"Building a Levee in the Alaska Wilderness"
The Tanana River is a beautiful, yet harsh environment in which to build a levee. The Tanana is a sand- and gravel-bedded, braided river draining approximately 20,000 square miles of mostly mountainous terrain. The river can experience a wide variety of conditions, ranging from total ice coverage during the harsh Alaska winter, to severe ice jams and flooding from spring mountain snowmelt and rains, to low placid flows in the late summer. The river braids and banks constantly are changing locations, with the convergence of channel braids creating 50-foot-deep scour holes. The thick forest alongside the river results in heavy debris in the main channel, raising potential for major debris jams at bridge piers and uncertainty in water surface elevations against the levee.
In order to protect against these severe conditions and protect the Salcha community, this project required careful risk analysis and robust design. The engineer, contractor and owner worked together to undertake a comprehensive analysis to evaluate innovative scour and erosion protection alternatives. The levee design accounted for uncertain debris and ice conditions, while the team evaluated design alternatives for construction risk and performance reliability. Design of scour protection, the levee cross section, and the levee alignment balanced balancing economics against environmental impacts.
Project construction began in July 2011 and is scheduled to be completed in summer 2014.