Geodetic Survey: Gulf states are sinking

Geodetic Survey: Gulf states are sinking

Two decades' worth of measurements by the National Geodetic Survey show that coastal states are steadily sinking into the Gulf of Mexico. NGS and National Oceanic and Atmospheric Administration officials, speaking this week at the National Hurricane Conference in New Orleans, said land there could subside as much as a foot or more over the next decade.

The Geodetic Survey used Global Positioning System real-time kinematic (RTK) technology to make the most recent measurements, mounting the RTK receiver apparatus on a tire towed behind a NOAA truck.

NGS scientists and Louisiana State University's Spatial Reference Center estimated that 15,000 square miles of southern Louisiana will be at or below sea level within the next 70 years. Subsidence has already caused parts of some cities such as New Orleans to sink several feet below sea level, they said.

NGS' primary responsibility is the National Spatial Reference System, a framework for measuring latitude, longitude, height, scale and other geospatial indicators.

NGS director Charlie Challstrom said the agency will combine its GPS RTK analysis 'with the National Weather Service's storm track and surge projections' to estimate the impact of storms and flooding on coastal communities.

'We are surveying [hurricane] evacuation routes' to see whether they would fall below sea level, said George Lee, a member of Challstrom's staff.

Meanwhile, NGS is recalibrating its spatial benchmarks in Louisiana used for so-called NAVD88 elevations to determine building heights and other municipal and surveying jobs. The Spatial Reference Center in February said that Louisiana Highway 1 has subsided by a foot since 1982.

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