Thorton Quarry Gap Dam Reservoir Report

Last Updated: December 5, 2025

Thorton Quarry Gap Dam, located in Thornton, Illinois, is a privately owned structure designed by MWRDGC to address flood risk reduction along the Thornton Quarry stream.


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Summary

Completed in 2013, this concrete dam stands at a height of 116 feet and has a length of 220 feet. With a storage capacity of 9,900 acre-feet, the dam plays a crucial role in managing water levels in the area.

Managed by the Illinois Department of Natural Resources, Thorton Quarry Gap Dam is regulated, inspected, and enforced to ensure its structural integrity and safety. The dam's uncontrolled spillway type and high hazard potential highlight the importance of its maintenance and monitoring. Despite its moderate risk assessment, the dam's emergency action plan is up to date, providing guidelines for emergency response in case of inundation events.

For water resource and climate enthusiasts, Thorton Quarry Gap Dam serves as a significant infrastructure for flood risk reduction in Cook County, Illinois. With its strategic location and design features, this dam plays a crucial role in managing water flow and protecting surrounding areas from potential flooding events. As a key part of the local water management system, Thorton Quarry Gap Dam exemplifies the importance of proactive measures in mitigating the impacts of extreme weather events on communities and ecosystems.

Year Completed

2013

Dam Length

220

Dam Height

116

River Or Stream

THORNTON QUARRY

Primary Dam Type

Concrete

Drainage Area

0.1

Nid Storage

9900

Hazard Potential

High

Foundations

Rock

Nid Height

116
       
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.