Brookdale Dam Reservoir Report

Last Updated: December 5, 2025

Brookdale Dam, located in Marengo, Illinois, along the North Branch Kishwaukee River, is a concrete structure primarily used for recreation purposes.


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Summary

Standing at a height of 8 feet and stretching 400 feet in length, this dam provides a storage capacity of 88 acre-feet and covers a surface area of 12.5 acres. Despite its modest size, the dam is deemed to have a significant hazard potential, warranting regular inspections every 3 years.

Managed by the local government and regulated by the Illinois Department of Natural Resources, Brookdale Dam is equipped with an uncontrolled spillway and outlet gates. The dam's design, featuring buttress and multi-arch cores supported by rock and soil foundations, reflects a blend of functionality and aesthetics. While the exact year of completion remains unknown, the dam's role in enhancing recreational activities in the area is evident.

With Congresswoman Lauren Underwood representing the district, Brookdale Dam contributes to the local ecosystem by maintaining a moderate risk level. Although specific risk management measures are yet to be defined, the dam's presence adds to the diverse water resource infrastructure in McHenry County, Illinois. As enthusiasts of water resources and climate, monitoring and understanding the impact of dams like Brookdale is crucial for sustainable environmental stewardship.

Dam Length

400

Dam Height

8

River Or Stream

NORTH BRANCH KISHWAUKEE RIVER

Primary Dam Type

Concrete

Surface Area

12.5

Drainage Area

21

Nid Storage

88

Outlet Gates

Uncontrolled

Hazard Potential

Significant

Foundations

Rock, Soil

Nid Height

8
       
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.