The relative magnitude of extreme Holocene paleofloods in the United States

Authors: Amanda M. Hefner*, University of Minnesota, Scott St. George, University of Minnesota
Topics: Paleoenvironmental Change, Hazards, Risks, and Disasters, Biogeography
Keywords: paleoflood, paleoflood hydrology, natural hazards, floods, flood magnitude, earth science, paleoenvironmental change, paleoenvironment, flooding
Session Type: Poster
Day: 4/5/2019
Start / End Time: 3:05 PM / 4:45 PM
Room: Lincoln 2, Marriott, Exhibition Level
Presentation File: No File Uploaded

Paleofloods, or past floods that occurred without being recorded by direct hydrological measurement or human observation, can tell us about older, and often much larger historic flooding events than those of the instrumental record. The instrumental record typically only extends back as far as a century, and is often the primary data used in flood risk assessment. In our research, we report the distribution, magnitude and timing of extreme paleoflood events in the United States during the Holocene in order to create a long term assessment of flood patterns. We created a synthesis of 14 paleoflood case studies on river systems in the U.S spanning all available proxy records. Nine out of 20 paleoflood records were derived from slackwater deposits, while four fluvial sediment and one stratigraphic record provided the foundation for the others. Paleoflood studies considered for this analysis must have reported flood magnitude, and must have taken place on a river system during the Holocene in the continental United States. We conducted a statistical analysis documenting each event’s location, magnitude and temporal occurrence. Our data shows that in the majority (12 out of 14) studies, Holocene paleoflood events are larger than the largest flood on record reported at the nearest stream gage. In extreme cases, paleoflood events can be up to 12 times larger than the observed flood of record. These results indicate that information reported in paleoflood studies can be both useful, and important in generating information about possible extreme flooding events.

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