Repairs to Spirit Lake Outlet Tunnel underway

 Construction workers exit Mount St. Helens' Spirit Lake Outlet Tunnel Jan. 11, 2016. (Photo by Jeffrey Henon, Corps of Engineers)

Construction workers exit Mount St. Helens’ Spirit Lake Outlet Tunnel Jan. 11, 2016. (Photo by Jeffrey Henon, Corps of Engineers)


By Jeffrey Henon, Public Affairs Office

The water level at Mount St. Helens’ Spirit Lake has been controlled by a drainage tunnel since 1985. A routine inspection of the tunnel in October 2014 revealed an area where the clay-like rock had bulged upwards on the tunnel floor, reducing its height about 2.5 feet. This reduction decreases the tunnel’s flow capacity, which increases the possibility of flooding in the Toutle River Valley.

New steel ribs and a remote controlled mining robot will be used by Catworks Construction to repair a constricted section of the Mount St. Helens' Spirit Lake Outlet Tunnel Jan. 11, 2016. (Photo by Jeffrey Henon, Corps of Engineers)

New steel ribs and a remote controlled mining robot will be used by Catworks Construction to repair a constricted section of the Mount St. Helens’ Spirit Lake Outlet Tunnel Jan. 11, 2016. (Photo by Jeffrey Henon, Corps of Engineers)

The U.S. Forest Service, which owns the tunnel, and the U.S. Army Corps of Engineers acted quickly to create an interim solution. Catworks Construction, a Battle Ground, Washington-based company, was awarded the $3 million contract to repair the tunnel and began work in January.

Catworks will grind away the bulging section, about 1 mile from the tunnel exit, with a remote-controlled mining robot. Steel ribs bolted together will strengthen the tunnel walls in the affected area. The ribs are covered in shotcrete, a concrete mixture applied from a pressurized gun, to add strength and protect the ribs from corrosion.

The Corps expects repairs to be completed by late February. “We are undertaking the repairs to allow the Forest Service and the Corps time to develop a long-term solution for managing the Spirit Lake water level,” said Chris Budai, the Spirit Lake Outlet Tunnel repair project manager. “Mount St. Helens’ 1980 eruption blocked the lake’s natural outlet, which, if left blocked, could increase the flood risk for downstream communities on the Cowlitz River. Protecting the residents, infrastructure, and transportation corridors is our top priority.”