Rock Rapids Milldam is a gravity dam located in Lyon County, Iowa, built in 1931. It carries a Low hazard potential classification.
Dam profile
NID height · 7 ft7 ft tall and 220 ft long. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic concrete gravity section and the water level is illustrative.
About Rock Rapids Milldam
The primary purpose of Rock Rapids Milldam 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 City of Rock Rapids (local government). It impounds the Rock River near Rock Rapids.
The dam stands 7 feet tall and stretches 220 feet across, creates a reservoir covering 10 acres, has a maximum storage capacity of 75 acre-feet, and collects water from a drainage area of 777 square miles. Completed in 1931, the structure is well-established, with more than 75 years of service.
This dam has a low hazard potential classification, meaning that failure would cause minimal damage, limited primarily to the dam owner's property, with no expected loss of life. The most recent inspection on record was 10/18/1989. That was over 37 years ago.
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Location
| State | Iowa |
| County | Lyon |
| Nearest City | Rock Rapids |
| River/Stream | Rock River |
| Coordinates | 43.43700, -96.16690 |
Physical Characteristics
| Dam Type | Gravity |
| NID Height | 7 ft |
| Dam Height | 7 ft |
| Dam Length | 220 ft |
| Year Completed | 1931 (95 years old) |
Storage & Hydraulics
| NID Storage | 75 acre-ft |
| Max Storage | 75 acre-ft |
| Normal Storage | 49 acre-ft |
| Surface Area | 10 acres |
| Drainage Area | 777 sq mi |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Water Supply |
| Owner | City of Rock Rapids |
| Owner Type | Local Government |
| Hazard Classification | Low |
| Condition Assessment | Not assessed |
| Last Inspection | 10/18/1989 |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | IA01317 |
| Federal ID | IA01317 |
| More Info | State Dam Safety Program |