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LaGrande Dam


LaGrande Dam

LaGrande Dam, one of two dams on the Nisqually River, generates enough electricity to power nearly 25,000 Northwest homes each year. In 1945, Tacoma Power built LaGrande Dam two miles down river from Alder Dam, which was also constructed that year.

LaGrande Dam feeds water to a unique powerhouse built in 1912. Tacoma Power updated the powerhouse in 1945 by adding a 40,000-kilowatt generator to the original four 6,000-kilowatt units.

LaGrande Dam is 217 feet high and 710 feet long. The reservoir behind the dam covers 45 acres and 3.5 miles of shoreline. It’s not publicly accessible because of the steep, rugged terrain that surrounds it.

In the 1.7-mile-long stretch of river between LaGrande Dam and its powerhouse, Tacoma Power maintains a continuous flow of water to enhance Chinook and coho salmon spawning habitat.


Statistics

  • Year completed - powerhouse, 1912; new dam, 1945
  • River system - Nisqually
  • Original investment - $9.7 million 
  • Type of dam - concrete gravity and embankment
  • Height - above riverbed, 192 feet; above bedrock, 217 feet
  • Length - 710 feet
  • Width - top, 12 feet; base, 85 feet
  • Volume of concrete in dam - 85,000 cubic yards
  • Average flow - 1,400 cubic feet/second
  • Drainage area - 292 square miles
  • Reservoir length - 1.5 miles
  • Miles of shoreline - 3.5 miles
  • Reservoir area at maximum elevation - 45 acres
  • Reservoir elevation - full, 935 feet; lowest allowable, 910 feet
  • Average annual generation - 345 million kilowatt-hours
  • Equivalent number of NW homes served - 24,500
  • Number of generators - four 6,000 kilowatt generators; one 40,000 kilowatt generator 
  • Installed capacity (nameplate rating) - 64,000 kilowatts