Surging seas and vicious winds whipping through coastal Louisiana, Mississippi, and Alabama weren’t the only causes of the enormous damage left behind after Hurricane Katrina. Human-made changes to the area’s natural environment amplified the effects of the storm, enabling it to become one of the largest natural disasters in the nation’s history.
Maximum sustained winds of nearly 175 mph and the breach of two key levees holding back the waters of Lake Pontchartrain conspired to create the devastating deluge. The death toll passed 1,000 in September, and hundreds of thousands of people have been left homeless. So far, over half a million cubic yards of debris have been removed from devastated areas in Louisiana while the cleanup continues from 12 oil spills along the Mississippi River.
Before large-scale, human-driven development, the Mississippi Delta maintained an equilibrium. Naturally occurring erosion and subsidence as soils sank under their own weight were off-set when the Mississippi flooded each year. New sediments were distributed over the delta, replenishing the wetlands. These wetlands and barrier islands protected the region along the Gulf Coast for thousands of years.
As the human population grew in the Delta region, the river’s annual flooding came to be seen as a problem. Levees were erected along the banks of the Mississippi to protect cities and farmlands. While this goal was achieved, the long term effects have been disastrous, for the natural environment of the region – and now the built environment as well.
The most problematic result of human alterations to the area has been the loss of sediments to replenish the wetlands. Levees channel the river’s flow far out into the Gulf of Mexico, allowing very little sediment to restock the marshes or reinforce the narrow barrier islands, which together are the coastal area’s last line of defense against storm surges. Dams upriver have reduced the overall amount of sediment in the river by 67 percent.
In addition to the deleterious effects of sediment loss, human activity has greatly accelerated the naturally ocurring rate of erosion. Oil and gas drilling and canals built for navigation have exposed more bare soil to the water, so that waves created by boats and wind further erode the shore.
The construction of canals has allowed salt water intrusion into brackish and freshwater marshes. This additional salinity kills native plants whose roots hold soil in place, causing even more soil to erode. Levees exacerbate this problem by preventing nutrient-rich sediments from nourishing the wetlands.
Draining land for agriculture, roads, canals, and urban development has impelled soil subsidence. As soils are exposed to the atmosphere after wetlands are drained, the soils oxidize, losing volume. This is a primary reason why much of New Orleans was below sea level. Oil and gas mining are also major causes of sinking. As fossil fuels are pumped from below the earth, the rock and soil above collapse into the now-empty geologic strata that held the oil or gas.
Of course, human-caused climate change is perhaps the most obvious potential cause of Katrina’s destructive power. The Gulf of Mexico was abnormally warm in August, and Katrina – a Class 1 storm when it entered the Gulf – quickly swelled to a terrifying Class 5 when it encountered the warmer Gulf water. Climatologists predict that warmer temperatures will cause tropical storms to become far stronger, and 2005 is already one of the stormiest years in history.
In 1998, state and federal agencies proposed a $14 billion, 40-year program to the federal government to provide for the reclamation and preservation of Louisiana’s coastal wetlands. The goal of the Louisiana Coastal Area Program was to restore or simulate the natural processes that created and sustained the delta. Unfortunately, the Bush administration cut funds from the project to pay for the war in Iraq and various homeland security programs. This year, the Bush administration afforded $10.4 million for the delta project, one sixth of the amount requested and insufficient to even initiate preventive measures.
Carrie Black is an Earth Island Journal intern.
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