Lake Roslyn Reservoir Report

Last Updated: December 13, 2025

Lake Roslyn in Clackamas, Oregon, is a fascinating hydroelectric reservoir managed by a public utility.


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Summary

The dam, completed in 1959, stands at a height of 45 feet and spans a length of 8000 feet, creating a storage capacity of 2011 acre-feet. With a surface area of 152 acres and a drainage area of 4.5 square miles, the reservoir is fed by the Big and Little Sandy Rivers and boasts a maximum discharge of 800 cubic feet per second.

Situated in a picturesque location in Troutdale, Lake Roslyn not only serves as a source of hydroelectric power but also provides recreational opportunities and supports wildlife habitats. The dam, primarily made of earth, features a slide gate for outlet control and is regulated by the Oregon Water Resources Department. Despite its significant hazard potential, the dam's condition is currently not rated, highlighting the importance of regular inspections and risk management measures to ensure its structural integrity and the safety of surrounding communities.

As a key water resource in the region, Lake Roslyn plays a vital role in water management and climate resilience efforts. Its strategic location and design make it a valuable asset for sustainable energy production and flood control. With proper maintenance and monitoring, this reservoir continues to contribute to the state's renewable energy goals while safeguarding against potential risks associated with dam infrastructure.

Year Completed

1959

Dam Length

8000

Dam Height

45

River Or Stream

BIG AND LITTLE SANDY RIVERS

Primary Dam Type

Earth

Surface Area

152

Hydraulic Height

40

Drainage Area

4.5

Nid Storage

2011

Structural Height

48.5

Outlet Gates

Slide (sluice gate)

Hazard Potential

Significant

Nid Height

49
       
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.