Nine Mile Reservoir Report

Last Updated: December 15, 2025

Nine Mile is a captivating hydroelectric facility located in Spokane, Washington, along the picturesque Spokane River.


°F

°F

mph

Wind

%

Humidity

Summary

This privately owned dam, completed in 1908, boasts a gravity design with a height of 58 feet and a hydraulic height of 68 feet. With a storage capacity of 4,600 acre-feet and a surface area of 440 acres, Nine Mile serves multiple purposes including hydroelectric power generation, fish and wildlife conservation, and recreation.

Managed by the Federal Energy Regulatory Commission, Nine Mile is a significant contributor to the region's energy production, with a maximum discharge capacity of 60,000 cubic feet per second. The dam's controlled spillway, with a width of 225 feet, ensures efficient water management during periods of high flow. However, the dam is classified as having a high hazard potential and a very high risk assessment due to its age and condition, highlighting the importance of regular inspections and emergency preparedness.

As a key player in the region's water resource management, Nine Mile is not only a source of renewable energy but also a vital contributor to the local ecosystem and recreational activities. Its historical significance and engineering marvel make it a must-visit destination for water resource and climate enthusiasts looking to witness firsthand the intersection of human ingenuity and natural beauty.

Year Completed

1908

Dam Length

466

Dam Height

58

River Or Stream

Spokane River

Primary Dam Type

Gravity

Surface Area

440

Hydraulic Height

68

Drainage Area

4998

Nid Storage

4600

Structural Height

87

Hazard Potential

High

Foundations

Rock

Nid Height

87
       
Seasonal Comparison

Weather Forecast

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.