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

这个快速反应研究项目将检查2011年8月下旬新英格兰中部艾琳飓风洪水的地貌特征，以记录佛蒙特州中部一系列流域的区域地貌反应，并测试河道对艾琳飓风洪水反应的协变方式，以及河道可能恢复建立洪水前平衡条件的方式。2011年8月28日至30日的洪水超过了美国地质勘探局长期测量的最大流量，在新英格兰的无数小流域（面积达50平方公里）到大流域（面积达1400平方公里），尤其是在佛蒙特州中东部，一些地方的峰值流量接近甚至超过了估计的500年复发间隔事件。研究人员将在2011年夏季（风暴前）洪水影响地区开展激烈的野外活动，重点区分冲积、基岩和混合水道流域支流沉积物输入的临界盾牌数的河段尺度调整。来自这些地点的数据提供了一个强有力的基线数据集，用于确定现有的边界条件如何与洪水功率、泥沙通量和流域结构（包括河谷约束和支流输入）相结合，限制或增强河道和洪泛区对大洪水的响应。将利用地理信息系统对这些实地数据进行详细的图像分析和分析。调查人员还将检查具有不同沉积物包的重要河岸沉积物。他们将使用沉降放射性核素铅-210（半衰期为22.3年）和铍-7（半衰期为53.4天）作为沉积物来源的指标，并检验具有显著放射性核素活动的岸上沉积物代表连接到相邻通道的山坡上的沉积物，而缺乏放射性核素活动的岸上沉积物来自侵蚀的河岸（这些是缺乏放射性沉降活动的“死亡”沉积物）的假设。该项目将加强对大洪水地貌调整的规模和性质的基本认识。该项目将在一系列冲积环境中捕获对河道响应的地貌控制，并评估河岸上沉积物的模式和同位素特征，以潜在地揭示沉积物的相对来源（山坡与河道）。该项目的结果将有助于指导州和联邦机构未来的防洪工作，并将为理解影响河流恢复工作的自然过程提供有价值的新见解。

This rapid-response research project will examine the geomorphic signature of the Hurricane Irene flooding in late August 2011 in central New England to document the regional geomorphic response across an array of watersheds in central Vermont and test the covariant ways that channels responded to Hurricane Irene flooding and the way channels may potentially recover to establish pre-flood equilibrium conditions. The floods of August 28-30, 2011, exceeded the largest measured discharge at longstanding USGS gages on innumerable small (up to 50 km-square in area) to large (up to 1,400 km-square) watersheds across New England, but especially in east-central Vermont, where peak discharges in places approached and even exceeded estimated 500-yr recurrence interval events. The investigators will build on an intense 2011 summer (pre-storm) field campaign in the flood-affected region that focused on differentiating reach-scale adjustments of the critical Shields number to inputs of sediment at tributaries in alluvial, bedrock, and mixed-channel reaches in regulated and unregulated watersheds. The data from these locations provide a strong baseline dataset to use in determining how extant boundary conditions in combination with flood power, sediment flux, and watershed structure (including valley confinement and tributary inputs) limit or enhance stream channel and floodplain responses to large floods. These field data will be augmented with detailed image analysis and analyses employing geographic information systems. The investigators also will examine significant overbank deposits with distinct sediment packages. They will use the fallout radionuclides lead-210 (with a half-life of 22.3 years) and beryllium-7 (with a half-life of 53.4 days) as indicators of sediment sourcing and test the hypothesis that overbank sediments with significant radionuclide activities represent sediment delivered from hillslopes connected to adjacent channels while overbank sediments lacking radionuclide activities come from eroded streambanks (with these being "dead" sediment lacking fallout activity).This project will enhance basic understanding of the magnitude and nature of geomorphic adjustments to large floods. The project will capture geomorphic controls on channel responses across an array of alluvial settings and evaluate the pattern and isotopic signature of overbank deposits to potentially reveal the relative sourcing of sediment (hillslope vs. channel banks). Results from this project will help guide state and federal agencies in future flood mitigation efforts and will provide valuable new insights for understanding natural processes that will impact on river-restoration efforts.