GARRISON RESERVOIR AND DAM
OperatingHydro power plant
- Capacity
- 614 MW
- Primary fuel
- Hydro
- County
- Mercer County
- Operator
- USACE-MISSOURI RIVER DISTRICT
- Status
- Operating
- Commissioned
- 1956
- EIA plant ID
- 2815
- Generators
- 5
- Technology
- Conventional Hydroelectric
- Net generation (2024)
- 2,061 GWh
- Capacity factor (2024, EIA nameplate)
- 40%
- Data vintage
- EIA-860 2024 final; EIA-923 2022-2024 final
- Coordinates
- 47.5025, -101.4318
GARRISON RESERVOIR AND DAM, a 614 MW Hydro power plant in Mercer County, North Dakota. Operated by USACE-MISSOURI RIVER DISTRICT, commissioned 1956.
How GARRISON RESERVOIR AND DAM compares
With 614 MW of capacity, GARRISON RESERVOIR AND DAM ranks 5th among the 40 operating power plants Bywatts maps in North Dakota. It accounts for about 9.5% of all operating capacity in North Dakota. Nationally it is the 36th-largest of the 1,243 operating Hydro plants in the database. Commissioned in 1956, it is older than 95% of the 40 operating North Dakota plants with a recorded commissioning year. It shares Mercer County with 3 other operating plants, including ANTELOPE VALLEY and LELAND OLDS.
EIA-860 lists 5 generators at the site with 583 MW of nameplate capacity, all conventional hydroelectric technology. Net generation was 2,061 GWh in 2024 (a 40% capacity factor), up 15% from 2022. Its generators came online between 1956 and 1960.
Grid neighborhood
The closest transmission line found within 10 miles is a 230 kV line, under 0.1 miles away. Another 3 operating power plants totaling 2,737 MW sit within 25 miles; the largest is COAL CREEK (1,212 MW, Coal).
Computed by Bywatts from HIFLD power plant and transmission line records and EIA-860/923 survey data; distances are straight-line. Sources and methodology
Weather peril exposure
GARRISON RESERVOIR AND DAM is a 614 MW hydro power plant in Mercer County, ND, operated by USACE-MISSOURI RIVER DISTRICT, commissioned in 1956. Mercer County carries critical modeled catastrophe exposure in the FEMA National Risk Index, scoring 4.8 of 5 at the 95th national percentile. Winter weather is the leading peril, rated Relatively Moderate by FEMA at the 98th percentile.
The Bywatts loss layer is calibrated to solar PV hardware, so it is not applied to a hydro plant. The ratings below are the FEMA National Risk Index county hazard ratings for this location.
Mercer County hazard ratings
| Peril | FEMA rating | National percentile | Peril score | Events per year |
|---|---|---|---|---|
| Winter weather | Relatively Moderate | 98th | 4.9 of 5 | 18.4 |
| Hail | Relatively Moderate | 96th | 4.8 of 5 | 2.5 |
| Heat wave | Very Low | 90th | 4.6 of 5 | 1.6 |
| Ice storm | Relatively Moderate | 87th | 4.5 of 5 | 0.64 |
| Wildfire | Very Low | 66th | 3.6 of 5 | <0.01 |
| Strong wind | Relatively Low | 64th | 3.6 of 5 | 1.5 |
| Tornado | Relatively Low | 48th | 2.9 of 5 | 0.32 |
| Riverine flooding | Very Low | 40th | 2.6 of 5 | 0.43 |
| Lightning | Very Low | 36th | 2.5 of 5 | 29.7 |
| Earthquake | Very Low | 6th | 1.3 of 5 | <0.01 |
Perils not assessed in Mercer County
These perils carry no usable National Risk Index figure for this county, so they are excluded from the scoring rather than scored zero. A zero would claim the peril was assessed and found benign.
| Peril | Why it is not scored |
|---|---|
| Hurricane | FEMA rating is "Not Applicable" for this county |
| Coastal flooding | FEMA rating is "Not Applicable" for this county |
Model hail, wind and flood exposure for Mercer County in the weather risk calculator
Ratings are the FEMA National Risk Index county hazard ratings; the peril score is a Bywatts transform of the FEMA national percentile. Full data sources and the solar vulnerability methodology are in the weather risk calculator.
Modeled estimate for screening and negotiation. Built from FEMA National Risk Index county hazard data and a solar vulnerability layer documented above. Not a quote, a binder, or actuarial advice, and not a substitute for a carrier's own model. Hazard data: FEMA National Risk Index December 2025, synced 2026-07-24. Resolution is county level, not site level.