Landscape response to the intentional use of the Birds Point New Madrid Floodway on May 3, 2011

• The mechanical action of floodwaters generated visible land modifications.
• Net increase and decrease of topographic elevation occurred in preferential zones.
• Water depth and velocity changes formed sand and gravel bars, and ripple fields.
• Strong, concentrated flow formed scour features and stripped agricultural soil.
• Inundation on the floodway exceeded geomorphic thresholds.

SummaryDuring the spring of 2011 massive, coalescing storm fronts in the upper Mississippi, and Ohio River basins caused extreme weather conditions that flooded the bottleneck section of the Mississippi River in the vicinity of Cairo, IL. In order to alleviate the volume of floodwaters acting on downstream levees and to stop flooding near Cairo, IL, the US Army Corps. of Engineers activated the Birds Point New Madrid Floodway by intentionally breaching the Birds Point Levee, releasing floodwaters onto active agricultural fields. The impacts of floodwater on the landscape were regionally significant. Concentrated erosion generated deep scour holes, rills, and gullies in localized areas of the floodway. Inflow and outflow of waters formed large deposits of sands and gravels. Sand sheets of a few centimeters to a meter thick blanketed the vicinity of the impacted areas, and in some cases sand accumulations exhibited current ripples indicating multiple flow directions. This study directly addresses geomorphic changes in the New Madrid Floodway resulting from activation and the diversion of floodwaters from the Mississippi River. Results from this study can be used along with other field data to conduct a thorough flood damage assessment that includes the costs associated with geomorphic alteration within the floodway.