Pond Boss Forums POND CONSTRUCTION Building a dam Dam for Auxiliary Pond at Existing Pond Entrance

Last year I asked about the feasibility of adding a small 30' diameter auxiliary pond at the entrance of a wet-weather ditch to my existing 1 acre pond.
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=218864#Post218864
The main purpose would be to provide an area for the frogs and other critters that disappeared when I added bass to the existing pond. I sure would appreciate some advice before I start digging.

Even though the two ponds would be essentially the same level at full pool, I am thinking about using a dam between the two, so that I could pump water from the existing pond during dry weather to keep the auxiliary pond full. I gave some thought to a concrete dam, but I'm thinking now that I ought to stick with a small earth dam. Right now looks like a good time to do it, since the existing pond is down about three feet due to the extreme drought we had for the last two years. Here is a schematic diagram of what I am thinking about.

At full pool the two ponds would be at the same level. The red pipe would be for keeping the auxiliary pond full. The submersible pump would be in the existing pond about 4 feet below full pool and connected with a 2” PVC pipe. The green pipe is the main overflow pipe. The emergency spillway would be the existing low areas off to the West side of the new dam. Some remaining questions are what pump to use, how to construct the clay core, how to make the anti-seep collar, and whether I would need some sort of flap valve to keep water from leaking backwards through the pump.

Here is an image looking from the East to the existing junction between the two ponds along with overlays of what I am considering. My main concern is the dam itself. It would be only about 10 feet long, about 4 feet tall, and about 10 feet wide. I thought I would dig a trench and fill it with clay that I saved from the original pond. I would make the rest of the dam from dirt I excavate from the new pond area. Would a trench about four feet wide by 4 feet deep be close to right for the clay core? And would a mechanical vibrating packer be sufficient for a small dam like this? I'm not sure how I would pack it any other way.

Here is a view looking from the existing pond up the ditch.

And here is a view from the ditch looking towards the existing pond.

Addendum: I've been thinking some more about the pipe from the pump to the auxiliary pond. It seams to me that it really doesn't need to pass through the bottom of the new dam, but could pass through the dam above the water level alongside the overflow pipe.
Here is the modified schematic drawing:

Note: Although the drawing shows the red filling pipe below the green overflow pipe, I would actually probably have both at about the same height and above the full pool level. Would that eliminate the need for anti-seep collars?

I'm a belt and suspenders type of guy, I'd go with the anti-seep collar anyway. For the small extra $$, I would think of it as a cheap insurance policy that you only have to pay for once.

I have to make a decision Thursday on whether to rent the excavator, and I sure would appreciate comments on the overall plan. Is a three foot wide clay core enough for this small dam? And what would be the best way to compact it? One friend recommended a trench jumping jack compactor, and another recommended just using the bucket of the excavator. Bobcat makes a packer wheel for their minis, but the local rental company does not have anything like that. There will never be more than about 3.5 feet of head pressure on the dam, and I will be able to pump water from the main pond to compensate for small leaks; but I still would like to try to do it right.

Thanks,
Charles

I'd think that the Whacker packer would do a better job of compacting the clay, provided it was laid down in small enough lifts. But, the downside is that it'd probably take more time to do it.

I wish one of the dirt guys would chime in!

Me too. The guy who built the original pond keeps saying he's interested in doing the frog pond, but I'm about to give up on him. Can't wait any longer, because I need to do it while the main pond is still down.

Well, it took a few years, but I finally got back to this old project. A few days after my last post I got started digging the core about 4' wide until I hit hit fresh clay, and then filling it in about 6" lifts with clay that I had saved from the original pond. This is a view of the work from the west side, with the pond on the right and the upstream side to the left.
We started with a packer with a small footprint, figuring it would do a better job, but it broke down, and we had to switch to a larger footprint packer. We got the core up to almost the top of the trench when I ran into a problem with the tractor and had to postpone the project. I covered the trench with topsoil, sodded it, and left it to be completed later. That was in November, 2011.

Just before the predicted rains this past November I finally got back to the project. The first step was to remove the sod and get back to where we had left off two years ago. Here we are using a flat shovel and bucket to locate the original clay core. The white PVC pipe to the right is an irrigation pipe that runs along the edge of the pond.

Then we exposed the rest of the two-year-old clay core.

Next we started adding and packing new clay and added the white PVC overflow pipe and black poly pipe for filling and draining.

I had planned to add more clay to make the dam wider, but a heavy rain was predicted, so we decided to add some temporary top soil and rye grass seed.

If the dam survives the spring rains, then I will drain it, remove the top soil on the sides, add more clay and new top soil, and then add permanent grass sod. Finally, if the dam is still surviving, I will excavate the pond to give a more consistent depth. The frog pond has been a couple feet higher than the main pond since late November, and it seems to be holding water pretty well. It has been essentially full for the last few weeks.

Last night we had a real gully washer, and I half expected to find the whole dam completely washed away. The overflow pipe was totally covered over, but the excess water was flowing around the low area to the west of the dam as it was supposed to.

I do need to add a little more dirt to the west side of the dam to push the overflow area a little farther away from the dam itself, but it's looking like this amateurish job may actually turn out better than I had any right to expect.
This is the view from upstream looking down at the frog pond and the main pond. The frog pond is about six inches above full pool.

This has been a long project, and it has been interspersed with other projects such as finishing the gazebo, planting the birch, cypress, sweet bay magnolias, native azaleas, and other landscaping. And it still has a way to go before it's really done.

I did check the pond again later this afternoon. The dam was still holding. and the level had dropped to the point that the flow was all passing through the overflow pipe. But the best part was listening to the chorus of appreciation from the spring peepers and the upland chorus frogs.
http://youtu.be/maTn8Cn8QTU
I just hope the bull frogs return, and that some of them will be smart enough to stay away from the big pond and the LMB that lurk therein.

Nice! I like seeing a well thought out plan come together and work as intended.

Thanks. But I think it has been more luck than careful planning so far. I do admit to always having a backup plan, and I have had to implement several of them.

Any ideas on how best to proceed? I think I do need to add a little height to the dam and push the emergency spillway farther from the dam itself. And I think I ought to try to add some more dirt to the width to bring it up to the 10' originally planned.

Current plans are to try to weather the spring rains and if the dam is still holding, drain it, add to the dam and excavate the pond to about four feet with somewhat steep edges. But I have been reading that most of the critters I want to attract prefer gradual slopes and shallow water. That would suggest that I should leave it pretty much as is (about three feet deep in the center with gradually sloping sides).

BTW. In looking this over I guess it sounds pretty strange to build a dam, let the pond fill, then plan to drain it and only then excavate it to its final depth. My reasoning was that with my lack of experience there was and still is a pretty good chance of the dam just washing away entirely. If that does happen, then I will be left with just a lot of wasted time and effort and a wet-weather stream pretty much as it was. That's a lot better in my book than a big ugly muddy hole in the ground.

Like the video. Sounds quite relaxing...... Good job on the dam.

It sounds like you have a pretty good plan in place. I'm not going to tell you any different because it seems to be working very well! I think your ideas and suggestions are headed in the right direction.

I would add a few feet of height to the levee and probably add more pipe to handle the flow from large storms. The fish from the larger pond will invade the smaller pond each time water goes over the top or through e-spillway and create a similar situation to what you have in the larger pond.

-HH

Progress Report:
Here it is in the middle of June, the spring flood has receded, plants have found their way into the pond, and critters are showing up. The pond is about one foot deep with boggy areas at the edges. I had originally planned to drain the pond at the end of summer and excavate it to about three to four feet, but I'm beginning to like the bog look.

Anyway, here is a view from the dam between the ponds looking up towards the wet weather stream. The stream is lined with river birch, sweet bay magnolias, and bald cypress trees that I have been planting the last three years.


And here is a view from the field between the house and the pond. The dam is marked by the dead rye grass to the right of the bald cypress on the left. You can see part of he main pond behind the cypress. The emergency spillway is on the far side of the dam.


As suggested, I definitely plan to increase the width and height of the dam in August and probably replace the six inch pipe with at least an eight inch one at that time. But I accept the fact that there is no way to really separate the two ponds when we have floods like we had this year. Although the frog pond was connected to the main pond with probably six inches of water in the spillway for more than a week this spring, I have not seen any bass or even large bluegill in the frog pond so far. Or course the blue heron and the green herons might have taken care of that for me.

I might need to consider adding some sort of small fish for mosquito control. Other than that, I guess I'll just enjoy the frog pond/bog until August and then decide whether to make it bigger and deeper or just add to the dam and leave the rest pretty much as is.