Engineering a better future for the Mississippi Delta

April 28, 2015, Geological Society of America
Mississippi River Delta, 2001. Credit: NASA.

River deltas, low-lying landforms that host critical and diverse ecosystems as well as high concentrations of human population, face an uncertain future. Even as some deltas experience decreased sediment supply from damming, others will see increased sediment discharge from land-use changes. Accurate estimates of the current rate of subsidence in the Mississippi Delta (southern USA) are important for planning wetland restoration and predictions of storm surge flooding.

Parts of coastal Louisiana (southern USA) are undergoing accelerated land loss due to the combined effects of and land subsidence. In the Mississippi Delta, where rates of land loss are especially severe, subsidence of the land surface reflects natural processes, such as compaction and crustal loading, but this is exacerbated by anthropogenic withdrawal of fluids (water, oil, natural gas).

In this study for Geology, Makan Karegar and colleagues use precise Global Positioning System (GPS) data to measure subsidence rates of the Mississippi Delta. They also use tide gauge records to better understand the relationship between subsidence and sea-level rise in southern Louisiana.

The authors show that while the majority of the delta is relatively stable, parts of the delta may not be viable in the long term. The southern portion of the delta continues to experience high rates of subsidence (5 to 6 mm per year). The current rate of relative sea-level rise (the combined effect of land subsidence and sea-level rise) along parts of the coastal delta is nearly 8 to 9 mm per year.

Given stable sea level and , a delta will tend toward an equilibrium state where subsidence is more or less balanced by sediment deposition. In the Mississippi River system, however, a series of dams on various upstream tributaries have reduced sediment supply to the delta, while levees on the lower part of the river have artificially channelized the flow, forcing sediments to be deposited beyond the in the deeper Gulf of Mexico.

The data presented by Karegar and colleagues have implications for land reclamation and wetland restoration in the region. Mitigation efforts may include river diversion to encourage resedimentation, and pumping of offshore sands to restore barrier islands.

Explore further: Geologist calls for advances in restoration sedimentology

More information: A three-dimensional surface velocity field for the Mississippi Delta: Implications for coastal restoration and flood potential, Makan A. Karegar et al., University of South Florida, Tampa, Florida, USA. Published online ahead of print on 27 Apr. 2015; http://dx.doi.org/10.1130/G36598.1.

Related Stories

Geologist calls for advances in restoration sedimentology

November 7, 2012

Rapid advances in the new and developing field of restoration sedimentology will be needed to protect the world's river deltas from an array of threats, Indiana University Bloomington geologist Douglas A. Edmonds writes in ...

Protect the world's deltas

December 3, 2014

Extensive areas of the world's deltas—which accommodate major cities such as Shanghai, Dhaka and Bangkok—will be drowned in the next century by rising sea levels, according to a Comment piece in this week's Nature.

Recommended for you

How our plants have turned into thieves to survive

February 18, 2019

Scientists have discovered that grasses are able to short cut evolution by taking genes from their neighbours. The findings suggest wild grasses are naturally genetically modifying themselves to gain a competitive advantage.

Great white shark genome decoded

February 18, 2019

The great white shark is one of the most recognized marine creatures on Earth, generating widespread public fascination and media attention, including spawning one of the most successful movies in Hollywood history. This ...

Light-based production of drug-discovery molecules

February 18, 2019

Photoelectrochemical (PEC) cells are widely studied for the conversion of solar energy into chemical fuels. They use photocathodes and photoanodes to "split" water into hydrogen and oxygen respectively. PEC cells can work ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.