Mayfield Reservoir Report

Last Updated: December 13, 2025

Mayfield, located in Lewis, Washington, is a public utility owned hydroelectric dam on the Cowlitz River.


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Summary

Built in 1963 by Harza Engineering Co., this arch-type dam stands at a height of 200 feet and has a structural height of 250 feet. With a storage capacity of 184,194 acre-feet and a normal storage of 133,718 acre-feet, Mayfield serves multiple purposes including hydroelectric power generation and recreation.

The dam's controlled spillway has a width of 205 feet, and it is equipped with five Tainter radial gates for water release. Mayfield's hazard potential is rated as high, with a very high risk assessment score of 1. Despite its age, the dam's condition assessment is currently not available. The Federal Energy Regulatory Commission oversees its regulatory and inspection activities, ensuring its safe operation and maintenance.

Mayfield's strategic location and significant storage capacity make it a vital water resource in the region. Its impressive hydraulic height of 230 feet contributes to its efficient power generation capabilities. With its rich history and crucial role in water management and energy production, Mayfield remains a fascinating site for water resource and climate enthusiasts to explore and learn from.

Year Completed

1963

Dam Length

850

Dam Height

200

River Or Stream

Cowlitz River

Primary Dam Type

Arch

Surface Area

2250

Hydraulic Height

230

Drainage Area

1392

Nid Storage

184194

Structural Height

250

Outlet Gates

Tainter (radial) - 5

Hazard Potential

High

Foundations

Rock

Nid Height

250
       
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.