Weathering The Storm

In the wake of Hurricanes Katrina, Rita, and Wilma, Building Teams are turning to advanced flood-mitigation techniques to protect structures from water damage.
August 11, 2010

Two-thousand five will go down in the record books as one of the costliest hurricane seasons in modern U.S. history.

Twenty-seven named storms and 15 hurricanes were recorded in the Atlantic region alone, shattering records that date back more than 40 years, according to the National Oceanic and Atmospheric Administration's National Weather Service.

Four major hurricanes hit U.S. soil last year, including three Category 5 storms (Katrina, Rita, and Wilma), leaving in their wake a path of destruction that exceeded $100 billion—more than double the previous record, established in 2004.

If the 2005 hurricane season was a sign of things to come, then Building Teams along U.S. coastlines will have their hands full protecting new developments from flood- and wind-related damage.

Most local building codes follow guidelines and standards established by the Federal Emergency Management Agency and the National Flood Insurance Program. FEMA and NFIP recommend prescriptive design and construction measures for flood-proofing a structure (see sidebar) based on several considerations: building use, flood warning time, mode of entry and exit from the building and site, floodwater velocities, flood depths, debris impact potential, and flood frequency.

 
Stop logs are similar to lift-out barriers, but are built up one “log” at a time to reach the required protection height. Stop logs are suitable for wide openings where a single lift-out barrier would be too heavy. This approach requires much less labor than lift-out barriers, but considerable deployment time and bolting are needed to create a watertight seal.

FEMA dictates, for instance, that the first occupied floor of buildings located in moderate- and high-risk flood zones be elevated to or above the base flood elevation of the area, which can range from several feet to more than a story-height, depending on the location and building type. NFIP provides further incentive for doing so by offering reduced flood insurance premiums for buildings that exceed the FEMA guidelines.



But this approach is not ideal for retail and other commercial structures that rely on the ground floor for business. As a result, some commercial developers are investing big dollars to "buy" back the ground floor by designing their buildings to exceed the FEMA/NFIP baseline codes. A case in point is Boca Grande Partners of Boca Grande, Fla., an upscale senior resort community near Sarasota.

"What most developers and builders don't fully realize is that we have another choice," said Bob Melvin, co-owner of Boca Grande Partners.

Instead of placing its 4,400-sf Gasparilla Marketplace on stilts, and making its patrons (much of them elderly) walk up ramps and stairs to enter the retail stores, the developer entrusted its Building Team to create a floodproof structure that maintained street-level entrances. The site is located in the heart of Boca Grande's shopping district, an area designated by FEMA as zone A (quiescent water flood zone), the second-most-stringent FEMA designation.

"Ground-level construction in flood areas may raise the up-front price of a retail project, but it improves the return far more," said Melvin. One immediate return was 350 sf of additional leasable space by eliminating the ramps and stairs.

The first step was to design a structure that would keep water out, and that would not shift or float away when submersed in floodwaters.

Local architect Hank Browne worked closely with engineer Karl Kokomoor of DMK Group, Englewood, Fla., to design a structure that was essentially an "inside-out swimming pool." The walls are reinforced poured-in-place concrete to the roof height. The slab is double-reinforced 12-inch-thick poured-in-place concrete. To keep the building in place, the slab is anchored with 72 eight-inch helical anchors drilled 10–13 feet into the subsurface.

To seal the building's 26 windows and five doors during a flood, Browne specified removable flood barriers. Manufactured by Pawling, N.Y.-based Presray Corp., the aluminum flood barriers feature a one-piece molded rubber compression seal that creates a watertight barrier between the barrier panels and the irregular surface of the concrete structure. When bolted in place, the barriers keep leakage to a minimum. The barriers are mounted onto custom aluminum frames that were polished and primed to match the window and door trim.

Gasparilla's facility management team was trained in installing, dismantling, and storing the flood barriers, and a flood management plan was put in place to ensure that the building is sealed well before a storm hits.

Hospitals, schools, and other vital entities have also seen the advantages of advanced flood-mitigation approaches.

In the case of the Center for Creative Arts in the flood-prone area of Yorklyn, Del., establishing a floodproofing plan that involved installing removable flood barriers and check valves meant that the school could remain in its 50-year-old home, which regularly took in upwards of four feet of water following hurricanes. School staff members are trained to deploy the facility's sliding flood barriers and side-hinged gates in the event of a flood.

The Texas Children's Hospital in Houston employs similar measures to ensure that its doors remain open during flash floods, which occur three to six times a year, according to Dan Samora, the hospital's facility manager. Even with sub-basements and loading docks that are 25 feet below grade, the hospital has remained bone-dry through numerous hurricanes and flash floods. "Though floodwaters were up to five feet around some entrances, not a single drop of water got in through the flood doors," said Samora.

Outfitting a structure with such robust systems is not cheap. Flood barriers alone can add anywhere from ½–1% to the total construction cost of a new building, according to Presray's Jason Smith. These systems also require a detailed operations and maintenance plan; most units rely heavily on human intervention for deployment.

But if it means being able to remain open during a flood or regain use of the ground floor, these systems can have a quick payback for building owners.

         
 

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