RAPID: Quantifying the Geomorphic and Sedimentological Responses to Dam Removal

随着人们越来越意识到大坝对生态的严重影响，公众对拆除大坝的兴趣也越来越大，尤其是有人估计，美国现有的7.5万座大坝中，有许多将在几十年内达到使用寿命。拆除大坝是生态改善的一个重要选择，但仍有几个悬而未决的问题，如泥沙路线的具体情况、河道与洪泛平原之间的连通性，以及拆除大坝前后地貌调整的类型和幅度。即将拆除的位于新罕布什尔州南部Ashuelot河沿岸的Swanzey大坝为测试和改进泥沙通量和河道调整的预测模型以及指导河流恢复科学的未来发展提供了难得的机会。大坝的拆除本质上是沉积物的一点释放，在空间和时间上是离散的，并在自然河流中提供了实际规模的实验。达特茅斯学院地学系的Francis Magilligan教授将结合传统和创新的实验室技术，包括航空激光雷达分析和使用同位素（铍-7和铅-210）作为沉积物示踪剂和计时器，收集拆除水坝前后的地貌和沉积学数据，以量化生物物理条件的变化。本项目收集的数据将用于推进在坡度、河道形成流量、粒度、泥沙通量和河道宽度等协变参数下河道平衡调整的长度和时间尺度的定量建模。这项研究将有助于了解河流响应和从扰动移除中恢复过程中沉积物的运输和储存，特别是河道和洪泛区之间的相互作用。这些地貌信息将揭示河流达到新的平衡条件的途径，并将进一步证明与这些调整相对应的关键过程。除了推进河流恢复的基础科学，这项研究的结果将被主要利益相关者和机构利用，以推进正在进行的河流生态区域研究。该项目的结果将进一步为管理人员和科学家提供信息，并将有助于指导全国的恢复工作。随着美国各地即将拆除的众多水坝，这些结果也将为预测河道恢复的自然过程提供重要模板，并将进一步为区域河流恢复工作建立基线条件。

The growing awareness of the acute ecological impacts associated with dams has resulted in increasing public interest in their removal, especially as some estimates indicate that many of the existing 75,000 dams in the U.S. will reach the end of their operational lives within decades. Dam removal represents one important option in ecological amelioration, yet several unanswered questions remain about the specifics of sediment routing, the connectivity between the channel and the floodplain, and the type and magnitude of geomorphic adjustments above and below removed dams. The imminent removal of the Swanzey Dam along the Ashuelot River in southern New Hampshire provides a rare opportunity to test and improve predictive models of sediment flux and channel adjustments and to guide the future development of river restoration science. The removal of the dam is essentially a point release of sediment, discrete in space and time and provides an actual-scale experiment in a natural river. Professor Francis Magilligan from the Department of Geography at Dartmouth College will use a combination of traditional and innovative laboratory techniques, including aerial lidar analysis and the use of isotopes (Beryllium-7 and Lead-210) as sediment tracers and chronometers, to collect pre- and post-dam removal geomorphic and sedimentological data to quantify changes in biophysical conditions. The data collected in this project will be used to advance quantitative modeling of the length and time scale of channel equilibrium adjustments in the covariant parameters of slope, channel forming flows, grain size, sediment flux, and channel width following dam removal.This research will contribute basic knowledge on sediment transport and storage, especially the interaction between the channel and floodplain, during river response and recovery from the removal of a disturbance. This geomorphologic information will reveal the ways that streams attain new equilibrium conditions and will further demonstrate the key processes corresponding with these adjustments. In addition to advancing the science fundamental to river restoration, the results of this research will be leveraged by key stakeholders and agencies to advance ongoing regional studies on riverine ecology. Results from this project will further inform managers and scientists and will help guide restoration efforts nationally. With the upcoming removal of numerous dams across the U.S., these results will also provide an important template for predicting the natural processes of channel recovery and will further establish baseline conditions for regional river restoration efforts.