Abstract
Milltown Dam was constructed in 1906 and 1907 as a rock fill timber-crib dam located at the confluence of the Blackfoot and Clark Fork Rivers at the community of Milltown. It was constructed by the W. A. Clark interests and acquired by the Montana Power Company in 1929. The dam has been modified over the years and now consists of a composite of timber and concrete construction. It presently is 668 feet long with an operating head of 30 feet and a structural height of about 60 feet. It has an installed capacity of 3400 kW. It generates at an average capacity of 2000 kW and produces about 17 million kWh of electric power annually. It is operated as a run-of-river plant utilizing the natural flow of the rivers. The reservoir behind the dam covers about 500 acres and holds about 820 acre/feet. The reservoir is essentially filled with sediments with depths of up to about 25 feet. Indications are that much of the sediment contains elevated concentrations of heavy metals.
Due to its age and type of construction, the project has become increasingly difficult to maintain as a functional and safe project. On three occasions since 1973, the dam has experienced extensive damage due to deteriorated timbers and excessive leakage through the structure. Minor continuous movement in the structure is occurring. In response to these problems, the Montana Power Company studied options for the future use of the project. Three primary objectives governed these studies. They were:
- Modifications to the project must be such that any water-retaining structures must be safe so there is no hazard to downstream residents and property.
- Modifications must minimize environmental impacts. Of primary importance are measures to prevent the release of sediments in hazardous quantities to the Clark Fork River.
- Modifications must be done in a cost-effective manner to minimize impact upon the rising cost of energy.
Three basic options were considered: (1) retirement of the project with removal of the structures, (2) semi-retirement with partial structure removal, and (3) rehabilitation of the project.
Start Date
19-4-1985 12:00 AM
End Date
19-4-1985 12:00 AM
Document Type
Panel Session/Paper
Milltown Project Rehabilitation
Milltown Dam was constructed in 1906 and 1907 as a rock fill timber-crib dam located at the confluence of the Blackfoot and Clark Fork Rivers at the community of Milltown. It was constructed by the W. A. Clark interests and acquired by the Montana Power Company in 1929. The dam has been modified over the years and now consists of a composite of timber and concrete construction. It presently is 668 feet long with an operating head of 30 feet and a structural height of about 60 feet. It has an installed capacity of 3400 kW. It generates at an average capacity of 2000 kW and produces about 17 million kWh of electric power annually. It is operated as a run-of-river plant utilizing the natural flow of the rivers. The reservoir behind the dam covers about 500 acres and holds about 820 acre/feet. The reservoir is essentially filled with sediments with depths of up to about 25 feet. Indications are that much of the sediment contains elevated concentrations of heavy metals.
Due to its age and type of construction, the project has become increasingly difficult to maintain as a functional and safe project. On three occasions since 1973, the dam has experienced extensive damage due to deteriorated timbers and excessive leakage through the structure. Minor continuous movement in the structure is occurring. In response to these problems, the Montana Power Company studied options for the future use of the project. Three primary objectives governed these studies. They were:
- Modifications to the project must be such that any water-retaining structures must be safe so there is no hazard to downstream residents and property.
- Modifications must minimize environmental impacts. Of primary importance are measures to prevent the release of sediments in hazardous quantities to the Clark Fork River.
- Modifications must be done in a cost-effective manner to minimize impact upon the rising cost of energy.
Three basic options were considered: (1) retirement of the project with removal of the structures, (2) semi-retirement with partial structure removal, and (3) rehabilitation of the project.