Rapidly deployable flood barrier systems
BY MARK E. WILLIAMS, PH.D., P.E., AND DILIP CHOUDHURI, P.E.
The effort to combat flooding currently is being pursued on a national basis. In light of the recent hurricane events that affected Louisiana and Mississippi, there are several regions, particularly in the Gulf Coast, that require careful consideration as rebuilding and new construction efforts are pursued.
A variety of flood control systems are used around structures today. The most common systems include flood gates, flood walls, submarine doors, inflatable barriers, and sandbags. Many of these systems are unfavorable because of high installation and material costs or their lengthy mobilization time. Additionally, since the cost of retrofitting existing structures with new flood barrier systems typically is absorbed by building maintenance budgets, costs must be kept to a minimum. Also, for flash flood events, the 4- to 8-hour deployment time of some systems can be too long to block impending flood waters.
Furthermore, some of these systems are permanent and are impassible to pedestrian and vehicle traffic. However, an affordable, rapidly deployable flood barrier system that is well-suited for protecting structures without impeding the serviceability of those structures is gaining popularity.
Its effectiveness was tested during Hurricane Rita this past fall.
Fabric flood barrier systems, originally developed to combat flooding in the United Kingdom, are now being implemented across the United States to address a variety of flood control problems. These systems typically consist of an inclined waterproof fabric dam that is secured along its length with tension straps and locked into a recessed anchor track that can be installed much like a roadway expansion joint. The advantage of such a system is that the fabric can be stored easily and then rolled out and anchored in a minimal amount of time in advance of an impending flooding condition.
Equally important is that the flood barrier installation in high traffic areas does not impede pedestrian and vehicle flow because of the recessed anchorage during normal (non-flood conditions) operating conditions. The installation of a fabric flood barrier system is easy and economical as a result of its design simplicity.
Flood barrier components A fabric flood barrier system consists of several components. First, the fabric barrier, used to contain the flood water, consists of a reusable waterproof PVC-coated canvas that is chemically treated to resist fungal growth, ultraviolet deterioration, and temperature damage. The fabric can be customized to meet project specific demands, with the most common dam heights ranging from 2 to 6 feet. Second, an aluminum extrusion channel frame or built-up steel section typically is provided to anchor the fabric barrier (Figure 1). This anchor frame can be recessed and bolted into a block-out made into a roadway surface or building slab. This anchor frame also can be extended vertically to anchor the sides of the fabric barrier. Housed within the anchor frame are dual-purpose, continuous rubber blocks that function as channel gap filler during normal traffic use and also act as a wedge to lock the barrier fabric inplace for deployment. The fabric barrier also is fitted with a lip along one edge to ensure that the fabric will not slip out of the channel when deployed. A prototype of the flood barrier system is shown in the photo on page 32. The fabric material color shown is "safety yellow" to alert passersby of the emergency situation.
Many structures are subject to vehicle traffic either around the perimeter or by driveways through the structure. For structures subject to truck traffic (such as loading docks and parking garages), the anchor channel can be designed to accommodate heavy vehicle loads. For driveway installations near or within structures, the International Building Code 2000 recommends that an 8,000-pound design wheel load be applied over a 20-square-inch contact area (equivalent to a contact pressure of 400 psi). Special consideration in the channel design also is given to vehicle impact forces, load placement, fatigue, and hydrostatic loads on the anchor channel.
The channel design geometry is openended and can be optimized for the demands of a specific project.
Flood barrier implementation At times of an impending flood alert, the flood barrier fabric can be removed from storage and rolled out along the track.
Next, one of the rubber blocks housed in the anchor track can be removed using a hand tool. The lip of the fabric barrier can then be inserted into the channel and the rubber block can then be reinserted to lock the barrier into place. The fabric barrier will automatically rise as the flood waters reach the outside of the barrier installation and will remain watertight during the flood event. This process is shown in Figure 2 for an installation at the entrance of a parking garage that is part of a multi-structure flood mitigation project. The performance criterion at this particular location is an emergency flood barrier fabric installation by two designated individuals in less than 15 minutes. This criterion was tested successfully in preparation for Hurricane Rita.
The fabric flood barrier system described here is easy to install, rapidly deployable, and reusable.
For a small initial investment cost, the benefits far outweigh the devastation brought by uncontrolled flood waters.
Mark E. Williams, Ph.D, P.E., an associate with Walter P. Moore, can be reached via e-mail at email@example.com. Dilip Choudhuri, P.E., a principal with Walter P. Moore, can be reached via e-mail at dchoudhuri@ walterpmoore.com. Special acknowledgement is given to Hendee Enterprises for providing the flood barrier specifications and implementation discussed in this article.