Mother Nature again takes control of Lake Oahe
By Katie Zerr
In 2011, levels on Lake Oahe were as high as possible with the water lapping the top of dam at in Pierre. In 2012, vast areas of shoreline and floating trees that have not been seen in years are visible above the surface of the water.
What a difference a year makes.
During August in 2011, the level of Lake Oahe was at 1617.5 feet above mean sea level. On Aug. 21, 2012, the level was 1601.8 feet above mean sea level.
The difference in the level of the lake can be directly linked to the weather. Anyone who has lived in this area knows Mother Nature has the top hand when it comes to the water in the Missouri River System.
In 2011, record flooding occurred along the system, wiping out farmland and homes along the river. Homes below the dams in the system were overcome by water as the U.S. Army Corps of Engineers was forced to open the gates of those dams to let the water through.
Areas from Montana to Missouri, including the cities of Bismarck, North Dakota, Pierre, Fort Pierre, Yankton and Dakota Dunes in South Dakota, as well as thousands of acres downstream from Sioux City, Iowa, were impacted by the rapidly rising water.
The flooding was triggered by record snowfall in May in Montana and Wyoming, along with near-record spring rainfall in central and eastern Montana.
Record amounts of water were released from the dams in the spring to prevent the water from breaching the dams. In the last two weeks of May 2011, almost a year’s worth of rain fell over the Upper Basin, according to the National Weather Service. That, on top of an estimated 140 percent of normal snowpack in the Rocky Mountains, created the perfect storm for what was called “The 500-year Flood.”
In 2012, much of the same area is gripped by drought. According to the National Weather Service Drought Monitor, most of the Midwest, especially the states along the Missouri River System, are experiencing either severe, extreme or exceptional drought in most areas.
The northern areas of Montana and South Dakota, and along the river basin in North Dakota, are the areas where the drought is not as severe. In Mobridge, it is considered abnormally dry, but in Pierre, the city is in a moderate drought. The farther downstream the drier it becomes.
These conditions, coupled with a below average mountain snow pack and spring run-off, have created the formula that resulted in the lower levels of Lake Oahe.
Warm, dry weather in the spring, coupled with a drier than normal winter in the Upper Basin, led to lower than expected run-off and lower spring reservoir levels according to the Corps.
In its August forecast, the Corps projected the 2012 annual runoff to be 85 percent of normal above Sioux City, Iowa.
Runoff above Gavins Point Dam is expected to be 83 percent of normal by the end of 2012. The total volume of water stored in the Missouri River Mainstem Reservoir System will be down 1.2 million acre feet by the end of August, according to Corps estimates
Releases from Oahe Dam are expected to average 38,200 cubic feet per second (cfs) during the month of August, down from a peak of 160,000 cfs in June of 2011. The reservoir fell 2.5 feet during July and is expected to drop another 3.5 feet during August, ending the month at 1600.5 feet.
According to the National Weather Service, the three-month forecast for the Missouri River System is above normal temperatures through November and an equal chance of either above or below normal precipitation in the next three months.