Blair Mill Reservoir Report

Last Updated: December 13, 2025

Blair Mill, located in Trempealeau, Wisconsin, is a historic dam completed in 1869 on the Trempealeau River.


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Summary

Owned by the local government, this buttress dam serves purposes such as recreation and water management. With a height of 13 feet and a length of 150 feet, Blair Mill has a storage capacity of 170 acre-feet and a normal storage of 120 acre-feet. The dam has a controlled spillway with a width of 73 feet and a low hazard potential, rated in fair condition as of May 2020.

Despite being over 150 years old, Blair Mill has undergone modifications in 1919 and 1998 to ensure its structural integrity. Inspected every 10 years, the dam meets regulatory requirements set by the Wisconsin Department of Natural Resources. The risk assessment for Blair Mill is rated as very high (1), emphasizing the importance of ongoing risk management measures. With its picturesque location and historical significance, Blair Mill continues to play a vital role in water resource management and recreation in the region, under the oversight of the local government and state regulatory agency.

Years Modified

1919 - Other, 1998 - Other

Year Completed

1869

Dam Length

150

Dam Height

13

River Or Stream

TREMPEALEAU

Primary Dam Type

Buttress

Surface Area

44

Hydraulic Height

9

Drainage Area

175

Nid Storage

170

Structural Height

13

Hazard Potential

Low

Nid Height

13
       
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.