Paleohydrological Assessment of Extreme Flooding Events

该研究项目将考察利用古环境记录识别大洪水的程度，从而延长洪水识别的历史时期，并增强分析地表水文、气候和其他自然和人类相关变量之间关系的能力。研究人员将把重点放在分隔明尼苏达州和北达科他州的北部红河上，他们将从长寿树木的年轮序列、历史建筑的木材和冲积沉积物的亚化石原木中收集数据，以产生一个跨越过去几个世纪的综合记录。这些记录将有助于更准确地估计20世纪以前洪水的频率和规模。该项目将增加对长期影响洪水的因素的理解，替代记录提供的数据是基于仪器的洪水记录持续时间的两倍或更多。洪水记录的历史扩展对于研究不经常发生的特大洪水特别有价值。通过该项目产生的新见解可以帮助确定，随着流域自然和人为因素的变化，主要河流系统的极端洪水是否正变得越来越普遍。通过展示洪水信息的自然来源如何在主要基础设施建设之前为洪水缓解决策做出贡献，该项目将在更广泛的灾害准备领域重新定位古洪水水文学。调查人员将与美国地质调查局在达科他水科学中心的工作人员合作，利用古洪水估算来评估未来的洪水风险。项目结果将帮助那些负责管理河流的人、居民和决策者评估洪水的脆弱性，并权衡拟议的基础设施的潜在效益，比如建设一条36英里、耗资17亿美元的引水通道，该通道将重新引导法戈-穆尔黑德大都会地区周围的洪水。该项目将确定历史记载中1826年在加拿大下游发生的红河特大洪水是如何影响到这条河在美国的延伸的。在过去的二十年里，红河洪水给美国社区造成了超过35亿美元的直接损失，并刺激了近25亿美元的防洪基础设施建设或拟议建设。由于红河洪水的已知记录只能追溯到19世纪晚期，因此需要其他信息来源来估计未来严重洪水的风险。使用模拟方法，将与最近的大洪水相关的树木年轮证据与仅存在于树木年轮记录中的已知阶段和较早事件的流量进行比较，研究人员将得出早期洪水的相对规模的估计。对于那些可以追溯到19世纪早期或更早的老树，过去洪水的最大阶段将从树干上解剖异常的垂直位置推断出来。红河的新古洪水记录将使研究人员能够回答有关整个河流流域洪水同步性的问题，并评估大平原北部的洪水与当地和区域尺度上的气候变化和其他环境因素的关系。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This research project will examine the degree to which major floods can be identified using paleoenvironmental records, thereby lengthening the historical time periods over which flooding can be identified and enhancing capabilities for analyzing relationships among surface hydrology, climate, and other natural and human-related variables. Focusing on the Red River of the North, which separates Minnesota and North Dakota, the investigators will compile data from tree-ring sequences of long-lived trees, timbers from historical buildings, and subfossil logs from alluvial deposits to produce a composite record that spans the last several centuries. These records will facilitate more accurate estimates of the frequency and magnitude of floods prior to the 20th century. The project will increase understanding of the factors that influence flooding over longer time periods, with surrogate records providing data for two or more times the duration of instrument-based flood records. The historical extension of flood records is especially valuable for studying very large floods that occur infrequently. New insights generated through this project can help to determine whether extreme floods on major river systems are becoming more common as natural and human-related factors change in river basins. By demonstrating how natural sources of flood information can contribute to flood mitigation decisions prior to the construction of major infrastructure, this project will reposition paleoflood hydrology within the broader field of hazard preparedness. The investigators will collaborate with U.S. Geological Survey staff at the Dakota Water Science Center to use paleoflood estimates in the assessment of future flood risks. Project results will help those responsible for managing rivers as well as residents and decision makers to evaluate vulnerability to floods and to weigh the potential benefits of proposed infrastructure, such as the construction of a 36-mile, $1.7 billion diversion channel that would redirect floodwaters around the Fargo-Moorhead metropolitan area.This project will determine how the extraordinary 1826 Red River flood documented downstream in Canada in historical accounts also affected the American stretch of the river. Red River floods have caused more than $3.5 billion in direct damages to American communities over the past two decades and have spurred the construction or proposed construction of nearly $2.5 billion in flood mitigation infrastructure. Because the known record of Red River floods only extends back to the late 19th century, other sources of information are needed to estimate the risks of future severe floods. Using an analog approach to compare tree-ring evidence associated with recent major floods with known stage and discharges of older events only present in the tree-ring record, the investigators will produce estimates of the relative magnitudes of earlier floods. For old trees that extend back into the early 19th century or earlier, the maximum stage of past floods will be inferred from the vertical position of anatomical abnormalities along the tree stem. The new paleoflood record for the Red River will enable the investigators to answer questions regarding the synchrony of flooding along the entire reach of the river and to gauge how flooding on the northern Great Plains is related to variability in climate and other environmental factors at local and regional scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.