Increasing Stage Variability of the Mississippi River

The likelihood of catastrophic floods in the Mississippi River correlates with a direct measure of variability, the magnitude of the day-to-day variations in river stage. At several sites along the Middle Mississippi River, the annual average daily stage change has increased twofold, from $\sim 0.12\mathrm{m}/\mathrm{day}$ in the mid to late 1800s to $0.2–0.25\mathrm{m}/\mathrm{day}$ at the present time; this increase is much higher than the increases we document at most sites on the Upper and Lower Mississippi River. Recent record floods have occurred in the highly channelized Middle Mississippi River where channel constriction is most extreme and the daily stage changes and annual amplitude of stage variations are largest. The long-term difference in the magnitude of daily stage change roughly correlates with the reduction in width of the river channel that was done to facilitate navigation, an effect that is consistent with theoretical predictions. Daily stage changes are well constrained compared to catastrophic floods, which are rare and have poorly defined frequency.