The U.S. Army Corps of Engineers (Corps) Missouri River Basin Water Management Division reduced releases from Gavins Point in early May. Downstream Missouri River and tributary flows increased due to widespread, heavy rainfall in parts of Nebraska, Kansas, and Missouri. “Rainfall events like we've seen recently can cause localized flooding downstream of the reservoir system. Gavins Point releases were reduced from 30,000 cfs to 21,000 cfs over several days to lesson downstream flooding,” said Jody Farhat, chief of the Corps' Missouri River Basin Water Management Division.
The U.S. Army Corps of Engineers (Corps) Missouri River Basin Water Management Division reduced releases from Gavins Point in early May. Downstream Missouri River and tributary flows increased due to widespread, heavy rainfall in parts of Nebraska, Kansas, and Missouri. “Rainfall events like we’ve seen recently can cause localized flooding downstream of the reservoir system. Gavins Point releases were reduced from 30,000 cfs to 21,000 cfs over several days to lesson downstream flooding,” said Jody Farhat, chief of the Corps’ Missouri River Basin Water Management Division.
Releases from Gavins Point will be increased as downstream flows recede. “Flood risk reduction remains a primary consideration. While the risk of widespread flooding from upper basin runoff is low this year, floods can and will occur as a result of spring and summer thunderstorms, particularly along the lower Missouri River,” said Farhat. When possible, the Corps will utilize the available flood control space in the reservoirs to limit downstream river levels; however, the ability to significantly reduce flood risk along the lower Missouri River diminishes at locations further downstream due to the large uncontrolled drainage area and the travel time from Gavins Point Dam.
The mainstem reservoir system began the 2017 runoff season at the base of the annual flood control pool, providing the full 16.3 million acre-feet (MAF) of flood control storage. The total volume of water stored in the reservoir system is currently 59.0 MAF. “System storage currently occupies 2.9 MAF of the 16.3 MAF flood control zone,” said Farhat, “Approximately 82 percent of the flood control storage remains available to capture runoff from the spring rainfall and mountain snowmelt.”
The 2017 runoff forecast in the Missouri River Basin above Sioux City, Iowa, is 29.7 MAF, 117 percent of normal. Runoff above Sioux City, Iowa in April was 2.7 MAF, 93 percent of normal. As of May 1, the mountain snowpack was 98 percent of the normal peak in the reach above Fort Peck and 147 percent of the normal peak in the reach from Fort Peck to Garrison. Normally the mountain snowpack peaks in mid-April; this year’s mountain snowpack will have a later-than-normal melt. View the mountain snowpack graphic here: http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf.
Navigation flow support for the start of the navigation season was at full service levels, which is designed to provide a 9-feet deep navigation channel. “Because of the higher-than-normal runoff forecast, navigation flow support was increased in mid-April to a level slightly above full service to provide beneficial use of the excess runoff while reducing flood risk,” said Farhat. “Based on the current forecast that higher service level will continue.”
Weekly updates on plains and mountain snowpack conditions, reservoir levels and other topics of interest can be viewed here: http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/weeklyupdate.pdf.
The Corps will continue to monitor basinconditions, including rainfall and mountain snow accumulation, and will adjust the regulation of the reservoir system based on the most up-to-date information.
Gavins Point Dam releases averaged 28,500 cubic feet per second (cfs) during April. Releases will be increased around mid-May, downstream conditions permitting, to prevent endangered least terns and threatened piping plovers from nesting on low sandbars. These sandbars could be inundated later in the summer when higher releases are needed to meet downstream flow targets. Releases are expected to be increased to approximately 34,000 cfs as the nesting season begins. The Gavins Point reservoir ended April at elevation 1206.1 feet and will remain near 1206.0 feet during May.
Fort Randall Dam releases averaged 26,000 cfs in April. Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point Dam. The reservoir ended April at elevation 1356.0 feet, rising 1.0 feet during the month.
Big Bend Dam releases averaged 23,200 cfs in April. Releases are expected to average 25,400 cfs this month. The reservoir will remain near its normal elevation of 1420.0 feet during May.
Oahe Dam releases averaged 26,100 cfs during April. Releases are expected to average 24,800 cfs in May. The reservoir ended April at elevation 1608.3 feet, rising 0.5 feet during the month. The reservoir level is expected to rise during May due to increases in Garrison releases and spring rains, ending the month near elevation 1610.2 feet.
Garrison Dam releases averaged 26,700 cfs during the month of April. Releases were increased from 28,000 cfs to 30,000 cfs in early May. Releases will be increased to 35,000 cfs around mid-May. Garrison reservoir ended April at elevation 1841.2 feet, falling 0.2 feet during the month. The reservoir level is expected to rise to elevation 1842.2 during May.
Fort Peck Dam releases averaged 6,300 cfs during April. Releases were increased from 6,500 cfs to 8,000 cfs in early May, and will be increased to 10,000 cfs around mid-May. The reservoir ended April at elevation 2237.2 feet, rising 1.0 feet during the month. The reservoir is expected to rise during May ending the month near elevation 2238.2 feet.
The forecast reservoir releases and elevations discussed above are not definitive. Additional precipitation, lack of precipitation or other circumstances could cause adjustments to the reservoir release rates.
The six mainstem power plants generated 819 million kWh of electricity in April. Typical energy generation for April is 690 million kWh. The power plants are projected to generate 10.6 billion kWh of electricity this year, compared to the long-term average of 9.3 billion kWh.
To view the detailed three-week release forecast for the mainstem dams, go to http://www.nwd-mr.usace.army.mil/rcc/reports/twregfcast.pdf.