Poster Winner, Gartner
Congratulations to graduate student John Gartner, in the Department of Earth Sciences, who was one of four winners of the Graduate Poster Session held recently in Alumni Hall! (Below is a summary of Gartner’s poster.)
Poster Title: Irene Landslides and Sedimentation in Vermont Rivers: Importance of Gradients in Transport Capacity
How do rivers transport sediment from the mountains to the sea? This question has implications for every species that lives in and near rivers, including humans. Hurricane Irene, as devastating as it was to so many people, provided an unprecedented opportunity to observe how rivers cut into and also bury the local landscape with sediment.
For decades, geomorphologists have measured stream power at spot locations along rivers to determine if the capacity at a point is high enough to transport sediment. Yet the stream power of rivers is seldom constant from the headwaters downstream, and this change should affect sediment transport dynamics. Specifically, if the stream power is decreasing downstream, going from high to low power along a given segment, then the river cannot carry the sediment load delivered from upstream and must deposit material. In contrast, if stream power increases moving downstream, then the river can entrain all sediment delivered from upstream and more, possibly exporting material from the riverbanks, undercutting the adjacent hillslopes, and inducing landslides. I hypothesized that river segments with decreasing stream power should exhibit widespread floodplain deposition and few landslides, and, conversely, segments with increasing stream power should exhibit abundant landslides and minimal floodplain deposition.
To test these ideas, landslides and floodplain deposits were mapped based on field surveys and aerial photos in two Vermont watersheds after Irene. Freely available digital elevation data were used to compute stream power and, more importantly, gradients in stream power on the two rivers. The hypotheses were supported by the preponderance of floodplain deposits occurring in reaches with decreasing stream power and an abundance of landslides in reaches with increasing stream power.
This novel approach to characterizing sediment transport dynamics shows that gradients in stream power can affect both the downstream and lateral mobility of sediment. In particular, decreasing downstream sediment transport capacity favors the movement of material from the river onto the adjacent landscape. However, reaches of increasing downstream capacity have an opposite dynamic, with material moving from adjacent areas into river channels. One critical broader implication is that maps of stream power gradients can be an important tool for protection and management of human infrastructure and riparian ecosystems.
poster summary by John Gartner