Johnsonville Fossil Plant - Ash Disposal Area Perimeter Dike (island) is an earth dam located in Humphreys County, Tennessee, built in 1968. It carries a Significant hazard potential classification.
Dam profile
NID height · 41 ft41 ft tall and 10,066 ft long, taller than 87% 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 embankment section and the water level is illustrative.
About Johnsonville Fossil Plant - Ash Disposal Area Perimeter Dike (island)
Johnsonville Fossil Plant - Ash Disposal Area Perimeter Dike (island) is a dam in Humphreys, Tennessee. The dam is owned by TVA (federal). It impounds the Tennessee River - Offstream near New Johnsonville.
The dam stands 41 feet tall and stretches 10,066 feet across, creates a reservoir covering 101 acres, has a maximum storage capacity of 323 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1968, 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. An emergency action plan is in place for this dam. The most recent inspection on record was 03/06/2025.
At 41 feet, this dam is taller than 87% of dams nationwide.
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Location
| State | Tennessee |
| County | Humphreys |
| Nearest City | New Johnsonville |
| River/Stream | Tennessee River - Offstream |
| Coordinates | 36.02300, -87.99500 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 41 ft |
| Dam Height | 41 ft |
| Dam Length | 10,066 ft |
| Year Completed | 1968 (58 years old) |
Storage & Hydraulics
| NID Storage | 323 acre-ft |
| Max Storage | 323 acre-ft |
| Normal Storage | 228 acre-ft |
| Surface Area | 101 acres |
| Drainage Area | 0 sq mi |
| Max Discharge | 279 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Other |
| Owner | TVA |
| Owner Type | Federal |
| Hazard Classification | Significant |
| Condition Assessment | Not assessed |
| Last Inspection | 03/06/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | TN08512 |
| Federal ID | TN08512 |
| More Info | State Dam Safety Program |