Mississippi River Lock And Dam 21
Mississippi River Lock And Dam 21 is a concrete dam located in Adams County, Missouri, built in 1938. It carries a Significant hazard potential classification.
About Mississippi River Lock And Dam 21
The primary purpose of Mississippi River Lock And Dam 21 is navigation. The dam maintains water levels sufficient for boat and barge traffic, supporting commercial or recreational navigation on the waterway. The dam is owned by Usace - Rock Island District (federal). It impounds the Mississippi River near Hannibal.
The dam stands 48 feet tall and stretches 3,116 feet across, creates a reservoir covering 8,843 acres, has a maximum storage capacity of 62,000 acre-feet, and collects water from a drainage area of 135,000 square miles. Completed in 1938, the structure is well-established, with more than 75 years of service.
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 07/27/2023.
At 48 feet, this dam is taller than 92% of dams nationwide.
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Location
| State | Missouri |
| County | Adams |
| Nearest City | Hannibal |
| River/Stream | Mississippi River |
| Coordinates | 39.90448, -91.42988 |
Physical Characteristics
| Dam Type | Concrete |
| NID Height | 48 ft |
| Dam Length | 3,116 ft |
| Year Completed | 1938 (88 years old) |
Storage & Hydraulics
| NID Storage | 62,000 acre-ft |
| Max Storage | 62,000 acre-ft |
| Surface Area | 8,843 acres |
| Drainage Area | 135,000 sq mi |
| Max Discharge | 529,000 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Navigation |
| Owner | USACE - Rock Island District |
| Owner Type | Federal |
| Hazard Classification | Significant |
| Condition Assessment | Not Available |
| Last Inspection | 07/27/2023 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | MO10304 |
| Federal ID | MO10304 |
| More Info | State Dam Safety Program |