Building a Pond When Soil Conditions Are Less Than Perfect
Building a pond is a great way to improve your property and, technically, is quite easy. With just a handful of tools and a few building materials, you can dig a hole in the ground and fill it with water. What is hard is the sheer amount of heavy work: digging, lifting, prying, and cutting. If you happen to have grass sod that needs to be chopped out and transplanted, that is another layer of work. Tree roots in the ground need to be sawn or chopped up.
But what really makes the pond building project difficult is when the soil conditions are not favorable. Soft, mushy, sandy, and otherwise unstable soil will not maintain the shape that you initially create. Or sometimes, a perfectly level spot of ground is not available. The solution is to use retaining wall blocks to shore up part or all of the perimeter.
Tools and Materials You Will Need
- Laser level
- Tape measure
- 25 feet of rope
- Pond liner
- Retaining wall blocks
- Ground hardware cloth
- Pond underlayment to be placed under the liner
- Natural stone for the inner walls
- Check with your permitting and planning departments to see if building permits are required or if there are zoning restrictions.
- Before you begin digging, call your local utility locator service. This free service will help you avoid gas, electrical, water, and other vital services.
- Pick a dry time of year for this project: spring or summer. Work at times of the day when you have the most energy. Wear only the worst of your work clothes, as this is very dirty work.
- Estimate that it will take a couple of months from the moment your shovel first contacts earth to the moment you turn on the hose to fill the pond.
- Cost is mainly determined by the most expensive item of all: the pond liner. Unless you are able to find natural stone to form the inner, decorative portion of your pond walls, you will need to purchase this from a quarry or masonry supply yard.
Lay Out Pond Boundary
The classic way to mark pond boundaries is with a garden hose. A hose works better than rope because it naturally lays down in wide curves. If this is a hose that you value, you can sprinkle flour over it. After removing the hose, the shape will be retained by the flour outline. If this is an old hose that you do not care about, you can start digging next to the hose.
Dig Out Pond Border
Start by digging out the pond border. Make shovel-width cuts in the grass or dirt. For grass sod, it helps to use a spade. This tool allows you to make narrower cuts in the grass. Slide the spade under the segmented turf to remove it. With the border established, you can now remove the hose.
Dig Out Center of Pond
After the pond perimeter is established, the back-breaking work of digging out the majority of the earth begins.
First, remove all dirt within your border, but dig no deeper than the border. Next, dig down to the lowest point in your pond, wherever that may be located laterally. This helps you establish a base-line for your pond’s depth. No other part of the pond bottom can go lower than this.
Shore Pond Walls With Retaining Wall Block
If your soil is especially sandy or loose, you may have to shore up the walls with retaining wall blocks. These blocks essentially do what the earth cannot do: retain the pond’s shape and height. Smaller retaining wall blocks give you better flexibility and are easier to work with.
If your soil is firm, you do not have to use retaining wall blocks.
Create Graduated Pond Levels
As you progress downward, create graduated levels, each level no more than about 8 inches high. This is a key part of the process because if you build walls that are too high, you have more work to do later on when you add rock to the inner portion of the walls. You will have to build very thick, wide mounds of rock so that you can reach these heights. By keeping your levels short, you can vertically span the distance with one or two rocks.
Shoot Pond Level With Laser Level
A laser level is a highly valuable tool when building a pond. If you own a bubble level only, or no level at all, you should purchase a laser level, if only for this one project.
You should continually shoot the level so that all pond walls are the same height. Remember at all times that your pond is only as high as its lowest point. In other words, if your walls are 34 inches high all the way around, except for one spot where it dips down to 32 inches, you cannot fill your pond above 32 inches. While this may sound like an obvious point, it is a point that can get lost in the midst of construction.
Lay Ground Hardware
If your yard has burrowing animals such as groundhogs or moles, eventually they may find your pond and burrow upwards, piercing your expensive liner. To ward against this, purchase rolls of ground hardware cloth (1/4-inch screen) and lay it out all the way across the pond bottom. Then spread about a minimum of 2 inches of dirt over the ground hardware.
Use Rope to Estimate Liner Size
In theory, you should be able to first create your pond layout with complete freedom, and next purchase a pond liner to accommodate that size. In reality, though, pond liners are very expensive, and you may want to size your pond according to how much you are willing to pay for a liner.
One way to keep yourself in continual check during your dig is to cut off a length of rope as long as your liner’s longest size. Lay this rope through the hole, going down one side, across the pond bottom, and then up the other size. The rope should extend about 2 feet beyond the pond edge, as well.
Measure from at least two different directions to obtain the correct measurement for the liner.
Install the Pond Underlayment
Before installing the liner, lay down an underlayment. The underlayment will protect the liner from roots, rocks, and other objects that may damage the liner. You can use old carpeting or you may purchase a specialty underlayment from a pond supply store.
Install Pond Liner
With a helper, roll out the liner across the pond bottom. Then, unfold it so that it drapes over the sides of the pond. Be patient with this step as you slowly and painstakingly press the liner down onto the pond bottom, creating pleats. While the bottom may have a few pleats, all of your sides will be pleated.
Add Rock to the Pond Walls
Using natural rocks, begin to add decorative rock to the pond bottom and walls. Start with large and medium-sized rocks, building up the sides until no pond liner is visible. During this stage, it will become immediately apparent why you earlier kept your graduated levels low. After the walls are entirely covered, use small stones or smooth river pebbles to cover the bottom of the pond bottom.