Not Many were Awake in Juneau when the Lights Flickered in the early morning hours of a rainy April 16, 2008. At around 3:30 a.m., Alaska Electric Light & Power Co.'s (Juneau, Alaska, U.S.) backup diesel generators spun to life. This meant only one thing: something had tripped the Snettisham 138-kV line connecting Juneau to the primary hydroelectric power source at the mouth of the famous Speel Arm waterway.

The Snettisham 138-kV line runs 40 miles (64 km) from Juneau to the 78-MW Snettisham hydroelectric plant. It traverses steep slopes under towering mountains. In the winter, the mountains collect snow from massive storms passing through. In the spring, temperatures fluctuate, transforming the snowpack into dangerous slabs that can release when they become too heavy. Spring means avalanche season.

MONSTER PART ONE

As soon as there was a break in the storm the morning of April 16, AEL&P personnel hopped into a helicopter to fly the line. Behind a rainy windshield, they flew south over the Taku Inlet and along the coastal mountain range, looking for the cause of the line fault. The storm had dumped a mix of heavy snow and rain, causing thick slabs on the lower- to mid-elevation mountain slopes.

Turning north up the Speel Arm waterway, they spotted flotsam in the fjord, swollen from a gnarled mixture of snow, trees and earth, the source hidden from view around a jutting ridge. Rounding the bend, however, they saw the massive destruction. Where once the Snettisham-to-Thane 138-kV transmission line had stood, there was nothing but a scarred avalanche path.

The monster slide — categorized as the most destructive class R5 D5 avalanche, 10,000 ft (3 km) wide and capable of wiping out forests and gouging the landscape — had crashed down the mountain, destroying self-supporting angle Structure 4/6, damaging the arms of two adjacent towers (Structures 4/4 and 4/5), damaging a guyed three-pole structure (Structure 3/5) and pulling an adjacent guyed delta structure (Structure 3/4) down with it. Later in the morning, a second major slide completely destroyed Structure 3/5.

When the snow finally settled, the powerful slides had knocked out three transmission towers, damaged another two and wiped out service from Juneau's primary hydroelectric power plant. As a backup, AEL&P had aged-but-proven diesel generators. Though the lights had not gone dark, it was costing AEL&P almost a US$1 million in diesel fuel every three days because of the record-high diesel prices. Getting the line back in service as quickly as possible was essential.

RECONSTRUCTION BEGINS

After the outage, AEL&P called T&D consultant POWER Engineers Inc. (Hailey, Idaho, U.S.), utility line contractor City Electric (Anchorage, Alaska), several local barge operators, Bill Glude and his colleagues at Alaska Avalanche Specialists, and others into a conference room — later dubbed the “war room” — at AEL&P offices, with Allen MacPhail of Cabletricity Connections Ltd. (Vancouver, Canada) on speakerphone. The goal was to identify known, unknown and possible solutions.

During the meeting, the team reviewed hours of maintenance video taken of the line, examined hundreds of photographs and pored over piles of record drawings to identify possible restoration options. The team considered everything, putting durations and values to every possible scenario, and evaluating them for constructability, avalanche danger, meteorological conditions and material availability.

For an entire day, the team brainstormed, systematically assessing every option: routing the transmission line to the upper elevation slopes above the existing line; temporarily routing the line on barges in the fjord; installing submarine cable for the damaged area; spanning the bowls where the worst slides occurred (thereby eliminating the need to replace towers in the most avalanche-prone locations); hauling in and setting up emergency restoration towers; or replacing towers and structures on the same locations, once crews could clear snow and debris to find anchors and foundations.

Luckily, there was enough information to determine the exact locations of the downed towers. The slide had occurred close to the old Snettisham work yard, which meant AEL&P had a nearby staging location for personnel, material and equipment for whichever restoration scenario was pursued. This meant the fastest and least-expensive solution would be to put new towers in the exact same locations using the same designs; the technical data, materials and qualified labor were all available to make it happen.

Within days of the disaster, POWER and AEL&P put together preliminary materials lists and began making calls to order necessary line hardware, and conductor and tower materials from structure suppliers in the United States and Mexico. Meanwhile, AEL&P hired City Electric to prepare for a fast-track repair of the line. Crews began digging out and prepping the staging area at Snettisham, which was still buried under 10 ft (3 m) of snow, and inventorying materials and equipment at the Juneau yard.

Loaded with tower parts, heavy equipment, fuel supply and camp supplies, the first barge of materials launched on April 19 for the 12-hour one-way trip to Snettisham. Alaska Avalanche Specialists' Glude and his team equipped linemen with avalanche safety belts (small electronic transponders) from RECCO (Lidingö, Sweden) and taught them how to work in avalanche conditions while they monitored the slopes. Crews cleared and caught-off downed cable to protect still-standing structures. In some cases to clear conductor, crews had to use a .300 Winchester Magnum to drop the porcelain insulators.

After all the conductor was either tied off or removed, City Electric began the slow process of uncovering foundations and anchor points for Structures 3/5 and 3/4 by lighting 55-gal (208-liter) barrels loaded with charcoal where the team thought anchor points were located. City Electric even flew in two mini-excavators to help dig out the snow to expose foundation and anchor locations (there were 15 such locations alone on Structure 3/5).

Concurrent with tower and anchor snow excavation, crews at Snettisham began assembling towers, fabricating some tower members and hardware assemblies from parts found at the two yards. The towers have between 800 and 900 different parts, so rebuilding was a minor miracle, especially considering nearly all of the parts were pulled from existing material in AEL&P's yards — only a few pieces had to be newly fabricated. Crews installed guyed delta Structure 3/4 on May 18 without incident using a Bell 214 helicopter operated by TEMSCO Helicopters (Juneau).