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

 

[charlz]

So maybe think of it this way:

If you were to re-create your dam exactly as it is today but out of wood chips... would you expect it to hold the water back?

If you wanted to re-build your dam using solid steel... would you need it to be the exact same dimensions as your earth dam?


Material used has everything to do with the design of the dam.

Charles

 

[have_blue]

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.

If the water depth right behind the dam is "all dam", it's important for the dam to be a bit extra thick and high.

Say the water is 12' behind the dam, and the dam is 12' high. In this case, there is huge pressure on the base of the dam, and it needs to be very wide and a built up extra high in order to strengthen it.

Say the water is 12' deep, but 6' of it is dug into the ground, and 6' is behind the dam itself. In that case, the pressure is very negilagable at the base of the dam, and it is far less likely to creep when saturated.

Another principle is, for a given thickness and height, the shorter the dam, the stronger it is.

 

[patrick_g]

I got $5 and will give 4:1 odds that the dam will still be in place 3 yrs from now and the lake will be doing fine.

Any takers? Anyone want to bet I'm wrong? Deadline is midnight 23 Dec '06.

Pat

 

[Renze]

I dont know if any of you can use some metric caluclation examples, but here it goes:

1 bar is 1 kg per square centimeter.
1 bar is 10 meters of water column. (which means that the force applied to 1 square centimeter of lake bottom with a water weight of 10 meter, is 1 kg.)

This is logical because 1 liter of water weighs a kilo. To place a liter of water (is 10x10x10 cm) on a footage of 1 square cm, means that you have to put it into a column of 10x10x10 cm is 1000 cm or 10 meters.


The water pressure at a certain depth:
Exactly at the water level, the sideway force of the water against the dam is zero. At 10 meters depth it is 1 bar, (which is 1kg/cm2) so over the total 10 meters of dam height, the pressure is 0,5 kg/cm so with 10 meters of height this is 500 kg per centimeter of dam length, or 5 ton per meter of dam length. the weight of the dam has to be so high, that it generates enough friction with the undersoil to keep the dirt mass from sliding off.

With very high water levels, as we had in 1953 with the big disaster in holland, the water level was so high that the dikes saturated. the moisture saturation lowered the friction of the dirt, which caused dikes to be slid off and break.

I cant help you with the friction factors for dirt so it wont be of much help anyways. But at least, you can sleep well by the thought that if a dam held the first year, the next years will be no problem because the dirt is settled by natural ways and natural processes aid the cohesion of the dirt.

Hope this helps.

Renze

 

[patrick_g]

Renze, That calculation did not include a small boy with a well practiced finger did it?

Great example. It also reminds me how disappointed I was when the USA didn't get with the metric program and stayed with the crap we inherited from the nobles of England.

Locally we have "programs" that can assist with "erosion control structures" AKA ponds. Actually they make a distinction on naming based on whether the dam has a drain pipe or not. Anyway, the programs pay for a varying percentage of the cost of building the "pond", typically 1/2 (50%.) BUT not for making the depth greater than 8 ft!

Luckily the previous owner of my place was a DOZER DUDE who build golf courses, roads, lakes, etc. I had 8 stocked ponds when I bought the place, have added 2, and have plans for at least 2 more. Mine are significantly deeper than 8 ft. I measured the thickness of the base of one of my dams at the level of the overflow pipe and it was a couple feet under 100 ft thick. Given its slope the dam is really thick 10 ft down.

Pat

 

[EddieWalker]

Renze,

After reading your post, I realized that I had misunderstood another aspect of the dam construction process. The keyway. I keyed the entire dam, but did so under the beliefe that it was to stop water from seeping throught the layer of dirt on top of the original dirt. My misunderstanding was that water would work it's way through the layer of the two materials and keep going if there wasn't that thrench there. When I filled the trench, compacted it and build up the dam from there, I was creating a barrier for the path of the water.

I read that the keyway locks the dam in place, but didn't understand how that worked. Now it's making more sense to me. The weight of the dam is held in place by the keyway from moving sideways from the weight and preasure of the water. Since my dam is only holding back four feet of water when full, I'm way overbuilt. the majority of my depth is from digging out a big bowl into the virgin soil and using that dirt for the dam.

Thanks to everyone else for your help in explaining this to me. I think I did it right, but can see now that I totally misunderstood the engineering. Luckily there are examples of what is supposed to be done and I just copied them, then then doubled what was required and then added some more.

Eddie

 

[RobJ]

I got $5 and will give 4:1 odds that the dam will still be in place 3 yrs from now and the lake will be doing fine.

Any takers? Anyone want to bet I'm wrong? Deadline is midnight 23 Dec '06.

Pat

Is that with or without water? It might be there but may not have much water in it unless Eddie keeps pumping. With our drought we've had, Eddie has had 2 years of little rain and not much runoff into the lake. That's good when building, not good for sustaining a lake. I think I read recently that on a hot summer day Lake Conroe to the south drops 1/2 inch or more a day due to evaporation, humidity, wind, clouds all play a part. So lets hope in the spring we get out of this drought and some of the coastal rains move furhter north.

Down in Houston ours is really ended. We got some good timely rain here, about average, maybe slightly below because I did have to water the yard some. At Elkhart (just south of Eddie), they only got about 2-3 inches a month, just enough to keep the hay alive, not much more.

 

[patrick_g]

Eddie, You engineer like me. If a little is good then a lot more MUST be better.

Did you extend your keyway a good distance at the ends of the dam? Part of the keyway's job is as you originally thought, a water stop. The keyway can be extended with good results laterally at the ends of the dam to prevent water from making an end run around the end of the dam (below water level of course.)

Wherever there is a discontinuity water tends to try to flow through the interface. That is why large anti-erosion collars are placed around overflow pipes. It keeps the water from finding an easy path along the overflow pipe and eroding it out into a gusher.

Pat

 

[patrick_g]

Robj, You puttin' down any $ or are you just talkin'?

Actually I wasn't even considering the drought or location. I am in south central Oklahoma where we suffer a drought worse than any in the last 100 years. I have some cracks in a dam I built large enough to endanger small children but luckily they are parallel to the run of the dam and are not likely to leak or cause a failure.

I was just bragging on Eddies work and challenging any nay sayers to put their $ where there doubts are. With so much of the head of pressure being below original grade and so little head against the gravity dam, his work will probably hold, even if it gets water in it.

My pond held by the dam with cracks was full and overflowing within 30 days of completion but that was a few years when we were clueless about this terrible drought. The cracks are caused by expansive clay getting very dry and contracting a lot. The cracks will close up if we get back onto a normal rainfall era. I've seen the charts and there previously (as long as records have been kept) was about a 10 year cycle to wet and dry periods for this area. Not sure how that extrapolates down nearer the gulf coast, closer to you guys. With any luck we will get some good rain this winter and in a couple years if the cyclel isn't destroyed we'l start to get some pretty wet years.

Pat

 

[john_bud]

I got $5 and will give 4:1 odds that the dam will still be in place 3 yrs from now and the lake will be doing fine.

Any takers? Anyone want to bet I'm wrong? Deadline is midnight 23 Dec '06.

Pat

Pat,

Now if you can raise that up to 5 million, I'm sure Eddie and I can mix up some moonshine and have a dozer "accident"......

Outside of that, I don't see his dam going anywhere either.

jb