If there is one area that exemplifies the what is at stake in the Louisiana coastal region, it is the state's storm protection value. Storm Protection refers to the function of wetlands in reducing storm energy and storm - generated water surges that cause flooding. This ecosystem service is very important to residents of the Mississippi Delta, the Gulf of Mexico and U.s. Eastern Seaboard.
Coastal wetlands serve as a buffer and retention area for storm surge, serving as part of the hurricane protection system. Hurricanes become weaker as they travel over land, therefore the more land these storms have to cover before reaching a major city like New Orleans, or even places further inland like Shreveport, the better. Unfortunately this also means that wetland and coastal buffer zones take most of the force and can therefore be worn away at a faster rate. Sustaining these natural buffer zones is one of the best things Louisiana can do to protect herself and foster a healthy ecosystem.
The USGS estimated that 138,000 acres of land were lost to open water due to the 2005 hurricane season (USGS 2006). Healthy wetlands are often horizontally compacted by the hurricanes only to re-expand after the storm. Similarly, storms can actually benefit wetlands by bringing in sediments from the continental shelf. However, if wetlands are unhealthy, as is largely the situation along the coast, hurricanes can break them up or bring in saltwater.
The above image is a conceptual plan for weakening the impact of storm surge in residential areas that may be threatened by storm surge. This concept includes the natural use of restored barrier islands as well as restored marsh to gradually weaken the flow of water in a storm/flood situation.
During Hurricane Katrina there was 60 foot waves in the Gulf Of Mexico. These huge waves did not hit land because the offshore shelf greatly reduces wave height by reducing the depth of the water.
South Louisiana has entered a period when the combination of two powerful forces is working against its survival:
(1) coastal land loss and
(2) more frequent intense hurricanes.
Since the 1950’s, the processes driving coastal loss have continued only slightly abated (USACE, 2004), reducing the effectiveness of Louisiana’s coast to buffer against storm surge. Since 1990, meteorological and oceanic processes driving tropical systems have more frequently generated Category 4 and 5 hurricanes (Webster et al., 2005). More destructive hurricanes are also predicted for coming decades (Emanuael, 2005). South Louisiana’s ongoing peril is the continued overlap of weakened hurricane protection with more frequent and intense hurricanes (Frischetti, 2001).
Four major hurricanes in last five years:
- Katrina (2005)
- Rita (2005)
- Gustav (2008)
- Ike (2008)
(Above) Based on probabilities calculated from the historical record from 1950 to 2005, storms striking New Orleans, LA are twice as likely to be a Cat 2 or higher storm than storms striking the Galveston, TX area.
- LACPR, Final Technical Report
USACE March 2009
The Great Flood of 1927 (shown above)
- Most destructive river flood
- 145 levee breaks
- 27,000 square miles flooded
- 246 deaths
2005 Hurricane Impacts
- Over 1400 Louisianans died
- Over 200,000 homes and businesses destroyed, damaged or flooded
- 1,000,000 displaced citizens
- Economic Impact Exceeded $100 billion
- State/parish budget/economy devastated
Katrina first struck the U.S. in Florida as a category 1 hurricane on August 24, 2005. Fueled by the Gulf of Mexico's hot water, it quickly powered up into a massive category 5 hurricane. As Katrina moved inland, it crossed wetlands which then put more physical drag on the storm, slowed its progress, lowered the storm surge and reduced fetch (the area of open water where waves can gain in size and momentum). As the storm hit the coastline, it weakened quickly to a category 4 and then a category 3 as it made landfall on August 29, 2005. New Orleans experienced storm surges from 14 - 18 feet.
Land Area Changes in Coastal Louisiana After Hurricanes Katrina and Rita
By John A. Barras
Wetlands reduce hurricane impact. Hurricanes Katrina and Rita passed through areas of the Mississippi River Delta that had the greatest wetland loss between 1932 and 1990. This includes the Birdfoot Delta of the Mississippi River which lost 50% of its land area, St. Bernard Parish wetlands lost 17%, Plaquimines Parish lost 12% and the East Orleans land bridge lost 17.6% (USGS, 2002). If the original wetlands still existed, they would have buffered the storm surge and both hurricanes would have caused far less damage.
While the typical land loss rate is about 24 square miles per year, Hurricanes Katrina and Rita eliminated 217 square miles of coastal wetlands in two days.
“Coastal wetland losses in Louisiana account for up to 90 percent of the total coastal wetlands loss occurring in the lower 48 states today and expose the state’s coastal areas to the devastating effects of hurricane storm surges.”
- Coastal Wetlands: Lessons Learned From Past Efforts in Louisiana Could Help
Guide Future Restoration and Protection - GAO, December 2007
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