Estuary Processes and Managment - River Dynamics and Integrated River Management - page 477

Gulf coast. The most havoc hurricane was Katrina. On Aug. 29, 2005, hurricane Katrina made landfall on
the Gulf Coast near New Orleans. A 6-metre storm surge smashed levees protecting low-lying New Orleans
and much of New Orleans was flooded. The confirmed death toll (total of direct and indirect deaths)
stood at 1,836, mainly from Louisiana (1,577) and Mississippi (238) and 705 people remain missing in
Louisiana in 2006. Federal disaster declarations covered 233,000 km² of the United States. It is reported
that Katrina's storm surge caused 53 different levee breaches in greater New Orleans submerging 80% of
the city. Two-thirds of the flooding were due to levee breaches (Swenson and Marshall, 2005). The storm
surge also devastated the coasts of Mississippi and Alabama, making Katrina the most destructive and
costliest natural disaster in the history of the United States, and the deadliest hurricane since the 1928
Okeechobee Hurricane. The total damage from Katrina is estimated at $81.2 billion (2005 U.S. dollars)
(USDC, 2006).
As shown in Fig. 8.14 the city of New Orleans is located between the Mississippi River and lake
Pontchartrain. To its east is the Borgne Lake and Mexico Gulf. The lowest city ground is about -2 m (below
the sea level), but the annual flood stage of the Mississippi River is 4.2 m and the normal water level in
the Pontchartrain lake is 0.3 m. Hurricane Katrina brought heavy rain to Louisiana, with 200-250 mm
falling on a wide swath of the eastern part of the state. As a result of the rainfall and storm surge the level
of Lake Pontchartrain rose to 3.5 m and caused significant flooding along its northeastern shore. The city
was flooded due to breaching of the levees and water poured into the city from the gulf, the lake and the
river (http://en.wikipedia.org/wiki/Hurricane_Katrina).
Fig. 8.14 New Orleans is located between the Mississippi River and lake Pontchartrain
The main strategy to mitigate the hurricane disasters is warning. Warnings and watches are two levels
of alert issued by U.S. national weather forecasting bodies to coastal areas threatened by the imminent
approach of a tropical cyclone of tropical storm or hurricane intensity. They are notices to the local
population and civil authorities to make appropriate preparation for the cyclone, including evacuation of
vulnerable areas where necessary. It is important that interests throughout the area of an alert make
preparations to protect life and property. A hurricane warning is issued when a hurricane with sustained
winds of 118 km/h or higher is expected in a specified coastal area in 24 hours or less. Maritime flags
indicate this with two square red flags with a black square in the middle of each.
8.2.3 Rainstorm Flooding
Coastal areas and large cities at river mouths, such as Christchurch by the Waimakariri River, New York
at the Hudson River mouth, Shanghai at the Yangtze River mouth, Tianjin at the Haihe River mouth and