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

该项目将记录与新英格兰中部一系列流域的艾琳飓风洪水有关的河岸和洪泛区侵蚀和沉积模式。流域对极端洪水的响应是河流地貌学、水利工程和洪水风险管理领域长期以来的研究热点。先前的研究表明，仅凭降雨量、峰值流量和沉积物输运率并不能完全解释洪水塑造景观的能力。最初试图更全面地概括提高洪水地貌有效性的因素受到阻碍，部分原因是关注单一流域内的洪水影响。通过使用单位水流功率，在发展极端洪水对地貌影响的广义比较因果分析方面取得了一些成功。研究人员将探索这样一个概念，即除了单位水流功率的阈值外，河道对极端洪水的响应与主要形态变化（如河道重构或拓宽）和细粒沉积物的运输和沉积有关，对个别河段的地貌环境很敏感。结合先前收集的基线数据，他们将收集的数据将提供一个难得的机会来测试这一新的框架，以预测河段和区域尺度的地貌控制对大洪水的反应和恢复。研究人员将从迅速扩大的现成地理空间数据资源（如航空图像、高分辨率地形）中，推导和绘制与河流过程（如水流功率）相关的成熟度量的流域尺度关系。为了深入了解河道形态变化如何影响细沉积物动力学，他们将使用短寿命沉降放射性核素7Be和210Pb来确定细沉积物沉积的纵向变化。他们将把重点放在细沉积物动力学上，因为它对河岸生态过程和颗粒结合污染物的运输和命运有良好的控制。项目结果将有助于制定基于过程的指标，以评估流域在河道形态和细沉积物沉积方面从深刻扰动中作出的反应和恢复。该项目开发了一种简单但可靠的实地测试方法，使土地管理者能够使用现成的GIS数据集来预测和规划未来的河道变化，因此具有变革性影响的潜力。这些结果将有助于指导州和联邦机构未来的防洪工作，并为河流恢复的自然过程提供模板。参与该项目的本科生和研究生将受益于参与专业发展机会，如达特茅斯学院的GK-12计划及其学习促进中心，以及通过教育推广计划，如地区中学的青少年科学咖啡馆。

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.