Tech Brief: How Flooding Affects Structures
At press time in mid-September, the U.S. Army Corps of Engineers (USACE) had drained nearly 90 percent of the brackish, oily, bacteria-laden floodwaters that have inundated low-lying areas of New Orleans following Hurricane Katrina. Various federal, state, and local government agencies, assisted by private contractors and nonprofit groups, were scrambling to get drinking-water and wastewater treatment systems up and running. Once the city is drained of the deluge, it will face the arduous task of assessing the condition of thousands of damaged buildings as well as an environmental and public-health disaster of immense proportions.
The process of totaling up structural losses is only beginning. A full accounting will take several months, and detrimental effects to water quality and other local environmental and ecological conditions will surely be felt for years to come.
Many structures that sustain water damage after a flood can be repaired and occupied again, but then this was no ordinary flood.
The sheer volume of water, the number of days structures have been inundated, and contaminants in the water itself make it unlikely that any structures in the hardest-hit areas will survive (see main news story, page 42). In some areas in St. Bernard’s Parish, where flooding was particularly severe, a greasy film of oil coats houses and streets from an 819,000-gallon petroleum spill that occurred in Meraux, Louisiana, where a storage tank owned by Murphy Oil Corporation was lifted from its foundation. The spill was one of several in the region.
Among those buildings with only partial damage, exterior structures and interior materials will need to be inspected. Timber-framed structures warp and weaken when they get waterlogged, although they can sometimes resume their original shapes once dry. Mortar in brick structures and chimneys can dissolve when submerged, causing not only potential weaknesses and failures but also the possibility of carbon monoxide leaking from fireplace flues if they are used again. Wall systems composed of plywood, drywall, and insulation soak up moisture and lose strength and load-bearing capacity when wet. Floodwaters also corrode wiring and disrupt gas and utility lines and plumbing and septic systems. Furniture, light fixtures, ductwork, and appliances will be clogged with dirt and debris.
But mold and contamination might end up being the bigger problems in New Orleans, whose warm, humid climate provides a perfect breeding ground for mold even in the absence of flooding. Mold uses materials like wet gypsum and insulation as food sources, say experts. Damp conditions also cause bacteria, dust mites, and other unsavory microorganisms to thrive indoors. Mud and contaminants will foul interiors, along with solvents, glues, and particulate matter that can leach from building materials and furniture when they are saturated for a long period of time.
Experts agree that even if structures survive, many of their interiors would need to be gutted and replaced—which in many cases will prove costlier than demolition. The National Trust for Historic Preservation, the AIA, and others are working to ensure that landmark and historic structures are spared this fate.
Water quality plummets
Meanwhile, the USACE has had no choice but to pump the untreated floodwaters back into the confines of Lake Pontchartrain, whose levees were breached in five places in the aftermath of the floods. The other alternative was to pump the water directly into the Mississippi River—an even less appealing option because the river is the drinking-water source for area residents, and putting floodwaters into it would cause pollution to disperse even more widely throughout the region, according to the Environmental Protection Agency (EPA) and the Louisiana Department of Environmental Quality (LaDEQ).
The floodwater isn’t so much water as a putrid, black-green brew of decomposing remains, human waste, raw sewage, oil, gasoline, pesticides being sprayed to keep mosquitoes at bay, and a cocktail of pathogens and chemicals never intended for human consumption.
On September 3, EPA and LaDEQ tested the floodwaters in the city of New Orleans and found levels of coliform bacteria that were more than 10 times higher than the limit that would cause a recreational water body to be closed down. Elevated concentrations of lead and other metals were also found during testing. Three Superfund sites in the New Orleans area were also flooded: the Agriculture Street Landfill in New Orleans, where city residents dumped their trash for decades; the Bayou Bonfouca site in Slidell, Louisiana, and the Madisonville Creosote works. Environmental agencies don’t know yet how much or what types of contamination may have been released from these sites, but they stress that waterborne pathogens pose a greater immediate health threat.
EPA and the Centers for Disease Control have formed a joint task force with state and local agencies to assess water quality and environmental conditions in the region on a continual basis, including sampling of waters from a wider area than was covered by the first round of tests, which were confined to floodwaters within city limits. Although water-quality officials have repeatedly cautioned residents and recovery workers not to drink or make contact with the floodwater, and have been issuing vaccines against waterborne diseases, they have declined to call it “toxic” despite the fact that many of the chemicals and pollutants present in the water are classified as such.
A fragile system
Lake Pontchartrain, a shallow tidal estuary covering 630 square miles immediately north of New Orleans, is an important economic engine for the region and provides essential habitat for a variety of endangered and protected fauna and flora. The pollution problem will have repercussions there over a long time. Decomposing organic matter like raw sewage depletes dissolved oxygen from the water, which can kill off plants and aquatic life. Bacteria and contaminants taint the oysters, shrimp, and other seafood for which the region is prized. The lake itself will be closed to boating and recreation for the foreseeable future, and oyster and seafood harvesting beds in the entire region have also closed indefinitely, with devastating economic consequences to the area’s $2.7 billion fishing industry, which supplies 30 percent of the seafood consumed in the U.S.