Greenwood Afterbay Dam Reservoir Report
Last Updated: December 5, 2025
Greenwood Afterbay Dam, located in Gwinn, Michigan, stands as a critical water resource structure along the Middle Branch Escanaba River.
°F
°F
mph
Wind
%
Humidity
Summary
Completed in 1973, this concrete dam serves the primary purpose of water supply, with a storage capacity of 1080 acre-feet and a maximum discharge of 1200 cubic feet per second. The dam's significant hazard potential is managed through regular inspections by the Michigan Department of Environment, Great Lakes, and Energy (DEGLE), ensuring its satisfactory condition and safe operation.
The dam's structural height of 41 feet and length of 610 feet contribute to its vital role in regulating water flow and storage in the region. With a spillway width of 50 feet for uncontrolled discharge, the Greenwood Afterbay Dam plays a crucial role in flood control and water management efforts. Despite its moderate risk rating, the dam's operational integrity and adherence to regulatory standards underscore its importance in safeguarding the surrounding communities and ecosystems along the Middle Branch Escanaba River.
As a privately owned facility under state jurisdiction, Greenwood Afterbay Dam exemplifies the collaboration between private entities and government agencies in managing water resources sustainably. With its strategic location and functional design, the dam serves as a key component in the broader water infrastructure network, highlighting the intersection of engineering, environmental stewardship, and regulatory oversight in ensuring water security and climate resilience in Michigan's Marquette County.
Year Completed |
1973 |
Dam Length |
610 |
Dam Height |
41 |
River Or Stream |
Middle Branch Escanaba River |
Primary Dam Type |
Concrete |
Surface Area |
50 |
Hydraulic Height |
36 |
Drainage Area |
71.3 |
Nid Storage |
1080 |
Structural Height |
41 |
Hazard Potential |
Significant |
Nid Height |
41 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.
Hazard Potential Classification
HighDams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.
Greenwood Afterbay Dam
Greenwood Reservoir Near Greenwood
Schweitzer Reservoir Near Palmer
Greenwood Reservoir Road Ely Township