Miller City levee break and incipient meander cutoff

On July 15, 1993, the flooding Mississippi River broke through a levee near Miller City, Ill., at the head of the Mississippi Embayment, approximately 55 km upstream from Cairo, Ill. Flow through the break crossed a high-amplitude meander bend and reentered the main channel approximately 24 km upstream from Cairo, bypassing 31 km of the river channel. The incipient meander cutoff is one of the more dramatic examples of geomorphic change accompanying the 1993 flood. Discharge and bathymetry data were collected in the incipient cutoff channel every other day during the 2 weeks before and after the flood peak. During the peak on August 7, as much as 8,100 m3/s, or approximately 25 percent of the Mississippi flood discharge, was bypassing the meander bend. The flow excavated an irregular channel in the flood plain up to 25 m deep. This irregular channel extends as far as 2 km downstream from the levee break. By August 25, as much as 2,900 m3/s was still flowing through the levee break; with recession of the flood, extensive sand deposits were exposed on the margins and downstream from the scoured areas. Preliminary data indicate that local relief, such as relict channels and preexisting county roads, affected the extent of new channel formation.