Alton Power Dam is a concrete dam located in Belknap County, New Hampshire, built in 1923. It carries a High hazard potential classification and has a poor condition assessment.
Dam profile
NID height · 16 ft16 ft tall and 190 ft long. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic concrete gravity section and the water level is illustrative.
About Alton Power Dam
The primary purpose of Alton Power Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Nh Fish and Game Department (state). It impounds the Merrymeeting River near Alton.
The dam stands 16 feet tall and stretches 190 feet across, creates a reservoir covering 719 acres, has a maximum storage capacity of 3,392 acre-feet, and collects water from a drainage area of 35 square miles. Completed in 1923, the structure is over a century 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 poor, meaning the dam has recognized safety deficiencies that require remediation to address risks. An emergency action plan is in place for this dam. The most recent inspection on record was 04/26/2022.
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 New Hampshire 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 | New Hampshire |
| County | Belknap |
| Nearest City | Alton |
| River/Stream | Merrymeeting River |
| Coordinates | 43.45770, -71.23080 |
Physical Characteristics
| Dam Type | Concrete |
| NID Height | 16 ft |
| Dam Height | 16 ft |
| Dam Length | 190 ft |
| Year Completed | 1923 (103 years old) |
Storage & Hydraulics
| NID Storage | 3,392 acre-ft |
| Max Storage | 3,392 acre-ft |
| Normal Storage | 1,235 acre-ft |
| Surface Area | 719 acres |
| Drainage Area | 35 sq mi |
| Max Discharge | 3,900 cfs |
Ownership & Safety
| Purpose | Recreation |
| Owner | Nh Fish and Game Department |
| Owner Type | State |
| Hazard Classification | High |
| Condition Assessment | Poor |
| Last Inspection | 04/26/2022 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | NH00011 |
| Federal ID | NH00011 |
| More Info | State Dam Safety Program |