Control floods with geotextile cofferdams:

Portable water barriers provide an alternative method of preventing costly property damage.

 

     Floods are perennial hazards in many parts of the world. Hardly a year passes when stories about water-related natural disasters do not make headlines. For people who live on or near water or who work by it, or for those who are trusted with maintaining public safety, the challenges of flood protection have always been monumental.

     The standard method for flood prevention continues to be reservoirs and earthen levees. In North America, sandbagging is used as a last-ditch effort to augment existing reservoir and earthen levee protection. Sandbagging appears to offer several benefits. First, during emergency flooding, government officials often deliver sand to a flood site at no cost to the users. Secondly, sandbags appear to be inexpensive because empty sandbags are typically “given away” by government agencies. In reality, it is taxpayers’ dollars that pay for these giveaways. While sandbag dams offer moderately secure barriers against rising water, their construction is labor-intensive and time-consuming at a time when manpower and minutes are frequently lacking. Although sandbags offer bulk, they lack the substance to withstand constant wear and tear. In addition, sandbag dams are not easily disassembled and, because resources to remove them may be lacking, they are often left to deteriorate, and deteriorating sandbags can cause environmental damage.

   Environmentally friendly alternative.
   In the late 1980s, an alternative to sandbags emerged. Ironically, water, the very element that these barriers protect against, is their essential component. AquaDams® are fabricated geotextile water dams designed with four components: The first is water, which provides mass and weight for the dam. In essence, combined water molecules within the product’s water-filled tubes act as a force that is resistant to the water pressure meeting its exterior.

tubes is 97 percent 10-16 mm .3 low-density, virgin resin polyethylene with one percent anti-block and two percent UV inhibitors. Depending upon their configuration, the tubes may be filled from one or both ends. A typical three-ft-high by 100ft long unit contains approximately 14,000-15,000 gallons of water and weighs 78,000 pounds.

   The third component (in dams six ft high or less) is a 300lb/in.2 burst-strength geotextile outer tube manufactured to withstand high pressure and temperatures as low as -60 degrees. The ultraviolet (UV) inhibitor, present in both inner and outer tubes, retards potential exterior damage that might be caused by sunlight exposure.

    The fourth component, a collar made from the same geotextile as the outer tube, connects two or more units when needed. The collar, or sleeve, is an extension of the outside tube of the water barrier, without the plastic fill tubes. The plastic fill tubes slip inside the collar and are brought up onto the end of the first dam, which then becomes the bank for the second and any consecutive dams that may be required.

     Coupling two or more sections together creates a seal where the sections meet. Typically, the weight of the encased water seals the unit to the ground. The seal to the ground surface created by the water-filled dam is usually sufficient, but it depends upon two factors: first, the depth of the water being controlled compared to the size of the water-filled geomembrane, and secondly, the type of ground surface material upon which the dam is deployed. A 100 percent seal can be achieved on mud surfaces; a 99 percent seal can be achieved on large gravel or rock surfaces. In both cases, a pump is required to keep the area dewatered and dry. Since job sites vary considerably, pump size depends upon ground subsurface and subsurface material. To minimize leakage, a skirt can be placed down the side, extending out 1 ft in front of the dam. Fill material can also be placed behind the dam to decrease pressure.

     The water-filled geotextile barriers come in 1 ft high to 18 ft high units and lengths of 50, 100 and 200 feet. They can be custom-made to meet job site specifications. These water barriers can he used in applications requiring a straight line, an arc, or even a circle, which can be formed by bending or connecting a series of units into any desired shape. AquaDams® are safe when used within recommended guidelines, which require that 25 percent of a dams' height must remain above the level of the surrounding water that needs to be controlled.

     The units require no trenching. Since they are made of flexible geotextile and water, they conform to any terrain. The only equipment required to install these small moveable dams is one or more pumps. The units are deflated when they arrive on site, and they look like rolled carpets. The deflated package weight of a three-ft by 100ft unit is 250 lbs, so two laborers can easily unload a unit of this size.

     AquaDams® dams can be installed more quickly and at a fraction of the cost of sandbags. Furthermore, AquaDams® are reusable, and both their interior and exterior materials are replaceable, although this is seldom necessary. The ideal storage site is indoors, away from direct sunlight. If they are covered with a tarp, the units can be stored outside. While AquaDams® can potentially secure flood-prone areas, as with any means of flood protection, the dams can fail if floodwaters rise above the level for which they have been prepared.

 

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