Unadilla Mill Dam Reservoir Report

Last Updated: December 5, 2025

The Unadilla Mill Dam, located in Unadilla, Michigan, was completed in 1860 and serves primarily for recreation purposes.


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Summary

This earth dam spans 376 feet in length with a height of 10 feet, providing a storage capacity of 65 acre-feet. The dam is situated on Hell Creek, within Livingston County, and is under the jurisdiction of the Buffalo District. Despite its historical significance, the dam has not been regulated or inspected by the state, presenting a significant hazard potential.

With a spillway width of 4 feet and a controlled spillway type, the Unadilla Mill Dam has a very high risk assessment rating. However, the condition of the dam has not been officially assessed or rated, and there is no Emergency Action Plan (EAP) in place. The dam's risk management measures, as well as its compliance with guidelines and preparation for emergencies, are currently unknown. The dam's location and structural characteristics make it a water resource and climate enthusiast's point of interest, given its historical significance and potential risks associated with its condition.

Although the Unadilla Mill Dam does not have state permitting, inspection, or enforcement, its location on Hell Creek and its recreational purpose draw attention to the need for further assessment and potential risk mitigation measures. Enthusiasts interested in water resources and climate may find the dam's history, design, and risk profile fascinating, as it presents a unique case study for the intersection of historical infrastructure and modern safety considerations in the face of changing environmental conditions.

Year Completed

1860

Dam Length

376

Dam Height

10

River Or Stream

Hell Creek

Primary Dam Type

Earth

Surface Area

4.3

Hydraulic Height

10

Nid Storage

65

Structural Height

10

Hazard Potential

Significant

Nid Height

10
       
Seasonal Comparison

Weather Forecast

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.