Geomembranes certainly work well as floating covers, especially when built with the right materials from the start. However, they won’t work alone to keep a pond or tank covered in difficult conditions with gas accumulation, wind lifting, or rain and snow weight pressing down from above. This is where accessories like floats, supports, rails, rods, reels, tensioners, and even automatic retraction hardware come in. Pumps and other drainage equipment are also required since covers made with geomembranes are impermeable and won’t drain on their own when filled with rainwater. Make sure you’re budgeting for all the required parts of a floating cover system with this handy guide.
Floats and Supports
Almost all floating covers rely on some kind of foam-based float to provide buoyancy. Most liner materials, including relatively thin and light polymer geomembranes, are still heavier than water and therefore unable to float on their own. For smaller tanks and ponds, tensioners and rails may work alone to keep the material stretched tightly across the surface. Larger areas tend to require floats, at least in the center, to add buoyancy. Lateral floats are recommended for wastewater floating covers since the channels created by the floats allow gas to flow to the edges from under the cover. This allows for passive and effective collection to discharge pipes or storage tanks. On the top surface, the same channels encourage water to flow away to where pumps can remove it. Without floats, even the lightest covers will sink during the first rainfall event. Floating covers that rely on air trapped under the surface are at risk for more wear and tear from wind exposure than those that spread smoothly over the surface of the water with the help of floats.
Anchor and Attachment Systems
Even with the help of floats to keep the cover above the surface of the water, anchors and attachments are needed at the edges of the floating cover to seal it to the liner or bank. These attachments are particularly important on storage tanks used for biogas generation, since even tiny gaps allow valuable methane to escape. Edge attachments come in vertical and horizontal arrangements, each with their own benefits and drawbacks. Some systems feature tensioners along the edges that pull the liner tightly across the surface, eliminating the folds or sagging at the center of floating covers primarily supported by floats alone. This improves drainage and reduces maintenance dramatically over time.
Drainage Channels and Pumps
If the drainage channels in the floating cover aren’t provided by the shape of the floats alone, other reinforcements and frames must be added to create the right depressions. These channels need to lead outward to accumulation trenches around the perimeter of the cover. Pumps and pipes are connected along the edges to suck out every gallon that gathers before it can weigh down the cover and sink it below the surface. If the drainage system isn’t planned to deal with water as soon as it accumulates, it’s easy to end up with an overloaded cover system. Don’t forget to leave space for the pumps that are needed for keeping the cover clear along with maintenance paths for accessing them.
Some floating covers also rely on a layer of ballast weights to maintain the right amount of tension and buoyancy. These covers require floats to balance out the force exerted by the weights resting on the surface. Weights are carefully spaced, and placed, so that rainwater and melted snow channels directly to the sump pumps. Unlike drainage channels created by floats alone, ballast weight systems usually drain water to multiple smaller pump areas rather than one large perimeter trench. Pulleys are used to reduce the pressure exerted by each weight, when needed, to keep the cover floating lightly on the surface.
Vent pipes must penetrate the cover at certain points to release gas before it builds up enough to rupture the cover or stretch it too much. This is a problem with most types of wastewater, but it’s particularly challenging in the biodigester full of sewage or manure. Since these structures are designed to generate and capture as much gas as possible, venting is essential to route the methane to storage or pressurization equipment. Whenever possible, design vents to pass through the seams rather than directly through a solid layer of geomembrane cover. It’s easier to patch and seal a seam that’s already being treated during construction rather than stipulating a penetration right in the middle of an area that’s hard to reach.
Complete your floating cover with the right accessories for a system you can trust to keep your water under control. Don’t let evaporation or odors cause issues with your treatment ponds or storage areas. Lean on our advice here at BTL Liners with expert guidance tailored to your particular project.