Hurricane Katrina, 2005

Setting

Katrina crossed the northern Gulf coast on 29 August 2005. New Orleans depended on levees, floodwalls and pumps to manage flood risk.

Sources: mvn.usace.army.mil

Why flood defences failed

Storm surge strained the protection system. Some floodwalls failed before water reached their tops; other structures were overtopped. Floodwater eventually covered about 80% of New Orleans.

Sources: upload.wikimedia.org

Human and economic costs

The NHC's 2023 revision gives 1,392 fatalities across direct, indirect and indeterminate causes. Its US damage estimate is $125 billion in 2005 dollars. These figures cover Katrina's US impacts, not New Orleans alone.

Sources: upload.wikimedia.org

Emergency response

The Coast Guard and other responders rescued survivors from rooftops. Engineers repaired flood defences and pumped water out while planning a stronger regional system.

Sources: usace.army.mil

Reducing future risk

The replacement system combines levees, floodwalls, gates and pumps. FEMA accredited it in February 2014 for a 1% annual chance level of flood risk reduction. Evacuation planning remains necessary because greater events and failures remain possible.

Sources: usace.army.mil 1 · mvd.usace.army.mil 2

Using this case in an answer

Connect the storm with coastal exposure and flood-protection failures. Evaluate emergency response and later engineering separately, including the continuing need for evacuation.

• Use the revised NHC fatality total with its report date. Older sources give different totals.
• A 1% annual-chance standard reduces risk; it does not prevent every flood or replace evacuation.