Thomas J. O'Brien Lock And Controlling Works Reservoir Report

Last Updated: December 5, 2025

The Thomas J.


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Summary

O'Brien Lock and Controlling Works, also known as Lake Calumet, is a vital infrastructure project located in Chicago, Illinois. Completed in 1960, this Federal-owned structure serves multiple purposes, including navigation and flood risk reduction along the Calumet River. With a primary purpose of facilitating navigation between Lake Michigan and the Chicago Area Waterways, the lock plays a crucial role in connecting the region to the Illinois Waterway.

In addition to its navigational function, the T.J. O'Brien Lock and Controlling Works also serves as a key flood control mechanism, allowing for backflow to Lake Michigan and reducing flood damages in the event of high water levels. The project's design includes a concrete dam and various gates to manage water levels and prevent downstream flooding, particularly in the southern part of Chicago. With a high hazard potential, the lock's operators continuously monitor and maintain the facility, working in collaboration with other agencies to ensure effective risk management measures are in place.

Overall, the T.J. O'Brien Lock and Controlling Works plays a critical role in safeguarding the surrounding communities from flood events while supporting essential navigation in the region. By closely coordinating with local authorities and implementing rigorous inspection and emergency response protocols, the lock remains a vital component of water resource management and climate resilience efforts in the area.

Year Completed

1960

Dam Length

430

River Or Stream

CALUMET RIVER

Primary Dam Type

Concrete

Length Of Locks

1000

Hydraulic Height

9

Drainage Area

250

Nid Storage

9700

Structural Height

37

Outlet Gates

Other Controlled - 1, Slide (sluice gate) - 4

Hazard Potential

High

Foundations

Soil

Nid Height

37
       
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.