Our Views: Study to understand what's going on beneath New Orleans vital to city, state

Jul 27, 2018

In the next century, Louisiana is one of the most vulnerable states in the nation, not just because of hurricanes and tropical storms but the additional problems of sea-level rise and subsiding land along the coast.

That's why it makes sense for the U.S. government and the city of New Orleans to put significant money into a long-term study that is about "understanding what is going on underneath the city," in the words of the Water Institute of the Gulf, the Baton Rouge-based team of scientists working on these issues.

Building on the city's 2015 resilience strategy, the U.S. Department of Housing and Urban Development will fund a $141 million grant to generate solutions to subsidence in the city. It is a project focused on the Gentilly area.

Researchers at Tulane University, the Water Institute and Deltares, the Dutch water management gurus, will drill sample wells and analyze the process of subsidence, estimated at a seemingly tiny 6 mm a year. But those millimeters add up, and how to mitigate the damage is vital in a city where a lot of land is already below sea level, albeit protected by the levee system.

Based on the analysis over about 18 months, the goal is managing rainwater and groundwater to mitigate subsidence, which is often made worse by pumping water out of the ground, or paving over surfaces so that water does not soak into the soil.

The project is of far wider significance than just in New Orleans, or even the broader metropolitan area around the city.

A great deal of south Louisiana was built over centuries by sediments that were brought to the Gulf of Mexico by the Mississippi River. That process was largely ended in the early 20th century as the long levee system was established to avoid flooding and to help protect navigation.

The impact of storms and climate change, with its resulting rise in sea levels worldwide, are obvious threats to Louisiana's coastal areas. But subsidence is another issue. While inevitable to some extent, scientists and public officials seeking ways to avoid making subsidence worse.

The alluvial soils that make up much of south Louisiana are prone to subsidence. That is why there is reason for a project to identify ways in the future to mitigate the land loss.

In the urban areas of the state, the impact of impermeable surfaces in parking lots, for just one example, can contribute to subsidence. One of the new strategies is to build structures so that water can soak into the soil instead of flowing away as stormwater.

It's also vital to places beyond the city limits and the knowledge gained by this series of studies should be of wider value to Louisiana.