Extensive precipitation-induced flooding in southern Louisiana, from west of Baton Rouge to Mississippi, has resulted in six deaths, tens of thousands of rescues and significant property damage, catastrophe modelling firm AIR Worldwide said in media advisory issued late Monday.
In this Sunday, Aug. 14, 2016 photo, Louisiana Army National Guard dump truck, loaded with rescued flood victims, makes it way back to dry land in Walker, La., after heavy rains inundating the region. (AP Photo/Max Becherer)
AIR Worldwide said that thousands of homes, as well as farmland, highways and commercial and industrial property have suffered flood damage. Water continues to rise in some locales and additional rain could initiate flash floods. States of emergency have been declared for Louisiana and impacted counties in Mississippi, and United States President Barack Obama has designated parts of Louisiana as federal disaster areas.
The Louisiana Department of Transportation and Development reported that approximately 200 roadways became impassable due to flooding, including parts of both interstates 10 and 12, AIR said in the release. As many as 1,400 bridges need to be inspected before they can be reopened and, in some areas, stranded cars remain on highways.
Louisiana Governor John Bel Edwards declared a state of emergency for the entire state and called up 1,700 Louisiana National Guard troops to support rescue work. Governor Phil Bryant of Mississippi also declared a state of emergency for counties impacted in his state.
“Record rainfall fell across a large portion of southern Louisiana as a slow-moving tropical depression-like system crawled across the region this past week,” said Dr. Hemant Chowdhary, principal scientist at AIR Worldwide, in the media release. “Rainfall amount ranged from 12 to more than 24 inches, with 31.39 inches recorded near Watson and 27.47 inches in Brownfields; 8.49 inches fell at the Baton Rouge Metropolitan Airport in one day. Parts of the region received two to four times the average total monthly rainfall for August in just three days,” Dr. Chowdhary reported.
TONIGHT – S. Louisiana & Mississippi still recovering from devastating & historic flooding, but is more on the way? pic.twitter.com/p0QK9UbJQv
As of Aug. 15, at least 10 rivers had surpassed moderate-to-major flood stages at several locations along their course: Amite, Bogue Chitto, Calcasieu, Comite, Mermentau, Pearl, Tangipahoa, Tchefuncte, Tickfaw and Vermilion. “As many as eight rivers have reached record flood levels, including the Amite River, which crested at Magnolia at about 6.5 feet above the 65-year historical record of 51.91 feet (set in 1977),” Dr. Chowdhary said, “and the Comite River, which crested near Comite Joor Road about 4 feet above the 70-year historical record of 30.99 feet (set in 2001).”
General outlook for significant river flooding. Source: National Weather Service.
Although the heaviest rainfall has passed, many rivers will continue to rise, some for a few days, AIR reported. Because of saturated ground and the current high river levels, additional rain events that occur before waterways have started to recede could result in flash flooding. “The drenching rain in southern Louisiana during the past week, from west of Baton Rouge to New Orleans and Mississippi, brought historic inland flooding in many communities,” Dr. Chowdhary said.
In addition, upwards of 20,000 people have been rescued, plucked from porches and roofs and inundated vehicles by emergency personnel in high-water vehicles, boats, and Coast Guard helicopters. Upwards of 12,000 people have sought refuge in shelters, some of which have been filled to capacity. Some shelters, too, have been evacuated due to flooding, the release said.
AIR pointed out that more than 40% of buildings in the U.S. Gulf Coast region meet Flood Insurance Rate Map (FIRM) standards set in 1980. While the specifics of the FIRM standards vary somewhat by building construction and occupancy class, these standards dictate that buildings must be elevated above base flood elevation, as defined by the Federal Emergency Management Agency, and that any parts of a building that remain below base flood elevation must be constructed of flood-resistant materials.
According to AIR, only 0 to 10% of buildings constructed since 1980 in the Gulf States have basements, which increase vulnerability to flood damage. Buildings in the region are more typically built on slab foundations, which are designed to withstand flotation, collapse or lateral movement that can be inflicted by floodwaters.
In Louisiana, more than 80% of the residential construction is wood, with an estimated 5% of structures having basements, AIR said. Over half of the commercial buildings are steel and concrete. Unlike residential structures, commercial buildings often are engineered and built to stricter standards, and are thus less vulnerable than single-family homes. Still, mechanical, electrical, and plumbing systems can experience severe damage, which results in high losses, the release said.
On Sunday, Aon Benfield’s Impact Forecasting said that the flooding in parts of Louisiana and Mississippi could approach or possibly exceed US$.15 billion in economic damage, calling it “one of the most catastrophic non-tropical cyclone triggered flood events in the state of Louisiana since 1983.” However, from an insurance perspective, “it is anticipated that the insured portion of the economic loss will be substantially less,” Impact Forecasting said.