Beardsley Afterbay is a rockfill dam located in Tuolumne County, California, built in 1958. It carries a Low hazard potential classification and has a satisfactory condition assessment.
Dam profile
NID height · 33 ft33 ft tall and 240 ft long, taller than 76% of U.S. dams with a recorded height. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic rockfill embankment section and the water level is illustrative.
About Beardsley Afterbay
The primary purpose of Beardsley Afterbay 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 South San Joaquin Irrigation District (public utility). It impounds the Middle Fork Stanislaus River near Sonora.
The dam stands 33 feet tall and stretches 240 feet across, creates a reservoir covering 26 acres, and has a maximum storage capacity of 355 acre-feet. Completed in 1958, the structure is well into its service life at over 50 years old.
This dam has a low hazard potential classification, meaning that failure would cause minimal damage, limited primarily to the dam owner's property, with no expected loss of life. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. The most recent inspection on record was 07/25/2023.
At 33 feet, this dam is taller than 76% of dams nationwide.
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Location
| State | California |
| County | Tuolumne |
| Nearest City | Sonora |
| River/Stream | Middle Fork Stanislaus River |
| Coordinates | 38.19615, -120.09026 |
Physical Characteristics
| Dam Type | Rockfill |
| NID Height | 33 ft |
| Dam Height | 33 ft |
| Dam Length | 240 ft |
| Year Completed | 1958 (68 years old) |
Storage & Hydraulics
| NID Storage | 355 acre-ft |
| Max Storage | 355 acre-ft |
| Normal Storage | 320 acre-ft |
| Surface Area | 26 acres |
| Max Discharge | 1 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Hydroelectric |
| Owner | South San Joaquin Irrigation District |
| Owner Type | Public Utility |
| Hazard Classification | Low |
| Condition Assessment | Satisfactory |
| Last Inspection | 07/25/2023 |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | CA00266 |
| Federal ID | CA00266 |
| More Info | State Dam Safety Program |