Union Valley
Union Valley is an earth dam located in El Dorado County, California, built in 1962. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Union Valley
The primary purpose of Union Valley is hydroelectric. The dam generates hydroelectric power by channeling water through turbines, converting the energy of flowing water into electricity. The dam is owned by Sacramento Municipal Utility District (public utility). It impounds the Big Silver Creek near Coloma.
The dam stands 455 feet tall and stretches 1,990 feet across, creates a reservoir covering 2,860 acres, has a maximum storage capacity of 266,369 acre-feet, and collects water from a drainage area of 83 square miles. Completed in 1962, the structure is well into its service life at over 50 years old.
This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 08/30/2023.
At 455 feet, this dam is taller than 99% of all dams in the United States.
Living Downstream
If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The California dam safety program can provide more specific information about emergency planning for this structure.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | California |
| County | El Dorado |
| Nearest City | Coloma |
| River/Stream | Big Silver Creek |
| Coordinates | 38.86650, -120.44050 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 455 ft |
| Dam Height | 440 ft |
| Dam Length | 1,990 ft |
| Year Completed | 1962 (64 years old) |
Storage & Hydraulics
| NID Storage | 266,369 acre-ft |
| Max Storage | 266,369 acre-ft |
| Normal Storage | 204,000 acre-ft |
| Surface Area | 2,860 acres |
| Drainage Area | 83 sq mi |
| Max Discharge | 44,500 cfs |
| Spillway Type | Controlled |
Ownership & Safety
| Purpose | Hydroelectric |
| Owner | Sacramento Municipal Utility District |
| Owner Type | Public Utility |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 08/30/2023 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00816 |
| Federal ID | CA00816 |
| More Info | State Dam Safety Program |