Creating a Lake

[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