LOWER MONUMENTAL
OperatingHydro power plant
- Capacity
- 810 MW
- Primary fuel
- Hydro
- County
- Walla Walla County
- Operator
- USACE NORTHWESTERN DIVISION
- Status
- Operating
- Commissioned
- 1969
- EIA plant ID
- 3927
- Generators
- 6
- Technology
- Conventional Hydroelectric
- Net generation (2024)
- 1,281 GWh
- Capacity factor (2024, EIA nameplate)
- 18%
- Data vintage
- EIA-860 2024 final; EIA-923 2022-2024 final
- Coordinates
- 46.5634, -118.5394
LOWER MONUMENTAL, an 810 MW Hydro power plant in Walla Walla County, Washington. Operated by USACE NORTHWESTERN DIVISION, commissioned 1969.
How LOWER MONUMENTAL compares
With 810 MW of capacity, LOWER MONUMENTAL ranks 8th among the 126 operating power plants Bywatts maps in Washington and 7th of the 65 operating Hydro plants in the state. It accounts for about 3.8% of Washington's operating Hydro capacity and 2.7% of all operating capacity in the state. Nationally it is the 26th-largest of the 1,243 operating Hydro plants in the database. Commissioned in 1969, it is older than 63% of the 125 operating Washington plants with a recorded commissioning year. Its operator, USACE NORTHWESTERN DIVISION, runs 5 operating plants in Washington totaling 5,489 MW. It shares Walla Walla County with 3 other operating plants, including ICE HARBOR and FPL ENERGY VANSYCLE LLC (WA).
EIA-860 lists 6 generators at the site with 810 MW of nameplate capacity, all conventional hydroelectric technology. Net generation was 1,281 GWh in 2024 (an 18% capacity factor), down 24% from 2022. Its generators came online between 1969 and 1979.
Grid neighborhood
The nearest named substation is LOWER MONUMENTAL (500 kV), about 0.9 miles away; the closest transmission line found within 10 miles is a 500 kV line owned by BONNEVILLE POWER ADMINISTRATION, under 0.1 miles away. One other operating power plant sits within 25 miles: LITTLE GOOSE (810 MW, Hydro).
Computed by Bywatts from HIFLD power plant, substation and transmission line records and EIA-860/923 survey data; distances are straight-line. Sources and methodology
Weather peril exposure
LOWER MONUMENTAL is an 810 MW hydro power plant in Walla Walla County, WA, operated by USACE NORTHWESTERN DIVISION, commissioned in 1969. Walla Walla County carries low modeled catastrophe exposure in the FEMA National Risk Index, scoring 1.0 of 5 at the 1st national percentile. Earthquake is the leading peril, rated Relatively Moderate by FEMA at the 90th 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.
Walla Walla County hazard ratings
| Peril | FEMA rating | National percentile | Peril score | Events per year |
|---|---|---|---|---|
| Earthquake | Relatively Moderate | 90th | 4.6 of 5 | <0.01 |
| Wildfire | Relatively Low | 76th | 4.1 of 5 | <0.01 |
| Heat wave | Relatively Moderate | 67th | 3.7 of 5 | 7.2 |
| Riverine flooding | Relatively Low | 48th | 2.9 of 5 | 0.61 |
| Strong wind | Relatively Low | 26th | 2.0 of 5 | 0.33 |
| Lightning | Relatively Low | 9th | 1.3 of 5 | 10.5 |
| Hail | Relatively Low | 9th | 1.3 of 5 | 0.32 |
| Ice storm | Relatively High | 6th | 1.2 of 5 | 0.54 |
| Winter weather | Relatively Moderate | 6th | 1.2 of 5 | 9.2 |
| Tornado | Very Low | 6th | 1.2 of 5 | 0.04 |
Perils not assessed in Walla Walla 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 Walla Walla 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.