There was no good time for the BP-Deepwater Horizon oil gusher to erupt, but at the beginning of the nesting season for birds and turtles, at the beginning of the spawning season for fishes and shrimp, and, now, at the beginning of the hurricane season, it’s the worst possible time for oil to be washing into Louisiana’s marshes and killing the vegetation that holds them together. Never mind what’s happening in the water column in the Gulf of Mexico, where the big fish, the dolphins and the whales, are swimming in oil and toxic dispersants.
“Conventional wisdom has long stated that Louisiana’s intricate web of natural levees and basins containing marshes and swamps soaked up the power of a storm surges produced by hurricanes and reduced the flooding that followed. Until 1992 it was just that: conventional wisdom with no data to back it up. On August 26, 1992 while Americans focused on the damage Hurricane Andrew produced in Homestead, Florida, the storm surged across the Gulf of Mexico, made a second landfall as a category three storm at Point Chevreuil, Louisiana, and racked up numbers on continuous water level recorders in the Terrebonne marshes south of Houma. A storm surge that measured at 9.3 feet at Cocodrie swept across the Houma Navigation Canal at Houma, twenty-three miles to the north, at 3.3 feet. That translates into an amplitude loss of 3.1 inches per mile of marsh and open water between Cocodrie and Houma. Between Oyster Bayou and Kent Bayou, the storm surge was reduced by 2.8 inches per mile across nineteen miles. Clearly, conventional wisdom was correct, even allowing for different hurricanes following different storm tracks across different coastal landscapes. Coastal wetlands soak up the power of hurricanes. Hence, when Katrina’s storm surge ripped across Breton Sound and Lake Borgne thirteen years later and wiped out the string of lovely towns on Mississippi’s coastline, it demonstrated the destructive power of a Category 3 storm unimpeded by healthy marshes.”
In 2008 Hurricane Gustav, a mild Category 2 storm made landfall on Louisiana’s only inhabited Grand Isle on September 1 with a twelve-foot storm surge. Grand Isle took some of the punch out of the surge. The hurricane levees and the Bayou Lafourche ridge weakened it more.
So did the Barataria Landbridge, that stretches across the Barataria Basin from Bayou Lafourche to the Mississippi and protects the fresh marshes and swamp to its north from salt water intrusion from its south. By the time it reached the hurricane levees at Montegut, the surge had been reduced to eight-feet. Gustav crossed more levees and other ridges and arrived in Houma as wind and rain, lots of wind and rain, but no storm surge washed through its streets.
The barrier islands, the natural ridges, the salt marshes, the landbridges, the hurricane levees, and the bottomland forests that anchor the northern extent of the ridges had done their job, protected the cities like Houma from Gustav’s storm surge.
This was the point of the Comprehensive Recommendations Supporting the Use of the Multiple Lines of Defense Strategy to Sustain Coastal Louisiana, published in August 2007 , a point that needs to be repeated over and over.
Imagine Louisiana without such protection. Imagine a storm surge, loaded with oil, crossing a barrier island; imagine it washing oil through the salt marshes; imagine it covering the landbridges with oil; imagine it swamping the forests that protect cities with oil. It’s not a pretty picture.
Update #1, June 3: Speaking of defense, Gov. Bobby Jindal has gotten approval from President Obama and the Coast Guard to build his temporary barrier island out front of existing barrier islands. Len Bahr at LaCoastPost has a discussion coastal scientists’ take on the efficacy of the plan, which includes building sacrificial marshes behind the sand berms. He also included a link to Louisiana’s PBS Station’s series of broadcasts on the artificial barrier islands and the fate of the brown pelican. It is worth a listen.
Update #2, June 3: On Wednesday, June 2, Rachel Maddow interviewed David Muth and Larry McKinney at the Barataria Preserve, where they discussed the value of Louisiana’s wetlands in soaking up the power of a hurricane storm surge. Follow the link to the June 2 broadcast, which comes in 5 parts. Each is worth the time it takes to watch it. On Thursday, June 3, she will move south to Grand Isle.
Update, June 4: Environment 360 Yale University’s School of Forestry and Environmental Studies enlarges on NOAA’s 2010 hurricane outlook.