Geomorphic Response and Recovery to Hurricane Irene Floods: Characterizing Reach-Scale and Regional Controls on Fluvial Adjustments and Fine Sediment Deposition

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This project will document the pattern of river bank and floodplain erosion and deposition associated with Hurricane Irene flooding across an array of watersheds in central New England. The response of watersheds to extreme floods is a long-standing research focus in fluvial geomorphology, hydraulic engineering, and flood risk management. Previous studies demonstrated that rainfall, peak discharge, and sediment transport rates alone cannot fully explain the ability of a flood to shape the landscape. Initial attempts to more fully generalize the factors that enhance the geomorphic effectiveness of floods were hindered, in part, by a focus on flooding impacts within a single river basin. Some success in developing a generalized comparative cause-effect analysis of the geomorphic impact of extreme flooding has been achieved through the use of unit stream power. The investigators will explore the concept that in addition to a threshold value in unit stream power, the response of a channel to extreme floods with respect to major morphological changes (e.g. channel reconfiguration or widening) and fine-grained sediment transport and deposition is sensitive to the geomorphic context of individual reaches. In conjunction with previously collected baseline data, they will collect data that will provide a rare opportunity to test this novel framework for predicting reach and regional-scale geomorphic controls on channel response and recovery to large floods. The investigators will derive and map watershed scale relationships of well-established metrics linked to fluvial processes, such as stream power, from the rapidly expanding resources of readily available geospatial data (e.g., aerial imagery, high-resolution topography). To gain insight into how channel morphological changes impact fine sediment dynamics, they will use the short-lived fallout radionuclides 7Be and 210Pb to determine the longitudinal variations in fine sediment aggradation. They will focus on fine sediment dynamics because of its well-established controls on riparian ecological processes and its control on the transport and fate of particle-bound contaminants.Project results will help develop process-based metrics for evaluating the response and recovery of watersheds from a profound disturbance in terms of both channel morphology and fine sediment sedimentation. The project has potential for transformative impact through its development of a simple but robust field-tested methodology that will enable land managers to use readily-available GIS datasets to predict and plan for future stream channel changes. These outcomes will help guide state and federal agencies in future flood mitigation efforts and provide a template for natural processes of river restoration. Undergraduate and graduate students involved in this project will benefit from participation in professional development opportunities, such as Dartmouth College's GK-12 program and its Center for the Advancement of Learning, and through educational outreach programs, such as Junior Science Cafes in regional secondary schools.