Manchester Mill Dam Reservoir Report

Last Updated: December 5, 2025

The Manchester Mill Dam, located in Manchester, Michigan, on the River Raisin, is a gravity dam primarily designed for recreation purposes.


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Summary

Built in 1908, the dam stands at 18 feet high and spans 82 feet in length, with a storage capacity of 210 acre-feet. The dam is regulated by the Michigan Department of Environment, Great Lakes, and Energy (DEGLE) and undergoes regular inspections to ensure its structural integrity.

With a hazard potential rated as high and a condition assessment deemed as fair during its last inspection in 2016, the Manchester Mill Dam poses a risk to the surrounding area in the event of a failure. Despite its age, the dam continues to serve its recreational purpose, offering a surface area of 12 acres for activities such as fishing and boating. The dam's controlled spillway and maximum discharge capacity of 1550 cubic feet per second help manage water flow during periods of high precipitation, reducing the risk of flooding downstream.

As water resource and climate enthusiasts, the Manchester Mill Dam presents an interesting case study in the management and maintenance of aging infrastructure. Its location on the River Raisin, within the Buffalo District of the US Army Corps of Engineers, highlights the importance of proper regulation and inspection protocols to ensure public safety and environmental protection. With its very high risk designation and fair condition assessment, the ongoing monitoring and potential upgrades to the dam are crucial to mitigate any potential hazards and maintain its functionality for future generations to enjoy.

Year Completed

1908

Dam Length

82

Dam Height

18

River Or Stream

River Raisin

Primary Dam Type

Gravity

Surface Area

12

Hydraulic Height

18

Drainage Area

144

Nid Storage

210

Structural Height

18

Hazard Potential

High

Nid Height

18
       
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.