The majority of covered ponds and lagoons in use today are covered with a system known as the defined sump/tensioned plate design. You’ll also find this referred to as the Columbia or Burke system. The combination of floats and weights are used to gently press channels into the surface of the liner that are adjustable as needed. This method has been used to cover ponds for decades, while a more recent alternative method is the use of floating ballast balls or plates. Floating balls and plates are made from plastic and offer some of the benefits of floating covers. However, they can’t compare in many other ways. Compare the two modern options for covering fresh or wastewater ponds to decide if solid floating covers or masses of individual objects are a better choice.
Cost
This is difficult to quantify since prices vary depending on float options and the manufacturer. However, the sheer newness of floating ball and cell covers tend to make them more expensive than well-known geomembrane materials. It’s possible to shop around find a wider range of geomembrane manufacturers than suppliers of loose ballast covers. If you have to order a specialty design to deal with specific requirements for evaporation control or light exposure, you’ll end up spending far more on these custom designs than on the usual tensioned floating cover made from affordable geomembrane material.
Availability
In addition to a higher cost, floating ballast balls and plates are often unavailable in some areas. Global shipping is costly when you’re ordering tens of thousands of individual items to cover a large surface area of a pond or tank. Unless you can source these relatively new products somewhere nearby, you’re better off sticking with widely available geomembranes. The best geomembrane materials like RPE are widely available and easy to ship long distances with minimal expenses.
Maintenance
One of the biggest benefits of floating ball and hex covers is their general lack of maintenance requirements. Since the balls individually move and leave gaps between them to allow debris and water to flow through, there’s no need for the annual cleaning and checkup required for geomembrane covers. However, this means that covers made of individual pieces also lose many of the benefits directly needed from a floating cover. For example, the balls and plates can’t stop rainwater from diluting the water supply or carrying in contaminants. They also only offer visual deterrence to prevent animal and human visitors. If an animal or person actually walks up to the surface, there’s nothing to keep them from getting in the water once they push the balls aside. Floating covers may require some attention and care, but they offer many more benefits in return.
Wind Resistance
Even relatively small ponds and tanks can experience intense wind forces that cause waves to damage the banks surrounding the water. Adding a cover stops the waves and prevents erosion or damage, but it doesn’t entirely solve the problem of wear and tear from wind. Floating balls move with the wind and are rarely damaged by it, but they’re also prone to blowing away entirely in a bad enough storm. Floating geomembranes covers are anchored to the banks or sides of the pond, preventing lifting and securing the material against wind damage. Of course, some geomembranes will tear or crack over time due to the constant movement caused by wind. So, make sure you choose a geomembrane cover material designed to handle this kind of wear and tear, such as RPE from BTL Liners.
Vapor and Water Control
Choosing a floating ball system to avoid the maintenance required by a geomembrane floating cover will cost you one of the biggest benefits of a cover, which is vapor control. In addition to lacking control over water entering the pond or reservoir, floating balls do nothing to stop the escape of gases generated by the water they’re covering. Only an impermeable layer of geomembrane will capture gases so they can be safely released or stored and put to good use. Selling or using the methane generated by manure and sewage lagoons is a great way to offset the costs of building these management structures and covering them. Since wastewater ponds pose a high risk of environmental damage if water runs in and floods out their contents, geomembrane covers with sump pumps are the best option for keeping them at a steady level.
Using the Two Systems Together
It is possible in some cases to combine the two materials for greater benefits. A layer of geomembrane is installed first, with floats, to control evaporation and contain gases. The ballast balls are then added over the surface to replace the usual weights and to add extra UV protection to extend the life of the solid cover. However, this method tends to cost more than the savings it offers through extended lifespan and easier maintenance. The floating ballast must be removed annually so the impermeable layer below can be cleaned. If you’re working with a fixed budget for a project, stick with durable, UV resistant geomembranes for the floating covers and you shouldn’t need to combine them with floating ballasts.
Various floating ball and hex plate methods get a lot of attention because they’re new to the market, but there are typically not the best option for wastewater treatment and storage applications. The control over makeup water and gas production just isn’t available with the loose floating cover idea. For true control of your water conditions, stick with a weight or mechanically tensioned floating cover instead.
