Paleohydrological Assessment of Extreme Flooding Events

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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.