PPL Montana Rainbow Dam Redevelopment Fact Sheet

Company: PPL Montana, Billings.

General Contractor: Walsh Construction Co., Chicago

Project cost: Approximately $230 million, paid by PPL.

Capacity: A single 62-megawatt unit will help provide more clean, renewable energy for the people of Montana. It will replace aging units, installed between 1909 and 1930, which have a combined capacity of 37 megawatts.

Perspective: The new unit will be big enough to power about 45,000 homes.

New powerhouse: A concrete paneled structure, about 160 feet long and 80 feet wide, will be about 200 feet downstream of the old powerhouse.

Downstream Fish Passage: The large single hydro turbine runner, which looks like a ship propeller in a vertical position, will offer wider flow passages and fewer rotating surfaces, making it easier for fish to pass through unharmed. There will also be a new intake structure with an automated trash rake to remove debris and significantly reduce obstacles to fish passage.

Turbine speed: The lower rotating speed of the turbine (approximately 225-240 revolutions per minute to 133-144 revolutions per minute) will reduce turbulence, decrease fish mortality by more than 95 percent and make it easier for fish to pass through safely.

Jobs: The project will result in a peak work force of 200 jobs, paying prevailing wage, for local contractors over the next 30 months.

History: Rainbow Dam, which began operation in 1910, is 1,055 feet long and 29 feet high. Its reservoir is 4 miles long and has a storage capacity of 1,050 acre-feet. The dam is classified as a “run-of-river” project because it can generate electricity using the water that flows down the river, without the need to store additional supplies. Immediately downstream from Rainbow Dam is Rainbow Falls, which has a drop of 47 feet. Further downstream is Horseshoe Falls, with a drop of 12 feet.

About six miles northeast of Great Falls, Rainbow Dam is one of eight hydroelectric plants and one reservoir along the Missouri and Madison rivers covered under PPL Montana’s federal operating license. Through this license, PPL Montana works with state and federal agencies and private groups to implement a diverse array of environmental stewardship projects to protect habitats on or near the banks of the Missouri and Madison rivers.

Other construction/project facts:

• More than a half million tons of earth and rock will be moved during the project.
• More than 50,000 cubic yards of concrete will be poured.
• More than seven million pounds of rebar will be used.