Next Meeting January 27th in Boulder

Our next speaker will Dr. John Moody from the US Geological Survey. He will be giving a talk titled:

30+ Years of Geomorphic Observations on Powder River in Southeastern, Montana

Abstract:

Powder River heads in the Big Horn Mountains of Wyoming and flows north to the Yellowstone River in Montana. For the most part, it is a meandering and muddy river with suspended-sediment concentrations during annual floods, ranging from 1,000 to 50,000 mg/L transported in a channel about 50 m wide and 2-3 m deep. Powder River carries, on average, 2-3 million metric tons of suspended sediment per year, but has not been subjected to any major human modifications. It is a “natural river”, and, as such, is an ideal mega-laboratory in which to study some of the natural geomorphic processes that create and destroy fluvial features over several different time scales.
Extreme floods with recurrence intervals on the order of 100 years have modified essentially all features ranging from large-scale terraces down to floodplains, channels and point bars. Partly because Powder River flows north, it can have four types of annual floods (ice-break up, snowmelt, flash, and fall floods). All four types of floods create, alter, and destroy floodplains, channels, and point bars. All this geomorphic activity is intricately linked to the vegetation that ranges from sedge near the water’s edge, to willows on the point bars, and cottonwoods on the floodplains and terraces. Observations of these geomorphic processes provide insights into the behavior of a vanishing “species”, the “natural” (i.e. unengineered) river, and these insights, therefore, become important as a guide to future multifaceted efforts to restore rivers to their natural condition.