The report from the corps said the flood hit 119 counties in the lower Mississippi River states of Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee. More than 21,000 homes and businesses and 1.2 million acres of agricultural land were affected, and more than 43,000 people felt some effects.
The Mississippi River and Tributaries system operated as it was designed and was mostly successful in fighting the flood along most of the nation's most important inland waterway, the corps said. However, the spring floods exposed vulnerabilities in many parts of the system and the plans used to operate it. The report said there is room for improvement in nearly all areas.
"The magnitude of the event tested the system and its individual components like no flood before it," the report said.
Nearly all of the levee or floodwall systems experienced some damage. The floodways at Birds Point-New Madrid in Illinois, and the Morganza Floodway and Bonnet Carre Spillway in Louisiana were opened to relieve the stress on the system, marking the first time that three floodways had been operated during a single flood, the report said.
Total economic damages were pegged at $2.8 billion. The corps spent nearly $60 million while directly fighting the flood from March to August.
Levee-related problems that emerged during included instability of levee slopes, seepage and sand boils, which are pools of water that bubble up near levees. The corps identified where repairs to levees and other parts of the system are needed and is using $802 million approved by Congress in 2011 to make critical and non-critical fixes "to prepare for the next high water event."
Most will be completed this year, but several "critical repair" projects are expected to extend into 2015 and 2016.
"The system will be restored to a pre-flood condition and in some cases be a better system," the report said.
The lengthy report identified several deficiencies exposed during the flood. In and near Cairo, Ill., city pumping stations could not be used due to poor maintenance—resulting in localized flooding—and some neighborhoods were under water as engineers fought to deal with growing sand boils.
There were river bank failures in President's Island in Memphis and Tiptonville, both in Tennessee. Hundreds of homes in three Memphis-area trailer parks were inundated when two tributaries overtopped their banks.
High water in and around Eagle Lake, Miss., where levels were raised to offset pressure from the rising river, caused damage to piers and boat houses around the lake and affected boating and fishing.
In Louisiana, officials ordered mandatory evacuations for hundreds of residents in the Atchafalaya Basin after the Morganza floodway was opened. But flooding in those areas wound up being far less severe than the corps initially projected.
The corps said it was able to use technologies such as smart phones and social media to its advantage, at times.
"When they were not applied properly, confusion and frustration resulted and special rules for the proper use of social media were found to be needed," the report said.
Other technology-related problems included poor cell phone reception in some remote areas, a shortage of phones and radios, and that too few people were trained to use some information collection and sharing tools at the beginning of the flood.
The report also said that the flood affected the estuarine system and the oyster industry in Mississippi Sound, Lake Borgne, and Breton Sound, La. Economic losses to the oyster industry in Mississippi alone in 2011 were approximately $60 million, according to the report.