Minnawanna Dam Reservoir Report

Last Updated: December 5, 2025

Minnawanna Dam, located in Hadley, Michigan, along the South Branch Farmers Creek, is a state-regulated earth dam completed in 1963 for recreational purposes.


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Summary

Standing at a height of 33 feet with a hydraulic height of 32.1 feet, the dam boasts a length of 1245 feet and a storage capacity of 900 acre-feet. With a surface area of 60 acres and a drainage area of 6.7 square miles, the dam plays a significant role in water resource management in the region.

The dam's spillway, which is uncontrolled and 27 feet wide, helps regulate the maximum discharge of 285 cubic feet per second. Despite being classified as having a significant hazard potential, the condition assessment in June 2019 deemed the dam to be in satisfactory condition. Regular inspections are conducted every four years to ensure the safety and integrity of the structure. While the risk assessment is moderate, with a rating of 3, there is no designated risk management plan in place at this time.

Overall, Minnawanna Dam serves as a vital recreational resource in Lapeer County, Michigan, while also playing a crucial role in water management and flood control along the South Branch Farmers Creek. As climate change continues to impact water resources, the proper maintenance and monitoring of dams like Minnawanna are essential to ensure the safety of surrounding communities and the sustainability of the local ecosystem.

Year Completed

1963

Dam Length

1245

Dam Height

33

River Or Stream

South Branch Farmers Creek

Primary Dam Type

Earth

Surface Area

60

Hydraulic Height

32.1

Drainage Area

6.7

Nid Storage

900

Structural Height

33

Hazard Potential

Significant

Nid Height

33
       
Seasonal Comparison

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Dam Data Reference

Condition Assessment

Satisfactory
No 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

High
Dams 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.