Coffeen Gmf Gypsum Stack Dam Reservoir Report
Last Updated: December 5, 2025
The Coffeen Gmf Gypsum Stack Dam, also known as the Ameren Coffeen Gmf Gypsum Stack Dam, is a critical infrastructure located in Coffeen, Illinois, within Montgomery County.
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Summary
Managed by a public utility, this dam serves the primary purpose of debris control along the McDavid Branch East Fork Shoal. The dam is of Earth type, with a height of 108 feet and a length of 5100 feet, providing a storage capacity of 2355 acre-feet.
With a controlled spillway and vertical lift outlet gates, the Coffeen Gmf Gypsum Stack Dam has a high hazard potential and is classified as having a very high risk level. Despite its significance in managing water resources and mitigating potential risks, the dam's condition assessment is currently not available. It is regulated by the Illinois Department of Natural Resources (IDNR) and undergoes regular inspections to ensure its structural integrity and operational effectiveness, with the last inspection conducted in November 2020.
For water resource and climate enthusiasts, the Coffeen Gmf Gypsum Stack Dam presents an intriguing case study in dam management and risk assessment. As a vital structure for debris control in the region, understanding its design, operation, and maintenance is essential for ensuring the safety and resilience of the surrounding communities. With its high hazard potential and very high risk classification, the dam serves as a focal point for ongoing monitoring and risk management measures to safeguard against potential emergencies and protect the local environment and infrastructure.
Dam Length |
5100 |
Dam Height |
108 |
River Or Stream |
MCDAVID BRANCH EAST FORK SHOAL |
Primary Dam Type |
Earth |
Surface Area |
38.5 |
Drainage Area |
38.5 |
Nid Storage |
2355 |
Outlet Gates |
Vertical Lift |
Hazard Potential |
High |
Foundations |
Soil |
Nid Height |
108 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Coffeen Gmf Gypsum Stack Dam