Grand Coulee Dam


Grand Coulee Dam is one of the largest concrete structures in the world. This dam, which raises the water surface 350 feet above the old riverbed, is 5,223 feet long, 550 feet high, and contains about 12 million cubic yards of concrete. The original dam was modified for the Third Powerplant by construction of a 1,170-foot-long, 201-foot-high forebay dam along the right abutment approximately parallel to the river and at an angle of 64 degrees to the axis of Grand Coulee Dam. The total length of the main dam, forebay dam, and wing dam is 5,223 feet. The spillway of the dam is controlled by 11 drum gates, each 135 feet long, and is capable of spilling 1 million cubic feet of water per second with Lake Roosevelt at fullpool (1290.0 feet above sea level). The dam also contains forty 102- inch-diameter outlet tubes. Within the dam are 8.5 miles of inspection galleries and 2.5 miles of shafts.

Franklin D. Roosevelt Lake, the reservoir behind the dam, extends 151 miles northeast to the Canadian border and up the Spokane River, a tributary of the Columbia, to within 37 miles of Spokane. The total storage capacity of the reservoir is about 9.6 million acre-feet, and the active capacity is about 5.2 million acre-feet.


The average discharge at Grand Coulee over a period of years is approximately 100,000 cubic feet per second. On June 12, 1948, during an historic Columbia River flood period, the maximum discharge (turbine and spill) recorded was 637,800 cubic feet per second. The annual volume inflow has varied from a minimum of 48.5 million acre-feet to a maximum of 111.8 million acre-feet. The average annual inflow to Lake Roosevelt is 99.3 million acre-feet. The April through July inflow accounts for 65 to 70 percent of the total annual inflow volume.



Foundation: Hard, sound, massive granite varying from coarse-grained in right abutment to fine-grained porphyritic in left abutment.

RegionFacilities in Pacific Northwest | Pacific Northwest Home Page
CountyGrant, Okanogan
ProjectColumbia Basin
Dam TypeConcrete Gravity
ReservoirFranklin D. Roosevelt Lake
WatercourseColumbia River
Net Generation24,543,686,116 kWh
Original Construction1933-1941
Modified Construction1967-1974
National ID NumberWA00262
Hydrologic Unit Code

Structural Height550.0 ft
Hydraulic Height (Normal Operating Depth at Dam)350.0 ft
Top Parapet (Elevation)1314.58 ft
Spillway Crest Elevation1290.0 ft
Crest Elevation1311.1 ft
Crest Length5223.0 ft
Crest Width30 ft
Base Width500 ft
Volume of Dam Construction Materials11,975,520 cu yd
Streambed at Dam Axis
Top of Exclusive Flood Control Pool (Elevation)
Top of Joint Use Pool (Elevation)
Top of Active Conservation Pool (Elevation)1290.0 ft
Top of Inactive Conservation Pool (Elevation)
Top of Dead Storage Pool (Elevation)

Hydraulics & Hydrology
Total Water Storage at Elevation9,652,000 ac-ft total; 5,185,400 ac-ft active
Maximum Water Surface Elevation1311.1 ft
Normal Water Surface Elevation1290.0 ft
Spillway TypeDrum gates
Auxiliary Spillway
Spillway Capacity at Elevation1,000,000 cfs at 1290.0 ft
Auxiliary Spillway Capacity at Elevation
Uncontrolled Spillway Capacity at Elevation
Outlet Works Capacity at Elevation265,000 cfs; Powerplant 280,000 cfs
Diversion Capacity at Elevation
Drainage Area74100 sq mi
Hydrometeorological Report (HMR)HMR 18

Contact Information
OrganizationGrand Coulee Power Office
AddressPO Box 620
CityGrand Coulee, WA 99133-0620
Phone (Fax)509 633-9138
Phone (Office)509 633-1360
OrganizationGrand Coulee Power Office
AddressPO Box 620
CityGrand Coulee, WA 99133-0620
Phone (Fax)509 633-9138
Phone (Office)509 633-1360

Last updated: Jan 03, 2013