Analysis and Inundation Mapping of the April–May 2011 Flood at Selected Locations in Northern and Eastern Arkansas and Southern Missouri

Precipitation that fell from April 19 through May 3,
2011, resulted in widespread flooding across northern and
eastern Arkansas and southern Missouri. The first storm
produced a total of approximately 16 inches of precipitation
over an 8-day period, and the following storms produced
as much as 12 inches of precipitation over a 2-day period.
Moderate to major flooding occurred quickly along many
streams within Arkansas and Missouri (including the Black,
Cache, Illinois, St. Francis, and White Rivers) at levels that
had not been seen since the historic 1927 floods. The 2011
flood claimed an estimated 21 lives in Arkansas and Missouri,
and damage caused by the flooding resulted in a Federal
Disaster Declaration for 59 Arkansas counties that received
Federal or State assistance. To further the goal of documenting
and understanding floods, the U.S. Geological Survey, in
cooperation with the Federal Emergency Management Agency,
the U.S. Army Corps of Engineers–Little Rock and Memphis
Districts, and Arkansas Natural Resources Commission,
conducted a study to summarize meteorological and
hydrological conditions before the flood; computed flood-peak
magnitudes for 39 streamgages; estimated annual exceedance
probabilities for 37 of those streamgages; determined the joint
probabilities for 11 streamgages paired to the Mississippi
River at Helena, Arkansas, which refers to the probability that
locations on two paired streams simultaneously experience
floods of a magnitude greater than or equal to a given
annual exceedance probability; collected high-water marks;
constructed flood-peak inundation maps showing maximum
flood extent and water depths; and summarized flood damages
and effects.