Skagway’s rockslide mitigation report shows significant progress

Skagway’s rockslide mitigation project on the hillside above its largest cruise ship dock is going so well that geotechnical engineers expect the dock to be safe enough for two ships to use it next season. KHNS’ Mike Swasey reports.

During Skagway’s November 17th borough assembly meeting, Rex Whistler from the Geotechnical Engineering firm Shannon and Wilson gave a positive assessment of the mitigation project currently underway above White Pass and Yukon Route’s Railroad Dock. 

“It’s a monster of a rockslide, there’s no denying that. But it is going really, really well,” Whistler said.

Last week the subcontractor Rock Supremacy, started drilling into larger rocks, placing charges inside, and detonating them in order to break apart large rocks that need to be sent down the slide area. Originally, the plan only called for workers to use pry bars and airbags to move those rocks.

The team will also remove the mid-slope bump that launches falling rocks outward from the hillside on their way down the slope. Once this scaling process is complete, a series of attenuators will be installed after a break for Christmas.

The attenuators are like large nets, there will be one installed mid-slope and another installed near the bottom of the slide area. A mesh netting will be used at the top of the slope. These will help slow any rocks that fall and force them underneath the dock.

Whistler said that the project will provide 99% protection which is the standard highway projects use before considering roadways safe. But 99% isn’t sufficient to fully open up the Railroad Dock. The operational plan for cruise passengers is to allow busses to travel across the dock using spotters to assist them. The typical time it takes for rocks to reach the dock area during a fall is 10-20 seconds, which Whistler said will give those busses enough time to complete their journey through the slide area without being hit by any rocks that begin falling while the vehicles are in transit.

If White Pass signs off on the plan, the busses will transport passengers from the larger cruise ships, which can include post-Panamax-sized ships with up to 4,000 passengers. Those ships will dock at the aft, or south berth of the Railroad Dock, while smaller ships will use the forward berth and tender passengers ashore. 

This plan does not address the large monolith locals call the Death Rock of Doom. Shannon and Wilson have renamed it Ship Rock. Earlier this year alarms were sounded as measurements showed that rock is separating from the hillside at a rate of 2 and ½ inches per year. This mitigation project does not address that threat.

The assembly unanimously approved $70,000 to install a modern monitoring system for that monolith.

The final step in the mitigation project will be a live test of the system in the spring in which they will send rocks down the slope to make sure the attenuators work as planned.