Twin Lake Reservoir Report

Last Updated: December 4, 2025

Twin Lake, located in Alpine County, California, is a privately owned reservoir with a primary purpose of hydroelectric power generation.


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Summary

Built in 1903, this earth dam stands at 22 feet high and spans 1520 feet in length. With a storage capacity of 21,581 acre-feet, it serves as a crucial water resource for the surrounding area, particularly during dry seasons. The dam is regulated by both state and federal agencies, ensuring its safety and compliance with inspection and enforcement protocols.

The North Fork Mokelumne River-tr flows through Twin Lake, providing a source of water for the reservoir. The dam's spillway, with a width of 296 feet, is uncontrolled and can handle a maximum discharge of 12,400 cubic feet per second. Despite its low hazard potential, Twin Lake is subject to moderate risk assessment due to its age and condition assessment being unavailable. Emergency action plans have been prepared and revised periodically, with maintenance measures in place to mitigate any potential risks associated with the dam's operation.

The picturesque setting of Twin Lake, nestled in the scenic Kirkwood area, offers not only a source of hydroelectric power but also a recreational spot for visitors to enjoy. With its historical significance dating back over a century, Twin Lake stands as a testament to the intersection of water resource management, climate resilience, and sustainable energy generation in the California landscape.

Year Completed

1903

Dam Length

1520

Dam Height

22

River Or Stream

North Fork Mokelumne River-tr

Primary Dam Type

Earth

Surface Area

600

Drainage Area

13.5

Nid Storage

21581

Hazard Potential

Low

Nid Height

22
       
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.