Altered States: Natural and Man-made Changes to the Missouri, Mississippi and Meramec Rivers

Dr. Robert Criss, Professor, Department of Earth and Planetary Sciences
Washington University, St. Louis

The Missouri River has been dramatically modified by humans, primarily to improve the navigational channel, to prevent frequent but shallow inundation of the floodplain, and to provide power and water supply. However, these modifications have caused the river to evolve in unexpected ways, with diverse and deleterious consequences. The ecosystem has been profoundly degraded, and the river disconnected from its natural floodplain, causing severe reductions in the populations and diversity of aquatic and riparian species. Daily fluctuations in river stages have undergone a three-fold increase that destroys nesting and spawning sites. Significant floods have become more frequent and severe, opposite to the intended effect of "preventative" engineering structures. Regional rivers that have not undergone such extensive channel projects behave much as they did long ago, maintaining their large and diverse natural populations, and their high aesthetic and recreational quality. Such comparisons link the cause of river degradation to man-made structures and not to climate change. The rich observational records acquired by dedicated scientists and engineers document these effects and suggest appropriate responses, but needed efforts will continue to be impeded by misunderstanding and by parties with special or vested interests.