“Conditions are dire for much of the coastal region of the Mississippi River Delta and our children’s children will see a coastal landscape that we might not recognize.”
That’s the warning of Sam Bentley, associate dean for research at Louisiana State University College of Science, as well as the Billy and Ann Harrison chair in sedimentary geology at the school.
“In coastal river deltas, land loss and land gain (and also buildup and erosion of the seabed) are natural processes that go on all the time. For the last 8,000 years or so, as one part of the Mississippi River Delta has been building, another part has been degrading due to natural processes,” he said.
That, however, has changed – or, at least, that balance between the building and the degradation has changed.
Much of this work has been done by the LSU Coastal Studies Institute, which was formed in the early 1950s to evaluate the environmental challenges faced by the U.S. Defense Department during World War II. After the war, it quickly became the go-to organization for universities and governments to study the geomorphology and coastal processes of the world’s coastlines.
“Human actions,” said Bentley, who is past president of CSI, “have altered how sediment is delivered down the river and to the delta plain, and also locally accelerated subsidence rates” by construction of huge levees to control the river and protect communities, economic infrastructure and river flooding.
“We have actually known for over a century that our actions would reduce the long-term sustainability of the MRD, by reducing sediment that is required to offset subsidence and erosion that occur constantly,” he added.
What we didn’t know, it seems, is how human intervention would exacerbate the problem.
“Dams on the Missouri cut the sediment load to the MRD by 50 percent or more, oil field canals in the MRD have produced hydrological changes in the wetlands that have been directly connected to land loss, and many of the canals have never been filled or restored,” he said.
Bentley said these are some of the biggest factors – erosion plus subsidence plus sea level rise – that have tilted the mass balance of sediment deposition: toward a delta that is shrinking, not growing overall.
How much has been lost?
According to mississippiriverdelta.org, the Mississippi River Delta and coastal Louisiana are losing a football field of wetlands every 100 minutes. Since the 1930s, Louisiana has lost more than 2,000 square miles of land – that’s roughly the size of Delaware.
“If rates of sea level rise predicted by the Intergovernmental Panel of Climate Change hold true, then the coast of Louisiana will be unrecognizable within two or three generations to those now living,” said Bentley.
Clearly something has to be done. In Louisiana and around the world, attempts have been made for decades to reverse trends of coastal land loss and preserve coastal communities. State and federal agencies have been active in the MRD since at least the 1970’s to address this problem. And one of the solutions – and nobody really wants to talk about this – is the business of determining how many can actually live along the coast.
“At the moment, the conversation is taking place in people’s living rooms,” where, Bentley believes, it should be discussed, as any government movement to force relocation is a “touchy and painful one … that can become a heated debate in public meetings when it comes up.”
People have been relocating voluntarily for decades, largely because of flood risk, he said. He calls this dynamic “environmental disenfranchisement.”
Specifically, in Louisiana, attempts have been made to reverse trends of coastal land loss, and preserve coastal communities, so people don’t have to move. This effort has been part of the Louisiana Coastal Master Plan, a series of extensive and intense scientific and engineering investigation and modeling efforts which explore how different restoration strategies will work in different environmental scenarios of sea level rise, sediment supply, hurricane frequency and intensity, even overall climate. The plan will eventually become the state’s official roadmap.
The problem of coastal loss, it should be noted, is not limited to the Mississippi Delta.
“The Netherlands has been working on this for decades, or centuries really, and has had both success and failure in securing communities from coastal hazards,” said Bentley. “In China, as well, notably the Yellow River, efforts have been made to flush sediment through dammed reservoirs and deliver more of that sediment to the coastal delta.”
The results have been mixed but are still promising. This work comes at a huge financial cost, which will unlikely be replicated in the MRD “because important processes like hurricanes are more powerful and frequent” and “because we cannot spend as much per unit area of land, to do the work.”
The problem is enormous.
“At present, the biggest hotspots for coastal land loss around the world are river deltas, which are inhabited by about 1 in 14 people around the world, but, if and when rates of global sea level rise begin to accelerate, many other low-relief coastal settings will experience similar threats. Much of Florida, much of the eastern U.S. coast, and many other non-deltaic locations around the world will experience these threats. In this way, coastal river deltas can be considered sentinels, the “canary in the coal mine.”
The Role of Education
As an educator, Bentley said students must be made aware of what’s at stake.
“In most cases, in my opinion, the importance of sustainability of the environment and energy resources is a good and logical outcome from a good geoscience education, but not necessarily a specific goal. For example, if a student understands the physics of the sun’s heating of the atmosphere, and the role that different gas compositions play on that heating, then she or he can evaluate such human impacts on the environment, from a rigorous logical and scientific perspective.”
CSI is invested in this pursuit, as virtually all of its fellows teach in their respective academic department and all its faculty have academic appointments in the LSU Department of Oceanography and Coastal Sciences.
So, the $64 billion question (or however much it will take to reverse these deleterious effects): is climate change the culprit?
Bentley said the answer keeps changing.
“My understanding is that the present trends of land loss in Louisiana are largely driven by anthropogenic alterations to the Mississippi System, on top of natural deltaic cycles, so, a case can be made that land loss measured since circa 1932 (the start time for the most important studies) is not strongly impacted by climate. However, modeling done in conjunction with the Louisiana Coastal Master Plan shows that even the more modest IPCC predictions of future sea level rise will play a progressively stronger role in shaping our coast. That, plus the fact that the frequency of major hurricanes is forecast to increase in a warming climate, both suggest that climate change, even in the very near term (decades) is likely to become a driving force for major coastal change.”
On a scale of 1-10, then, where are we?
“I would say that for those individuals who sustain that type of personal impact, on a scale of 1-10, it would be moving towards 10, especially for people such as Louisiana residents, many of whom have a profound sense of place.”