THE DISTRIBUTION AND GEOMORPHIC IMPACTS OF LARGE WOOD FROM HIGH MAGNITUDE, DAM-ERA FLOODS

The Missouri River has historically contained extensive amounts of large wood along its banks and within its river channel. Large wood serve as important geomorphic influences, critical ecological habitats, and act as navigational hazards. Beginning in the 1950’s, the river has been regulated by large dams which limited peak flood discharges and created backwater areas near reservoirs. Over the following decades, large wood was reduced and redistributed throughout the river system as the river adjusted to the new flow conditions. In late spring of 2011, the Missouri River experienced its first major flooding event since dam emplacement. For several months, the river sustained discharge levels well above flood stage with water levels in Bismarck, ND surpassing 150,000 cfs, roughly three times the record dam level flood stage for the area (USGS stream gage 06342500). We investigated the distribution of large wood on a free flowing stretch of the Missouri River between Garrison Dam and Lake Oahe in North Dakota. Using high resolution imagery (0.4m), we plotted the spatial distribution, trunk orientations, and channel positions of large wood along roughly 120km of the river. By comparing post-flood distributions of large wood to pre-flood conditions, we aim to better understand the impacts major floods have on this critical component of river systems.