Ayers Island
Ayers Island is a concrete dam located in Grafton County, New Hampshire, built in 1924. It carries a Significant hazard potential classification and has a satisfactory condition assessment.
About Ayers Island
The primary purpose of Ayers Island is hydroelectric. The dam generates hydroelectric power by channeling water through turbines, converting the energy of flowing water into electricity. It impounds the Pemigewasset River near Bristol.
The dam stands 80 feet tall and stretches 699 feet across, creates a reservoir covering 800 acres, has a maximum storage capacity of 10,000 acre-feet, and collects water from a drainage area of 746 square miles. Completed in 1924, the structure is over a century 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 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 07/26/2022.
At 80 feet, this dam is taller than 97% of all dams in the United States.
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Location
| State | New Hampshire |
| County | Grafton |
| Nearest City | Bristol |
| River/Stream | Pemigewasset River |
| Coordinates | 43.59779, -71.71751 |
Physical Characteristics
| Dam Type | Concrete |
| NID Height | 80 ft |
| Dam Height | 80 ft |
| Dam Length | 699 ft |
| Year Completed | 1924 (102 years old) |
Storage & Hydraulics
| NID Storage | 10,000 acre-ft |
| Max Storage | 10,000 acre-ft |
| Normal Storage | 10,000 acre-ft |
| Surface Area | 800 acres |
| Drainage Area | 746 sq mi |
| Max Discharge | 92,100 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Hydroelectric |
| Owner Type | Not Listed |
| Hazard Classification | Significant |
| Condition Assessment | Satisfactory |
| Last Inspection | 07/26/2022 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | NH00160 |
| Federal ID | NH00160 |
| More Info | State Dam Safety Program |