Drainage in New Orleans - Hurricane Katrina

Hurricane Katrina

The greatest catastrophe in the city's drainage history occurred at the end of August 2005 when it was hit by Hurricane Katrina, after which eighty percent of the city flooded. Katrina brought tropical storm conditions to the city starting the night of 28 August, with hurricane conditions beginning the following day and lasting through the afternoon.

The hurricane itself did not flood 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 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.

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 caused 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 much of town west of the Industrial Canal, 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 the series of levee breaches. 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 (0.91 m) of water within half an hour.

By the evening of August 30, 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 those reached in mid-19th century storms when, like Katrina, major hurricanes created a "lake flood" by pushing Lake Pontchartrain up into the South Shore. 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.

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 31, 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 United States Army 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.

Read more about this topic:  Drainage In New Orleans

Famous quotes containing the word hurricane:

    Staid middle age loves the hurricane passions of opera.
    Mason Cooley (b. 1927)