Union Valley Reservoir Report

Last Updated: December 4, 2025

Union Valley is a reservoir located in El Dorado County, California.


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Summary

The reservoir was created in 1963 with the construction of the Union Valley Dam, which is part of the American River watershed. The hydrology of Union Valley is primarily fed by the Rubicon River, and the reservoir provides water for hydroelectric power generation, irrigation, and municipal use. The area is also popular for recreational activities such as fishing, boating, camping, and hiking. The surrounding forests and hills are home to a diverse range of wildlife, including deer, elk, and black bears. The Union Valley Snowpack, which is a significant provider of water to the region, is particularly important for the agricultural community, with crops such as potatoes, grapes, and apples requiring water from the snowpack for irrigation.

Reservoir Details

Storage 24hr Change -0.33%
Percent of Normal 164%
Minimum 90,130.0 acre-ft
2021-10-22
Maximum 275,518.0 acre-ft
2005-07-02
Average 155,273 acre-ft
Dam_Height 440
Hydraulic_Height 440
Drainage_Area 83.7
Year_Completed 1962
Nid_Storage 266369
Structural_Height 455
Surface_Area 2860
Outlet_Gates Tainter (radial) - 2
River_Or_Stream Big Silver Creek
Dam_Length 1990
Hazard_Potential High
Primary_Dam_Type Earth
Nid_Height 455
       
Seasonal Comparison
Storage Levels
Pool Elevation Levels
Top Conserv Storage Levels
Inflow Levels

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.