Editing New Orleans (section)

===Elevation===
{{See also|Drainage in New Orleans}}

[[File:New Orleans Levee System.svg|thumb|upright=1.15|right|Vertical cross-section, showing maximum levee height of {{convert|23|ft|m}}]]

New Orleans was originally settled on the river's natural [[levee]]s or high ground. After the [[Flood Control Act of 1965]], the [[United States Army Corps of Engineers|U.S. Army Corps of Engineers]] built floodwalls and man-made levees around a much larger geographic footprint that included previous marshland and swamp. Over time, pumping of water from marshland allowed for development into lower elevation areas. Today, half of the city is at or below local mean sea level, while the other half is slightly above sea level. Evidence suggests that portions of the city may be dropping in elevation due to [[subsidence]].<ref>{{cite web |title=New Study Maps Rate of New Orleans Sinking |url=https://www.nasa.gov/feature/jpl/new-study-maps-rate-of-new-orleans-sinking/ |website=NASA |date=May 16, 2016 |access-date=16 May 2016 |archive-date=March 8, 2021 |archive-url=https://web.archive.org/web/20210308185136/https://www.nasa.gov/feature/jpl/new-study-maps-rate-of-new-orleans-sinking/ |url-status=dead}}</ref>

A 2007 study by [[Tulane University|Tulane]] and [[Xavier University of Louisiana|Xavier University]] suggested that "51%... of the contiguous urbanized portions of Orleans, Jefferson, and St. Bernard parishes lie at or above sea level," with the more densely populated areas generally on higher ground. The average elevation of the city is currently between {{convert|1|and|2|ft|m}} below sea level, with some portions of the city as high as {{convert|20|ft|m|0}} at the base of the river levee in [[Uptown, New Orleans|Uptown]] and others as low as {{convert|7|ft|m|0}} below sea level in the farthest reaches of [[Eastern New Orleans]].<ref>Campanella, R. [http://richcampanella.com/assets/pdf/study_Campanella%20analysis%20on%20Above-Sea-Level%20New%20Orleans.pdf Above-Sea-Level New Orleans] {{Webarchive|url=https://web.archive.org/web/20160304071726/http://richcampanella.com/assets/pdf/study_Campanella%20analysis%20on%20Above-Sea-Level%20New%20Orleans.pdf |date=March 4, 2016 }} April 2007.</ref><ref>Williams, L. [http://blog.nola.com/topnews/2007/04/higher_ground.html Higher Ground] {{Webarchive |url=https://web.archive.org/web/20170819232938/http://blog.nola.com/topnews/2007/04/higher_ground.html |date=August 19, 2017 }} A study finds that New Orleans has plenty of real estate above sea level that is being underutilized. ''The Times Picayune'', April 21, 2007.</ref> A study published by the [[American Society of Civil Engineers|ASCE]] ''[[Journal of Hydrologic Engineering]]'' in 2016, however, stated:

{{blockquote|...most of New Orleans proper—about 65%—is at or below mean sea level, as defined by the average elevation of Lake Pontchartrain<ref>{{Cite journal |doi=10.1061/(ASCE)HE.1943-5584.0001338 |title=Using New Orleans Pumping Data to Reconcile Gauge Observations of Isolated Extreme Rainfall due to Hurricane Isaac |journal=Journal of Hydrologic Engineering |volume=21 |issue=9 |page=05016020 |year=2016 |last1=Schlotzhauer |first1=David |last2=Lincoln |first2=W. Scott| issn = 1084-0699}}</ref>}}

The magnitude of subsidence potentially caused by the draining of natural marsh in the New Orleans area and southeast Louisiana is a topic of debate. A study published in [[Geology (journal)|''Geology'']] in 2006 by an associate professor at Tulane University claims:

{{blockquote|While erosion and wetland loss are huge problems along Louisiana's coast, the basement {{convert|30|ft|m}} to {{convert|50|ft|m}} beneath much of the Mississippi Delta has been highly stable for the past 8,000 years with negligible subsidence rates.<ref>{{cite web |url=http://www2.tulane.edu/news/newwave/072406_a_new_look_at_subsidence_issues.cfm |title=A New Look at Subsidence Issues |author=Strecker, M. |date=July 24, 2006}}{{Dead link |date=May 2020 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>}}

The study noted, however, that the results did not necessarily apply to the Mississippi River Delta, nor the New Orleans metropolitan area proper. On the other hand, a report by the [[American Society of Civil Engineers]] claims that "New Orleans is subsiding (sinking)":<ref name="ASCE">[http://www.asce.org/files/pdf/ERPreport.pdf The New Orleans Hurricane Protection System: What Went Wrong and Why.] {{webarchive |url=https://web.archive.org/web/20070702194739/http://www.asce.org/files/pdf/ERPreport.pdf |date=July 2, 2007 }} Report by the American Society of Civil Engineers.</ref>

{{blockquote|Large portions of Orleans, [[St. Bernard Parish, Louisiana|St. Bernard]], and [[Jefferson Parish, Louisiana|Jefferson]] parishes are currently below sea level—and continue to sink. New Orleans is built on thousands of feet of soft sand, silt, and clay. Subsidence, or settling of the ground surface, occurs naturally due to the consolidation and oxidation of organic soils (called "marsh" in New Orleans) and local groundwater pumping. In the past, flooding and deposition of sediments from the Mississippi River counterbalanced the natural subsidence, leaving southeast Louisiana at or [[Above mean sea level|above sea level]]. However, due to major flood control structures being built upstream on the Mississippi River and levees being built around New Orleans, fresh layers of sediment are not replenishing the ground lost by subsidence.<ref name="ASCE"/>}}

In May 2016, NASA published a study which suggested that most areas were, in fact, experiencing subsidence at a "highly variable rate" which was "generally consistent with, but somewhat higher than, previous studies."<ref>{{cite web |url=https://www.nasa.gov/feature/jpl/new-study-maps-rate-of-new-orleans-sinking |title=New Study Maps Rate of New Orleans Sinking |date=May 16, 2016 |access-date=June 15, 2016 |archive-date=June 8, 2016 |archive-url=https://web.archive.org/web/20160608115437/http://www.nasa.gov/feature/jpl/new-study-maps-rate-of-new-orleans-sinking/ |url-status=dead}}</ref>