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DAM! Now THAT’S a Good Liner

Insights - Dam Liners - Gannett Fleming.
Authors: Chad Hoover, PE, Gannett Fleming Dams and Hydraulics Business Line project manager, and Sophia Liskovich, PE, Gannett Fleming Water Global Business Line project manager

Water, our most critical resource, must not be wasted. That’s why geomembranes, impermeable barriers that line dams and reservoirs to prevent water seepage, have been used for nearly 60 years. Scores of geomembrane systems are available today, and though polyvinylchloride (PVC) is the most prevalent, another technology—bituminous geomembrane (BGM)—has had strong success in Europe and Canada. Now, BGMs are gaining momentum within the domestic dams market.

BGMs are comprised of non-woven geotextile, dipped in elastomeric bitumen—a rubbery polymer made from hydrocarbons obtained naturally, or as a residue from petroleum distillation. Reinforcing materials, such as a glass fleece, often are added for increased strength. BGMs are easy to install and, due to their bitumen composition, are easy to patch or repair, if necessary. They are flexible, durable, and conform well to the underlying substrate—allowing lightweight, rubber-wheeled equipment to travel across them. The dimensional stability of BGMs limits movement during temperature fluctuations, rendering the liner suitable for an exposed or uncovered system. BGMs also are textured, a unique safety feature that allows a person or animal to gain traction for exit, should they fall into the impoundment. These characteristics make them ideal for embankment construction.

The very first BGMs were made of oxidized bitumen, instead of the elastomeric bitumen used today. Because the elastomeric bitumen application is fairly new, little third-party performance data is available on the service life of elastomeric BGMs—although it is estimated at 40 years. We do know that with age, BGMs are susceptible to mud curling, a phenomenon affecting their physical appearance but not their strength or permeability.

We recently put a BGM to the test at Maryland American Water’s Bel Air Impoundment, a 90-million-gallon reservoir that can sustain more than 14,000 people for as long as the 100-day drought of record. In selecting the liner, our team knew the volume of stored water could fluctuate, exposing the liner to weather events, such as extreme heat, freezing, wind, and ultraviolet radiation. After evaluating nine lining systems, we determined the BGM to be the most economical, resilient, and watertight barrier for the impoundment. The project marks just the second time a BGM has been used on a dam embankment in the U.S. In fact, 13 years ago, only 20 dams worldwide were known to feature a BGM. This number is steadily increasing as engineers and infrastructure owners learn more about the advantages of BGM.

Though we anticipate a strong trajectory for BGMs in the domestic dams market, choosing just the right geomembrane is site- and project-specific. Many factors must be considered, including exposure conditions, installation configuration, facility usage, operation and maintenance criteria, material availability, project size, service life, and owner preferences. We invite you to read our white paper to learn more about selecting the right geomembrane system for your next dam or reservoir project.

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