MILLENNIAL TO DECADAL INSTABILITY PATTERNS AND THEIR IMPLICATIONS FOR DETECTING CLIMATE CHANGE IMPACTS ON THE PELLY RIVER, YUKON TERRITORY, CANADA

Climate driven changes in snow accumulation and snow melt timing are expected to substantially alter the hydrology of northern river systems, especially the magnitude and timing of annual peaks. Given the projected impacts of climate change on fluvial processes, cataloging recent vertical and horizontal channel change is needed to assess current and future impacts of climate change on stability of northern rivers. We use gauge data to calculate bed elevation changes and the White River Ash, dendrochronology, and remote sensing to investigate horizontal channel change in the Pelly River basin between Ross River and Faro, Yukon Territory, Canada. Average vertical changes of 0.2 to 1.9 meters were calculated at gauges. These vertical changes did not demonstrate aggradation or degradation through time or in relation to flow magnitude. Mapping of White River Ash, dendrochronologic, and photogrammetric evidence gathered from selected bars between Ross River and Faro on the Pelly River indicate that some river reaches experience migration and avulsion which reworked substantial portions of the valley bottom in the last 50 years, whereas others have not changed substantially within the last 1,200 years. These results suggest that the rate of floodplain reworking is spatially variable and it is unclear how the Pelly River is responding to current climate change.