Gulf of Mexico
Bucket dredge builds a wall around new wetland cells in the Upper Barataria Basin south of New Orleans. (CPRA)

LA - Levees, oil wells biggest causes of Barataria Basin land loss: study

A new study of the dramatic loss of wetlands in the Barataria Basin south of New Orleans during the last 130 years concludes that the two main causes have been construction of levees along the Mississippi River and subsidence due to oil and gas activity.

But the study also contains potential good news: There may be enough sediment in the river to rebuild coastal land, disputing earlier estimates.

The peer-reviewed study was published Monday in the scientific journal Nature Sustainability. Co-authors include scientists with Indiana University, LSU and the Moffatt and Nichol infrastructure advisory firm.

“The question that I’m really interested in is how well do we understand why that land loss is occurring, and do we know enough to actually make a reasonably accurate prediction that matches that land loss curve,” said lead author Douglas Edmonds, associate professor of geology at Indiana University. Co-authors included LSU coastal sustainability Prof. Robert Twilley and LSU geology Prof. Samuel Bentley.

The Barataria Basin includes land south of New Orleans between the east bank of Bayou Lafourche and the west bank of the Mississippi River. It is part of the Mississippi River Delta, formed over the past 7,000 years through sediment deposition from the river, a process now blocked by flood-prevention levees. The flow of water and sediment from the Mississippi into Bayou Lafourche and the basin was also blocked off by a dam in 1903.

A key part of the study is its conclusion that the rapid development of oil and gas exploration and production in the Barataria Basin tracks the accelerated increase in land loss that began in about 1930 and peaked in 1978. As oil and gas development – and the pumping of oil, gas and the water accompanying it – dramatically dropped between then and 1990, the reduction in land loss mirrored it.

The rapid changes in the rate of land loss were documented in a 2017 study led by U.S. Geological Survey geographer Brady Couvillion, which concluded the state’s coastline lost an estimated football field every 34 minutes in 1978. That rate slowed to a football field every 100 minutes by 2016. Some of the slowing is also linked to construction of federal, state and local wetland restoration projects.

Edmonds said the fluid extraction resulted in increased rates of deep subsidence, where water and other fluids withdrawn from underground sediment or rock reduced pressure, allowing layers above it to sink, even causing geological faulting in some cases, until oil and gas production in the basin slowed.

The study points to 2005 research by USGS geologist Robert Morton that found subsidence caused by wells in the basin extended to between 3 and 6 miles from each wellfield. There are 125 wellfields, spaced about 5 miles apart – containing about 26,600 individual wells – in the basin.

Read more.