Drainage in New Orleans
Thus, flood threats to metropolitan New Orleans include the Mississippi River, Lake Pontchartrain, canals throughout the city, and natural rainfall.
A 2007 study by Tulane and 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.
A more recent study published by the ASCE Journal of Hydrologic Engineering in 2016, however, stated, "...most of New Orleans proper - about 65% - is at or below mean sea level, as defined by the average elevation of Lake Pontchartrain.
[4] Because of the low flat terrain of the New Orleans area, a complex system of levees, canals, and pumps are required to reduce the risk of flooding.
Because it sits where distance between the river and Lake Pontchartrain is shortest, Louisiana Indians had long used the area as a depot and market for goods carried between the two waterways.
The narrow strip of land also aided rapid troop movements, and the river's crescent shape slowed ships approaching from downriver and exposed them to gunfire.
In the 1830s state engineer George T. Dunbar proposed an ambitious system of underground drainage canals beneath the streets.
The first of the city's steam engine powered drainage pumps, adapted from a ship's paddle wheel and used to push water along the Orleans Canal out to Bayou St. John, was constructed in this decade.
In 1899, a bond was floated, and a 2 mill per dollar property tax approved, which funded and founded the Sewerage & Water Board of New Orleans.
As the 20th century progressed, much of the land that had previously been swampland or considered fit for no other use than cow pasture (due to periodic flooding), was drained.
Wood's drainage pumps kept the city proper mostly dry, while the neighboring suburbs on the East Bank of Jefferson Parish (which at the time did not have a comparable system operational), flooded under up to 6 feet (1.8 m) of water.
Most of the city weathered Hurricane Betsy in 1965 without severe flooding, with the major exception of the Lower Ninth Ward neighborhood.
In May 1995, torrential rains (up to 20 inches (510 mm) in 12 hours in some places) overwhelmed pumping capacity, flooding substantial portions of the city.
Rather, a series of failures in mis-designed levees and floodwalls allowed water from the Gulf of Mexico and Lake Pontchartrain to flow into the city.
The Industrial Canal was overwhelmed when a storm surge, funneled in by the Mississippi River Gulf Outlet, overflowed and breached levees and floodwalls in several locations, flooding not only the Lower Ninth Ward, but also Eastern New Orleans and portions of the Upper Ninth Ward west of the Canal.
The storm caused the flow to reverse, and as water levels rose the entire drainage system failed.
At the time of these earlier storms the lower lying areas of the city had little development, so effects on life and property were much less severe.
An article in the New Orleans Times-Picayune on 30 November 2005 reported that studies showed the 17th Street Canal levee was "destined to fail" as a result of fundamental design mistakes by the United States Army Corps of Engineers.
[9] In 2012, slow-moving Hurricane Isaac dropped up to 20 inches (51 cm) of rainfall on isolated parts of the city which exceeded New Orleans' pumping capacity, however minimal flood impacts were noted.
[10] On the afternoon of August 5, 2017, heavy rainfall over a roughly 3-4 hour period caused significant flooding across central sections of New Orleans.
