Twin Falls Auxiliary Spillway Reservoir Report
Nearby: Twin Falls Twin Falls Auxiliary Dike
Last Updated: December 5, 2025
Located on the Menominee River in Iron Mountain, Michigan, the Twin Falls Auxiliary Spillway is a concrete dam with a primary purpose of hydroelectric power generation.
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Summary
Designed by Mead & Hunt and completed in 1960, this structure stands at a height of 30 feet and has a hydraulic height of 16.4 feet. With a maximum discharge capacity of 58,900 cubic feet per second, this controlled spillway has a width of 81 feet and a length of 101 feet.
The Twin Falls Auxiliary Spillway has a normal storage capacity of 9,750 acre-feet and serves multiple purposes including hydroelectric power generation and recreational activities. The dam is situated in a high hazard potential area with a very high risk assessment rating. Despite not being state regulated, the Federal Energy Regulatory Commission oversees its operations, inspections, and regulatory compliance. While its condition assessment is not available, the spillway has not undergone any modifications in recent years and its emergency action plan was last revised in 2005.
With its strategic location and significant role in water resource management, the Twin Falls Auxiliary Spillway stands as a crucial infrastructure for the region. Its efficient design, impressive storage capacity, and controlled spillway feature make it a key asset for both energy production and recreational use along the Menominee River. As climate and water resource enthusiasts, understanding the importance of maintaining and monitoring this dam is essential for ensuring the safety and sustainability of the surrounding area.
Year Completed |
1960 |
Dam Length |
101 |
Dam Height |
30 |
River Or Stream |
Menominee River |
Primary Dam Type |
Concrete |
Surface Area |
960 |
Hydraulic Height |
16.4 |
Drainage Area |
1790 |
Nid Storage |
9750 |
Structural Height |
26 |
Hazard Potential |
High |
Nid Height |
30 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Menominee River At Twin Falls Near Iron Mt
|
3420cfs |
Pine River Below Pine R Powerplant Nr Florence
|
273cfs |
Menominee River Near Florence
|
1050cfs |
Menominee River At Niagara
|
1290cfs |
Brule River Near Commonwealth
|
408cfs |
Paint River Nr Alpha
|
328cfs |
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.
Twin Falls Auxiliary Spillway
Twin Falls Flowage -- Access