Big Muddy Speaker Series presents:

Recent flooding on the Lower Missouri River – especially in the "Great Floods" of 1993, 2011, and 2019 – owes much of its severity to the convergence of three factors. First, dams, channelization, and levees have altered how water and sediment are transported down the river, resulting in some parts of the river that have incised (and therefore have reduced flood risk) and others that have aggraded through sedimentation on the bed and banks (resulting in increased flood risk).

The second factor is the atmospheric origin of floodwaters. The mainstem reservoir system was designed to handle the relatively predictable snowmelt from the Rocky Mountains, but the 1993, 2011, and 2019 floods demonstrated that unpredictable changes in the jet stream can bring large amounts of moist Gulf air into the Missouri River basin, a situation that is especially hazardous when rain falls on frozen ground and/or downstream of the mainstem reservoir system.

The third factor is changing climate. Although climate-change models have predicted increased precipitation throughout most of the Missouri River drainage basin, statistically significant trends in flow records have been difficult to demonstrate because of high hydrologic variability ("noise"). Measurement data are now picking up a trend of increasing runoff that is consistent with climate-change models. Convergence of these three factors has created a sense of urgency to reduce flood risk on the Missouri River. Diagnosis of the factors that contribute to increased flood risk provides some guidance for the very challenging policy questions about how to manage the river for future resilience.