Main Street Triangle Dam Reservoir Report

Last Updated: December 5, 2025

Main Street Triangle Dam, located in Orland Park, Illinois, is a concrete structure designed by CBBEL with a primary purpose of flood risk reduction.


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Summary

Standing at a height of 9 feet and stretching 395 feet in length, this dam plays a crucial role in managing water flow along Mill Creek. The dam is state-regulated by the Illinois Department of Natural Resources, with provisions for state permitting, inspection, and enforcement in place to ensure its safe operation.

Despite its modest size, Main Street Triangle Dam has a significant hazard potential, as classified by risk assessments. The dam features an uncontrolled spillway with a width of 61 feet and is associated with the Mill Creek offstream. While the condition assessment is not available, regular inspections are carried out, with the last one conducted in September 2019. The dam poses a moderate risk, with risk management measures yet to be specified, highlighting the importance of ongoing monitoring and maintenance to mitigate potential hazards.

Water resource and climate enthusiasts interested in the intricate infrastructure of Main Street Triangle Dam will find its design features and regulatory oversight captivating. As a critical component in flood risk reduction in Cook County, Illinois, the dam serves as a vital asset in water management efforts. With a focus on public safety and environmental protection, the dam's operation and maintenance protocols are essential for ensuring the resilience of the surrounding communities in the face of changing climate patterns and water resource challenges.

Dam Length

395

Dam Height

9

River Or Stream

MILL CREEK - OFFSTREAM

Primary Dam Type

Concrete

Surface Area

1.2

Drainage Area

0.04

Outlet Gates

Uncontrolled

Hazard Potential

Significant

Foundations

Unlisted/Unknown

Nid Height

9
       
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.