Hidden Valley Lake Dam is an earth dam located in Ogle County, Illinois, built in 1968. It carries a Significant hazard potential classification.
Dam profile
NID height · 16 ft16 ft tall and 505 ft long. 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 Hidden Valley Lake Dam
The primary purpose of Hidden Valley Lake Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Rasmussen & Giannini (private). It impounds the Trib Stillman Creek near Stillman Valley.
The dam stands 16 feet tall and stretches 505 feet across, creates a reservoir covering 19 acres, has a maximum storage capacity of 256 acre-feet, and collects water from a drainage area of 2 square miles. Completed in 1968, 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 06/04/2024.
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Location
| State | Illinois |
| County | Ogle |
| Nearest City | Stillman Valley |
| River/Stream | Trib Stillman Creek |
| Coordinates | 42.03572, -89.14262 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 16 ft |
| Dam Height | 16 ft |
| Dam Length | 505 ft |
| Year Completed | 1968 (58 years old) |
Storage & Hydraulics
| NID Storage | 256 acre-ft |
| Max Storage | 256 acre-ft |
| Normal Storage | 40 acre-ft |
| Surface Area | 19 acres |
| Drainage Area | 2 sq mi |
| Max Discharge | 2,116 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Recreation |
| Owner | Rasmussen & Giannini |
| Owner Type | Private |
| Hazard Classification | Significant |
| Condition Assessment | Not assessed |
| Last Inspection | 06/04/2024 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL00671 |
| Federal ID | IL00671 |
| More Info | State Dam Safety Program |