30 tons of dynamite at Caernavon in 1927

The Great Flood of 1927 inudated thousands of square miles around Greenville, Mississippi killing 1,000 people and forcing 700,000 to evacuate. The river temporarily became an 80 mile wide inland sea. The levees were the only high ground and provided refuge for people and livestock.

As the crest approached, the high water levels scared New Orleans into dynamiting the levee in St. Bernard Parish. It really happened then. Most historians now agree that it was unnecessary because levee breaks up river took pressure off the city's levees. (The Bonne Carre spillway was built six years later.)

Intentional levee breaks have not been used to fight flooding since then. However, Hurricane Betsy survivors of the 9'th ward claim somebody dynamited the levees then to save the French Quarter and Katrina survivors of the 9'th ward claim the same. Both of these claims have to do with the Industrial Canal levee just to the west of the Lower Ninth Ward. Most responsible sources discount these claims.

Apparently when the levee breaks, it is loud.

If you want to know more about 1927, the Corps of Engineers, Levee Engineers Ellett, Eads and Humphries and Greenville, MS read about the Great Flood in John Barry's classic Rising Tide