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Study says seas may rise faster than expected

Molly Keogh, fifth year PhD student, shot this photo near Bohemia and looked northeast across the swamps of Breton Sound in southeastern Louisiana. Picture credits: Tulane University

A recent Tulane University study questions the reliability of measuring sea-level rise in lower-lying coastal areas, such as southern Louisiana, and suggests that the current method underestimates the severity of the problem. This research is at the center of a news article published this week in the journal Science .

Relative sea-level rise, which is a combination of rising water levels and sinking land, has traditionally been measured using tide gauges. Researchers Molly Keogh and Torbjörn Törnqvist, however, argue that in coastal Louisiana tide gauges tell only part of the story.

Tide gauges in such areas are anchored on average 20 meters in the earth and not at the ground surface. "As a result, the gauges do not detect subsidence in the shallow subsurface and thus underestimate the relative sea-level rise," said Keogh, a fifth-year PhD student. Student and principal author of the study.

"This study shows that we need to completely rethink how we measure sea-level rise when the lowlands of the coast subsides rapidly," said Törnqvist, Vokes geology professor at the Tulane School of Science and Engineering. 1

9659005] The study, published in the open access journal Ocean Science says that while flood gauges can accurately measure the subsidence underlying their foundations, the flat subsidence component is missing. Since at least 60 percent of the subsidence occurs in the top 5 meters of the sediment column, the main factor for relative sea-level rise is not dependent on the level gauges.

An alternative approach is to measure the flat subsidence using surface survey tables. cost-effective mechanical instruments for measuring height differences in wetlands. Coastal Louisiana already has a network of more than 300 of these instruments. The data can then be combined with measurements of the deepening of GPS data and satellite measurements of sea-level rise.

The rates of relative sea-level rise in this approach are much higher than those from tidal measurements. "We therefore conclude that coastal zones with lower altitudes are at a higher risk of flooding and have a shorter time horizon than previously thought," said Keogh.

She said research has had an impact on coastal communities around the world. 19659005] "Around the world, communities in low-lying coastal areas may be more susceptible to flooding than we were aware of, affecting coastal management, urban planners, and emergency planners." "They plan to rise faster than that based on a specific timetable and sea level What they are going to do will be a problem. "

Explore further:
New map marks the sinking coast of Louisiana

Further information:
Molly E. Keogh et al., Measuring rates of today's relative sea-level rise in low-altitude coastal areas: a critical assessment Ocean Science (2019). DOI: 10.5194 / os-15-61-2019

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Tulane University

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