Once a prospective pond owner has decided to take the plunge and figured out important details like location, layout, and the best depth to protect the residents of their pond, it’s time to start getting down to the nitty gritty.
The first step, before a shovel ever hits the soil, is to call 811 (in the US) and have someone come to your home to mark utility lines. In Canada, separate services exist for each province, but are generally referred to as One-Call. Be sure to let them know how deep you’ll be excavating. No one ever intends to cut a gas line or a buried telephone cable, but it happens. Stay safe and protect your pocketbook by calling first.
All-in-One Kits
First time pond owners often choose to buy a “pond-in-a-box” which is marketed as “everything you need to build a beautiful pond, in any space.” It’s tempting to avoid the chores of measuring, calculating, researching, and sometimes simply guessing when you’re deciding on which equipment you need. These may, indeed, be a great solution for the nervous novice pond owner, but keep in mind that a one-size-fits-all solution will come along with some significant limitations. If pre-made pond kits are analogous to round holes, your unique vision of an oasis perfectly nestled into your yard is likely to be the proverbial square peg.
Empty Promises
It can be extremely difficult to evaluate the suitability of a given kit for your goals. One kit widely available online or in home improvement centers promises to provide materials for a 400 gallon “beautiful backyard koi pond” with a 10x10 liner. It even suggests in the specs that you’ll be able to build a 7x7 foot koi pond with an average depth of 18 inches. First, that’s physically impossible since it leaves zero allowance for anchoring the liner. The other problem is that koi mature into large fish, and they require a pond with an average depth of at least 3 feet to thrive. A 7x7 foot pond averaging 3 feet deep should start with a liner that is about 15 x 15 ft. The volume of a pond this size will be approximately 1100 gallons, so if you started off with this kit, you’d need not only a completely new liner but a significantly more powerful pump. Oddly enough, this pond kit doesn’t appear to come with any kind of filtration, either, which is an absolute must if you’re keeping fish.
Your Local Pond Pros
A word to the wise: stick with a local pond store that can help you realistically evaluate whether a kit will meet both your and your fishes’ needs. Even a deluxe pond kit sold online by a recognized pond specialist promises a 16 x 11-foot pond from 20 x 15-foot liner. That will build a pond only 12 inches deep. A neighborhood pond specialist can help even novice pond owners understand how many fish you can safely keep in a 1000-gallon pond, how to compare pump specs, what it takes in your region to overwinter fish in the pond, and what the best options are for effective filtration systems.
Measuring for a Pond Liner
It may be apparent by now, that calculating how big your pond liner should be isn’t such a simple task - at least not for the marketing folks out there. But it’s not exactly rocket science, either. The most important thing to remember is that you need to account not only for the surface area of the pond, but also for the sides, and for enough excess to securely anchor the liner so it doesn’t move once it’s filled with water. There’s not much worse than excavating a hole and starting to place the liner, only to realize that it’s not quite wide enough to reach the other side. That kind of mistake can be both expensive and extremely disappointing.
Start with sketches of your pond and consider the shape, both from a bird’s eye view and from the side. From top down, what is the distance at its widest point? At its longest? Don’t worry about measuring the narrower portions - we’re not trying to do calculus here. From the side view, how deep is the deepest part of the pond? You can take these numbers and calculate your liner size on your own, or you can visit one of the handy-dandy pond liner calculators available online.
Of course, if you’re an unflinching DIY type, here’s how it goes:
Maximum pond width + (maximum pond depth x 2) + 4 = liner width
Maximum pond length + (maximum pond depth x 2) + 4 = liner length
These are the dimensions you should use to order your liner. Keep in mind that you want as few seams as possible (zero seams is ideal!) so plan to order your sheet material in the width that matches your smallest number, and then as long as you need it to be. For example, if your pond final calculations call for a liner that’s 10 x 20 feet, you would order 20 feet of EPDM from the 10-foot roll. (Of course, it’s always a good idea to order extra for some wiggle room.)
Measure Twice, Cut Once
Once your excavation is complete, measure it again. If your digging team got enthusiastic and extended your 20-foot pond to 23 feet, you’ll need to do some quick problem solving. For EPDM liners, it’s a fairly simple fix, as long as you have some extra material to play with. You can cut a panel that’s 4 feet long, and the same width, and attach it to your original panel. A 1-foot overlap, reinforced with seam tape, will provide an excellent seal. Be sure to perform the seaming on a hard, flat surface so your roller tool can ensure the adhesion is complete, with no gaps.
