Rainbow Dam History & Community Impact
Rainbow Dam is an eight-unit hydroelectric plant on the Missouri River, about six miles northeast of Great Falls. The original units have a total generating capacity of 37 megawatts. (One megawatt can satisfy the average energy needs of 750 households.)
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.
Rainbow Dam is one of eight hydroelectric plants and one reservoir along the Missouri and Madison rivers covered under PPL Montana’s Project 2188 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.
For example, PPL Montana contributed $100,000 toward the completion of the Lewis and Clark Overlook and the construction of both the Rainbow and Crooked Falls overlooks near Rainbow Dam. In 2003, the company contributed $150,000 for construction of a pedestrian-bike trail from Rainbow Dam to the Sulfur Springs Trailhead.
The Sulfur Springs Trailhead was made possible in part through a $100,000 contribution from PPL Montana, which continues to contribute $10,000 a year toward operation and maintenance expenses at the site. The company retains and manages as a natural area the lands it owns on the north shore adjacent to the Rainbow reservoir.
Rainbow Dam is part of the Great Falls Portage National Historic Landmark. It is located between PPL Montana’s Black Eagle and Cochrane dams. The company also operates the Ryan and Morony dams on the Missouri River near Great Falls.