20010228 Nisqually, Washington, Mw 6.8 Earthquake, Pictures of Howard Hansen Dam

February 28, 2001, Mw 6.8 Nisqually, Washington Earthquake

U.S. Army Corps of Engineers (ACOE) Howard Hansen Dam

U.S. Army Corps of Engineers Howard Hansen Dam. Small, white, square enclosure on crest in middle of dam houses strong-motion recorder. Motions recorded by instrument are suspect due to damage to enclosure. Next two pictures are from left of instrument enclosure looking along the dam crest towards the one-story building in upper-right-hand side of this picture.

Click on image for larger version. Image courtesy of ACOE.

Crack in embankment in center of picture due to strong ground shaking. Strong-motion instrument enclosure (white building in background) moved several inches downslope (to right of picture) during shaking.

Click on image for larger version. Image courtesy of ACOE.

Closeup of instrument housing building. Note tilt due to downslope movement of building.

Click on image for larger version. Image courtesy of ACOE.

Closeup of instrument housing building from opposite side of previous picture. Note cracks in embankment and tilt of building due to strong ground motion.

Click on image for larger version. Image courtesy of Marion Salsman, USGS.

View inside instrument housing building (downslope direction to left of picture). Downslope movement of building arrested by instrument pier (cylindrical structure in center of picture)

Click on image for larger version. Image courtesy of ACOE.

Dam Statistics (Source, ACOE)

Howard A. Hanson Dam is located on the Green River northeast of Enumclaw, Washington.

Height Above Bedrock: 235 ft (71.6 m)
Length at Crest: 450 ft (137.2 m)
Total Length, Including Spillway and Abutments: 675 ft (205.7 m)
Thickness: Base 960 ft (292.6 m), Crest 23 ft (7 m)
Concrete Spillway: Capacity 107,000 cubic ft per sec (3030 cubic m per sec)
2 Spillway Tainter Gates (each): 45 x 30 ft (13.7 x 9.1 m)
Outlet Tunnel, Concrete Lined, Horseshoe Shape 19 ft wide x 900 ft long
2 Tunnel Tainter Gates: 10 x 12 ft (3.05 x 3.7 m)
Reservoir Length: 7 miles (11.3 km) Green River, 4 miles (6.4 km) North Fork
Reservoir Capacity: 106,000 acre-ft (130,753,000 cubic m)

Links

U.S. Army Corps of Engineers (ACOE), Seattle District

ACOE Description of Howard Hansen Dam

NSMP 20010228 Nisqually earthquake page

Return to top of page.
Return to NSMP Homepage

This page was posted on March 07, 2001 (updated 03/15/2001).