HR: 17:00h
AN: G44A-05    [Abstracts]
TI: High Subsidence and Low Elevation in New Orleans
AU: * Dixon, T H
EM: tdixon@rsmas.miami.edu
AF: University of Miami, 4600 Rickembacker Cswy, Miami, FL 33149,
AB: On-going problems in New Orleans related to recovery from Hurricane Katrina highlight important issues related to the role of Earth science in society. Earth science has not played a significant role in New Orleans' current recovery or past planning, but probably should. Low elevations and subsidence are clearly key factors in past and future flood hazard, but have not yet had a major influence on zoning or rebuilding guidelines for the city. One problem is that the Earth science community has not spoken with a clear voice on this topic. A recent AGU report on New Orleans by a group of experts concluded that "Presently, there is considerable discussion and debate among the scientific community regarding mechanisms and rates of subsidence in the Mississippi delta area ("Hurricanes and the U.S. Gulf Coast…", http://www.agu.org/report/hurricanes/). Here I argue that this assessment is flawed: there is clear evidence of rapid subsidence in the city, and this subsidence explains the current pattern of low elevation. Our community's failure to issue clear statements on this relatively simple problem has confused the public. In particular, we have mixed legitimate scientific discussion of the larger issue of relative sea level change over a range of time scales and over a broad section of the Gulf Coast, a complex problem, with the narrower and more easily understood issue of subsidence in New Orleans over the last 100- 150 years. In the latter case, geodetic techniques (leveling, GPS, INSAR) indicate high subsidence rates, up to 15-25 mm/yr in some areas. These high rates, presumably applicable for the period after major drainage projects began in the mid 1800's, explain the current low elevations for most parts of the city. Assuming elevations close to sea level prior to major drainage, 20 mm/yr subsidence for 100 years yields 2.0 meters elevation below sea level, typical of regions that experienced flooding from Hurricane Katrina. While several processes contribute to high subsidence rate and low elevation, oxidation of organic-rich soils in former marshland, drained for agriculture or urbanization, is probably the major contributor in the lowest-lying areas of the city. These areas have high flood hazard, and should either be converted to other uses, or re-built with elevated structures.
DE: 1211 Non-tectonic deformation
DE: 1223 Ocean/Earth/atmosphere/hydrosphere/cryosphere interactions (0762, 1218, 3319, 4550)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
SC: Geodesy [G]
MN: 2007 Fall Meeting