Damming the Des Moines: Geomorphic and Hydrologic Change in a Multi-Dam System on an Upper Midwest River

Large dams intrinsically change the geomorphic and hydrologic forms and processes of the rivers they reside in, yet the complexity of their impacts in different settings is not fully understood. In the Upper Midwest, Saylorville and Red Rock Dam are constructed on the Des Moines River, in a region undergoing drastic alterations due to climate and land use change. In this study, I seek to quantify these alterations, using the principles of Lane’s Balance to evaluate dam impacts on river aggradation and degradation. I use historical aerial imagery to measure channel width and other geomorphic properties from the 1930s to the 2020s. Stream gauge data from the United States Geological Survey is used to construct a temporal and spatial hydrologic understanding of the Des Moines River during this time period. I find that channel width is increasing significantly, driven by both the trapping of sediments by dams and the climate-driven increase in annual mean flows. These width increases are variable spatially, with the inter-dam reach widening slower than the reach downstream of both dams. These results demonstrate the control of other factors such as climate and land use on the geomorphic changes seen downstream of dams, illustrating the importance of considering regional characteristics of watersheds in geomorphic analysis.