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A sink hole swallowed my pond last week.  RSS feed

 
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Last Thursday night, a sink hole opened up under my pond and by Friday morning it had swallowed half the water in my 1.8 Acre pond. As of this Monday morning it had swallowed about 3/4 of the water. The first image shows the hole and a good bit of the pond. Except along the dam side of the pond the water's edge has receded about 40 feet and formerly covered to the vegetation at the trees seen at the left. The water level is down vertically by about 4 feet or a bit more.
The second image is looking directly into the hole the 6 foot depth plus the 1.5 foot depth of water is only to the top of the mud below the water and the hole goes even deeper than that to where the mud is being washed into the fissures or caverns of the limestone bedrock. An interesting point is the the bottom of the hole is actually lower than the deep spot in the pond by a few feet.
The third image shows the even larger subsidence zone where the surface has dropped about 6 inches as the adjacent soil on the west side of the hole started to shift toward the hole. For the present this has stopped as the pond is so low that it is not supplying much if any water to the problem zone The subsidence area measures about 15 x 25 feet. The bamboo pole is 15 feet long. Today I had to use a 20 foot pole to get measurements.

My wonderful pond, a great feature of our land has mostly gone away but the dam is unaffected as this happened about 40 to 50 yards away from the dam. I have been getting information from the Missouri Geological Survey people on the topic of sink hole remediation and apparently this thing is fixable. The procedure is to dig it out to bed rock (think large back hoe) and fill it with rocks (I have maybe 30 to 40 tons in piles cleared from my open fields) going from big ones in the bottom and small to coarse gravel near the top and then form a clay cap over the top (maybe including geotechnical (aka landscaper's) cloth to further reduce erosion. I have one preliminary estimate of $600 to $700 to fix a hole of this size. (a days work with a backhoe and dump truck to move the rocks). If we can get it fixed we may well have to restock it with fish, depending on how depleted the water gets before the rains fill it back up.

I am posting this here because some of you may have useful experience to share, and this might prove useful discussion for others to read. Fortunately the hole is 100 yards from the house and super monster sink holes are not the rule here in Missouri whereas many small ones like this one are. But if any records of the occurrence or the repair of this one are recorded they may also benefit others.

So if you have any words of advice that may benefit me or others, please offer what you can.
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Sink hole and 3/4 drained pond
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The Abyss
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Subsidence zone on one side of the hole
 
master pollinator
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Yikes! I'm glad it doesn't look horrifically expensive to repair.

 
pollinator
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has there ever been any mining in your area ? are you sure its because of the limestone ?
 
Don Goddard
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David Livingston wrote:has there ever been any mining in your area ? are you sure its because of the limestone ?


While historically there was some lead mining in Missouri. The geology of this area is known as "Karst" which in this area means the bedrock is limestone and around here caves, and drainage through fissures and springs are frequent occurances and sink holes are as common as spots on a leopard. The nearst town has numerous sink holes within the town and remediation of sink holes is commonly done in this area. There are few house swollowing sink hole that take down a whole house but the nearby city of Springfield has tales of woe where the foundation of a house was sitting on a sinkhole which then destroyed the foundation. Most sink holes are not over cavern but are draining into cracks in the lime stone can over centuries become caverns. Water going into sink holes around here have been traced with dye which comes out of springs about 16 miles north of here in the Lake of the Ozarks area.

As for what it will cost to fix the problem and how expensive it will likely be seems to depend on how deep it is to bed rock as a good remediation requires the overburden to be dug out down to bed rock. There are estimates that in this region that values in the range of maybe 12 feet to as much as 40 feet may be encountered. The shallower values are within reach of a backhoe but the deeper values could require a dragline preferably with at clamshell bucket.

I will try to keep you posted and with pictures when possible. My first approach will be to go out with a steel rod, and descend as safely as possible and try to drive the rod to bed rock to see how far down it is.

 
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Yikes! Bet you're glad it didn't take your house...
 
Don Goddard
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Heather Petersen wrote:Yikes! Bet you're glad it didn't take your house...


I most certainly am, but for an extra reason that most people might expect. We are in an earthquake zone which if the New Madrid fault really cut loose could see home damage (albeit not all that severe as limestone substrate is know to really dampen the effects of an earthquake. However for that kind of earth movement you can get coverage. What you cannot get coverage for is sink hole damage. Rare is the house that is completely swollowed by a sink hole. If there is sinkhole damage it is ususlly foundation damage which is often repairable and even if not a house can be moved to a new foundation usually and none of the contents is likely to be lost or damaged. But you cannot get sinkhole insurance. They refuse to sell it. If you compare the number of houses lost to fire in part or in whole, the likelihood is far higher for fire, but for sink hole damage you are on your own and if it happens you are S.O.L. I don't get it !! I would much like to have that coverage at a reasonable price but they just do not offer it. And I would think that they could figure out the likelihood of it happening and come up with an appropriate price, but they just won't do it. We tried.
 
Don Goddard
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I have been sending out updates to family to let them know what has been going on as I continue to assess what has been happening on this topic, and you guys are kind of like family in that we have similar interests in stewardship of the earth during our sojourn on this planet, so this update might be interesting to those with the potential for similar problems. Just a little lingo first however. The kind of geology that gives rise to a lot of sinkholes is called Karst and wikipedia has a pretty good primer at Karst geology, the basics and while you are at it you might want to look up Suffosion the more common and more manageable sort of sink hole.Suffosion Sinkhole, the more manageable sort, (sometimes)

That being said here is what went on around here today. Today, Monday, Jan. 22, 2016, I made some additional observations with respect to the sink hole, The first of these was present all along but went unnoticed but as this first picture from a few days ago shows it was there all along, though its significance if any is not yet clear. This is represented in the first image below.
--------------SEE FIRST IMAGE----------------------
Admittedly it looks like a shadow but it is not and it was further obfuscated in this image due to the lighting in which the photo was taken

And while I am apologizing for illumination in the photographs I will include this one taken today where I had to circle the key feature in the bottom of the hole lest the viewer miss it.
--------------SEE SECOND IMAGE --------------------------
And how did that post get there you might rightly ask, and the answer is found in the next image.
--------------SEE THIRD IMAGE----------------------------
The post is there because I went down there, threw out the ice shards and in put it in!

The objective of my trip into the abyss was to try to make a better assessment of what we were dealing with. Conflicting reports of soil depth down to bed rock in the area have been ranging anywhere from 13 to 80 feet, and a remediation of the sinkhole is best done by excavating down to bed rock. Given that the rim of the sink hole was a good 4 feet below the surrounding lay of the land, and the hole was 7 feet deep to the mud of previous days, and a 6 foot probe would end up probing to a total of 17 feet; it seemed worth the effort while getting more information on this undesirable new feature.

If one does not mind being cold, today had some advantages, except for the very bottom of the hole, everything was pretty much frozen solid and not inclined to move. It was advantageous that the ice shards were cold enough to not be melting, as that made them easier to handle as I picked them up and lofted them up to an elevation well over my head. However, another discovery made matters slightly worse. As I got the first few slabs of ice out of the way I found my self standing on mud, or as the situation soon changed, standing in mud! But after clearing away just a few inches of red mud from the material that had slid into the hole, I discovered that I was standing in a much smoother rather plastic light gray clay mud. It was then I realized that the bottom of the shear wall in the first picture was the same shade of gray (not exactly as shown in the "distorted" lighting of the picture). When I say "standing in mud" I should put the emphasis on IN. With just a bit of activity I sank to my boot tops, and if you look at them you may appreciate that at 15 inches tall, that is a serious consideration, so I was having to periodically extract myself to continue.

I had taken the precaution of driving a steel fence post into the frozen ground 20 or so feet back from the brink of the hole, and tying one end of a rope around myself and with the rope looped around the base of the post, I could move freely but still pull against the post. My wife manged the rope tension so as to allow me to work more freely. The rope was a great aid in extricating my feet from time to time and also my final exit from the hole.

I had managed to get my wife to act as the "top side" & safety person for this effort. and she brought me tools such as the post and post driver. Having cleared the ice shards, a rock or two and the last of the red mud on the bottom of the hole. I took the steel post which was rusted to a sharp point and lacked the "spade plate" of such posts, and jammed it into mud and applied the post driver. The post went easily until the driver was hitting the surrounding ground. I had dug out a spot so that the driver would be able to get the top of the post down to the previous level of the bottom of the hole.

It would have been most pleasing had the post hit bed rock but it was not so. As a result, remediating this sink hole will be more difficult and perhaps not as permanent as one would prefer. I am hoping that the geologist I am working with can tell me if that gray clay reveals what the meaning of that stratum being that color might be. I know that from working in my garden that if one digs to the hard pan there is a discernible color change from dark to yellowish but once the hard pan is broken it turns to the same dark shade after about a month or two. So possibly the gray color will give additional information about what is going on at that depth in the soil and maybe it will be helpful.

Having made my observations for the day, Diane took the tools I handed up and then brought the rope around to one side so that I could get my feet free once again, and then make my way up the 45 degree subsidence slope rather than having to scale a shear wall.

If there is any message I want to get across in this message it is one of caution in dealing with sinkholes. This one has about have of its perimeter walls as a shear vertical drop. And in some places it is quite clear that the surface of the wall is not all that well attached to what is behind it. Such a wall as that can fall over on top of you. The rest of the wall of this hole is slumped in loose material and today it was niether loose or wet because it was frozen. The collpase of a wall can suffocate you simple by squeezing your chest so you cannot inhale and you die of compression suffocation. That is why the rope and the safety person up top, But the bottom of the hole is equally problematic because it may not support you but it can in a manner of speaking glue you down there, and that would be very important if the walls started to collapse and thereby prevent you from getting out of the way quickly enough. It was for that reason that I kept freeing myself before I got stuck really badly. The rope was largely used to keep myself upright while I freed first one foot and the other. Of course in the case of a collapse it could be useful in either getting up or being found. But it has to be long enough to reach a reliable anchor.

The sink hole I have appears to be a suffosion sink hole. One where a relativly small crevice in the sub strata provides a place for water to drain to and it takes the soil with it. The other kind is what is called a cavern collapse where the roof of a substantial cavity in the bedrock suddenly falls in. These can be "instant sinkholes" and whileworking around what is thought to be a suffosion sinkhole it can be disasterous if it suddenly proves to be a cavern collapse that was just getting started and suddenly progresses and the bottom drops out of the hole and maybe the hole suddenly enlarges. Think safety and realize that what might be a sure fire safety approach may prove to only improve your odds. And do not be too hasty to assume you understand accurately what you are dealing with.

Hey we need all the permies we got

Ah well, just another day in the life of retirement.
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Color Change
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Post in the Hole
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Going Downhole
 
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I was purchasing insurance for my farm today in Springfield Mo and inquired about sinkhole coverage for you. It is available through fema and Missouri government but they told me its quite expensive, I didn't get any quotes myself

Information on sink hole information]Information on sinkhole insurance

As far as your pond damage....that looks catastrophic. There is no way that can be repaired cheaply, if at all. A back hoe is way to small of a machine, your going to need a track hoe/excavator and a sheeps foot compactor. Once dug to bedrock and filled in, it must be covered with a MINIMUM of 3 feet of PURE clay with no aggregate to seal. Make sure to compact in layers of 6 inches deep with a sheeps foot compactor....but honestly I don't think that pond will ever hold again. 1.8 acres of water is a substantial amount of force to try and seal. Just buying and bringing the clay is going to set you back 1K easy
 
Don Goddard
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"Eric Hammond wrote:As far as your pond damage....that looks catastrophic. There is no way that can be repaired cheaply, if at all.

-- A back hoe is way to small
-- need a track hoe/excavator and a
-- sheep's foot compactor.
-- dug to bedrock
-- must be covered with a MINIMUM of 3 feet of PURE clay
-- Just buying and bringing the clay is going to set you back 1K easy
-- but honestly I don't think that pond will ever hold again



Eric, you describe a credible scenario. Do you have expertise in this area?

Ahh what dismal news, but reality is not always cherry. Even the geologist suggested that I look for another pond site. But alas the lay of my land offers no other.
Actually if $1,000 plus labor such has been initially estimated to be about that much more would likely do the trick I would certainly consider it. However it is doubtful that even a track hoe could reach bedrock around here if the geologist is right that bedrock is 30 to 80 feet down.

One option that has been suggested is to simply fill with rock the hole that it there there seal it with geotechnical cloth and clay and then build an Island on top of it with an intent to create a large thick seal over it and provide that if the rock fill continues to settle that the island would provide additional material to settle into the hole to maintain a seal. The Island would be topped with bamboo so the root network would hold it together. Since the hole is actually on the edge of what becomes a peninsula during drought low water. building up a permanent peninsula would be an similar alternate.

If I abandon the idea of ever having a pond again, there remains the question of what to do with the dam. I suppose it could be pushed into the pond to eliminate a swampy remnant becoming a pest hole of mosquitoes. restoring the original contour would leave me with a field sloping toward the middle with a "sometimes water course" running down the middle. (woe be to any poor soul who 40 years from now thinks that would be a good place to build a pond.

A large pond liner is probably not a fix as there is reason to believe that the water that triggered the opening of the sink hole did not come from the pond but rather was a subterranean flow originating from the adjacent woods. which then undermined the pond floor and allowed the pond water into the hole.

Before initiating the expensive options, I could always try to carry out some repairs on my own. That would be the only cheap option and it would keep me busy for a while. mostly I would just need a way to haul and dump rock,, the rest of the equipment I already have.

The cheapest alternative to avoid having a mess might be to simply breach the dam at the original water course to drain the remnant of the pond
 
pollinator
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Hey Dan,

That seems quite a pickle you are in.

600 to 700 dollar is actually cheap but it may be a lot more if your rock base is deeper of if the crack is wider than expected.


An old geologist friend of mine had a project once where he had to survey caverns. He had good succes using an ad hoc technique measuring electric resistance. He could tell cheaply where there were caverns. I'm sorry to say that i have no details about the technique and we lost touch.

If your consultant knows about the technique you could ask him whether this is something for you. If there is a technical college nearby, you could perhaps consult their technical library? From the discription of my friend. He used not much more than a car battery, a couple of metal wires and a multimeter. He then used some spreadsheet to calculate the presence and size of a cavern.

An alternative is groundradar. That may be more expensive but at least you may find out whether you have sinkhole risk near buildings or not. The technique has been meer advanced so imaging is more common. However check you findings - if possible - by (hand-) drilling. Phantom results are possible.


Concerning the grey colour you observed. That may just be an indication for reducing (lack of oxygen) circumstances in the soil. That type of colour (grey, bluisch or greenish grey) is normal when you reach a level in the soil that is usually below groundwater.

Descending in that sinkhole is not advisable. The sides look anything but stable. How deep is the watertable at present ?

Greetings
Erwin












 
Don Goddard
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Erwin Decoene wrote:
Concerning the grey colour you observed. That may just be an indication for reducing (lack of oxygen) circumstances in the soil. That type of colour (grey, bluisch or greenish grey) is normal when you reach a level in the soil that is usually below groundwater.

I cannot claim any professional level expertise in geology, however what you suggest that the color of clay means is consistent with what I have understood and I would think it is relevant to my current problems. However in exactly what way it is relevant is not yet clear to me. If that is the usual water level there, I would think it odd that water would continue to descend into the ground at that point unless that water level was quite local and able to overflow into some nearby lower area.

Erwin Decoene wrote:How deep is the watertable at present ?

Given the soupy nature of the clay that I was sinking into I would say that at that point I was at the level of the water table even if my feet were about 15 inches into it. As in each position I sank to the boot tops, I would stop and extricate myself before continuing with the task at hand.

Erwin Decoene wrote:
Descending in that sinkhole is not advisable. The sides look anything but stable.

Since you have only the photographs to judge by I would certainly agree that from those appearances they show cause for concern. However:
-- Due to 0 F (-18 C) temperatures
-- no above freezing temperature for several days
-- no circumferential cracks around the hole on the shear wall sides,
-- Shear walls frozen like concrete
-- Sloped subsidance sides being frozen like concrete.
-- Safety rope
-- Safety person on site
-- continuous observation of the walls by two persons throughout the operation
-- Solid rope anchor 20 feet back from the hole

I considered the risk minimal and manageable. Now if it all thawed out I doubt I would go down there and would be more careful about even approaching the edge. I believe that the risk benefit ratio for obtaining more information in a timely manner was easily justified. Probably comparable to getting injured crossing the road to get my mail out of the mail box. That is to say manageable! Definitely no more dangerous than climbing a tree to cut a 8 inch branch with a chainsaw. (Granted, I have more experience with that). But you are correct, that the risk is not zero and deserves considerable care. I do know some people who probably would have just walked down the slope with no particularl assessment or preparation. But not me! Which is why I took time to expound the nature of the risks and various preparations lest I should encourage someone else to be careless.

 
Don Goddard
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The photo shown is sort of a visible update of my pond situation. The top view is high water in the pond and was taken in the summertime. It is taken from a slightly different angle but is representative of the water level of the pond before the sinkhole. The lower view was taken just a few days ago.

I have now had the guy most frequently recommended for pond repairs in this area come out and tell me what he can do for me.:

-- First of all he does not think the sinkhole went directly into the bedrock but rather thinks it probably went into a "gravel Pipe/vein/bed" (equivalent terms). He claims to have encountered these often and describes them as looking like the gravel drain beds used in septic tank drain fields except that they do not have a tile. He says he has even encountered them with water flowing in them. Such pipes may break out at lower elevations or may drain into bedrock flaws.
-- He estimates that it would take him about 6 hours with his track loader (30,000 lb size)

-- He would first hook the bucket into the hole and back away to break back the edge of the hole and widen the top.
-- He would then go into the hole to widen it into a bowl.
-- Adjacent to the hole is a high zone that becomes a peninsula during low water, which has ample clay that he says is excellent to pack into the hole

-- He recommends putting a truck load of "screenings" from the quarry into the bottom of the hole (lime stone dust) as he says this is highly effective at plugging up "gravel pipes" by moving with the water and setting up in the gravel. He says he has had excellent results sometimes simply dumping it into a pond near where the gravel pipe is drawing from
-- He would scrape off the top 3 inches of the shallow spot as the surface is mixed with debris from the adjacent forest.
-- He would then push the clean red clay into the hole packing down the layers.

-- He thinks the geologist's one suggestion has merit, and that is to build up a mound on top of the hole that will become an island which could automatically provide more fill in the event of any settling of the plug.
-- The forest contaminated clay that he stripped off could go on top of the island so something woluld more readily grow there.
-- My rock piles might serve to provide a causeway out to the island.

-- He estimates about $720 for the whole job.

Since bedrock is very deep (30 to 80 feet as estimated from well drilling logs in the vicinity) and the clay layer that was there sufficed for 30 years or more. He seems to be offering a plausible cost effective fix. Based on his expertise in this area I think that is probably a safe amount to risk to get my pond back. and if it works it will probably last longer than I do.

The one delay is that he says the clay is too wet to work now as he would simply sink in it, and it cannot be left to dry out too much or it will not back well. The first likely window would be in march before the spring rains come (likely April) .

There is a 1.25 inch pipe that runs under the dam which has a valve on it and I have it running to draw down the pond further. As the pipe is small, (plenty large enough to fill a stock tank but that is about all it can do well), It can only lower the pond about an inch in 2 1/2 days. It is currently draining about 10,800 gallons per day (5 gallon bucket every 40 seconds) which is running through the culvert under the road and down the gully on my neighbor's property (Neibhbor said it would not bother anything there) .

The drainage effort is to draw the water's edge back from the sinkhole to provide working space, and the water in the deep spot of the pond may be enough to keep the fish alive in it if we do not have to drain it all, but I may have to use a pump to aerate that water if I have too many fish for so little water. If I lose the fish, I will have to restock the pond. Fortunately there is a commercial hatchery about 20 miles from here.
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Before and After
 
steward
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6 hours of machine labor at that price is astounding. Will your guy travel
 
Don Goddard
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Ann Torrence wrote:6 hours of machine labor at that price is astounding. Will your guy travel


------------------
Just moving a 30000 pound machine a considerable distance would probably have to count as labor. At $100 per hour he was substantially higher than another excavator I contacted by phone though the estimated hours were the same. However in this case I figured it worth it because I was not just paying for his time and his machine but also his expertise.

One of the things that impressed me upon moving to rural Missouri was how low the taxes were, and how low the cost of hiring local tradesmen. When we remodelled the kitchen the contractor we had hired for other work told us who to go to for cabinets. We discovered that the recommended cabinet maker could deliver finished oak cabinets with either solid oak or oak plywood parts, custom finished and installed for less money than any big box lumber/home improvement/ store could and the quality of workmanship was superior. And the local guy even did a custom modification to the cabinetry caused by the sill of the kitchen window being 1.5 inches lower than standard counter height. and that even included a custom new oak window sill. I even take my car for body work to a guy that lives about 5 miles beyond me because he does great work much cheaper and will rework something that does not come out right without charging extra. Of course being 12 miles outside of town his overhead is way lower. It is sort of the saying about building a better mouse trap and living in the woods. That and he depends on word of mouth and I would recommend him to anybody.

We of course always responded in kind by paying them the final payment before they left the job site in cash or check according to their preference. And on larger jobs weekly progress payments. We always found them easy to work with even when changes were necessary. As an engineer, on any major jobs I always wrote a job specification. One contractor said he had not had a private customer do that before and he really enjoyed having the results spelled out on paper before he even started.

Of course we depended on our local real estate agent for initial recommendations and also got later recommendations from contractors who had served us well. We would have them come out and look at the work site, ask for how they recommend our goals be reached before we got any work scheduled. I was always present during the work and where possible if safety allowed I would assist. The specification always specified the end point of the job as my wife and I were doing the finish work on walls and ceilings. So we would specify that sheet rock wall were to be taped and sanded and ceilings were to be taped sanded and textured (ceilings can be tricky). And on really big longer duration jobs my wife would fix and share with them a Lunch (she is a great! cook). Basically being good Ozark neighbors. The contractor that did the most of our work having seen some of my construction solutions to tricky problems so as to meet code even asked my advice on how to proceed on other jobs he had going and I learned a lot from him.

It is partly the economy here and partly the culture.

 
Ann Torrence
steward
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Don Goddard wrote: It is partly the economy here and partly the culture.


Count your blessings brother. Here the economy is poor but the skilled workforce is limited and we pay as much or more as we did in the big city. Except for some things. I just had my dog neutered for $95, which boggles my mind. In SLC, if they did it for that the poor fella wouldn't have gotten an anesthetic! And my haircuts cost half or a third. Sometimes in those situations, I try to pay more but it never works out, so I move into the gift economy and bring eggs or what I can. But an excavator - no way I'd get anyone to show for $100 an hour.
 
Don Goddard
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As the pond repair project progresses I have been draining additional water from the pond at 10,000 gallons per day for 10 days, and the pond now looks like the first attached picture. In case you can't visualize how much water that is, just think of a box 23 feet 2 1/2 inches on a side full of water. That is a bunch! The object of draining water from the pond is to achieve the result shown in the second picture. I now have 20 feet between the edge of the hole and the water's edge. Hopefully that will be enough to allow room for the 15 ton track loader to work to fill in the hole and pack it down. To assess just how much water was lost during the initial stages and now that I have drained a bit more. If I were to stand where the water's edge is now, when the pond is fairly full, I would be up to my chin in water. I have lost about 5 feet of depth and there is only about 3 feet left at the deep spot. If the repair can be done while the weather is cool The fish shold be ok, as cool water holds more oxygen. If the water warms too much, I have a pump I can put in to spray water into the air to aerate it. Then the only problem would be if there was enough food for them. Hopefully the pond can be repaired before the spring rains come and try to refill the pond.

I have however been doing other prep to accommodate the excavation work. Oak trees will put out some tremendously long branches to get more sun, and with no competing trees growing in the pond I had some oaks on the bank putting out branches as long as 35 to 40 feet which used to droop down dipping into the water. It was necessary to cut these branches off so as not to interfere with the access to where there is a depth of good clay that will be used to fill in the hole and raise it to an Island. the largest branch was about 16 inches through at the trunk. The only practical way to haul the wood out required me to drive along the "beach" created where the water has receded from the dam, (on the far side of the first image) This is a little dicey as the clay there is still soft and slippery and that embankment has about a 15 degree slope (about 1 in 4) and the tractor kept trying to slide toward the water so I had to "crab" the tractor into the slope slightly. This causes me some concern as the flat relatively smooth tracks on the track loader can side slip pretty easily (they need to in order to accommodate steering) So I am also looking for alternate paths to get the machine in there. I think I have found one that will allow it to come through the woods from the power line right of way on my south border. And I should not have to destroy a bunch of trees to gain access that way. There is a small "sometimes creek" that feeds water in at the west side of the pond and currently the slight trickle is able to keep that side of the pond as a quagmire.

The shear vertical wall if tge subj gike ((3rd image), has started to collapse a bit as the soil dries out some. It is not so much filling the hole as it is just putting some slope to the south side of the hole. As the water has drained, the subsidence on the pond side of the hole has stabilized. Talking to a neighbor who has lived here all his life and is well aware of this pond from his childhood days he says there was a small pond here for quite some time and then in the 1960's the present dam was built that holds this pond. that makes the dam 50 years old, and if the excavator can fix it as well as that, it will last as long as I have any interest in it.
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Looking west to east across the pond at the dam
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There is a 20 foot bamboo pole in there if yo zoom it
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Shear wall caving in a bit as the soil dries.
 
Don Goddard
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Thursday March 3 the excavator called and said he could come out at 10 AM the next day. He said that conditions were about right and this coming week we are supposed to get about 6 inches of rain. We needed to get the fix done before the spring rains start. He had agreed with me on the need to beat the spring rains the first time he came out.

The next mornng I busied myself building brush piles brush pile that I built to protect the fingerling fish to aid recovery from the drought a few summers ago. At that time I could not even get to the pile as the water was too high and I had to throw the brush onto the pile as best I could. Now that pile is about 15 feet from the water's edge. This is a much worse depletion than the drought ever was. The sink hole swallowed half the pond in one night and another quarter of the water over the next week or so as water seeped through subsidence cracks into the hole to continue to drain. Then I had to drain water from the pond to get space between the hole and the water's edge. About half way to the other end on the right side you can see a dark spot on the "beach" which is the sink hole. I had got 20 feet between it and the water by draining about another 150,000 gallons out of the pond.
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Worst state of pond seen from the west.
 
Don Goddard
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Thursday March 3 the excavator called and said he could come out at 10 AM the next day. He said that conditions were about right and this coming week we are supposed to get about 6 inches of rain. We needed to get the fix done before the spring rains start. He had agreed with me on the need to beat the spring rains the first time he came out.

The next mornng I busied myself building brush piles to aid recovery from the drought a few summers ago. The first image shows the ramp dug out to the bottom of the hole with the tack loader ready to make a ramp on the opposite side so that it would be possible to drive through while packing the fill material in with the weight of the machine. The clay where this first ramp was built was essentially nothing but clay, However on the other side of the hole was clay with grit gravel and rocks which the excavator said was ideal for packing in the hole to create a stable water tight plug.

The Process carried on for about 6 hours, and as the hole filled with the excavator using both the gritty gravelly clay and some custom blended clay and rockier stuff that he had dug in the process of making the trench through the hole he filled the hole about 6 inches at a time packing each layer with the track loader..

It is now 17 days later and the the pond is refilling. If you look in the third image, the upper picture the dark spot on the far shore just to the right of the double oak trees on the near side is the sinkhole. Iin the lower image there is an interesting structure that only cost me $33.33 as it took 20 extra minutes for the operator to build. It is a 6 feet high at the near end and extends about 50 feet into the pond from the far shore. It is a peninsula whose near end is positioned to be on top of the filled hole to provide extra fill if it subsides again and the rest of the peninsula is to get out onto it. I have always wanted to be able to swim in the pond but the numerous rocks on the bottom made that a pain (literally) But on the viewers right of the peninsula the pond bottom is rock free clay. I now have a place to swim on one side and a new place to fish from on the other. Total fee from the excavator $600, and I did a lot of the tidy up details. Now I just have to wait for the heavier rains to finsh filling the pond.
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Ramp down intothe hole
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Packing the fill while driving through the trench
 
Don Goddard
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For some reason the third image did not load, so I will try again
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Don Goddard
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It is now8- 9 months post sinkhole disaster.  The pond has not yet completely refilled but  it is still coming back.   The water has risen to the point where it is just up to the end of the peninsula and with any luck the winter and spring precipitation will fill it back up and surround the peninsula.   As the peninsula is simply a compacted earthwork of gravelly clay, I wanted to add stability to it and I figured that while I was at it I would like to beautify it and make it practical for swimming and fishing access.  Because of the way it juts out from the shore, if the pond reaches high water stage this spring the peninsula will have only about 1 foot of freeboard,  and will give fishing access to 8foot depth on an easy cast from the end.  Swimming depth adjacent to the end of the peninsula will be about 4 feet.   Conveniently the peninsula has on the west side a rock free clay bottom and on the east side it is still quite rocky, but on the east side the water will be mostly deeper and a good place to fish.   So I am thinking Fish east, swim west.

Considering the above situation I decided to try to enhance the stability by planting trees on it, and to that end I selected Silax Babylonica aka Weeping Willows.   These trees are very tolerant of wet locations and are great for stabilizing the soil along creek pond and lake banks.   Being flooded from time to time will not bother them at all.  and they thrive in such locations.   The folks at Arbor Day foundation were able to supply me with 4 such trees at a reasonable price.   But as it was late in the season for planting them, Only one of the trees survived.   They graciously agreed to send replacements but I had to wait for this fall when they would have new bare root stock to ship.  They arrived last week and I got them planted.   And then I placed wire cages around them lest the deer decide that they are tasty sometime this winter.  

The tree size was suitable to plant 4 trees along the peninsula evenly spaced.   They should just about reach one to the next when they are mature.   I expect to have to do a bunch of trimming to be able to walk out along the peninsula when they grow large but one should be able to sit in their shade and still cast a line to gather some unwary Bass or crappies from the pond.  (or the occasional @%$($^! snapping turtle).  

As the peninsula sits atop the zone of the sink hole, I expect that the root system of the willows will enhance the security of our sink hole repair efforts.   For those who may have missed previous comments, apparently the sink hole was not the sort in which the limestone base rock had collapsed directly below the pond, but rather the result of a rocky/gravely seam in the clay soil that runs horizontally to some place where the water can drain to.  The soil depth here is about 50 to 80 feet thick but apparently such rocky/gravelly seams are a common feature in this region. and the bane of many a pond, but relatively cheap and easy to repair.

 
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This happened to us on May 4, 2017, also in Missouri.  Just wondering if you are close enough to our area to take a look and give us some much needed direction.  Thanks.
 
Don Goddard
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Ron Wilson wrote:This happened to us on May 4, 2017, also in Missouri.

 Bummer, Because of the limestone formations underlying much of the state this is an occurance which is much more common that most landowners to concern themselves with.  But really severe sitiations are not actually that common though they do happen.

Ron Wilson wrote: Just wondering if you are close enough to our area to take a look and give us some much needed direction.  

Well Missouri is a big state, so the definition of "Close enough needs a bit of definition.   I live in the vicinity of Camdenton south of Lake of the ozarks and I just was up in Kansas City yesterday and it took 6 hours round trip.  And that is not even half the way across the state.  I can tell you that the state geologists would be happy to come out and take a look at it.  The fellow that helped me was from the Missouri Geological survey and he dealt with this area.

John Corley - Geologist
Missouri Geological Survey
Missouri Department of Natural Resources
111 Fairgrounds Road Rolla, Mo 65401 2909
573-368-2132
john.corley@dnr.mo.gov

He will need to know where you are located and perhaps you can get map coordinates from Google maps or some such and maybe even capture the screen after you have found your place on the map.  However your postal address will probably suffice.  If you are not in his region he can probably put you in touch with the correct geologist.

They appreciate being contacted and coming out to look at things because part of their responsibilities are to track where caverns and drainage via caverns or under ground rivers may lie and they gather information from reports that they can develop in situations like yours.  They also may be able to advise on what sorts of remedial action you might or ought not to take. (some kinds of repairs can make matters worse and other situations there nothing is required. Geologist Coreley was able to tell me that the soil depth where I am is about 80 feet which he was able to discern from well drilling logs in the area.   That turned out to be confirmatory about what sort of sink hole I was dealing with.

Sink holes come in different varieties.  He told me about one sink hole that opened up at Fort Leonard Wood with a big crash and suddenly there was a huge hole in the ground as the result of a "caveren" collapse where a giant room in a cavern had the whole roof a chamber suddenly fall in.   More commonly a sink hole will be simply a place where acidic water draining into cracks in the bed rock has eaten out a cavern which soil is draied into making a depression in the soil above, and in my case the hole was identified as a bed of gravel underlying the clay bottom of the pond drained away the water when the clay bottom of the pond developed a leak.  If you are not too far from here I would be glad to consider coming out to take a look for what good it will do.  If by chance yours has opened up into a cavern then cave explorer clubs (Spelunkers) would probably love to explore it for you and if you are really lucky it has opened up into a cave where you might find quantrill's gold from the civil war.  Or perhaps more likely yours will be more like mine where a gravel and rock seam just needs to be plugged and burried and you may have good clay on site that can be used for fill.  In my case, I got lucky and found a local excavator who is an expert at building and repairing ponds, very knowledgeable and a real artist with a track loader.  He who was able to fix my pond with about 6 hours for what I considered a very reasonable price.

Because of not all that much rain last spring and then a hot dry summer last year my pond was still quite low until a week ago.  Then it came up about 3 feet in depth from the recent rains in about 5 days.  Be sure to post more on how this all goes, as you may be able to help others.   I do not know if there is a way to send personal messages on this website without publishing our contact information but if the webmaster wanted to send you my e-mail address I would not object.

Best of Luck (it is now your turn for some of that)
Don Goddard

 
Ron Wilson
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Went by DNR center last week  and pled my case,  got name of local engineer and called immediately.  Still no return call.  Also called the contact in Rolla, left message and also emailed.   Still waiting.  Email contact for me is juliew85@hotmail.com
Thanks for your reply.
 
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With a hole that tiny I have to wonder if just a wide thick blanket of clay would suffice.  It is all in how long you need it to last.  if the last hole took decades to form, you might try more of a spot fix.  You might also check with the NRCS for pond assistance
 
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