Palmyra-modesto City Lake Dam is an earth dam located in Macoupin County, Illinois, built in 1965. It carries a Significant hazard potential classification.
Dam profile
NID height · 50 ft50 ft tall and 620 ft long, taller than 92% of U.S. dams with a recorded height. Height is drawn to scale against a ten-story building, about 100 ft; the profile is a generic embankment section and the water level is illustrative.
About Palmyra-modesto City Lake Dam
The primary purpose of Palmyra-modesto City Lake Dam is water supply. The dam stores water for municipal, industrial, or agricultural use, helping ensure a reliable supply for the surrounding area. The dam is owned by Palmyra-modesto Water Commission (public utility). It impounds the Trib Nassa Creek near Hettick-offstream.
The dam stands 50 feet tall and stretches 620 feet across, creates a reservoir covering 37 acres, has a maximum storage capacity of 967 acre-feet, and collects water from a drainage area of 1 square miles. Completed in 1965, the structure is well into its service life at over 50 years old.
This dam has a significant hazard potential classification, meaning that a failure could cause significant economic damage — flooding roads, bridges, or property downstream — but is not expected to result in loss of life. An emergency action plan is in place for this dam. The most recent inspection on record was 08/07/2024.
At 50 feet, this dam is taller than 92% of dams nationwide.
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Location
| State | Illinois |
| County | Macoupin |
| Nearest City | Hettick-offstream |
| River/Stream | Trib Nassa Creek |
| Coordinates | 39.44421, -89.95745 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 50 ft |
| Dam Height | 50 ft |
| Dam Length | 620 ft |
| Year Completed | 1965 (61 years old) |
Storage & Hydraulics
| NID Storage | 967 acre-ft |
| Max Storage | 967 acre-ft |
| Normal Storage | 565 acre-ft |
| Surface Area | 37 acres |
| Drainage Area | 1 sq mi |
| Max Discharge | 4,179 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Palmyra-modesto Water Commission |
| Owner Type | Public Utility |
| Hazard Classification | Significant |
| Condition Assessment | Not assessed |
| Last Inspection | 08/07/2024 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL00772 |
| Federal ID | IL00772 |
| More Info | State Dam Safety Program |