Grand Coulee Dam: America's Largest Concrete Structure

**Grand Coulee Dam** on the Columbia River in eastern Washington State is the largest concrete structure in the United States and the sixth-largest hydroelectric power station in the world by installed capacity. With **6,809 MW** spread across three powerhouses, the dam generates approximately **21 TWh** of electricity annually while also supplying irrigation water to over **240,000 hectares** of farmland in the Columbia Basin.

Introduction

Built between 1933 and 1942, with a third powerhouse added in 1974, Grand Coulee was a centerpiece of President Franklin Roosevelt's New Deal and the broader federal effort to develop the Columbia River system. The dam's cheap electricity powered the aluminum smelters that built World War II aircraft and later fueled the growth of the Pacific Northwest's technology industry.

Engineering & Structure

• Type: Concrete gravity dam
• Height: 168 meters
• Crest Length: 1,592 meters
• Concrete Volume: 8.09 million m³

Grand Coulee Dam contains 8.09 million cubic meters of concrete, making it the largest concrete structure in the United States and one of the largest in the world. The dam stretches 1,592 meters across the Columbia River valley — nearly a mile — and rises 168 meters from its foundation. Its mass is so great that the dam weighs an estimated 21 million tonnes.

The facility includes three powerhouses built in stages. The original Left and Right powerhouses (1941-1950) contain 18 generators, while the Third Powerhouse (1975-1983) added six generators including three 805 MW units that were the world's largest when installed. A pump-generating station lifts Columbia River water 85 meters into Banks Lake for the Columbia Basin Irrigation Project.

Geographic Setting

• River: Columbia River
• Location: Grant County, Washington State, United States
• Coordinates: 47.96°N, 118.98°W
• Lake Roosevelt: 243 km long

The dam is located in the arid shrub-steppe of eastern Washington, where the Columbia River has carved a dramatic gorge through layered basalt flows deposited by ancient volcanic eruptions. Annual rainfall averages less than 250 millimeters, and the surrounding landscape is dominated by sagebrush and bunchgrass — a stark contrast to the lush forests of western Washington.

Lake Roosevelt, the reservoir behind the dam, extends 243 kilometers upstream to the Canadian border, making it one of the longest reservoirs in North America. The lake fills the Columbia River valley and portions of the adjacent Grand Coulee, a massive dry canyon carved by catastrophic Ice Age floods that scoured the landscape roughly 15,000 years ago. These Missoula Floods created the "channeled scablands" visible throughout the region.

Hydroelectric Power

• Installed Capacity: 6,809 MW
• Annual Output: ~21 TWh
• Turbines: 33 total across three powerhouses
• Transmission: Bonneville Power Administration grid

Grand Coulee's 6,809 MW of installed capacity produces approximately 21 terawatt-hours of electricity per year, distributed through the Bonneville Power Administration to utilities across the Pacific Northwest. The dam's output is critical to the region's electricity supply, providing reliable baseload power alongside the other 13 federal dams on the Columbia and Snake rivers.

During World War II, Grand Coulee's electricity powered aluminum smelters that produced one-third of all aluminum used in Allied aircraft manufacturing. The folk singer Woody Guthrie was hired by the Bonneville Power Administration in 1941 to write songs promoting the dam, producing 26 songs including "Roll On, Columbia, Roll On," which became Washington State's official folk song.

Environmental & Social Impact

• Salmon Blocked: No fish passage — all upstream salmon runs eliminated
• Indigenous Impact: Displaced Colville and Spokane tribes
• Irrigation: 240,000+ hectares via Columbia Basin Project

Grand Coulee Dam has no fish ladders or fish passage facilities, permanently blocking salmon and steelhead from over 1,770 kilometers of upstream spawning habitat. This decision, made during construction, devastated the Columbia River's once-legendary salmon runs and profoundly harmed the Native American tribes that depended on them. The Colville and Spokane tribes lost ancestral fishing sites, burial grounds, and communities to the rising waters of Lake Roosevelt.

The dam's irrigation legacy is transformative. The Columbia Basin Project, fed by water pumped from Lake Roosevelt into Banks Lake, irrigates over 240,000 hectares of formerly arid land, producing potatoes, wheat, corn, and fruit. The project turned desert into farmland but at the cost of aquatic ecosystems and indigenous lifeways that had sustained the region for millennia.

Key Facts

• Grand Coulee Dam is the largest concrete structure in the United States.
• Its 6,809 MW capacity makes it the sixth-largest hydroelectric station in the world.
• Lake Roosevelt extends 243 km upstream to the Canadian border.
• The dam permanently blocked salmon from over 1,770 km of upstream habitat.
• Its electricity powered the aluminum production that built World War II aircraft.

Fun Facts

• Woody Guthrie wrote 26 folk songs about the Columbia River and Grand Coulee Dam in just 30 days while on the government payroll.
• Grand Coulee's nightly laser light show projected onto the dam's spillway is the world's largest, illuminating a surface area of over 300 by 50 meters.
• The Ice Age floods that carved the Grand Coulee released more water than all the world's current rivers combined, flowing at roughly 60 km/h.

Final Thoughts

Grand Coulee Dam shaped the Pacific Northwest as profoundly as any natural feature, bringing electricity, irrigation, and industry to the arid Columbia Basin. Its legacy is both triumphant and tragic — a marvel of engineering that came at the permanent cost of the Columbia River's wild salmon runs and the indigenous cultures that depended on them.