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Why was the Morganza Spillway opened during the Mississippi River flood of 2011?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Map of the United States showing the Mississippi River and its major tributaries flowing south from Minnesota to the Gulf of Mexico. A shaded area marks the Mississippi River basin, and New Orleans is labeled near the river's mouth.
Mississippi River

During the Mississippi River flood of 2011, the Morganza Spillway was opened on May 14 to prevent catastrophic levee breaches in the Louisiana cities of Baton Rouge and New Orleans.1

As water levels approached a flow rate of 1.25 million cubic feet (35,000 cubic metres) per second, officials determined there was a significant risk to these urban areas, which would have displaced thousands of residents and disrupted a critical network of petroleum refineries. By opening the spillway, the U.S. Army Corps of Engineers diverted floodwaters into the Atchafalaya River basin. While this action successfully protected the cities, it resulted in the evacuation of nearly 3,500 people and the inundation of approximately 3,000 square miles of land, much of which was cropland.12