CEE Rapid Response grant supports study of 2016 Louisiana flooding
10/17/2016 10:06:51 AM
In August 2016, catastrophic flooding inundated southern Louisiana and resulted in 13 deaths, evacuation of more than 20,000 people, and damage to at least 60,000 homes. This extreme event was the result of prolonged rainfall — exceeding two feet, in some locations — that overwhelmed local flood control systems and poured into residential and commercial areas. CEE at Illinois professor Tim Stark received a CEE Rapid Response Grant to join a Geotechnical Extreme Events Reconnaissance (GEER) team in Louisiana to survey the damage and assess the performance of public infrastructure. Stark plans to use the data they collected to update his 2011 study of Mississippi River flooding.The team looked at various sites in Livingston Parish, Ascension Parish, and areas along the Amite River on September 9, 2016. Initial findings suggest the public infrastructure performed fairly well, but there were some problem areas. For example, a levee near Sorrento that overtopped during the flood did not show evidence of significant erosion; however, the team thinks the way the levee was constructed had the inadvertent effect of channeling floodwaters directly into a nearby housing development. A closer look at interactions between rainfall-induced flooding and vertical structures such as levees is needed, Stark said.
In other locations, the team found bridge abutments and piers that experienced some scour (the removal of soil caused by floodwaters diverting and accelerating around these obstructions). Some residential areas experienced scouring as well.
“We observed significant scour and erosion of a residential community located on the Amite River near French Settlement, Louisiana,” Stark said. “The combination of high water and already damaged bulkheads allowed the river to scour beneath the foundation of these homes, destroying boat homes and leaving several homes overhanging the Amite River in critical condition.”
In spite of public infrastructure performing as expected, the overall impact of this flood on southern Louisiana was more devastating than the 2011 flood. In 2011, the Mississippi River flooded due to upper Midwest rainfall. In 2016, the flooding resulted from local rainfall. This difference is significant because the origin of the rainfall determines where the water gets channeled into the flood control system.
“If flood levels in the [Mississippi River] are high as they were in 2011, the U.S. Army Corps of Engineers can open the Morganza Spillway to divert flow to the Atchafalaya Basin, thus bypassing flow away from New Orleans,” Stark said. “The Bonnet Carré Spillway is another diversion to Lake Pontchartrain that further reduces the Mississippi’s flow before New Orleans. In January of 2011, this spillway was opened to divert the deluge from the Midwest to Lake Pontchartrain and finally to the Gulf of Mexico. Both structures work to relieve upstream pressure so the river levels are sufficiently managed by the time the flood reaches New Orleans. The 2016 flood was totally different than 2011. It didn’t impact the Mississippi River at all so the spillways were not opened.”
Instead, local flood control systems—which include a diversion into the much smaller Lake Maurepas —were quickly overwhelmed in 2016. A state of emergency was declared as thousands of homes and businesses were inundated with water. The flood was, according to the Red Cross, the worst natural disaster since Hurricane Sandy.During their trip, the research team encountered another effect of the 2016 flooding: a massive amount of waste generation from inundated homes. Although not part of their original research goals, the scale of the problem was such that it has been added to their plans for further study. “We didn’t go down there thinking we would look at storm related waste in particular,” Stark said. “However, just going down street after street, it was unbelievable. Basically, every house emptied out everything from the house including the walls, appliances, furniture, fixtures, etcetera, and placed it near the curb for collection. It was like a tunnel of debris on each side of the street, all the way down.”
Stark said that there is a need to better predict debris volumes from extreme events so that efficient and sustainable management of waste debris can be developed and coordinated to accelerate pickup. The team plans to document the waste generation and disposal process so that more accurate estimates of resources needed in the aftermath of future disasters can be made.
The GEER team will publish a report with their findings in the coming months. Other members of the GEER team include: Navid Jafari (Principal Investigator), Louisiana State University (LSU); Murad Abu-Farsakh, Louisiana Transportation Research Center (LTRC); Shengli Chen, LSU; Milad Saghebfar, LTRC; Jeff Beasley, LSU; Kory Konsoer, LSU; and Brian Harris, LSU.
The CEE Rapid Response Grant program was developed to facilitate rapid-response, high-impact research related to infrastructure improvement and risk management in the aftermath of natural and man-made disasters. Previous grants have allowed CEE researchers to study flooding in the Midwest, a bridge collapse in Washington state, and tornado damage in Oklahoma.
At top: photo of his submerged house, courtesy of Jonathan Luna.