OMAHA, Neb. — Drought conditions in the Missouri River basin expanded during the month of August resulting in reduced inflows to the six Missouri River Mainstem reservoirs.
Runoff into the Missouri River basin above Sioux City, Iowa during the month of August was 64 percent of normal.The calendar year runoff forecast is 20.7 million acre feet (83 percent of normal). Last month’s forecast was 21 million acre feet (85 percent of normal). Last year’s historic runoff totaled 61 MAF above Sioux City, nearly 3 times more than this year.
"During August, runoff in the upper basin was significantly below normal, especially in the reach between the Fort Peck and Garrison dams where it was only 46 percent of normal," said Jody Farhat, Chief of the Missouri Water Management Division.Aside from a few areas in northern Montana and central North Dakota that have received slightly above normal precipitation, the majority of the upper basin received less than 50 percent of normal August precipitation.
As a result, reservoir levels in the upper three large reservoirs, Fort Peck, Garrison and Oahe, fell 2 to 3.5 feet during the month.The total volume of water stored in the Missouri River Mainstem Reservoir System on Sept. 1 was 54.2 million acre feet, down from 56.4 maf on Aug.1. The base of the flood control and multiple use zone is 56.8 maf. The annual flood control pool is the desired operating zone for the system because it allows the Corps to serve all eight congressionally authorized purposes.
"Drought conservation measures will be implemented beginning this winter based on the Sept. 1 storage check," said Farhat."Winter releases from Gavins Point will be at minimum levels, averaging near 12,000 cfs from December through February. Temporary increases above 12,000 cfs will be provided during periods of ice formation to keep water intakes along the lower river operational."When the reservoir system is full, Gavins Point winter releases are generally scheduled near 17,000 cfs, or higher if flood water is being evacuated.
Although the runoff forecast continues to shift downward, there is enough water in the reservoir system to continue to provide good service to all eight of the congressionally authorized purposes for the remainder of the calendar year.The purposes include flood control, navigation, hydropower, irrigation, water supply, water quality control, recreation, and fish and wildlife.
Based on the July 1 storage check, the Corps is providing a full 8-month navigation season (April 1 to Dec. 1) and full service flows, which are designed to provide a 9-foot-deep by 300-foot-wide navigation channel.The navigation season’s normal start and end dates are indicated below:
Normal Navigation Season Start/End Dates
Sioux City, Iowa
Nebraska City, Nebraska
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Kansas City, Missouri
Mouth near St. Louis, Missouri
Drier than normal conditions in the lower basin have necessitated above normal releases from the reservoir system to meet navigation targets along the river.With very little water coming into the Missouri River from the tributaries, Gavins Point releases have been set at 38,500 cfs to meet the 41,000 cfs flow target at Kansas City.Without additional rain, releases may need to be increased to 39,000 cfs by mid-September. Releases typically average 32,000 to 34,000 cfs at this time of year to meet full service navigation targets.
Gavins Point releases averaged 37,800 cfs during the month of August. The end of month elevation was 1206.4 feet.The reservoir will gradually rise to its normal fall pool elevation of 1207.5 feet in September.
Fort Randall releases averaged 36,500 cfs during August. September releases are expected to average 36,800 cfs as necessary to maintain the elevation at Gavins Point.The reservoir ended the month near elevation 1354.7 feet, up 0.2 feet from the previous month.It is expected to decrease by 1.2 feet this month, ending September near elevation 1353.5 feet.The reservoir is normally drawn down to 1337.5 feet in the fall to provide space for winter hydropower generation at Oahe and Big Bend.The annual drawdown will continue in October and November.
Big Bend releases averaged 34,700 cfs during the month of August. They are expected to average 35,200 cfs during the month of September.The reservoir will remain near its normal elevation of 1420 feet this month.
Oahe releases averaged 38,100 cfs during the month of August.Releases are expected to average 35,500 cfs during the month of September. The reservoir ended the month at elevation 1600.5 feet, down 3.5 feet during the month. The reservoir is expected to drop another 3 feet during September, ending the month at 1597.5 feet.
Garrison releases averaged 24,600 cfs in August. Releases will remain at 24,500 cfs until mid-September and then be decreased to 19,500 cfs.The reservoir ended the month at elevation 1834.8 feet, down 2.4 feet from the previous month. It is forecast to decline 1.2 feet in September, ending the month near 1833.6 feet.
Fort Peck releases averaged 10,900 cfs in August.Releases will remain near 10,000 cfs in September with the exception of higher flows early in the month for spillway testing. The reservoir ended the month at elevation 2233.9 feet, down 2 feet from the previous month.It is expected to decline by 1.9 feet this month, ending the month near elevation 2232.0 feet.
The reservoir releases and elevations discussed above should not be assumed to be definitive.Additional precipitation or lack of precipitation in the basin could cause adjustments to the reservoir release rates.
The six mainstem power plants generated 1,106 million kilowatt hours of electricity in August. Typical power generation for the month of August is 1,053 million kWh.The power plants are projected to generate a 10.3 billion kWh of electricity this year, which is near the normal amount of 10 billion kWh hours.
Page 3 of 3 - To view the detailed three-week release forecast for the mainstem dams, go to: http://www.nwd-mr.usace.army.mil/rcc/reports/twout.html.