Erika L Wertz* - University of Minnesota
Scott St. George - University of Minnesota
Joseph D Zeleznik - North Dakota State University
Severe flooding along the Red River of the North is a recurring hazard that affects thousands of people and causes major damages to local communities in Canada and the United States. The 1997 flood caused nearly 5 billion USD in damages and the 2009 flood set a new record for peak stage near Fargo, North Dakota. Within the United States, instrumental records of river stage began in 1897 and are not adequate to determine whether the recent spate of severe floods is unusual. In Canada, the flood history of the downstream portion of the Red River has been extended back to the middle of the 17th Century using anatomical tree-ring signatures ('flood rings') in bur oak (Quercus macrocarpa Michx.). In this study, we collected tree-ring samples from nearly 200 bur oak at 10 sites between the headwaters and the Canada-US border to test whether the same methods could be used to identify past floods in North Dakota and Minnesota. We observed anatomical anomalies in rings associated with some major floods, particularly 1950, but the degree of abnormality present in these rings ranged from obvious to very subtle. We have not yet identified anatomical signatures caused by flooding in either 2009 or 2010. Because not all known floods are associated with obvious signatures, it is possible that the occurrence and character of flood rings is influenced by other factors such as tree age or the timing of inundation.??