Bedload Transport During an Extreme Runoff Event in Arctic Alaska

While spring snowmelt floods are common annually in the Arctic, rainfall generated floods are rare or at least seldom documented. Since 1999, we have documented two rainfall events in the Upper Kuparuk River where the total precipitation for each storm approached 100 mm. These two floods (July 1999 and August 2002) produced flows that exceeded the maximum snowmelt runoff by a factor of three to four. It is these large events that shape the drainage network. Passive and active tracer rocks, scour chains and pre- and post-storm surveyed cross-sections were used to quantify bedload transport. The August 2002 event mobilized the entire bed. All of the tracer rocks moved and those that were recovered after the flood traveled an average of 72.8 m, with those in pools traveling farther than those in riffles. Lateral bank erosion exceeded 10 m in many areas; the bed degraded and aggraded more than 1 m. It is estimated that 870 cubic meters of bed material passed through the study area.