Bennettsen Lake Dam Reservoir Report

Last Updated: December 14, 2025

Bennettsen Lake Dam, located in Mason, Washington, is a state-owned structure that serves the primary purpose of recreation.


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Summary

Completed in 1971, this earth dam stands at a hydraulic height of 11 feet, with a structural height of 6 feet and a length of 150 feet. The dam has a storage capacity of 270 acre-feet, with a normal storage level of 253 acre-feet, covering a surface area of 28 acres and draining a small watershed of 0.18 square miles.

Situated on the Tr-Tahuya River, the Bennettsen Lake Dam poses a low hazard potential and is not currently rated for its condition. Although last inspected in June 2001, the dam is regulated and inspected by the Washington Department of Ecology, ensuring compliance with state safety and maintenance standards. Despite its low risk profile, the dam lacks an Emergency Action Plan (EAP) and other risk management measures, highlighting the need for continued monitoring and preparedness in the face of potential climate-related challenges.

With its picturesque location and recreational opportunities, Bennettsen Lake Dam stands as a vital water resource for the community, offering a serene setting for outdoor activities. As climate change impacts water resources across the region, the maintenance and safety of dams like Bennettsen Lake become increasingly important in ensuring the resilience of water infrastructure and the protection of surrounding ecosystems.

Year Completed

1971

Dam Length

150

River Or Stream

Tr-Tahuya River

Primary Dam Type

Earth

Surface Area

28

Hydraulic Height

11

Drainage Area

0.18

Nid Storage

270

Structural Height

6

Hazard Potential

Low

Foundations

Soil

Nid Height

11
       
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.