Chugach replacing towers downed by flooding at the Susitna River
Chugach Electric Association is in the process of repairing the damage done when Susitna River flooding took down transmission line towers last August. The utility and its contractors are on site installing six new transmission towers designed to withstand future floods and shifting river channels.
Between mid-August and early September 2006, flooding on the Susitna River eroded the bases of two 70-foot aluminum towers that subsequently toppled into the river. The towers had stood on an island, well back from the bank of a normally quiet side channel of the river known as Dynamite Slough. Heavy, prolonged rains in the Susitna drainage caused the river to rise rapidly and quickly eat away the banks of the island as the slough became one of the main channels of the river. After losing the first two towers, Chugach crews devised a clever way to save a third threatened structure by moving it to a temporary foundation 200 feet back from the river.
Governor Murkowski declared the Susitna flooding – which also damaged roads, bridges, homes and other structures – a disaster. That declaration was followed by the event being declared a federal disaster. Chugach has filed for FEMA funding for its damages, but that claim has not yet been finalized.
The towers support three separate transmission lines that parallel each other and carry power from Chugach's Beluga power plant to a substation at Point MacKenzie. Two of the lines are energized at 230 kilovolts, while the third is a 138-kv line.
The temporary repairs done after last summer's flooding allowed Chugach to keep the lines in service while waiting for cold weather that would allow heavy equipment to be moved to the site across frozen ground and rivers.
The current project began earlier this winter with the construction of an ice road from Point MacKenzie to the Susitna River. Once heavy equipment and materials were on site, crews drove piling 80 feet deep to anchor the new towers. Each pile is 1-inch-thick steel pipe 4 feet in diameter. Two piling support each of the new steel towers.
The towers themselves stand 90-105 feet tall, with one tower for each transmission line on either side of the river channel. The island is home to three of the new towers, with the others on the west bank of the river. Knowing the river's history of shifting its channels, forming, eroding and reforming islands, the new towers and their deep foundations have been designed and constructed to ensure they will remain strong and in-service even if someday they are standing in the middle of the river itself.
Chugach expects the project will cost between $5-6 million and be completed by early March.
For the press releases and photos of the flooding and downed towers from last summer, go to www.chugachelectric.com.
Chugach has about 620 megawatts of generation capacity available to ownership and contracts. It is the largest electric utility in Alaska, providing power for Alaskans throughout the Railbelt through retail, wholesale and economy energy sales.
EDITORIAL NOTE: This project was completed on March 4, 2007.