By Philip Reed

 Editor’s note: The following report summarizes data from WAPA’s Hydropower Conditions webpage for straight power purchase costs, which are based solely upon hydrology, actual hydropower generation and related generation shortages. Readers may review all data by visiting wapa.gov, Power Marketing, Hydropower Conditions.

 One of the biggest challenges for hydropower is water variability due to intermittent drought and flooding. By definition, hydropower needs water to generate electricity. Without it, WAPA must buy power on the open market from other sources to meet contractual obligations to its customers. This is referred to as purchased power.

 In an ideal year, snowpack around the West is average or above average, yielding snowmelt runoff to recharge reservoirs behind the dams and powerplants that provide the power WAPA markets.

 Federal dam owners such as the Bureau of Reclamation, the Army Corps of Engineers and the International Boundary and Water Commission move water to federal hydroelectric powerplants. WAPA markets the subsequent power generated to around 700 preference customers.  Its customers, in turn, sell that power to more than 40 million Americans.

​ Water around WAPA in 2020

WAPA’s actual generation was 100.3% of average in water year 2020, for a total generation of 26,985 gigawatt-hours. For the same period, total purchased power was 2,124 GWh with actual purchase power expenses of $65,959,195 equating to $31.06 per megawatt-hour.

The Colorado River Storage Project Management Center projected most probable purchase power expenses for water year 2020 to be $14,195,307. Actual purchase power expenses were $16,259,069. The cost per MWh was $28.63. Lake Powell ended the water year with an  elevation of 3,596 feet, which is about 104 feet below the maximum reservoir level and 106 feet above the minimum generation level. The storage volume for Lake Powell was 11.4 million acre-feet at the end of September, or about 46% of capacity. Drought conditions persist in the Upper Colorado River Basin with below average annual inflow forecasted for Lake Powell again in water year 2021. Currently 9.0 MAF is the forecasted annual release for WY 2021, but it could be reduced as low as 8.23 MAF.

 Desert Southwest’s hydrology is mostly dependent on the Colorado River Basin snowpack and precipitation above Lake Powell. Precipitation was 36% of average at the end of September. The region’s most probable projected purchase power expenses were $21,308,920. Actual purchase power expenses were higher at $22,548,678, with a cost per MWh of $54.00. Lake Mead ended the water year with an elevation of 1,083 feet, about 136 feet below the full storage level and 133 feet above the minimum generation level. Lake Mead’s elevation peaked at 1,099 feet in March.

 In Rocky Mountain, at the end of September, reservoir inflows were 66% of average and storage was 107% of average. The projected purchase power expenses were $10,116,670, but actual purchase power expenses were higher at $14,480,376. The cost per MWh was $32.37.

 Sierra Nevada ended the water year with 97% of the 15-year average reservoir storage for Trinity, 91% for Shasta, 92% for Folsom and 112% percent for New Melones. Accumulated inflow for the same date was 39% of the 15-year average for Trinity, 63% for Shasta, 57% for Folsom and 60% for New Melones. The region began water year 2020 with a most probable projection of purchase power of $3,130,909 but ended with an actual expense of $7,662,135. The cost per MWh was $15.39.

 Much of the Upper Great Plains service area is experiencing moderate drought conditions and small areas in South Dakota and Montana experiencing extreme drought. The Missouri River basin ended the water year with runoff of 24,400 MAF, or 105% of average. System storage is  7.8 MAF. About 89% of the designated flood control storage is available to store runoff from mountain snowmelt and spring and summer rainfall events. The region’s most probable projection for purchase power was $8,715,786. Actual purchase power expenses were significantly  power at $5,008,937. The cost per MWh was $25.97.

Anticipating water year 2021

The Seasonal Drought Outlook provided by the National Weather Service’s Climate Prediction Center in November 2020 predicted persistent drought throughout most of the western United States. Significant drought development is also predicted in states such as Texas, Oklahoma, Kansas and areas of Southern California.

 The predictions also show drought conditions improving in the northwest and northeast. Drought development is anticipated in the southeast. The NWS emphasized that its predictions are made in accordance with large-scale trends, which are based on “subjectively derived  probabilities guided by short-and long-range statistical and dynamical forecasts.” They emphasize caution and regular checking of updated drought predictions.

 Note: Reed is a public affairs specialist. ​

Hydropower Generation Average vs. Most probable vs. Actual graph depicting all three lines over time

Last modified on September 12th, 2023