Alder Dam
Completed in 1945, Alder Dam rises 330 feet above bedrock and stretches 1,600 feet. The powerhouse has two 25,000-kilowatt turbine generators that produce enough clean, renewable hydropower to serve about 18,000 homes each year. Along with LaGrande Dam, it is one of our two dams on the Nisqually River.
The dam forms 7-mile-long Alder Lake, which has 28 miles of shoreline and covers more than 3,000 acres at maximum elevation. The area includes Alder Lake Park, Rocky Point Campground and Sunny Beach Point, all of which are popular spots for boating, swimming, water skiing, fishing, camping and other outdoor recreation.
Statistics
- Year completed – 1945
- River system – Nisqually
- Original investment – $14.7 million
- Type of dam – concrete arch/gravity and embankment
- Height – above riverbed, 285 feet; above bedrock, 330 feet
- Length – 1,600 feet
- Width – top, 15 feet; base, 120 feet
- Volume of concrete in dam – 420,000 cubic yards
- Average flow – 1,400 cubic feet/second
- Drainage area – 286 square miles
- Reservoir length – 7 miles
- Miles of shoreline – 28 miles
- Reservoir area at maximum elevation – 3,065 acres
- Reservoir elevation – full, 1,207 feet; lowest allowable, 1,114 feet
- Average annual generation – 228 million kilowatt-hours
- Equivalent number of NW homes served – 18,000
- Number of generators – two 25,000 kilowatt generators
- Installed capacity (nameplate rating) – 50,000 kilowatts