Mianus Filter Plant Dam
Mianus Filter Plant Dam is a masonry dam located in Fairfield County, Connecticut, built in 1875. It carries a High hazard potential classification and has a fair condition assessment.
About Mianus Filter Plant Dam
The primary purpose of Mianus Filter Plant Dam 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 Aquarion Water Company Of Connecticut (public utility). It impounds the Mianus River near North Mianus.
The dam stands 31 feet tall and stretches 130 feet across, creates a reservoir covering 7 acres, has a maximum storage capacity of 118 acre-feet, and collects water from a drainage area of 29 square miles. Completed in 1875, the structure is one of the older dams in the region, with over a century and a half 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 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 09/15/2022.
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 Connecticut 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 | Connecticut |
| County | Fairfield |
| Nearest City | North Mianus |
| River/Stream | Mianus River |
| Coordinates | 41.06794, -73.57909 |
Physical Characteristics
| Dam Type | Masonry |
| NID Height | 31 ft |
| Dam Height | 31 ft |
| Dam Length | 130 ft |
| Year Completed | 1875 (151 years old) |
Storage & Hydraulics
| NID Storage | 118 acre-ft |
| Max Storage | 118 acre-ft |
| Normal Storage | 101 acre-ft |
| Surface Area | 7 acres |
| Drainage Area | 29 sq mi |
| Max Discharge | 680 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Aquarion Water Company of Connecticut |
| Owner Type | Public Utility |
| Hazard Classification | High |
| Condition Assessment | Fair |
| Last Inspection | 09/15/2022 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CT00040 |
| Federal ID | CT00040 |
| More Info | State Dam Safety Program |