Union Valley Reservoir Report

Last Updated: December 4, 2025

Union Valley is a captivating hydroelectric and recreational dam located in El Dorado, California.


°F

°F

mph

Wind

%

Humidity

Summary

Built in 1962 by Bechtel, this Earth-type dam stands at an impressive height of 440 feet and has a storage capacity of 266,369 acre-feet, with a normal storage level of 204,000 acre-feet. The dam is situated on the Big Silver Creek and covers a surface area of 2,860 acres, providing a picturesque backdrop for outdoor enthusiasts and climate aficionados alike.

Managed by the Federal Energy Regulatory Commission, Union Valley serves as a vital water resource in California, with a maximum discharge capacity of 44,500 cubic feet per second. The dam features a controlled spillway with a width of 85 feet and two Tainter radial gates for water regulation. Despite its high hazard potential, the dam is regularly inspected and regulated by both state and federal agencies to ensure public safety and environmental protection. With its scenic location and impressive engineering, Union Valley offers a unique blend of hydroelectric power generation and recreational opportunities for visitors to enjoy.

With its rich history and strategic location in the Coloma area, Union Valley continues to play a crucial role in California's water resource management efforts. The dam's risk assessment indicates a very high level of risk, emphasizing the importance of ongoing monitoring and maintenance to safeguard its structural integrity. As a popular destination for outdoor activities and nature enthusiasts, Union Valley stands as a symbol of sustainable water utilization and climate resilience in the region, highlighting the intersection of engineering ingenuity and environmental stewardship in the face of changing climate patterns.

Year Completed

1962

Dam Length

1990

Dam Height

440

River Or Stream

Big Silver Creek

Primary Dam Type

Earth

Surface Area

2860

Hydraulic Height

440

Drainage Area

83.7

Nid Storage

266369

Structural Height

455

Outlet Gates

Tainter (radial) - 2

Hazard Potential

High

Nid Height

455
       
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.