Greenwood Afterbay Dam is a concrete dam located in Marquette County, Michigan, built in 1973. It carries a Significant hazard potential classification and has a satisfactory condition assessment.
Dam profile
NID height · 41 ft41 ft tall and 610 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 concrete gravity section and the water level is illustrative.
About Greenwood Afterbay Dam
The primary purpose of Greenwood Afterbay 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 Tilden Mining Company Lc (private). It impounds the Middle Branch Escanaba River near Gwinn.
The dam stands 41 feet tall and stretches 610 feet across, creates a reservoir covering 50 acres, has a maximum storage capacity of 1,080 acre-feet, and collects water from a drainage area of 71 square miles. Completed in 1973, 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. 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 12/01/2016.
At 41 feet, this dam is taller than 87% of dams nationwide.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Michigan |
| County | Marquette |
| Nearest City | Gwinn |
| River/Stream | Middle Branch Escanaba River |
| Coordinates | 46.43474, -87.78537 |
Physical Characteristics
| Dam Type | Concrete |
| NID Height | 41 ft |
| Dam Height | 41 ft |
| Dam Length | 610 ft |
| Year Completed | 1973 (53 years old) |
Storage & Hydraulics
| NID Storage | 1,080 acre-ft |
| Max Storage | 1,080 acre-ft |
| Normal Storage | 480 acre-ft |
| Surface Area | 50 acres |
| Drainage Area | 71 sq mi |
| Max Discharge | 1,200 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Tilden Mining Company Lc |
| Owner Type | Private |
| Hazard Classification | Significant |
| Condition Assessment | Satisfactory |
| Last Inspection | 12/01/2016 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | MI00114 |
| Federal ID | MI00114 |
| More Info | State Dam Safety Program |