the rim. The danger is then the second rain comes and washes it all away. I could never afford to do this on my own, but I'm double lucky. First, the land naturally water sheds down to my property and second, because the gas company in the area needs water in the summer. They use it to fracture the shale and release the gas.

Typically my whole area of the state is bone dry from mid-June until Sep. So they really need a place to get water during that time. They build a pond and then the land owner agrees to let them take free water for 3-5 years in return. Dealing with these companies can be challenging but if I can get my lake it would be worth it.

Jarrett,
Welcome to the Ozarks. I love our little mountains. Nothing like the Rockys or Appalachians, but it sure is pretty to me.

Eddie,

Thanks for the suggestion of PondBoss.com it really has a LOT of information. I'm not going to post any more about my project/no project in your thread. Doing so doesn't seem appropriate to jump on the end of your great build. If this thing goes I'll start another thread. Thanks again. I hope your Christmas party goes well with a full lake.

p.s. Hey Eddie, you've been reading a while. With this much time going by, you had better go fill up that pump with oil and check the gas.

 

[EddieWalker]

Eddie, The pressure at any given depth is equal in all directions and the slope of the dam doesn't work the way you reconveyed the comments you heard. There are a lot of folks who can build a dam and lake that don't understand the physics. Bumble bees aren't aerodymanicists but they fly.

Earthen dams are "gravity dams" and require enough dirt in the air to provide enough weight to keep the submerged dirt held firmly in place. A slope as you suggest is a good practice, just not quite for the reason you were told. Bottom line is if the lake is what you want and the dam holds under all conditions of stress/overflow it doesn't matter why it works just that it does work. I have 10 ponds noiw and plans for some more but most are under 2-3 acres.

Pat

Thanks Pat, but you lost me on this. If a a dirt dam requires dirt above the water to hold it in place, wouldn't it have to be more dirt than water?

I'm confused on this because I would think the water far outweights the dirt by a overwhelming amount. If I understand what your saying, than the wouldn't I have to have more dirt than water? If the water was to rise to the top of the dam, would that cause the dam to fail?

I've seen poorly designed dams that didn't have a spillway and the water just flowed over the top. After awhile, erosion wears through the dam and the water flows out, leading to more erosion and more water comeing out faster and faster until it's all gone or there's no more dirt to erode.

I've never heard of a dam failing because of too much weight of the water, or not enough dirt holding it down. Of course, I'm not very knowledgable on these things and I'm just trying to understand it so it makes sense in my brain.

Another point that I'm confused is on the inner slope of the dam. If the slope doesn't affect the preasure of the water, why does it need to be 2:1 or more? Mine is 3:1 because I thought this would make it even stronger. Is this simply a formula to create enough weight to hold the dirt in place?

I know there is a formula for how thick the dam should be based on the height of the water when full, but again, I thought that was to hold back the water with the thickness of the dam. If I understand what you're saying, this is in fact to create enough weight to hold the water back.

Is the water presure determined by the height of the water on the dam alone? Wouldn't the large amount of water create more preasure? I'm really lost here. One acre foot would weigh so much, so would that weight have a certain amount of preasure on the dam? If so, would 4 acred feet have more preasure than one acre foot?

Thank you, this is very confusing.

Eddie

 

[EddieWalker]

Bailey,

Sounds like you have a very unique situation. Keep us posted at to how it turns out. As you can see by the number of views to this thread, there are allot of us interested in ponds and dam building.

Eddie

 

[john_bud]

Thanks Pat, but you lost me on this. If a a dirt dam requires dirt above the water to hold it in place, wouldn't it have to be more dirt than water?

I'm confused on this because I would think the water far outweights the dirt by a overwhelming amount. If I understand what your saying, than the wouldn't I have to have more dirt than water? If the water was to rise to the top of the dam, would that cause the dam to fail?

I've seen poorly designed dams that didn't have a spillway and the water just flowed over the top. After awhile, erosion wears through the dam and the water flows out, leading to more erosion and more water comeing out faster and faster until it's all gone or there's no more dirt to erode.

I've never heard of a dam failing because of too much weight of the water, or not enough dirt holding it down. Of course, I'm not very knowledgable on these things and I'm just trying to understand it so it makes sense in my brain.

Another point that I'm confused is on the inner slope of the dam. If the slope doesn't affect the preasure of the water, why does it need to be 2:1 or more? Mine is 3:1 because I thought this would make it even stronger. Is this simply a formula to create enough weight to hold the dirt in place?

I know there is a formula for how thick the dam should be based on the height of the water when full, but again, I thought that was to hold back the water with the thickness of the dam. If I understand what you're saying, this is in fact to create enough weight to hold the water back.

Is the water presure determined by the height of the water on the dam alone? Wouldn't the large amount of water create more preasure? I'm really lost here. One acre foot would weigh so much, so would that weight have a certain amount of preasure on the dam? If so, would 4 acred feet have more preasure than one acre foot?

Thank you, this is very confusing.

Eddie

Eddie,

I'm not a rocket surgeon and I didn't stay at Holiday Inn last night, but I think I have some answers to your questions. The weight of the water will build up hydraulic pressure based on the depth. This is a confusing point to many, depth is the ONLY factor that determines the pressure. Seems odd, right? A bigger pond seems like it should have more pressure than a little pond. But think about it differently. A scuba diver in 10' of water is at a certain pressure, right? That pressure isn't different when it's lake Superior, Havasu or your pond. It's still the same pressure for 10' of depth in water.

With me so far? Ok, the pressure will cause the water to push outward and potentially tunnel under the dam. Your 3:1 makes it go a longer distance to get out. The resistance to it getting out is from the weight of the dirt pressing down. It has to be above the water line to be effective as the parts below the water line when saturated will effectively weigh less. Just like you don't weigh much when you are standing nose deep in a pool, but weigh (guessing) 200# standing on dry land. The change is less for the dirt as it is much denser than water where you aren't (being mostly water). To get the greatest effect, you want as much weight as possible and every thing above the water line gives 100% of it's weight to press the dam down. The water, because it presses equally in all directions is pressing upward against the bottom of the dam. As long as you have the weight to over power it, by some safe margin, you're good. If you don't have enough weight, the water will pick up the dam and go merrily squirting out under it all in a gush.

Dams do fail by the water under cutting the dam. The engine that drives that undercut is the pressure from the weight of the water. The 2:1 or 3:1 moves the high pressure areas farther away from the center of the dam and farther away from the outside of the dam (at a constant depth). A 3:1 dam with a 10' depth has the 10' deep water area 30' away from the waters edge (right?). The other side of a symmetrical dam is 30' farther still, plus the width of the top of the dam away. The part of the dam above the water line is providing the downward force to compact the dirt and press the water out.

This answer is all based on physics and my theoretical understanding, not from a practical standpoint from years of experience. Could be wrong in a few particulars. Hope not, but could be. I won't feel bad when some one corrects me!
jb

 

[have_blue]

John nailed it.

With a given dam, it doesn't matter whether a dam is 1 acre or a million acres. The pressure is exactly the same.

The slope and height of the dam has a lot to do with dam reliability. A wider based dam uses the buttress effect, and makes it more resistant to creeping and catastrophic breaking due to horizontal water pressure. A dam that is high above the water line uses the great weigh of the dirt to compress itself, making it even more secure. Even a tall dam needs a nice wide base.

 

[EddieWalker]

Thanks, I think I understand, but it's kind of like a a few tests I remember in school. I can repeat the answer, but don't fully understand what it means.

I copied the charts and calculations for what I needed, then built it bigger. Otherwise, I can't explain how or why it works. I'm glad I just found out about the weight of the dirt on the dam being above the waterline and how important that is. I have quite a bit of it and might add a little more to smooth out a nice trail. Not much, maybe 20 or 30 yards over the full 940 feet.

Thank you,
Eddie