H.k. Thatcher Lock and Dam is a gravity dam located in Union County, Arkansas, built in 1983. It carries a Significant hazard potential classification.
Dam profile
NID height · 80 ft80 ft tall and 698 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 concrete gravity section and the water level is illustrative.
About H.k. Thatcher Lock and Dam
The primary purpose of H.k. Thatcher Lock and Dam 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 - Vicksburg District (federal). It impounds the Ouachita near Moro Bay.
The dam stands 80 feet tall and stretches 698 feet across, creates a reservoir covering 12,200 acres, has a maximum storage capacity of 108,000 acre-feet, and collects water from a drainage area of 6,569 square miles. Completed in 1983, the structure is 43 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 09/04/2025.
At 80 feet, this dam is taller than 97% of all dams in the United States.
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Location
| State | Arkansas |
| County | Union |
| Nearest City | Moro Bay |
| River/Stream | Ouachita |
| Coordinates | 33.30665, -92.48316 |
Physical Characteristics
| Dam Type | Gravity |
| NID Height | 80 ft |
| Dam Length | 698 ft |
| Year Completed | 1983 (43 years old) |
Storage & Hydraulics
| NID Storage | 108,000 acre-ft |
| Max Storage | 108,000 acre-ft |
| Normal Storage | 79,900 acre-ft |
| Surface Area | 12,200 acres |
| Drainage Area | 6,569 sq mi |
| Max Discharge | 250,000 cfs |
| Spillway Type | Controlled |
Ownership & Safety
| Purpose | Navigation |
| Owner | USACE - Vicksburg District |
| Owner Type | Federal |
| Hazard Classification | Significant |
| Condition Assessment | Not assessed |
| Last Inspection | 09/04/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | AR01515 |
| Federal ID | AR01515 |
| More Info | State Dam Safety Program |