Understanding Ice Processes on the Susitna River, Alaska

The Alaska Energy Authority (AEA) is currently in the study phase of a long and complex federal licensing process under the Federal Energy Regulatory Commission (FERC) for the Susitna Watana Hydro Project. The Proposed Study Plan, filed with FERC in July 2012, included 58 individual studies that cover everything from geology and soils to water resources, fish and aquatic resources, wildlife, recreation, subsistence, and transportation. The integrated studies will help determine the impacts of the proposed hydropower operation on the Susitna River basin. The development of hydropower on a cold region river like the Susitna entails significant changes to the natural hydrologic cycle as well as the ice regime of the river. The Ice Processes on the Susitna River Study was designed to provide an understanding of the existing ice regime, how the river freeze-up and breakup processes progress over the October to May ice season. This paper describes the existing freeze-up processes, ice cover progression, ice cover changes, and breakup dynamics but also discusses the variability of these natural conditions. The expected changes to the ice regime due to the proposed Susitna Watana hydropower operation include later freeze-up, higher flows during the winter, and earlier but more controlled breakup. These changes are discussed along with how they could affect other resources along the river.