Short answers, pulled from the story.
The National Hurricane Center attributes 1,836 fatalities to Hurricane Katrina, with 1,577 deaths in Louisiana, 238 in Mississippi, 14 in Florida, and smaller numbers in Alabama, Georgia, Ohio, and Kentucky. A 2014 report revised the total down to 1,392, and the NHC updated its official data to reflect that figure on the 4th of January 2023.
Katrina's storm surge caused 53 breaches in the flood protection system surrounding New Orleans on the 29th of August 2005. Investigators determined that the U.S. Army Corps of Engineers, which designed and built the levees under the Flood Control Act of 1965, used steel sheet pilings that were driven to only 17 feet deep when the correct depth was between 31 and 46 feet. A June 2007 report by the American Society of Civil Engineers concluded that the failures were primarily due to system design and construction flaws.
The total damage from Hurricane Katrina is estimated at $125 billion in 2005 U.S. dollars, making it tied with Hurricane Harvey as the costliest tropical cyclone in the Atlantic basin. The total economic impact in Louisiana and Mississippi was estimated to eventually exceed $150 billion, and the Bush administration sought $105 billion for repairs and reconstruction.
At its peak on the 28th of August 2005, at 1800 UTC, Hurricane Katrina had maximum sustained winds of 175 mph and a minimum central pressure of 902 mbar, making it the fifth most intense Atlantic hurricane on record at the time. It reached Category 5 status after intensifying from Category 3 in just nine hours over the warm waters of the Loop Current.
Hurricane Katrina displaced over one million people from the central Gulf Coast, creating what was described as the largest diaspora in the history of the United States. By late January 2006, only about 200,000 people had returned to live in New Orleans, less than half the pre-storm population. By July 2006, Louisiana's population had declined by 219,563, or 4.87%, according to the U.S. Census Bureau.
All major post-Katrina investigations concluded that the U.S. Army Corps of Engineers was responsible for the levee failures. The Corps misread a 1985 study and used steel sheet pilings driven to only 17 feet deep, rather than the required 31 to 46 feet, saving approximately $100 million but significantly reducing the system's reliability. A federal appeals court later ruled that the Corps could not be held financially liable because of sovereign immunity under the Flood Control Act of 1928.