Thomas J. O'brien Lock and Controlling Works is a concrete dam located in Cook County, Illinois, built in 1960. It carries a High hazard potential classification.
Dam profile
NID height · 37 ft37 ft tall and 430 ft long, taller than 83% of U.S. dams with a recorded height. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic concrete gravity section and the water level is illustrative.
About Thomas J. O'brien Lock and Controlling Works
The primary purpose of Thomas J. O'brien Lock and Controlling Works is navigation. The dam maintains water levels sufficient for boat and barge traffic, supporting commercial or recreational navigation on the waterway. The dam is owned by USACE - Chicago District (federal). It impounds the Calumet River near Chicago.
The dam stands 37 feet tall and stretches 430 feet across, has a maximum storage capacity of 9,700 acre-feet, and collects water from a drainage area of 250 square miles. Completed in 1960, the structure is well into its service life at over 50 years old.
This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. An emergency action plan is in place for this dam. The most recent inspection on record was 04/05/2022.
At 37 feet, this dam is taller than 83% of dams nationwide.
Living Downstream
If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Illinois dam safety program can provide more specific information about emergency planning for this structure.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Illinois |
| County | Cook |
| Nearest City | Chicago |
| River/Stream | Calumet River |
| Coordinates | 41.65214, -87.56711 |
Physical Characteristics
| Dam Type | Concrete |
| NID Height | 37 ft |
| Dam Length | 430 ft |
| Year Completed | 1960 (66 years old) |
Storage & Hydraulics
| NID Storage | 9,700 acre-ft |
| Max Storage | 9,700 acre-ft |
| Drainage Area | 250 sq mi |
| Max Discharge | 2,200 cfs |
| Spillway Type | None |
Ownership & Safety
| Purpose | Navigation |
| Owner | USACE - Chicago District |
| Owner Type | Federal |
| Hazard Classification | High |
| Condition Assessment | Not assessed |
| Last Inspection | 04/05/2022 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL01013 |
| Federal ID | IL01013 |
| More Info | State Dam Safety Program |