April 4, 2013

LSU Researcher Develops Models to Quantify Vulnerability of Hurricane Evacuation Routes to Subsidence and Climate Change

It is no secret that Louisiana’s coast if vanishing right before our eyes. Land subsidence and sea-level rise have contributed to a loss of approximately 1.2 million acres of Louisiana coast in the last century. While Louisiana only accounts for 30 percent of our nation’s coast, the state accounts for a whopping 90 percent of coastal land loss in the lower 48 states. The debate is not whether coastal land loss is occurring, but rather exactly how fast it is occurring and what consequences it will have for Louisiana roads, property and residents.

Joshua D. Kent, GIS Manager for LSU’s Center for GeoInformatics, is working to provide answers related to the consequences of global climate change and relative sea level rise in Louisiana on emergency evacuation routes. The project, funded by the Gulf Coast Evacuation & Transportation Resiliency Program and the U.S. Department of Transportation, is aimed at assessing the vulnerability of hurricane evacuation routes in coastal Louisiana to flooding and storm surge events, given current and future rates of land loss. Kent has harnessed the accurate measurement capabilities of the Center for GeoInformatics’ network of continuously operating global positioning system (GPS) stations to assess the consequences of relative sea-level rise on roads and communities in Louisiana.

“Land subsidence is a complicated process,” Kent said. “South Louisiana is essentially wet and mushy. Combined with natural processes including tectonic loading, shifting growth faults and sea-level rise caused by global climate change, agricultural and industrial activities have caused localized subsidence. The construction of levees have essentially dried up landscapes, preventing water from replenishing the land and accelerating compaction rates.  And the extensive use of water from natural aquifers further contributes to subsidence.”

Continuing research conducted by late LSU professor and researcher Roy K. Dokka, Kent and colleagues physically gathered more than 2,000 miles of road elevation data in south Louisiana and developed four different subsidence models to estimate surface elevations for the years 2015, 2025, 2050 and 2100. Kent and his research team drove their GPS equipment over approximately 90% of southern Louisiana major roadways, collecting elevation data at centimeter level accuracy. Applying factors of man-made subsidence to existing subsidence rate models, Kent used the elevation data to determine land loss rates due to subsidence ranging from approximately 6 to 16 millimeters per year. Using several models of land subsidence over time, Kent determined the vulnerability of thousands of miles of hurricane evacuation routes to flooding and storm surge events. 

According to Kent, nearly 60 percent of people in coastal Louisiana currently live at or below sea level. Cameron Parish, Jefferson Parish and New Orleans all have significant portions of land at or below sea level. In Jefferson parish, more than 60% of people live at or below sea level and are vulnerable to flood and surge events. Anthropogenic influences as well as natural processes have caused land subsidence in coastal Louisiana, to the extent that land in the region is overcome by water at a rate of nearly an entire football field every 45 minutes.

“People are living in these vulnerable landscapes,” Kent said. “These communities will eventually need to evacuate in the case of a flood event. Land subsidence is increasing vulnerability to disasters in these regions.”

In his research, Kent is working to match vulnerable land at or below sea level with population counts and paths of hurricane evacuation routes, quantifying vulnerability to storm surge and flooding disasters for people and property. According to worse case scenarios models developed for New Orleans, nearly 60 miles of roadways that serve as important transportation and evacuation routes will be vulnerable by 2100.

“The longer into the future we go, the more of our roads will be vulnerable,” Kent said. “We see that the consequences of land subsidence is significant in coastal Louisiana. A significant chunk of our coast will be at or below sea level by 2100. We have a dire looking future if we don’t do anything.”

Kent suggests that if we want to be good stewards of southern Louisiana landscapes, we must make good decisions related to restoration and sustainability.

“Sustainability is the way to go: rational people coming together to make rational decisions, backed by good science,” Kent said. “We need to correlate our industrial activities and highway construction plans with sustainability efforts.”

In his research, Kent combined SLOSH models, models of Sea, Lake, and Overland Surges from Hurricanes provided by the National Weather Service, to investigate effects of storm surge combined with land subsidence on hurricane evacuation routes. The goal was to determine how many miles of road would be inundated by storm surge events given current and future rates of land subsidence in coastal Louisiana. Kent found that storm surge events and land subsidence combine to increase vulnerability of roadways.

“We need to make communities managers cognizant of long-term consequences of storm surge and subsidence on land vulnerability,” Kent said. “There is no one answer or silver bullet to land subsidence. Everyone needs to work on the same science to accurately represent subsidence rates and to sustain vulnerable communities.”

In future research, Kent plants to develop improved subsidence rate models for coastal Louisiana based on higher resolution datasets, and to investigate localized subsidence rates in particular parishes, in order to better quantify and predict future vulnerability.

For more information about LSU’s Center of Geoinformatics, visit http://c4gnet.lsu.edu/c4g/.

For more information about storm surge models, visit http://www.nhc.noaa.gov/ssurge/ssurge_slosh.shtml.


Article written by LSU Office of Research Communication Staff. 

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