Grand Coulee Reservoir Report

Last Updated: December 14, 2025

Grand Coulee, located in Okanogan, Washington, is a concrete gravity dam on the Columbia River that was completed in 1941 by the Bureau of Reclamation.


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Summary

Standing at a height of 550 feet with a hydraulic height of 380 feet, this dam serves the primary purpose of flood risk reduction along with irrigation. With a normal storage capacity of 9,562,000 acre-feet and a maximum discharge of 265,000 cubic feet per second, Grand Coulee plays a crucial role in managing water resources in the region.

Owned and operated by the Bureau of Reclamation, Grand Coulee is a significant structure with a high hazard potential and very high risk assessment. The dam spans a length of 5,673 feet and has a spillway width of 1,485 feet, showcasing its impressive scale and engineering design. While the condition assessment of the dam is not available, regular inspections and emergency action plans are in place to ensure its safety and reliability in the face of potential hazards.

As a key component of the water infrastructure in the area, Grand Coulee contributes to the management of the Columbia River and plays a vital role in water supply, flood control, and irrigation for the region. With its strategic location and impressive specifications, this dam stands as a testament to human ingenuity in harnessing and managing water resources amidst changing climatic conditions.

Year Completed

1941

Dam Length

5673

Dam Height

550

River Or Stream

COLUMBIA RIVER

Primary Dam Type

Concrete

Surface Area

82300

Hydraulic Height

380

Drainage Area

74100

Nid Storage

9562000

Structural Height

550

Hazard Potential

High

Foundations

Rock

Nid Height

550
       
Seasonal Comparison

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Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.