Thompson Mill Dam (In-Channel) Reservoir Report

Last Updated: December 5, 2025

Thompson Mill Dam (In-Channel) is a historic stone dam located on the Big Blue River in Johnson County, Indiana.


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Summary

Built in 1884, this dam stands at a height of 10 feet and stretches 300 feet in length, creating a reservoir with a storage capacity of 321 acre-feet. The dam serves a primarily recreational purpose, with a surface area of 64 acres and a drainage area of 581.15 square miles.

Despite being classified as having a low hazard potential, Thompson Mill Dam is considered to be at high risk due to its age and condition. A condition assessment in 2012 rated the dam as fair, with the last inspection conducted in 2017. The dam is regulated by the Indiana Department of Natural Resources, with inspection, permitting, and enforcement protocols in place to ensure its safety and compliance with state regulations. While there are no spillways or outlet gates associated with the dam, it remains a notable structure within the Louisville District of the US Army Corps of Engineers.

Enthusiasts of water resources and climate will find Thompson Mill Dam an intriguing subject for study, given its historical significance, design characteristics, and risk assessment profile. The dam's location on the Big Blue River in Indiana, along with its unique features and regulatory oversight, make it a valuable case study for understanding the intersection of infrastructure, natural resources, and environmental management in the context of climate change and water resource conservation efforts.

Year Completed

1884

Dam Length

300

Dam Height

10

River Or Stream

BIG BLUE RIVER

Primary Dam Type

Stone

Surface Area

64

Drainage Area

581.15

Nid Storage

321

Outlet Gates

None

Hazard Potential

Low

Nid Height

10
       
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.