Patterson
Patterson is an earth dam located in Alameda County, California, built in 1962. It carries a Significant hazard potential classification and has a fair condition assessment.
About Patterson
The primary purpose of Patterson is water supply. The dam stores water for municipal, industrial, or agricultural use, helping ensure a reliable supply for the surrounding area. The dam is owned by Alameda County Water District (local government). It impounds the Offstream.
The dam stands 100 feet tall and stretches 1,306 feet across, creates a reservoir covering 2 acres, and has a maximum storage capacity of 46 acre-feet. Completed in 1962, the structure is well into its service life at over 50 years old.
This dam has a significant hazard potential classification, meaning that a failure could cause significant economic damage — flooding roads, bridges, or property downstream — but is not expected to result in loss of life. Its condition is rated fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. An emergency action plan is in place for this dam. The most recent inspection on record was 10/29/2024.
At 100 feet, this dam is taller than 98% of all dams in the United States.
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Location
| State | California |
| County | Alameda |
| River/Stream | Offstream |
| Coordinates | 37.54170, -122.08470 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 100 ft |
| Dam Height | 100 ft |
| Dam Length | 1,306 ft |
| Year Completed | 1962 (64 years old) |
Storage & Hydraulics
| NID Storage | 46 acre-ft |
| Max Storage | 46 acre-ft |
| Surface Area | 2 acres |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Alameda County Water District |
| Owner Type | Local Government |
| Hazard Classification | Significant |
| Condition Assessment | Fair |
| Last Inspection | 10/29/2024 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00895 |
| Federal ID | CA00895 |
| More Info | State Dam Safety Program |