There isn’t much worse than putting sweat (and tears) into your vision of a beautiful backyard water garden or ornamental fishpond only to see it literally drain away into the soil. Even if you choose a low spot in your backyard that always holds water when it rains, it’s unlikely that it will contain water reliably, especially during dry weather.
Keeping Water Where it Belongs
The fact is, every artificial pond needs a liner to prevent water from disappearing into the ground. After all, soil naturally absorbs liquids - that’s part of the water cycle and is a fundamental part of how plant life survives on the planet. Understanding this, it becomes clear that if there’s no barrier between the dirt and the water, there soon won’t be much of a pond.
Even ponds that you encounter in the wild, so to speak, are often constantly fed by natural springs or streams, while others have formed in soil that has a high clay content and over time has created its own natural liner. It’s possible to create a clay liner in your backyard, but for an average sized backyard pond, the expense, effort, and loss of water volume (due to the clay liner’s thickness) is rarely worth it.
Preventing Erosion & Excess Sediment
Pond liners serve other important purposes aside from keeping the water where you want it. Exposing pond water to disturbed soil invites erosion, whether it’s from curious fish nibbling at the walls, or wildlife like wading birds and raccoons looking for food. Erosion in your pond banks inevitably reduces the structural stability of your excavation, and a side or bank collapse will not only injure your fish and plants but could spell the end of the pond altogether.
Exposed pond walls allow sediment to wash into your pond, which lowers your water quality and can even impede your fish from finding food. Low water quality encourages the growth of algae, which can become a long, drawn-out struggle to bring under control. Geosynthetic liners protect your pond from erosion and sediment. They also prevent the incursion of outside water that may carry a variety of contaminants that can cause harm to your fish, your plants, and your pond.
Preventing Damage
All ponds need some degree of maintenance, whether yours is a strictly planted pond, a casual pond stocked with goldfish, or a showcase pond designed to exhibit your prizewinning koi. The best geosynthetic liners are durable and can withstand the rigors of cleanup. After a major storm that has dropped branches or washed debris into your pond, you may find yourself wading in and pulling items out. Cleaning muck from your pond during a fall cleanout may involve a few bumps and scrapes from the pond vac, and exceptionally harsh winters can lead to cold cracking if a liner isn’t rated for those temperatures (including both natural and bentonite clays).
Lots of Liner Choices
Geosynthetic pond liners are less expensive, less labor-intensive, more durable, and require less care than a natural clay or bentonite liner. There are several choices to consider when evaluating geosynthetic liners, and some of the most common include synthetic rubber liners known as EPDM (Ethylene Propylene Diene Monomer), RPE (reinforced polyethylene), Polypropylene, and HDPE (high density polyethylene). We’ll discuss the specific qualities, advantages, and disadvantages of each type in a later article.
Evaluating Your Budget
Liners can represent a significant line item in your pond budget, especially if you’re starting with a relatively simple project. Novice pond enthusiasts may find it tempting to cut corners here and “make do” with second-hand or repurposed sheet materials, but that’s a risky proposition.
Re-using materials
Flat roof liners are made with EPDM, essentially the same material used in some commercial pond liners, and it’s hard to turn down a large amount of free material that’s about to go to a landfill. But roofing EPDM isn’t the same as pond EPDM - it may have been treated with coatings to discourage the growth of algae, and years of exposure to the elements means it may have picked up plenty of pollution, including vehicle exhaust, toxic metals, and other contaminants. Certain plants may be able to absorb these pollutants, but your fish will suffer from exposure to any of these.
Maybe not such a great idea
Some budget-minded DIY enthusiasts choose to use tarps from the local home-improvement store, or even repurposed waterbed liners and pool liners. In one case, we even saw an individual planning on melting used roofing shingles together to line a pond. There are many concerns with each of these options, including the potential to leach plasticizers or other harmful chemicals into the pond, as well as introducing pollutants, mold, and troublesome microorganisms after years of exposure to the air.
In the End
In the end, if you’re investing physical, emotional, and monetary resources into your dream pond, there are areas where pinching pennies is simply not worth it. Experimenting with a homemade biofilter can be a great way to explore your own designs, and if it doesn’t work out, a quick trip to the pond supply store can quickly remedy problems. A homemade fountain can be a fun creative project, with potential frustration being the largest cost. But, the pond lining is part of the fundamental structure of your pond and it isn’t easily repaired or replaced when you discover problems with a make-do solution. In fact, the costs involved in draining and relining a failed pond are often so high that owners simply give up on the project instead.
