Antioch Reservoir
Antioch Reservoir is an earth dam located in Contra Costa County, California, built in 1935. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Antioch Reservoir
The primary purpose of Antioch Reservoir is flood risk reduction. The dam is designed to control downstream flooding by temporarily storing excess water during storms and releasing it at a controlled rate. The dam is owned by City Of Antioch (local government). It impounds the Tr San Joaquin Riv.
The dam stands 30 feet tall and stretches 450 feet across, creates a reservoir covering 61 acres, has a maximum storage capacity of 722 acre-feet, and collects water from a drainage area of 1 square miles. Completed in 1935, the structure is well-established, with more than 75 years of service.
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 10/17/2024.
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 | Contra Costa |
| River/Stream | Tr San Joaquin Riv |
| Coordinates | 37.97790, -121.80900 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 30 ft |
| Dam Height | 30 ft |
| Dam Length | 450 ft |
| Year Completed | 1935 (91 years old) |
Storage & Hydraulics
| NID Storage | 722 acre-ft |
| Max Storage | 722 acre-ft |
| Surface Area | 61 acres |
| Drainage Area | 1 sq mi |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | City of Antioch |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 10/17/2024 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00057 |
| Federal ID | CA00057 |
| More Info | State Dam Safety Program |