Old Gillespie Lake Dam Reservoir Report
Last Updated: December 23, 2025
Old Gillespie Lake Dam, located in Macoupin, Illinois, was completed in 1923 and stands at a height of 35 feet with a length of 335 feet.
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Summary
Managed by the local government, the dam's primary purpose is water supply, serving as a vital resource for the surrounding area. It is situated on the Dry Fork River and has a normal storage capacity of 592 acre-feet, with a maximum capacity of 1149 acre-feet.
Despite being classified as having a low hazard potential, the dam poses a moderate risk according to assessments, with a moderate risk management rating of 3. Inspected regularly by the Illinois Department of Natural Resources, the dam has an uncontrolled spillway type with a width of 70 feet, and an outlet gate system also listed as uncontrolled. While the condition assessment is currently not available, it is essential for water resource and climate enthusiasts to keep a close watch on the maintenance and management of Old Gillespie Lake Dam to ensure its continued safety and functionality for the community it serves.
Year Completed |
1923 |
Dam Length |
335 |
Dam Height |
35 |
River Or Stream |
DRY FORK |
Primary Dam Type |
Earth |
Surface Area |
71 |
Drainage Area |
5.7 |
Nid Storage |
1149 |
Outlet Gates |
Uncontrolled |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
35 |
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.
Old Gillespie Lake Dam