One Horse Gap is an earth dam located in Pope County, Illinois, built in 1973. It carries a Significant hazard potential classification and has a fair condition assessment.
Dam profile
NID height · 36 ft36 ft tall and 443 ft long, taller than 82% of U.S. dams with a recorded height. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic embankment section and the water level is illustrative.
About One Horse Gap
The primary purpose of One Horse Gap is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Usda Fs (federal). It impounds the Tr-grand Pierre.
The dam stands 36 feet tall and stretches 443 feet across, creates a reservoir covering 29 acres, and has a maximum storage capacity of 304 acre-feet. Completed in 1973, 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. Its condition is rated fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. The most recent inspection on record was 08/01/2019.
At 36 feet, this dam is taller than 82% of dams nationwide.
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Location
| State | Illinois |
| County | Pope |
| Nearest City | None |
| River/Stream | Tr-grand Pierre |
| Coordinates | 37.51757, -88.44607 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 36 ft |
| Dam Height | 30 ft |
| Dam Length | 443 ft |
| Year Completed | 1973 (53 years old) |
Storage & Hydraulics
| NID Storage | 304 acre-ft |
| Max Storage | 304 acre-ft |
| Normal Storage | 193 acre-ft |
| Surface Area | 29 acres |
| Max Discharge | 262 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Recreation |
| Owner | Usda Fs |
| Owner Type | Federal |
| Hazard Classification | Significant |
| Condition Assessment | Fair |
| Last Inspection | 08/01/2019 |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | IL50615 |
| Federal ID | IL50615 |
| More Info | State Dam Safety Program |