Rascally bridge #339 on the Copper River Highway is raising new questions for state of Alaska engineers.
Due to a river depth of almost 70 feet, fast-moving currents and access challenges, engineers find themselves challenged in determining how to construct a replacement for bridge #339 that failed two years ago this summer. As a result, project engineers have decided to hire a specialized bridge construction consultant.
"We're not sure how to remove the existing bridge or construct the new bridge," said Russell Johnson, an Alaska DOT engineer working on the project.
The fundamental questions that need to be answered are how to transport equipment and materials to the site and across the river.
Fluctuating winter temperatures and snow depths rule out a seasonal ice road. Extreme snow and wind challenge winter construction.
Bridge demolition and construction requires access to the far end of bridge #339. However, the embankment has completely eroded away.
Construction of a temporary bridge adjacent to the existing bridge is a technique often used in bridge replacement projects. However, this may not be technically feasible due to conditions at the site.
Engineers suspect that barge access to the site for transport of materials and equipment would be hindered by shallow depths of the highly braided delta. They also believe the deep and fast-moving river current would make pile placement and driving operations challenging. Engineers are also unsure if a temporary floatable bridge could withstand the fast-moving river current.
"These uncertainties create high risks that are correlated with high costs," said Johnson.
As a result, the timeline for design and construction has been pushed back.
Word of the new delay has several local business owners concerned about the impact to Cordova's tourism economy. If the annual spring Anchorage Sportsman Show is any measure, their concerns are justified. Approximately 50 percent of visitors to Cordova's booth were aware of the Copper River Highway closure, asking when access to Child's Glacier would re-open.
"The current schedule is to have the bridge design completed the winter of 2015-16. If things stay on track and funding becomes available, the earliest construction could begin would be the summer of 2016," said Johnson.