Now that you have chosen your site and have determined that you want to install a preformed pond, you will have to make sure the ground you are working on is level. Turn the shell upside down and trace its outline. This can be done with chalk, paint, sand or even kitty litter. Excavate the soil and follow the contour of the pond shell. Make sure you measure the depth of any shelves and try to dig to those measurements. If you dig to these measurements and add two inches of sand to the bottom of your hole this will fill all spaces between the shell and ground. This will elevate the upper edges slightly above ground level and will help avoid surface runoff from coming into your pond.
Check the depth of the hole periodically. Use a carpenters level and a 2x4 to check the bottom to see that it is relatively level. Move the sand around until it becomes level and firmly tamp into place. Check to make sure the upper edges are level by checking end-to-end and side-to-side at several points. Start filling the pond with water and simultaneously fill around the outside with soil (sand is better) and slowly add water around the outside. Keep the pressure on the walls the same inside and out so that you won’t press the walls in, resulting in an uneven top edge. If your pond level is off, jiggle the pond form in its sand setting to make it level to within 1/4 inch. Fill your pond. Now you can install the edging of your choice.
INSTALLING LINED POND
Depending on the size of your pond, you might want to hire or bribe some of your friends to help. If you are digging a larger size pond you might want to use a backhoe.
Before you start to dig try to preserve your topsoil and keep it separate from the clay. This is good for filling around your pond, building earth berms or even a garden. Remove the top of your lawn with a sharp spade by cutting strips of grass and slicing under them. Roll these up and place them in the shade and keep moist. These strips can be used to repair damaged spots in your yard.
Mark your excavation outline and check to see if its level using the same method as mentioned above. Dig a trench about a shovel's depth around the outline of your pond. Removal of sod around the edges of your pond will allow for edging of stones or flagstones. Put in any shelves that will be used for marginal plants. These should be wide enough to support your plants - at least 10-12 inches wide and approximately 8-12 inches from the top edge of your pond. Dig the pond to the desired depth and shape. If you are installing a bottom drain it should be located at the lowest point of the pond. It is often recommended to have a drain if you want a Koi pond. Your drain should have a wide diameter, no elbow curves and be directed to a good drainage site.
There are kits available for intrusion through the liner. If you do not have a drain, then you should have a low area on one side that is a couple of inches deeper than the rest of the pond so that when you clean your pond, fish and other residents will gather at this end, making them easy to scoop up. After you have finished digging your pond make sure it is level. Remove all stones or other sharp objects from the sides and bottom. Adding about 1-2 inches of sand will help cushion your pond liner from tearing. Cover the sand with underlayment or old carpeting. If you are using carpeting with rubber backing, slash through it in several places so groundwater will not collect between it and the liner and float the liner away. If you cover your pond liner with rocks, use round rocks or pea gravel when possible. Rocks with jagged edges or crushed stone can cause leaks in your liner. Put extra carpet or scraps of liner under rocks for extra protection.
Now you can purchase your liner. Figure your liner size by adding double the depth to both the length and width of the broadest points of the pond. Add at least another two feet to each dimension because you will tuck in the liner around the edges. Figure the liner for waterfalls and streams the same way.
Length + 2 x Depth + two feet = Length
Width + 2 x Depth + two feet = Width
Unfold your liner and spread it in the sun to warm it making it more flexible. If the sun is hot, make sure to wear gloves. Do not spread this on the lawn because heat builds up quickly underneath and will kill your grass. Center the liner over your pond to ensure that the ends will overlap all the way around. Smooth out the wrinkles working from the bottom up and pleat or fold the liner as necessary to fit curves and angles. Use bricks or stones to hold the liner edges in place. Adjust these as you fill the pond to avoid stretching the liner. Make sure the edges are level. As you fill your pond with water adjust the liner from the bottom up to ensure a good fit. Fill to within 1-2 inches from the top. You can now work the edges around your pond. Instead of cutting the excess liner, I like to fold it under to allow for any settling of your ground.
Flagstones can be put on top of this extra liner, which will help keep grass and weeds from growing between the stones and around your pond. A hole can be cut into this liner to allow for plantings. Before the edge of the pond is finished all waterfalls, streams or bog gardens whose liners overlap the main pond liner should be installed.
Safely Tip: Before any digging begins check for gas lines and underground electrical and cable lines. Call Consumers Energy if you are not sure where the lines are. Look out for overhead wires if you bring in a large backhoe.