Currently, our ability to predict the flux of fine sediment at the watershed scale is limited by the precision of erosion rate estimates for the many potential sources distributed throughout a landscape as well as our understanding of the connectivity of sediment pathways during transport. In absence of a robust predictive model which can be validated by measurements of sediment fluxes and use of geochemical tracers. Predicting fine sediment yield at the watershed scale requires multiple redundant lines of information. This thesis outlines the methods used, and the data sets collected in the Root River watershed in Southeastern Minnesota, all of which are multiple lines of evidence to the sediment dynamics in the Root River. The research indicates that the Root River is a very dynamic watershed. The hydrologic regime of the watershed has shifted over the last half century. Due to this shift sediment fluxes are very dependent of the magnitude and sequence of events. Geomorphic analysis of the landforms and the use of a developed tool, TerEx, indicate that many reaches of the river have easily accessible near-channel sources of sediment. Sediment fingerprinting results illustrate that source tracer concentrations are variable across the landscape, that as a whole, upland sources are still a major contributor to the suspended sediment load, and that in some sub-watersheds near-channel sources are dominate in the suspended load. Over all the channel-floodplain exchange exerts strong control on the flux of sediment through this river system.

A better understanding of transport and deposition of fine sediment in alluvial rivers, including their floodplains, is essential for improved understanding of sediment budgets and prediction of river morphological changes. Previous work in the Root River indicates that channel-floodplain sediment exchange exerts strong control on the sediment flux of this system. In addition, improvements in agricultural practices and increases in high and low flows during the past five decades have led us to believe that sediment sources in the Root River may be shifting from uplands to near-channel sources. This thesis estimated the total amount of fine sediment contributed to the channel from near-channel sources due to the processes of lateral channel adjustment (channel migration and channel widening) using a quantitative approach based on the use of multiple epochs of aerial photographs (1930s-2010s), lidar data available for the entire watershed from 2008, and other GIS analysis. The results obtained in this thesis serve as another line of evidence to constrain a sediment budget for the Root River watershed and to improve our understanding of the sediment dynamics within the watershed. In addition, we found that the Root River presents a marked division between its lateral channel adjustment trends before and after the 1970s. We also found that while increases in flows have affected lateral channel adjustment rates throughout the entire channel network, other factors like sediment supply and riparian vegetation may be playing an equally important role.