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Restoration continues at Minnesota's largest hydropower project

Minnesota Power is hoping to partially reopen the state's largest hydropower project by the end of the year, marking the end of a year-long restoration project necessitated by flooding in June 2012.

Record rainfalls caused flash flooding and river flows 40% above previous record flows, the utility said, damaging six turbines, topping Thomson reservoir and breaching a portion of an earthen dike at the 72-MW project's forebay. Washed out roads and mudslides also limited access to the powerhouse, making rehabilitation of the Thomson project difficult.

Minnesota Power estimated repairs to the forebay to be US$25 million, with work expected to begin in August when sheets of steel will be placed into the ground to reinforce around 3,000 feet of rebuilt earthen embankment. A new, permanent concrete spillway will also be installed at the breach site.

The company said it also expects to invest an additional $35 million for improvements at both Thomson and the other three hydropower projects it operates along the St. Louis River.

"Thomson is the very heart of our hydro system and has served our customers with low-cost renewable energy for more than 100 years," Minnesota Power chief operating officer Brad Oachs said. "Investing in repairs and other improvements to strengthen the system against future flood events will position Thomson as a reliable and cost-effective, emission-free resource for the next 100 years."

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