Alpine Auxiliary No. 3 Reservoir Report

Last Updated: December 5, 2025

Alpine Auxiliary No.


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Summary

3, located in Dorrington, California, is a privately owned rockfill dam completed in 1891 for hydroelectric purposes. With a height of 42 feet and a storage capacity of 4,300 acre-feet, this dam serves multiple functions including hydroelectric power generation, recreation, and water supply. Situated on Silver Creek, the dam has a low hazard potential and is regulated by both state and federal agencies, with inspection and enforcement measures in place to ensure its safety and compliance.

Managed by the Federal Energy Regulatory Commission, Alpine Auxiliary No. 3 is part of a network of three associated structures in the area. Its uncontrolled spillway and moderate risk assessment highlight the need for ongoing monitoring and risk management measures. Despite its age, the dam continues to provide essential services to the community while being subject to regular state inspections and regulatory oversight. With its historical significance and contributions to water resource management, Alpine Auxiliary No. 3 remains an important piece of California's infrastructure.

As a key component of the water supply and energy infrastructure in Alpine County, Alpine Auxiliary No. 3 plays a crucial role in supporting the region's water needs and power generation capacity. Its location within the San Francisco District and proximity to Tom McClintock's congressional district underscore its importance in the local and state landscape. With its storied past and ongoing relevance in the present day, this dam serves as a testament to the enduring impact of water resource management and climate resilience efforts in California.

Year Completed

1891

Dam Length

29

Dam Height

42

River Or Stream

Silver Creek

Primary Dam Type

Rockfill

Surface Area

172

Hydraulic Height

12

Drainage Area

5

Nid Storage

4300

Structural Height

12

Hazard Potential

Low

Nid Height

42
       
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.