CHANNEL STABILITY IN THE PELLY RIVER BASIN, YUKON TERRITORY, CANADA

Current climate change is predicted to alter the hydrology of northern streams through changes in precipitation and permafrost extent. The complex interactions expected among these hydrologic changes and fluvial processes make channel change and rates of change difficult to predict. Thus cataloging recent vertical and horizontal channel change is needed to assess current and future impacts of climate change on stability of northern rivers. This study uses dendrochronology, gauge data, and remote sensing to investigate vertical and horizontal channel change over last century in the Pelly River basin, Yukon Territory, Canada. The hydrology of the Pelly River system is snow-melt dominated, with little to no glacial contribution. The Pelly River and its tributaries have been gauged at 8 sites for periods of 6 years to 55 years since 1952 by the Water Survey of Canada; of these sites, 3 are still active. These gauges measure discharge for drainage areas ranging from 997 square km on the South MacMillan River at Km 407 on the North Canol Road, to 49,000 square km on the Pelly River at Pelly Crossing. Maximum ranges of 0.2 to 1.9 meters were calculated for average bed elevation at individual gauges over the 6 to 55 year period of record. Dendrochronologic study of bars near the gauge on the Pelly River below Vangorda Creek (22,100 square km) and near the gauge on the Ross River at Ross River (7,250 square km) indicate that Pelly River bars experience migration and avulsion which reworks substantial portions of bars in as little as 30 years, whereas bars on the Ross River have extensive areas near the channel that are over 100 years of age. Preliminary remote sensing results indicate vegetation communities on many bars and terraces are dominated by spruce vegetation, suggesting these areas have been stable for decades to a century. These results suggest that most of the Pelly basin is not currently experiencing climate change driven channel changes.