Earth Surgeon

One Junky, Seepy Dam

By Michael Gray

I’ve seen a lot of junky dams. Dams with trees buried in them, collarless pipes, and just plain mud dams where someone pushed chocolate pudding-looking muck into half-way decent dirt and buried it.

But almost every time I see a junky dam, it has something to do with rock. I just happen to live in a state blessed with limestone rock. Limestone also happens to be the state rock of Tennessee. Go figure.           

 A little while back I was invited to have a look at a problematic 12-acre lake. New owners were looking to improve it. The lake had a little bridge in the middle of the dam, crossing a stair-stepping rock waterfall primary spillway feature. As it left the waterfall, water traveled through a stacked-rock-lined ditch. There was also an emergency spillway on the far end of the dam. The problem? The waterfall didn’t always work, simply because the lake couldn’t stay full enough to keep water rolling out. This lake has a really nice watershed, along with some springs. It really has all anyone would want for a lake to be happy—especially its owners.

I took a stroll around the lake. I was on my own, the owners of the property were out of town and told me to make myself at home. Everything at a glance looked good—except for an odd white PVC pipe sticking out from under the rock wall in the ditch. Under that pipe was a big stream of water running across the top of our oldest and dearest friend—limestone. Then, if you looked back up toward the dam you could see what might be a ditch that had settled from the pipe installation. Looks to me like this is definitely the problem area. The owner and I had a discussion about what was going on. I told him we could work on it, from the inside or the outside of dam. He let me know real-quick he didn’t want to drain the lake. But he agreed I could drain it down to get some of the hydraulic pressure off this seepage area. So, the plan was to go in behind the dam and make a repair to half of the dam, by means of building a new core and lining the backside of the dam with a compacted clay blanket.

Sounds reasonable enough.

To get started on this project we would have to take some fence down and build a gravel mound over an asphalt driveway we were going to have to cross. We didn’t want our heavy equipment tearing up the pavement. Our borrow area and staging area was across this little road on the property from the dam site. Once we had the fence down and asphalt protection in place, we were going to build a haul road to the backside of the dam. We had a very limited working area behind the dam. So, everything we dig up will be loaded and hauled into the field and piled—for the time being. We stripped a big section in the field and got down to a really nice clay layer. We’ll use the clay for our haul road as well as for the dam repair. The haul road was necessary due to the fact we would be traveling through a soft area full of topsoil and next to drainage ditches. Those off-road trucks would sink out of sight without it. Oh, and by the way, the owner didn’t want me to lower the lake anymore.

Wouldn’t you know it too, the durn thing was almost full due to recent rains.

Once we had roads in place and everything prepped, we started digging the core trench for the dam. The first section was into the hillside and was quick to hit rock. The rock began to step down, which is normal. But then, kind of out nowhere, I began to see a lot of water. So, as is my nature, I started poking around with the bucket of the machine. I started hitting geotextile fabric, gravel and black drainage pipes. This was a very well thought out French drain someone had installed at one time. Apparently, this leak has been going on for some time. I kept digging and loading and sending material out, while at the same time the chase was on. There was a series of pipes coming from a couple of different spots.

Then I encountered the white PVC pipe I had seen sticking out from under that rock wall. I tried to be gentle and not injure it. But I accidently poked a hole in it, nothing came out, but the water raced in and out into the drainage ditch. This was actually a wonderful thing. I could actually see what needed to be done. The pipe didn’t work as designed.

Digging and loading continued. Pipes and gravel from the French drain were gone and we were starting to see more and more limestone and water blasting out of the rock as it started stepping up the hill. We had a pretty good mess going on, trying to dig with—let’s just say 500 gallons of water per minute pouring in definitely makes things interesting. Needless to say, I better bring a pump to work tomorrow. Pumps are basically a way of life for us. We’re always below natural ground at some point and the water has to go away.

At least we had a drain and it was great. But we still had a pretty deep hole and it would easily hold well over 100,000 gallons. With all the dirt out of the way for the deeper section it was time to get this rock cleaned up. While the rock was getting hammered and cut out, we had to let the pump run to control the water level. The junky spot in the rock turned to a crack and the layers began to step up. It appeared we were getting to a good spot. As the rock was broken into smaller pieces, it was loaded up and hauled out of the way as well. We managed to cut all the way across the section and get to a good place for packing clay tightly.

We decided we would start backfilling from the hill and work our way toward the flowing water. It was going to be a real magic trick to try and cork the hole with so much head pressure from the lake. I was running a number of different attacks in my head how to get this thing under control. Eventually I just kept closing the hole, making it a little smaller and smaller. Then I closed the door with heavy clay as fast as I could. It wasn’t long before water started squirting out in other places. We just kept pouring the dirt to it until it let up. My plan was to get the floor of the core in place and then cut benches in the dam so we could attach to it. Well, this is one of those super-junky dams. Not only did we have the rock issue, but water was coming straight through the dam as well, not pouring out like the rock hole, but just seeping through. The material in the dam is mushy and even muddy in places. We removed all the rotten material we could safely remove and started replacing it with good compactable clay.

Everything was coming together and really taking shape. A couple of days had passed when the water decided to show up again. It had found a way around us. I let the owners know what was going on and that we were going to have to go further into the hill to cut it off. So, the digging began again, and it wasn’t long until I could see what was going on. The water had found a crack that just happened to run right around our core. We were going to have to get a little bit higher than that crack to put this newest escape route to rest. More digging, loading, hauling, hammering, loading, and hauling until we made that nice solid step up from the water. This time, after we got it all cleaned out, filled back and compacted the only water we saw leaving was down that spillway.

Success!

Let me tell you it is a great looking spillway when that water falls off those rocks. Now the time had come to start removing our haul roads and bringing topsoil back and get this place back to normal. This one here really took the grand prize on its long list of problems. Junky, muddy, quirky, and rocky all in one.

But at least the spillway works and the thing is holding water