MARKHAM FERRY
OperatingHydro power plant
- Capacity
- 124 MW
- Primary fuel
- Hydro
- County
- Mayes County
- Operator
- GRAND RIVER DAM AUTHORITY
- Status
- Operating
- Commissioned
- 1964
- EIA plant ID
- 2980
- Generators
- 4
- Technology
- Conventional Hydroelectric
- Net generation (2024)
- 188 GWh
- Capacity factor (2024, EIA nameplate)
- 17%
- Data vintage
- EIA-860 2024 final; EIA-923 2022-2024 final
- Coordinates
- 36.2301, -95.1823
MARKHAM FERRY, a 124 MW Hydro power plant in Mayes County, Oklahoma. Operated by GRAND RIVER DAM AUTHORITY, commissioned 1964.
How MARKHAM FERRY compares
With 124 MW of capacity, MARKHAM FERRY ranks 37th among the 73 operating power plants Bywatts maps in Oklahoma and 3rd of the 11 operating Hydro plants in the state. It accounts for about 11% of Oklahoma's operating Hydro capacity and 0.5% of all operating capacity in the state. Nationally it is the 147th-largest of the 1,243 operating Hydro plants in the database. Commissioned in 1964, it is older than 76% of the 72 operating Oklahoma plants with a recorded commissioning year. Its operator, GRAND RIVER DAM AUTHORITY, runs 4 operating plants in Oklahoma totaling 1,676 MW. It shares Mayes County with 4 other operating plants, including GRDA COAL-FIRED COMPLEX and CHOUTEAU.
EIA-860 lists 4 generators at the site with 128 MW of nameplate capacity, all conventional hydroelectric technology. Net generation was 188 GWh in 2024 (a 17% capacity factor), down 11% from 2022.
Grid neighborhood
The closest transmission line found within 10 miles is a 161 kV line, about 0.1 miles away. Another 4 operating power plants totaling 2,622 MW sit within 25 miles; the largest is GRDA COAL-FIRED COMPLEX (1,134 MW, Coal). Within 50 miles are 2 mapped data centers; the nearest is TierPoint Tulsa-Archer in Tulsa, about 45.2 miles away.
Computed by Bywatts from HIFLD power plant and transmission line records, EIA-860/923 survey data and PeeringDB data center locations; distances are straight-line. Sources and methodology
Weather peril exposure
MARKHAM FERRY is a 124 MW hydro power plant in Mayes County, OK, operated by GRAND RIVER DAM AUTHORITY, commissioned in 1964. Mayes County carries high modeled catastrophe exposure in the FEMA National Risk Index, scoring 3.6 of 5 at the 64th national percentile. Ice storm is the leading peril, rated Very High by FEMA at the 99th 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.
Mayes County hazard ratings
| Peril | FEMA rating | National percentile | Peril score | Events per year |
|---|---|---|---|---|
| Ice storm | Very High | 99th | 4.9 of 5 | 1.4 |
| Riverine flooding | Relatively Moderate | 83rd | 4.3 of 5 | 1.7 |
| Winter weather | Relatively Moderate | 83rd | 4.3 of 5 | 9.3 |
| Wildfire | Relatively Low | 81st | 4.2 of 5 | <0.01 |
| Heat wave | Relatively Moderate | 79th | 4.2 of 5 | 23.3 |
| Lightning | Relatively High | 76th | 4.0 of 5 | 55.5 |
| Hail | Relatively Low | 63rd | 3.5 of 5 | 9.2 |
| Strong wind | Relatively High | 61st | 3.5 of 5 | 7.5 |
| Earthquake | Very Low | 54th | 3.2 of 5 | <0.01 |
| Tornado | Relatively Moderate | 34th | 2.3 of 5 | 0.76 |
| Hurricane | Very Low | 31st | 2.3 of 5 | <0.01 |
Perils not assessed in Mayes 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 |
|---|---|
| Coastal flooding | FEMA rating is "Not Applicable" for this county |
Model hail, wind and flood exposure for Mayes 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.