Vermont and Colorado as case studies for flood hazards

Catastrophic floods in 2011 in Vermont and 2013 in Colorado devastated many communities. While flood waters were the highest in recorded history, much of the damage done by these floods was not related to inundation by flood water, but instead caused by abundant erosion and sedimentation.

These floods provided a rare opportunity better to understand controls on the locations of these different hazards.

The Geological Society of America (GSAreports that in their study forGeology, John D. Gartner and colleagues explore the effects of downstream increases and decreases in stream power, which are linked in part to variations in river slope constrained by underlying geology. A physics-based relationship indicates that river reaches are susceptible to erosion, such as landslides and bank failures, where stream power increases in the downstream direction. Conversely, river reaches are prone to floodplain sedimentation where stream power decreases in the downstream direction, because the river cannot carry the load delivered from upstream.

These predictions are compared with observed locations of erosion and sedimentation along four rivers severely affected by these floods. Gartner and colleagues’ analysis successfully predicts river channel and floodplain responses in almost 90 percent of cases studied. This direct field evidence highlights the potential role of downstream changes in stream power in connections between river channels and laterally-adjacent banks, slopes, and floodplains.

— Read more in John D. Gartner et al., “Gradients in stream power influence lateral and down-stream sediment flux in floods,” Geology (7 October 2015) (doi: 10.1130/G36969.1)

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