Introduction to Floating Covers

Floating cover systems were first introduced over 60 years ago. The first flexible geomembrane civer were installed in the 1950s. Originally, most of them consisted of a solid fabric laying on top of the water. Flexible geosynthetic covers were very popular early on as they were the most cost effective solution to water conservation problems such as evaporation control. In fact, it was reported that geosynthetic covers are one-eighth the cost of metal covers and feature a longer life expectancy. The HDPE geomembrane cover has a density lower than water, floated on the surface of reservoir or dams, and no infrastructure is needed to support the fabric. This made it simple to install. When first introduced, materials and designs were not developed and in some cases had limited success.  Some have provided a service life beyond 20 years, although many fail because of the drawback of this type of design. Many advancements in design and materials have been done over the years. Some of the manufacture-approved newer materials includes hypalon, polypropylene, PVC, HDPE, LLDPE, geotextile, drainage composites, geosynthetic clay liners (GCL), woven coated fabrics, XR-5, XR-3, and more. Many covers use reinforced geomembranes to provide an extremely durable floating fabric to help control and off gas methane, odor control, and to protect reservoirs from evaporation and contaminations. These materials offer tough puncture and tear resistance and are available in a variety of thicknesses, generally from 20 to 50+ mil. Floating covers can also incorporate a buoyancy system underneath the geomembrane which allows the cover to rise and fall with the level of contained liquid.

Floating covers are still the preferred method of protecting large volumes of water at a fraction of the cost of tanks or other storage methods. It is a low cost quality solution of choice where water quality standards require potable water reservoirs be covered. In the past few decades, applications and installations of these geomembrane systems have increased significantly, as needs for cleaner water have increased.

However, despite progress in material and manufacturing process, geomembrane and solid covers in general still present several drawbacks:

• Geomembrane can tear, resulting in expensive repairs costs.
• High maintenance cost: they must be maintained according to the manufacturers guidelines.
• They must be custom designed to match the exact shape of the dam or reservoir.
• They are affected by rain, ice, frost and snow.
• They cannot be installed on full ponds.
• Insurance cost associated with those type of covers are high.
• They block access to the liquid.
• Limited warranty: 5-10 years.
• Overtime, vegetation growth appears on top of the cover.
• Install requires specialized equipment and trained crew.
• Recycling is generally not possible. Disposal is time consuming and expensive.
• Cannot be easily reuse or transferred to a different liquid containment.
• Are not easily compatible with certain type of surface aerators.
• Price becomes substantially higher for long lasting, thick, heavy duty geomembrane.

The need to overcome those obstacles has lead to a new type called modular floating covers. Those covers are slowly replacing geosynthetic membrane for most applications not requiring gas to be trapped, and where the cover permeability is a priority. Advanced Water Treatment Technologies is a pioneer of those type of covers and now offers a wide range of long lasting options.

Modular floating covers: a new type of floating covers

Modular floating covers are relatively new and were introduced in the last 2 decades.

Criteria to consider when opting for a floating cover for evaporation reduction

There are many criteria to consider when opting for a floating cover, regardless of the type (solid, modular, etc…).

• How much coverage do I need when the pond is full?
• How much wind is at the site? How stable will the cover be in high winds?
• How long will the cover last in dry, ice, snow, rain, high UV exposure climate?
• Will it be stable when the reservoir or dam is dry?
• Will it leach toxic substances into the water? What is it made of?
• How will it stand up to what is a corrosive environment? Will continual contact with water and chemicals affect it?
• How fast will exposure to ultra-violet light that can degrade some plastics?
• Can it be easily and cheaply installed? Do they require expensive installation by specialists or certified technicians?
• What warrantee is there and is the company likely to be around in five years if you need to call on the warrantee?
• How much do I need to cover: Does it need to cover only the water area? Or does it need to be large enough to allow for water level fluctuation your dam – potentially making a big impact on the final price?
• Does it need to cover part of the liner?
• Are there special requirements during install and during operation?
• What is the maintenance?

Those are some of the main questions to consider when size and pricing a cover for evaporation control.