- Step 1: Lay out a garden hose or string where the pond is to be located and in the desired shape of the pond. Stand back and view it from the surrounding garden, deck, and house. It is easier to make changes now than once you have started digging.
Once you are satisfied with the position and shape of the pond, remove the turf and any topsoil from the outlined area adding 2 inches to the width for a layer of cushioning sand to be included beneath the liner. If any edging such as rock or brick is to be laid around the pond, remove the turf and soil from this area as well. Then remark the actual area of the pond.
It is easier to level the edge of the pond at this point using the soil as it is removed by raising the lower end. It is extremely important that the edge of the pond be level since the water inside will always be level, thus revealing to the eye and exposing to the sun any liner that is not covered by water or in the shadow of an overhanging edge. Using a carpenter level and as long a 2X4 as needed (Figure 1), lay the board across the pond and the level on top of this. Check the pond in all directions to make sure it is level all the way around the edge. It may be helpful to use short wooden stakes to mark the level spots as you go around. Use these stakes as a reference to level the next one all the way around the pond, removing any soil above the stakes as you go. Once the rim of the pond is level, the rest of the pond’s dimensions can be measured using it as reference.
- Step 2: Spread enough polyethylene plastic to hold the soil being removed (Figure 1). Next, begin digging from the center of the pond toward the edge. Remember to allow for shelves if these were included in the design. It is easier to maintain shape and monitor depth if the entire pond is dug out at once to the depth of the shelves first (about 9 to 12 inches). Then start digging out again from the center of the pond, leaving the width of the shelves, 9 to 12 inches. If an edging other than grass is to be used, account for this portion as well. Flexible liners must be lapped under soil to hold them in place and prevent subsurface drainage into the pond (Figure 3). A slight fall of 1 inch per foot away from the pond is all that is necessary and looks best for the edging. The walls of the pond should slope from the shelves to the bottom of the pond at about 20 degrees off vertical, that is, 1 inch toward the center for every 3 inches down. Thus, if the overall depth of the pond is 24 inches plus 2 inches for sand and there is a 9 inch deep shelf plus 2 inches for sand, the wall for the shelf will come in 3.5 inches from top to base. Then, move out the width of the shelf and cut the wall at a slope down another 15 inches to the bottom coming in another 5 inches.
- Hint: when digging out the major portion of the soil use a round point shovel. Then, after getting as close as possible, cut the slopes for the walls using a square point shovel. Once you have cut two widths of the shovel to grade, cut the remainder with only half of the shovel at a time using the other half to follow the grade (Figure 2).
- Step 3: Once all of the soil has been removed, all surfaces are as smooth as possible, and the sides are all set to grade, check the walls, base of the pond, and shelves for rocks, sticks, glass, roots, and any other sharp objects that might puncture the pond liner. Next, begin placing the 2 inch layer of sand in the pond. The sand should be moist and packed in as tightly as possible.
- Step 4: Roll the liner out on the driveway or any nonturf area; allow time for it to warm enough to become flexible (less time may be needed if it is a particularly hot or sunny day). Once the liner is workable, reroll it and carry it — DO NOT DRAG IT — to the pond; a wheelbarrow is helpful with large liners. Unroll the liner and position it over the hole so that the lengths and widths match those of the pond. Carefully push the liner into the pond trying not to disturb the sand. It is not necessary to mold the liner exactly to the pond’s shape, but it is helpful to approximate it. The water will finish the job as it fills the pond. Lay some stones on the ends of the liner to produce some tension as it fills with water (this will prevent unnecessary folds in the liner)
- Step 5: Begin filling the pond with water (Figure 4). This will take some time. As the liner begins to fit the pond, excess liner will begin to gather naturally in certain areas. As the pond fills draw these areas tight and simply fold the material over into as many flaps as needed. Use of more and smaller flaps is best. The water will eventually cover these and they will become unnoticeable. As the pond nears full capacity, start to cut the excess liner from the edges. Save these pieces for patches later if the pond needs some repair, or place them under heavy pots and bricks (Figure 5).
- Step 6: With the pond full of water, the final step is to install any edging (Figure 3). Edging the pond should wait until it is full so that water pressure will aid the wall in withstanding any weight of material or people. A full pond also keeps the liner in place and well fitted before the edging seals it in place preventing any further changes. If the edging contains mortar, it is most important to avoid spillage into the pond. Cement is highly alkaline and reaction with water could create a severe pH problem. If enough falls in, it may necessitate draining and washing, before refilling the pond.
If edging the pond with bricks or other rectangular materials, orient them with their length towards the center of the pond. Be sure to allow for at least a 2 to 3 inch overhang to hide and protect any exposed liner (Figure 5). This gives the best appearance and stability to the surface which must be constructed well enough to support occasional foot traffic. The material should be laid with approximately 1 inch per foot fall away from the pond, thus preventing surrounding surface runoff from entering the pond. Edging looks best if you can maintain either an obviously intentionally irregular edge and surface or a perfectly straight and flat one. String lines, carpenter levels, long boards, and precut curved forms are useful here (Figure 1). Allow ample time, 48 hours, for concrete to dry before any foot traffic or potted plants are allowed on the edging.