Midwest FloodInformation on the Performance, Effects, and Control of Levees Gao ID: RCED-95-125 August 7, 1995
The intense rainfall that deluged the upper Mississippi River basin in the spring and summer of 1993 caused the largest flood ever measured at St. Lewis. This unprecedented event in nine midwestern states saw the highest flood crests ever recorded at 95 measuring stations on the region's rivers. The catastrophic flooding caused 95 deaths and extensive property damage and forced the evacuation of tens of thousands of people. The President declared 505 counties to be federal disaster areas, and estimates of the damage have ranged as high as $16 billion. This report examines the operation of the levees, which are earthen or masonry structures, including floodwalls, that are typically built along rivers to keep floodwaters from overflowing adjacent floodplains. GAO reviews the extent to which (1) the U.S. Army Corps of Engineers' flood control levees prevented flooding and reduced damage during the event; (2) the federal levees increased the height of the flooding and contributed to the damage; and (3) federal, state, and local governments exercise control over the design, construction, placement, and maintenance of nonfederal levees.
GAO found that: (1) 157 of the 193 Army Corps of Engineers levees found in the areas affected by the 1993 flood prevented rivers from flooding and $7.4 billion in damages; (2) 32 of the Corps levees withstood floodwaters until the water rose above the levees and overtopped them; (3) 4 of the Corps levees allowed water into protected areas before their design capacity was exceeded; (4) the Corps estimated that the breaching of these levees caused about $450 million in damages; (5) although levees allow floodwater to rise higher than it normally would because they confine a flood to a portion of a floodplain, the Corps believe that its levees have the net effect of reducing flooding; (6) no federal programs specifically regulate the design, placement, construction, or maintenance of nonfederal levees, however, flood insurance and disaster assistance programs may exercise control over certain levees; and (7) 17 states and various local governments have programs to regulate levees, many of which are in response to the requirements of the National Flood Insurance Program.