How to Build an Earthen Pond Part 1
It is extremely important that you choose your pond site wisely before bringing in the heavy equipment. I addressed how to do this in my pond planning article. In this article, we use the existing topography and soil types to make the best pond site choices.
Unfortunately for me, I really don’t have any site on my property that is a really good pond site. I picked the best site of my marginal choices, because I really wanted to have some open water on my property for diversity, wildlife habitat, fish, and amphibians. The main problems with my site is that I have a lot of slope, not a lot of catchment as I am at the top of the hill, and my soil is filled with silt, sand, and even some shale and rocks. So my site is pretty bad and complicated all around. Nevertheless I decided to go forward with the project.
I chose a site that was in a partial valley, and the slope wasn’t terrible. It was definitely my best option for catchment as well.
1. Peg your site out with stakes and mark your levels with a laser level. I also wrote the levels down on the pegs as well. The pegs will get moved around a bit. We also re-measured a few times as we went along.
2. Get your equipment and materials ready. For me, it was a sheepsfoot compactor, excavator, skid steer, and sodium bentonite to address my poor soil for ponds.
3. Remove the topsoil from the site. Ideally, you should save this to dress the walls after so your plants have something nice to grow in.
4*. Connect any diversion drains. When you do this really depends on your project. For me, it made sense to do it in the beginning as it made for less damage to my property, but you may want to wait until the end if you are going to have trouble keeping water out while you are working.
5. Build your keyway! This is extremely important. This must extent below the dam to lock it into the earth so it does not slide down and fail. We dug a 2 foot trench then mixed in bentonite with each 3 inch layer of soil that we applied. The process was to add 3 inches of soil, then rake and pull rocks out, then compact, then add the bentonite, then rototill, then rake and pull rocks out, then compact, and on and on and on until we got to the height we needed. This was unbelievably labor intensive. If I could do this over, I would have looked high and low to just truck in the appropriate clay. It took a week and a half just to get the wall up. Also, bear in mind that your bentonite amount is based on the layer of soil amount compacted. We put more than the recommended amount because we were applying the appropriate amount for the layer un-compacted. That made a big difference in the amount we used, but it does make me feel good about having a strong keyway and dam wall.
Recommended Application Amount of Sodium Bentonite
Clay: 1.0-1.5 pounds per square foot
Sandy silt: 2.0-2.5 pounds per square foot
Silty sand: 2.5-3.0 pounds per square foot
Clean sand: 3.5-4.0 pounds per square foot
Rock or gravel: 4.0-5.0 pounds per square foot
6. Build up your inner and outer walls as you build up your dam wall for stability. Every 6 inches of soil you add should be compacted. It is very important that the soil is neither too wet or to dry to compact properly. The moisture level is something you have to constantly monitor and address. We kept a garden hose out and add water as needed. It was very dry so we were not worried about it being too wet. The inside of your dam wall should not be any steeper than 3 to 1, and the outside 2 to 1. However, I would recommend no steeper anywhere than 3 to 1. We had some problems getting our compaction equipment up a 2 to 1 slope.
7. Rain can cause some interruptions, so be ready with a pump if necessary to get you back on track. You still have to pay for the equipment if it is just sitting there.