Engineers assess critical infrastructure damage in the wake of Hurricane Katrina to help design more resilient communities.
BY GILBERTO MOSQUEDA, PH.D.; JEROME O’CONNOR, P.E.; AND JAMES N. JENSEN, PH.D.
Hurricane Katrina made landfall on Aug. 29, 2005, at approximately 7:10 a.m. EDT in southern Plaquemines Parish, La., as a Category 4 hurricane and proceeded inland along the Louisiana- Mississippi state line. With top winds exceeding 175 mph, unprecedented storm surges higher than 30 feet, and hurricane force winds extending 125 miles from its center, the storm caused major flooding and damage that spanned more than 200 miles along the U.S. Gulf Coast. Damage extended beyond residential communities, with significant damage to engineered infrastructure, including roads and bridges, utility distribution systems for electric power and water, waste water collection facilities, and vital communication networks.
Investigators from the Multidisciplinary Center for Earthquake Engineering Research (MCEER) headquartered at the University at Buffalo, conducted postdisaster field reconnaissance to examine the impact of Hurricane Katrina on the built environment. Funded by the National Science Foundation, teams of investigators were deployed within a week of the hurricane (Sept. 6-11) along the Mississippi coastline, with a second deployment a month later (Oct. 3-9 and Oct. 17-22) focusing on the New Orleans area.
The objectives of MCEER reconnaissance missions were to collect perishable data and to examine damage from a multihazard perspective. Implications of lessons learned for Hurricane Katrina are being applied to mitigate damage not only from future hurricanes, but also from other extreme events such as earthquakes or terrorist attacks. One specific multi-hazard objective of this mission was to identify similarities between damage typically observed after earthquakes and damage caused by Hurricane Katrina with the goal of recommending seismic design principles that could mitigate structural damage caused by wind and storm surge forces.
Ultimately, MCEER is seeking to develop design strategies that will make communities more resilient against any extreme events.
Following is a brief summary of the observations related to damage to critical infrastructure (bridges and electrical power utilities) and impact on the restoration of drinking water and wastewater treatment.
More detailed reports of MCEER’s reconnaissance efforts can be found online at http://mceer.buffalo.edu.
Damage to bridges
Transportation systems including highways, bridges, and railroads are considered lifelines because they provide a safe route for evacuation before and after an extreme event and also are essential to emergency response and recovery efforts. Since railroads move heavy freight that is essential to the local economy, they also are an important part of the recovery and reconstruction operation.
Bridges in the Gulf Coast region have performed well for years. They have been designed according to American Association of State Highway and Transportation Officials’ standards to handle static forces and minor dynamic loading from wind, braking, and vibration.
However, Hurricane Katrina introduced unexpected loads as it brought in strong winds and storm surges higher than 30 feet in some areas. In addition to the direct storm surge forces, bridges were hit by large, surge-borne debris such as vessels and large containers. Further, the fast moving waters undermined bridge piers and flooded mechanical and control rooms of moveable bridges. Dozens of bridges in Louisiana, Mississippi, and Alabama were left debilitated in the aftermath of Hurricane Katrina.
Katrina’s fury is exemplified in Louisiana where the hurricane destroyed the twin, 5-mile-long I-10 bridges over Lake Pontchartrain. Though the storm came from the south, these low-lying bridges bore the brunt of the storm from their north side. With the eye of the storm passing to the east, the counterclockwise winds of the hurricane blew in fiercely from the north, stirring up waves that battered the bridges before submerging them. There is evidence that violent wave action repeatedly slammed the prefabricated spans into each other, up and down onto the pier caps, and snapped off cantilevered sidewalk sections of the westbound bridge. Many spans of both bridges were displaced laterally or fell off their pedestals into the water. The substructures survived without extensive damage. A railroad bridge across Lake Pontchartrain performed well structurally, but the tracks, ties, and ballast were washed off, rendering the bridge useless.
The state of Mississippi experienced the most extensive damage to long, multi-span bridges over inlets and bays that linked major east-west routes along its coastline.
U.S. Highway 90, a four-lane local access road, and a railroad line generally follow the Gulf coastline closely, and all of these transportation routes were rendered useless by the storm. Interstate 10, running roughly parallel to the coastline but several miles inland, was not affected as badly.
The U.S. 90 causeway-style bridges crossing the St. Louis Bay and Biloxi Bay in Mississippi were destroyed completely.
They were comprised mainly of simply supported spans approximately 60 feet long. Each bridge was more than 1.5 miles long, and a majority of the spans were left lying in the water after the storm.
Additionally, numerous piers in St. Louis Bay were lost, likely due to scour. Surge levels in the area were probably some of the highest recorded, since this was just east of the storm’s eye.
Impact to bridges caused substantial damage and interruption of service. North of Pascagoula, I-10 was closed when two barges that were swept inland by the surge hit a bridge. Although the bridge is several miles inland, the impact from the barges displaced the bridge superstructure about 4 feet to the north and tipped piers, causing a vertical drop of several inches. Closure of this bridge resulted in a 50-percent loss of capacity of this major highway and necessitated the sharing of lanes with the westbound bridge. The Mississippi Department of Transportation funded an emergency contract to repair the damage and successfully restored the bridge to service by Oct.1.
Spans of the Popps Ferry Road Bridge in Biloxi were pushed laterally off their bearings, evidently by a blockage of surge-borne debris. Though the spans did not drop, the bridge became unusable. This bridge, like many others in the coastal region, had moveable spans for the navigation channel.
The control and mechanical rooms of this and similar bridges typically flooded. The highly conductive and corrosive salt water damaged electrical and mechanical bridge controls, leaving them stuck either in the open or closed position. Popps Ferry remains closed, pending a repair contract.
As far east as Mobile Bay in Alabama, more than 100 miles from the eye of the hurricane, storm surge levels were reported to be on the order of 10 to 12 feet.
Apparently, storm surge forces were sufficient to displace several spans of an interstate ramp bridge by as much as 4 feet. In the same vicinity, the Cochrane- Africatown USA Bridge was hit and damaged by an oil platform that had broken loose from its mooring a mile downstream. This relatively new cable stay bridge remained operational with limited capacity.
Erosion at abutments also caused disruption of service. In some cases, bridge structures remained intact but were inaccessible because approaches were washed out. This damage was repaired in a matter of days. Roadways such as U.S. 90 along the Mississippi coast also were damaged by sink holes resulting from scour underneath the pavement.
Damage to electrical power utilities
Essentially all of the affected counties in Mississippi lost power. Because of an extensive mutual aid response and pre-contract support, electrical service was restored throughout most of the service area within 10 days after the storm. Utility companies from other states, and suppliers from as far north as Canada, shipped expected replacements for equipment within a safe distance before the storm and immediately moved in for repair after the storm. By Sept. 10, power had been restored to every industrial customer and most residential customers.
Although power was restored quickly—even to the most heavily damaged areas—most customers in those areas were unable to accept service.
Mississippi Power, the electric utility provider for the Mississippi Gulf Coast, reported that 402 electrical power structures were broken, leaning, or required significant work to repair. In most cases, the damage was attributed to trees falling on equipment, wind blown debris, and the effects of wind whipping the lines against insulators and equipment. In some instances, line failures resulted in cascading structure collapses caused by tension in the lines. There also was reported evidence of tornado activity. Additional damage to conductors, insulators, and switch gear resulted from flooding by salt water, which is highly conductive and provides a highly corrosive environment for electrical and mechanical components. Mississippi Power reported that 280 of the damaged structures had been restored by Oct. 20.
Impact on drinking water treatment and distribution Hurricanes Katrina and Rita caused the loss of potable water service to more than 13 million people in four states. More than 4,000 permitted treatment facilities were affected, as were thousands of private wells.
Louisiana was the focus of MCEER’s reconnaissance efforts related to drinking water, where nearly 1,600 facilities serving 5 million people were affected.
The main drinking water treatment plant in Orleans Parish is the Carrollton Water Purification Plant, a 120 milliongallon- per-day (mgd) conventional drinking water treatment plant. It treats water from the Mississippi River and serves 428,000 people. After power was restored, water was produced quickly. Initially, raw water was coagulated but not disinfected.
In general, chemical addition processes (coagulation and disinfection) were not affected significantly. However, filtration was impacted severely. The pipe galleries were flooded, rendering filter controllers and instrumentation inoperative. Filters were operated manually until controller operation was reestablished. The plant also switched from chloramination to the maintenance of about 1 mg/L free chlorine with no ammonia added.
The distribution system for the Carrollton Water Purification Plant was valved off in a controlled fashion, with service reestablished slowly. Large pipe breaks were repaired quickly. Distribution system problems came from numerous small breaks (perhaps hundreds) at service points, for example, hydrants sheared off by stormpropelled vehicles and broken plumbing from homes moved by the storm.
The boil water order for Carrollton was lifted on Oct. 6 for most of the distribution system. Plant personnel collected 300 to 400 samples in exploratory sampling and three days of compliance sampling. Most samples were collected at hydrants. Only 11 samples tested positive for coliforms (only one fecal coliform-positive sample).
Utilities outside of New Orleans faced different challenges in restoring drinking water service. Most of the rest of Louisiana relies on a large number of small facilities treating groundwater (rather than one or two large facilities treating surface water, as in New Orleans and vicinity). The maximum number of boil water orders from Hurricane Katrina was 246, 43, and 42 for St. Tammany, Livingston, and Washington Parishes, respectively. Hurricane Rita led to a maximum of 80 boil water orders in Calcasieu Parish and rendered inoperable all six public treatment facilities in Cameron Parish.
The two main problems in reestablishing drinking water service in areas relying on groundwater were flooded wells and loss of pressure in the distribution systems.
Even some systems with emergency backup generators lost power when fuel supplies were exhausted. In addition, public health officials struggled with how to communicate to the public whether the water was safe to drink. In some areas, sandwich-board signs were used to indicate the potability of the water.
Impact on wastewater collection and treatment
Hurricanes Katrina and Rita affected 800 permitted wastewater treatment facilities in four states, with 317 of the affected facilities in Louisiana. Wastewater collection and treatment relies on electrical power. For example, the conventional activated sludge process requires power for blowers. In affected facilities, the biomass died when the blowers went out of service.
As of mid-November, the two wastewater treatment plants in New Orleans—the East Bank (a 122-mgd activated sludge plant) and the West Bank (a 20-mgd trickling filter plant)—were still not operational.
Raw wastewater is being pumped to the Mississippi River. The collection system for the Sewerage and Water Board of New Orleans includes 83 electrically-operated pump and lift stations. When power was down, sewer backup caused the discharge of raw sewage into numerous homes. As with drinking water treatment and distribution, different challenges were faced in areas outside of New Orleans. For example, there are 20,000 permitted private treatment systems in the state of Louisiana. Private systems (typically oxidation ponds or small mechanical systems) frequently were flooded, especially in Calcasieu Parish and Cameron Parish. Flooding led to the dispersion of sewer odors in the affected areas.
MCEER researchers have collected the necessary data from Hurricane Katrina field investigations to expand on current multihazard studies that will extend the lessons learned to other extreme events such as earthquakes and terrorist attacks. One example is the use of seismic design details to mitigate hurricane induced damage. Throughout the Gulf Coast region, many simple-supported spans of bridges fell from their support, a similar failure mode that has often been observed after earthquakes. Use of seismic design and retrofit strategies may hold the key to protecting the nation’s bridges from other types of hazards, such as the devastating Hurricane Katrina.
Gilberto Mosqueda, Ph.D., is an assistant professor in the Department of Civil, Structural, and Environmental Engineering at the University at Buffalo (UB), where he teaches courses and conducts research in structural and earthquake engineering. He can be contacted at mosqueda@ eng.buffalo.edu. Jerome O’Connor, P.E., is senior program manager for Transportation Research of the Multidisciplinary Center for Earthquake Engineering Research, headquartered at UB. He can be contacted at firstname.lastname@example.org. James N. Jensen, Ph.D., is a professor in the Department of Civil, Structural, and Environmental Engineering at UB, where he teaches courses and conducts research in environmental engineering. He can be contacted at email@example.com.