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Home > About Tacoma Power > Dams & Our Power Sources > Hydro Power > Nisqually River Project > Alder Dam

Alder Dam


Alder Dam is 1,600 feet long

When Alder Dam was completed in 1945, it was one of the tallest dams in the nation, measuring 330 feet high and 1,600 feet long. The powerhouse has two 25,000-kilowatt turbine generators that produce enough electricity to serve 16,000 Northwest homes each year.

Alder Dam forms seven-mile-long Alder Lake. With 28 miles of shoreline and 3,065 acres of reservoir area at maximum elevation, Alder Lake is an inviting spot for boaters, water skiers, anglers and picnickers. Check out our parks and recreation facilities for Alder Lake.


Statistics

  • Year completed - 1945
  • River system - Nisqually
  • Original investment - $14.7 million
  • Type of dam - concrete arch
  • 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 - 16,000
  • Number of generators - two 25,000 kilowatt generators
  • Installed capacity (nameplate rating) - 50,000 kilowatts