Mill Creek Structure 1 Dam is an earth dam located in Clark County, Illinois, built in 1980. It carries a Significant hazard potential classification.
Dam profile
NID height · 81 ft81 ft tall and 1,470 ft long, taller than 97% 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 Mill Creek Structure 1 Dam
The primary purpose of Mill Creek Structure 1 Dam is flood risk reduction. The dam is designed to control downstream flooding by temporarily storing excess water during storms and releasing it at a controlled rate. The dam is owned by Clark County Park District (private). It impounds the Mill Creek near Marshall.
The dam stands 81 feet tall and stretches 1,470 feet across, creates a reservoir covering 811 acres, has a maximum storage capacity of 40,300 acre-feet, and collects water from a drainage area of 20 square miles. Completed in 1980, the structure is 46 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 04/20/2024.
At 81 feet, this dam is taller than 97% of all dams in the United States.
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Location
| State | Illinois |
| County | Clark |
| Nearest City | Marshall |
| River/Stream | Mill Creek |
| Coordinates | 39.40924, -87.79631 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 81 ft |
| Dam Height | 81 ft |
| Dam Length | 1,470 ft |
| Year Completed | 1980 (46 years old) |
Storage & Hydraulics
| NID Storage | 40,300 acre-ft |
| Max Storage | 40,300 acre-ft |
| Normal Storage | 17,549 acre-ft |
| Surface Area | 811 acres |
| Drainage Area | 20 sq mi |
| Max Discharge | 39,280 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | Clark County Park District |
| Owner Type | Private |
| Hazard Classification | Significant |
| Condition Assessment | Not assessed |
| Last Inspection | 04/20/2024 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL01233 |
| Federal ID | IL01233 |
| More Info | State Dam Safety Program |