Sep
22
2010

Last night, bkennedy, a couple other SMM staff members, and I attended the Bell Museum's Cafe Scientifique at Bryant-Lake Bowl in Minneapolis. Robert Twilley, a principal investigator with the National Center for Earth-Surface Dynamics, came to speak about the endangered environment of the Mississippi Delta and the BP Deep Horizon Oil Spill. I didn't expect to get a history lesson, but it's just this kind of broad-ranging perspective that will help us understand what is happening to our environment.

It was frustrating to hear Dr. Twilley recount how, as a result of the 1928 Flood Control Act, civil engineers literally remade the Mississippi River and its delta in response to severe flooding events. While this had the temporary effect of protecting area residents from flooding, the plan neglected an important quality of all coastlines: they're dynamic. As sea level has risen over the last century, diverted sediments no longer replenish key areas of the delta and vast stretches of wetland are drowning--the same stretches of wetland that would protect people in the event of a strong hurricane. As a result of the levees, regular floods no longer wash sediments into the area. To complicate matters, projects such as dams farther upstream have cut the overall sediment supply to the Mississippi by about 50 percent in the last couple centuries.

Dynamic Mississippi River Delta: The shaded areas of this image show how the river delta has shifted around over the last 4600 years.
Dynamic Mississippi River Delta: The shaded areas of this image show how the river delta has shifted around over the last 4600 years.Courtesy Urban

Twilley emphasized that it wasn't as if people didn't know the problems these strategies would cause; engineers who opposed flood control tried to call attention to the associated risks. But in the wake of disastrous floods, the public demanded visible public works projects and politicians wanted to please them. Engineers who supported flood control saw it as a noble enterprise to control nature and protect people. And so today we have a tricky situation in the delta area. Disasters increase in intensity, and with them, peoples' insistence on solutions grow. But Twilley cautioned that it is imprudent to act on impulse, especially due to a widespread lack of understanding about how coastal systems work, and to our tendency to favor human safety without consideration for the environment that supports our safety. In short, we undermine ourselves.

"Since 1932, the basin has lost approximately 70% of its total land area."
-lacoast.gov

When Hurricane Katrina hit, the same channel intended to give port access to ships funneled the storm surge farther inland. Twilley described how this perfect storm of civil engineering amplified the devastation brought by the Category 3 hurricane. The response to this devastation, rather than stepping back to reevaluate the situation and consider new ways to accommodate both the delta's needs and humans' needs, was to build a surge barrier that does nothing to restore the natural systems that once built and sustained that landscape over centuries. Contrary to engineers' intentions, Twilley asserted that these strategies will only exacerbate rising sea level and storm surge in the future as the wetlands drown further and the coastline moves inland.

Twilley also explained how, more recently, a lack of recognition of the complex systems in the river delta and along the Gulf Coast exacerbated BP's Deepwater Horizon Oil Spill. BP's front end study on the potential impacts of a spill found no cause for concern that the oil would reach the shore. And yet, in spite of booms placed along the coast, the oil did reach the shore, infiltrating wetlands already threatened by rising sea levels and weakened by lack of sedimentation. Thanks to the use of dispersants, the oil is difficult to find and we may not know the full impact of the spill for some time.

This paints a pretty grim picture of the future, but Twilley left us with cause for hope. In one of the areas to which a significant portion of sediment was diverted, the wetlands are actually growing (Atchafalaya). Twilley and his colleagues hope that this and other examples will demonstrate the importance of these natural wetland-building systems and garner support for their plain to mitigate the wetland loss. They want to add river outlets in strategically important places throughout the delta to rebuild the wetlands and help stabilize the landscape. These outlets would only operate during flooding episodes--an approach called controlled flooding (as opposed to the current strategy of flood control), siphoning off extra water and sediment to starved wetlands AND preventing flooding into human settlements. Currently, they're also involved in a project to pipe sediment to areas that need it.

Of course, the new outlet plan won't be without some compromise on the part of humans--some may have to relocate. But given projections of the area for 2100, relocation isn't far off anyway. And the long-term protective benefits of restoring the wetlands might just be worth it.

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