Grasslands Basin Dam Reservoir Report

Last Updated: December 5, 2025

Grasslands Basin Dam, located in Cook County, Illinois, is a crucial structure owned by the local government for flood risk reduction along the Marley Creek tributary.


°F

°F

mph

Wind

%

Humidity

Summary

Designed by CBBEL, this Earth-type dam stands at a height of 10 feet and has a storage capacity of 22 acre-feet. With a hazard potential rated as high and a moderate risk assessment, the dam is regulated, permitted, inspected, and enforced by the Illinois Department of Natural Resources.

The dam, with its uncontrolled spillway type and no outlet gates, plays a vital role in managing water flow and reducing flood risks in the area. Despite limited information on its condition assessment and completion date, the dam's emergency action plan was last revised in 2016, ensuring preparedness for any potential emergencies. With a risk management plan in place and a designated emergency contact protocol, Grasslands Basin Dam serves as a key infrastructure for water resource management in Illinois and demonstrates the importance of proactive risk mitigation measures for climate enthusiasts and water resource advocates.

Dam Height

10

River Or Stream

TRIB MARLEY CREEK

Primary Dam Type

Earth

Drainage Area

0.1

Nid Storage

22

Outlet Gates

None

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

10
       
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.