Walsh Wins $230M Rainbow Dam Upgrade

October 2009

Walsh Construction has been hired to oversee a $230 million upgrade to 99-year-old Rainbow Dam, which will almost double its electricity output while reducing threats to fish. The dam harnesses the flow of the Missouri River six miles northeast of Great Falls and turns it into power. As part of the complex project, a new 80 FT by 160 FT powerhouse will be constructed 200 feet downstream from the existing powerhouse, which is next to the 1,000-foot long, 29-foot high dam. It will house a single turbine that will produce 62 megawatts of electricity - enough to power 45,000 homes. The existing powerhouse contains eight turbines installed between 1909 and 1930 and produces 34 megawatts.

In addition to doubling the electricity output, the upgrade is expected to improve fish mortality rates by 95% by giving them a greater chance of making it through the turbine. Blades on the new turbine are larger, spread farther apart, and rotate more slowly - 133 to 144 revolutions per minute as opposed to the 230-rpm blades in the old powerhouse.