oahe dam releases

On Aug. 26, 2019, the U.S. Army Corps of Engineers began releasing water from Oahe Dam through the regulating tunnels on the west end of the dam, into the “stilling basin,” seen here, to handle increases release levels. The diversion of some of the dam releases from the power plant on the east end of the dam is to facilitate maintenance work on the power plant, which houses seven turbines, which will go on until nearly Christmas. (Patrick Callahan/OaheTV)

It was a wet August across South Dakota and other parts of the Upper Missouri River Basin. That means near-record runoffs will flow into the mainstem reservoirs, including Lake Oahe, and this will result in high levels of releases through the fall.

This was the key message Thursday from the managers of the Missouri River with the U.S. Army Corps of Engineers office in Omaha during a conference call across several states.

There could be above average precipitation this fall, they also said.

Rainfall in August was more than 150 percent of normal across much of South Dakota and Nebraska, parts of North Dakota and in eastern Montana.

Both the Fort Randall and Gavins Point reaches in southern South Dakota saw their wettest August on record. The Sioux City reach saw its second-wettest August. And the Lake Oahe reach experienced its third-wettest August on record, according to the Army Corps’ report on Thursday.

As evidence: the last day of August brought 0.19 inch of rain to Pierre, making the month’s total 3.73 inches on the city, measured at the airport. That’s more than double the 30-year norm for the month of 1.83 inches.

Pierre has seen 24.15 inches of precipitation in the first eight months of the year, 9 inches more than normal and more than a normal full year.

It’s been that way all over.

This prompted the Army Corps to hold more weekly phone conference calls with officials and news reporters from South Dakota, North Dakota, Montana, Wyoming, Iowa, Nebraska, Kansas and Missouri. The huge damage from flooding in the lower Missouri Basin has been the big story and Army Corps officials gave updates on the levee repair and reconstruction which will go on for a long time.

The forecast for 2019 runoff in the Upper Basin of the Missouri is 54.6 million acre-feet (MAF), which would be, if the rain continues, the second-highest runoff in 121 years of record-keeping.

Only 2011, with 61 MAF, saw more water; and that resulted in devastating floods in Pierre and Fort Pierre and across much of the basin.

Third-highest runoff was 49 MAF in 1997, following the big winter of blizzards.

In the four lower reaches alone — Sioux City, Gavins Point, Fort Randall and Oahe — the projected runoff by New Year’s Eve is about 30 MAF, which exceeds the average annual runoff for the entire Upper Basin, the Army Corps managers reported on Thursday.

The reservoirs behind Oahe Dam — Garrison Dam and Fort Peck Dam — have fallen slightly but steadily the past month. Still these reservoirs remain high as the Army Corps looks to drain more water to prepare for the winter.

“As a result of the high reservoir levels and the forecasted above-average runoff for the remainder of the summer and fall, releases from all the system’s projects will be much above average for the next several months, and possibly as late as November, to ensure evacuation of all stored flood waters prior to the start of the 2020 runoff season,” John Remus, chief of Army Corps river management division based in Omaha, said Thursday in a news release from the conference call.

Releases from Gavins Point, described as the bottom of the Upper Basin’s drainage, will remain at 70,000 cubic feet per second (cfs) — twice the normal release rate during this time of year — perhaps into November, Remus said. It all depends on how much rain comes down this fall.

Releases from Oahe Dam will remain at the current level of about 57,000 cfs, as a daily average into November, Army Corps managers said. (Releases vary during the day partly due to power generation needs),

Meanwhile, the work on the power plants at Oahe Dam will continue, with one or two turbines down at one time until nearly Christmas on the east end of the dam. This means the releases will continue to use the regulator tunnels on the dam’s west end, where the water comes out into the stilling basin.

Lake Oahe was at 1,615.7 feet above sea level on Aug. 31, after falling 1.7 feet during the month. The goal is to see it fall to 1,613.4 feet by Oct. 1. Earlier this summer it was into the “exclusive flood control zone,” the “top” three feet in the reservoir which begins at 1617 feet.

As of Aug. 31, there were 21.41 MAF stored behind Oahe Dam — more than any of the other five mainstem dams. This is 121 percent of the average storage from 1967-2018, according to figures provided by the Army Corps.

Gavins Point and Fort Randall are actually storing less than the 50-year average as of Aug. 31. Garrison was at 21.2 MAF, which is 119 percent of the 50-year average; Fort Peck was at 17.05 MAF, which is 118 percent of average.

The total system had 65.56 MAF stored, 118 percent of the 50-year average.

A collateral result of the high runoff and high reservoirs and high releases is power: The six mainstem dams all have power plants with turbines turning and in August they generated a record total of 1540 million kWh (kilowatt hours) of electricity, which was 153 percent of the “typical energy generation” in August of 1003 kWh, the Army Corps reported on Thursday.

The six dams’ power plants are projected to generate 13.4 billion kWh of electricity in 2019, the Army Corps says.

That would be about enough to power 1.3 million homes for the year and about 43 percent more than the long-term average of 9.4 billion kWh produced per year by the dams. (That’s based on U.S. Energy Department figures that an average U.S. home uses about 10,399 kWh per year.)

From Oct. 22 — 25, the Army Corps will hold seven public meetings up and down the Missouri River Basin. Usually Pierre or Fort Pierre hosts one such meeting, but details weren’t worked out yet, Army Corps officials said Thursday.

The meetings are to “update the region on the current hydrological conditions and the planned operation of the mainstem reservoir system during the remaining fall months.”

They also will present the draft plans for operating the management of the “system” in 2020.

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