Drainage in New Orleans

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Drainage has been a major concern since the founding of New Orleans in the early 18th century, remaining an important factor in the city's history today.

File:Msyelevst.jpg

Elevation map of New Orleans. Hotter (pink) shades are below the level of Lake Pontchartrain, cool browns and greens are above.

Flooding threatens New Orleans from three sources: the Mississippi River, Lake Pontchartrain, and natural rainfall. Artificial levees have been built to keep out rising river and lake waters but have had the negative effect of keeping rainfall in.

History

New Orleans was originally built on natural levees along the Mississippi River. This choice of location was a strategic one for trade but the potential for flooding was ignored.

The first artificial levees and canals were built in early colonial times. They were erected to protect New Orleans against disastrous flooding from the Mississippi River. The "back of town" away from the river originally drained down into the swamps running toward Lake Pontchartrain. Flooding from the lake side was rare and less severe as the town remained on high ground along the riverfront.

As the city grew, demand for more land encouraged expansion into lower areas more prone to periodic flooding. For most of the 19th century most residential buildings were raised up at least a foot above street level (often several feet), since flooding of the streets was a given at the time.

In the 1830s state engineer George T. Dunbar proposed an ambitious system of underground drainage canals beneath the streets. The goal was to drain water by gravity into the low lying swamps, supplementing this with canals and mechanical pumps. 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 constucted in this decade. However, only a few of Dunbar's plans were actually implemented as the panic of 1837 largely ended major systematic improvements for a generation.

In 1859 surveyor Louis H. Pilié improved the drainage canals, bricking in some portions. Four large steam "draining machines" were built to push water through the canals into the lake.

In 1871, some 36 miles of canals were built in the city for both improved drainage and small vessel shipping within town. However, despite earlier efforts, at the end of the 19th century, it was still common for water to cover streets from curb to curb after rainstorms, sometimes for days.

In 1893, the city government formed the Drainage Advisory Board to come up with better solutions to the city's drainage problems. Extensive topographical maps were made, and some of the nation's top engineers were consulted. In 1899, a bond was floated, and a 2 mil per dollar property tax approved, which funded and founded the Sewerage & Water Board of New Orleans. The Sewerage & Water Board had the responsibility of draining the city along with constructing a modern sewage and tap water system for the city, which, at the time, still relied heavily on cisterns and outhouses. (A different entity, the Orleans Levee Board, is in charge of supervision of the city's levee and floodwall system.)

The Sewerage & Water Board found A. Baldwin Wood, a young engineer who not only supervised the plans for improved drainage and pumping, but also invented a number of improvements in pumps and plumbing in the process. These improvements were not only used in New Orleans, but adopted all over the world.

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. The city then expanded back from the natural higher ground close to the river and natural bayou formed ridges.

On 15 April 1927, the city was deluged by a downpour of some 15 inches of rain within 19 hours. At the time, almost all of the city's pumps relied completely on the municipal electricity system, which went out early in the storm, thus knocking the pumps off line, which lead to extensive flooding in the city. After this, back up diesel generators with enough fuel to run the pumps for at least a day if electricity failed were added to the pumping stations. The "Good Friday Flood", as it was known locally, happened during the Great Mississippi Flood when the Mississippi River levels were dangerously high along the levees at the city, but was not directly connected to the more wide-ranging flood.

1927 also saw the start of a project to build a more extensive system of levees on the shoreline of Lake Pontchartrain. After 1945, all land up to the lake had been developed.

The city's system demonstrated its worth in times of crisis when the 1947 Fort Lauderdale Hurricane directly hit the city. 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 of water.

Most of the city weathered Hurricane Betsy in 1965 without severe floodings, with the major exception of the Lower Ninth Ward neighborhood. The Lower Ninth Ward is separated from the rest of the city by the Industrial Canal and Gulf Intracoastal Waterway. It was flooded not by rainfall, but by a breach in the Industrial Canal levee, resulting in catastrophic flooding and loss of life in the neighborhood.

By the 1980s, the city boasted a system of 20 pumping stations with 89 pumps, with a combined capacity of 15,642,000 gallons per minute, 22.5 billion gallons per day, equal to the flow of the Ohio River.

In May of 1995, torrential rains (up to 20 inches in 12 hours in some places) overwhelmed pumping capacity (compounded, according to some, by a few pumps not being turned on until the deluge was already well underway), flooding substantial portions of the city. Slab houses in some low areas were flooded, and great numbers of automobiles on the city's flooded streets were declared totaled. This prompted projects increasing drainage capacity in the worst hit areas.

By early 2005, the city had 148 drainage pumps.

Hurricane Katrina

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"This is the largest civil engineering disaster in the history of the United States. Nothing has come close to the $300 billion in damages and half-million people out of their homes and the lives lost."

The greatest catastrophe in the city's drainage history started at the end of August 2005, when the city was hit by Hurricane Katrina, after which the majority of the city flooded. Katrina brought tropical storm conditions to the city starting the night of 28 August, with Hurricane conditions the following day through the afternoon.

The hurricane itself did not flood the city. In much of town, residents who did not evacuate before the storm reported that after the storm they were relieved to see their streets dry and the precipitation from the storm successfully pumped out. However, disaster was already spreading from a series of levee breaches.

The Industrial Canal was overwhelmed when 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 New Orleans East and portions of the Ninth Ward west of the Canal.

Meanwhile, waters from storm-swollen Lake Pontchartrain poured into the city, first from a breach in the 17th Street Canal, and then from a pair of breaches in both sides of the London Avenue Canal. These canals were among those used to channel water pumped from city streets into the Lake. The storm cause the flow to reverse, and as water levels rose the entire drainage system failed. Examinations afterwards showed that water levels in these locations never topped the floodwalls, but instead the levees failed with a water level supposedly within their safe tolerance.

In areas of town far from the breaches, flood water came not in through the streets, but up from the storm drains beneath the street, in some places changing streets from dry to under 3 feet of water within half an hour.

Flood lines show levels of high water on this Mid City New Orleans house

By the evening of August 30th, some 80% of the city was under water. (This figure includes areas of widely differing flood levels, ranging from areas where streets were covered with water which never rose into homes to areas where homes were entirely submerged over the rooftops.) Most of the city's pumping stations were submerged. The few above the water line had no power and the emergency diesel fuel had run out. These few were often tiny islands in the flood, inaccessible even if intact enough to hypothetically be turned back on.

For most of the city to the west of the Industrial Canal, the flood levels were much the same as occurred in mid 19th century storms and most recently before in the Great Storm of 1909, when, like Katrina, major hurricanes created a "lake flood", pushing Lake Pontchartrain up into the South Shore. However during those earlier storms, most of the lower lying areas of the city had little development, so effects on life and property were much less severe.

West of the Industrial Canal, the parts of the city unflooded or minimally flooded largely corresponded with areas of the city developed on naturally higher ground before 1900.

On August 31st, flood levels started to subside. The water level in the city had reached that of Lake Pontchartrain, and as the lake started to drain back into the Gulf, some water in the city started to flow into the lake via the same levee breeches they had entered through. In 19th century lake floods, the water soon flowed back into the lake as there were no levees on that side. In 2005, while the levees proved inadequate to keep the lake out of the city, even in breached form they were sufficient to keep much of the flooding from flowing back out. As breaches were gradually filled, some city pumps were reactivated, supplemented by additional pumps brought in by the Corps of Engineers. Some of the city's pumps which survived could not be reactivated because of the failures of the canals that they pumped flood waters into. The combined task of closing breaches and pumping the flood waters out took weeks and was compounded by a setback in late September due to further flooding from Hurricane Rita. See: Civil engineering and infrastructure repair in New Orleans after Hurricane Katrina.

By the start of October, only a few small areas of flood waters remained within the city, but the disastrous flooding in the aftermath of Katrina left the majority of the city's houses and businesses so damaged as to be unusable until major renovations or repairs could be made. 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 Army Corps of Engineers .