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

这一快速反应研究项目将研究2011年8月下旬新英格兰中部飓风艾琳洪水的地貌特征，以记录佛蒙特州中部一系列流域的区域地貌响应，并测试航道对飓风艾琳洪水的响应方式以及航道可能恢复的方式，以建立洪水前的平衡条件。2011年8月28日至30日的洪水，超过了新英格兰无数小流域(面积高达50公里)和大流域(面积高达1,400公里)上USGS长期量测的最大流量，尤其是在佛蒙特州中东部，那里的峰值流量接近甚至超过了估计500年一次的重复事件。调查人员将在2011年夏季(风暴前)在受洪灾影响地区开展紧张的实地活动，重点是区分河段规模的临界屏蔽数调整与受管制和不受管制的流域中冲积、基岩和混合河道河段支流的泥沙输入。这些地点的数据提供了一个强大的基线数据集，用于确定现有边界条件结合洪水功率、泥沙通量和流域结构(包括山谷限制和支流输入)如何限制或加强河道和洪泛区对大洪水的反应。这些实地数据将通过详细的图像分析和利用地理信息系统进行的分析加以补充。调查人员还将检查具有不同沉积物包的大量岸上存款。他们将使用放射性沉降物铅-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示物，并测试以下假设：具有显著放射性核素活动的岸上沉积物代表从与邻近河道相连的山坡输送的沉积物，而缺乏放射性核素活动的岸上沉积物来自侵蚀的河岸(这些是缺乏沉降物活动的“死”沉积物)。这项计划将加深对大洪水地貌调整的规模和性质的基本了解。该项目将捕捉一系列冲积环境中对渠道响应的地貌控制，并评估岸上沉积的模式和同位素特征，以潜在地揭示沉积物的相对来源(山坡与渠道岸)。该项目的成果将有助于指导州和联邦机构未来的洪灾缓解工作，并将为理解将影响河流恢复工作的自然过程提供宝贵的新见解。

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.