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The Four Lower Snake River Dams Improving Salmon Passage, February 2002 Army Corps of Engineers, Walla Walla District

The Snake River is the principal tributary to the Columbia River, draining approximately 109,000 square miles in Idaho, Wyoming, Utah, Nevada, Washington, and Oregon. Flows in the lower Snake River are highest in the spring (average annual peak of approximately 165,000 cubic feet per second) and lowest in late summer (averaging 25,000 cubic feet per second). The Lower Snake River Project features four locks and dams in the state of Washington: Ice Harbor Dam, Lower Monumental Dam, Little Goose Dam, and Lower Granite Dam. The dams became operational between 1961 and 1975. The four dams are all run-of-river facilities, which means that they have limited storage capacity in their reservoirs and pass water through the dam at about the same rate as it enters the reservoir. All four of these dams are multiple-use facilities that provide navigation, hydropower, irrigation (pumped from reservoir behind Ice Harbor Dam), recreation, and fish and wildlife conservation benefits. These dams were not built to control floods.

Juvenile fish from the lower Snake River drainage system may have to travel past as many as eight Federal dams before reaching the Pacific Ocean.

	Lower Granite Dam	Little Goose Dam	Lower Monumental Dam	Ice Harbor Dam
Miles from Columbia River	107.5	70.3	41.6	9.7
Construction Date	1975 (units 1-3) 1978 (units 4-6)	1970 (units 1-3) 1978 (units 4-6)	1969 (units 1-3) 1981 (units 4-6)	1962 (units 1-3) 1976 (units 4-6)
Normal Operating Pool Elevation	733 - 738 feet	633 - 638 feet	537 - 540 feet	437 - 440 feet
Maximum Pool Elevation	746.5 feet	646.5 feet	548.3 feet	446.0 feet
Power House Hydraulic Capacity	130,000 cfs	130,000 cfs	130,000 cfs	106,000 cfs
Power House Nameplate Capacity	6 @ 135 MW 810 MW total	6 @ 135 MW 810 MW total	6 @ 135 MW 810 MW total	3 @ 90 MW 3 @ 111 MW 603 MW total
Power House Overload Capacity	6 @ 155.3 MW 932 MW total	6 @ 155.3 MW 932 MW total	6 @ 155.3 MW 930 MW total	3 @ 103.5 MW 3 @ 127.5 MW 693 MW total
Spillway	512 feet 8 gates	512 feet 8 gates	572 feet 8 gates	590 feet 10 gates
Maximum Spillway Design Capacity	850,000 cfs 19.5 acre*feet/second	(?)	(?)	(?)
Reservoir Name	Lower Granite Lake	Lake Bryan	Lake Herbert G West	Lake Sacajawea
Reservoir Length	39.3 miles (Snake) 4.6 miles (Clearwater)	37.2 miles	28.7 miles	31.9 miles
Shoreline Length	91 miles	92 miles	(?)	(?)
Reservoir Width	0.3 miles (avg.) 0.6 miles (max)	0.4 miles (avg.) 0.8 miles (max)	0.4 miles (avg.) 0.8 miles (max)	0.4 miles (avg.) 1.0 miles (max)
Reservoir Surface Area	8900 acres	10,025 acres	6,590 acres	8,375 acres
Reservoir Storage	483,800 acre-feet (elev. 738) 440,200 acre-feet (elev. 733)	565,200 acre-feet (elev. 638) 516,300 acre-feet (elev. 633)	20,000 acre-feet (between 537 & 540 feet elev.)	24,900 acre-feet (between 437 & 440 feet elev.)
Abutment Embankment	Gravel fill w/ rock facing, impervious silt core Top width 45 feet, Slope 1V on 2H	Gravel fill w/ rock facing, impervious silt core Top width 43 feet, Slope 1V on 2H	Length: 968 feet (north shore) 1,075 feet (south shore)	Length: 624 feet (north shore)
Dam Length	3200 feet	2655 feet	3791 feet	2822 feet
Dam Height	100 feet	98 feet	100 feet	100 feet