THE STUDY OF RIVERINE MORPHOLOGY IN MULTIPLE TIME SCALES, PELLY RIVER, YUKON TERRITORY, CANADA

Understanding river stability in a system with minor human influence is necessary to fully understand the impact of climate change in a natural environment. The Pelly River is a sub-arctic river draining 49,000 Km² upstream of Pelly Crossing located at 62^o 40' 5” North, 136^o 34' 9” West, Yukon Territory, Canada. The subset of the floodplain between the Ross River and Faro provides a unique opportunity to examine a natural system in multiple time scales. Field mapping of the preserved remnants of the 1,200 B.P. White River Ash from Mt. Churchill and pedologic analysis of the Pelly River floodplain together indicate floodplain stability on a millennial scale. In contrast, recent dendrochronologic field sampling and 50 years of aerial photos are available as a data source for assessment of short-term stability. The field portion of our study will verify the extent of preservation of White River Ash as well as provide floodplain age constraints based on pedologic and dendrochronologic sampling. Additionally, laboratory photogrammetry will provide a record of river morphology within this century. Initial mapping of White River Ash indicates that despite areas of localized channel change between Ross River and the Orchay River confluence (upstream reach), the Pelly River has generally remained stable or undergone approximately one meter of deposition, whereas between the Orchay River confluence and Faro (downstream reach) the river has undergone significant change. Short-term channel change in the latter areas appears to occur both as meandering and channel avulsion. Preliminary channel stability patterns appear to be related to glacial and alluvial fan deposits. As environmental stability emerges as an increasing global concern, this study will help to provide a baseline of natural river stability to accurately assess the impact of future climate change.