The St. Johns Basin-New Madrid Floodway Project

In the first part of this two-part series, I presented an outline of a project designed by the U.S. Army Corps of Engineers to close an engineered gap in the Mississippi River levee system in Southeast Missouri and prevent flooding on the last stretch of Mississippi River floodplain that maintains connection with the river during flood phase. The gap in question separates the front-line levee that generally follows the Missouri bank of the river, from a set-back levee that cuts across land from Bird’s Point to New Madrid as the river loops south and back north. From here downstream, the set-back levee continues as the one main levee (Figure 1). This arrangement created the New Madrid Floodway between the two levees over 10 miles apart at their greatest separation. This floodway was designed such that should severe floods threaten Cairo, located just upstream of Bird’s Point, the front-line levee could be blown (crevassed) at that the upstream end allowing the river to spread across the floodway and exit through the 1500 ft gap at the downstream end thus relieving the flood threat confronting Cairo and other towns. This feature was used once, in 1937, but its use has been considered since then, most recently in the 1990s (though ultimately it was not employed).

The gap in the levee at New Madrid (Figure 2) has the design consequence (for landowners and residents) of allowing Mississippi River water to flow backwards up the New Madrid Floodway causing backwater flooding (Figure 3). Over the last century, especially with the extensive and successful drainage afforded the region by ditches developed by the Little River Drainage District, many landowners have taken advantage of the fertile floodplain soils to grow crops: notably corn, soybeans, wheat, and cotton.

The problem for these farmers is that the frequent flooding (Figure 4) induced by a swollen Mississippi River reduces the profits that they potentially could gain from their farmlands. In addition, the economically depressed communities of Southeast Missouri, which are largely dependent on agriculture for their survival, enjoy less benefit from the vast acres of fertile soils surrounding them than they feel they should. Small rural residential communities, particularly those at the gap end of the New Madrid Floodway, also suffer at the hands of backwater flooding from Mississippi River. Meanwhile, communities such as East Prairie, located in Saint Johns Basin on the landward side of the set-back levee, suffer from headwater flooding(Figure 5) caused by the heavy seasonal rains of the region flowing through over-burdened channels and ditches to the Mississippi River. These ditches and channels flow into the St. Johns Bayou which then passes through a gate in the set-back levee (Figures 2 and 6) at New Madrid into the Mississippi River adjacent to the aforementioned gap. When the Mississippi River level exceeds the elevation of this bayou, the gates are closed and water accumulates behind the levee in the basin, backing up northwards to inundate croplands, and under severe flood conditions, ultimately to threaten East Prairie.