Palmyra-Modesto City Lake Dam Reservoir Report
Last Updated: December 21, 2025
Located in Hettick-Offstream, Illinois, the Palmyra-Modesto City Lake Dam is a vital infrastructure designed by Benton & Associates in 1965 for water supply purposes.
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Summary
This earth dam stands at a height of 50 feet and spans a length of 620 feet, with a maximum storage capacity of 967 acre-feet. The dam overlooks the Trib Nassau Creek, serving as a key component in water resource management for Macoupin County.
Managed by the Illinois Department of Natural Resources (IDNR), the Palmyra-Modesto City Lake Dam is regulated, inspected, and enforced for safety and compliance. With a spillway width of 209 feet and a maximum discharge capacity of 4179 cubic feet per second, the dam plays a crucial role in flood control and water storage. Despite its significant hazard potential, the dam's risk assessment is moderate, highlighting the importance of ongoing monitoring and maintenance to ensure its structural integrity and reliability.
For water resource and climate enthusiasts, the Palmyra-Modesto City Lake Dam offers a fascinating glimpse into the intersection of infrastructure, water supply, and environmental management. As a public utility structure serving the community, this dam embodies the balance between human needs and ecological stewardship, showcasing the intricate dynamics of water resource management in the heart of Illinois.
Year Completed |
1965 |
Dam Length |
620 |
Dam Height |
50 |
River Or Stream |
TRIB NASSA CREEK |
Primary Dam Type |
Earth |
Surface Area |
37 |
Drainage Area |
1.8 |
Nid Storage |
967 |
Outlet Gates |
Uncontrolled |
Hazard Potential |
Significant |
Foundations |
Unlisted/Unknown |
Nid Height |
50 |
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.
Palmyra-Modesto City Lake Dam