Sakakawea outlook plunges
Drought conditions throughout basin
RIVERDALE – Expectations for runoff into Lake Sakakawea this year have dropped considerably. According to the latest projections issued by the U.S. Army Corps of Engineers, the state’s largest body of water is now expected to peak at 1,834.4 feet, nearly four feet lower than expectations one month ago.
The reason? Drought conditions that exist or are continuing to develop throughout the Missouri River Basin.
2021 is shaping up to be one of the driest years on record with Missouri Basin runoff another indicator of just how dry the landscape has become over a wide section of the United States. One year ago the May 1 runoff forecast called for 32.2 million acre feet of water to enter the Missouri River Basin. This May the forecast has plunged to 17.8 maf, 69% of the 25.8 maf average.
The April 1 outlook called for an end-of-month elevation of 1,837.0 feet. The actual number was 1.7 feet less at 1,835.3 feet, making the ninth time in the past 10 months in which inflow fell short of expectations. The exception was December 2020 when runoff was a mere 0.4 maf more than projected.
While a summer peak elevation of 1,834.4 feet should not present any particular problems along the reservoir this year, it will leave the reservoir vulnerable to low water problems in 2022. The annual February target level for Lake Sakakawea is 1,837.5 feet, the lower level of the flood control zone that peaks at spillway level, slightly above 1,854 feet. Current projections show Lake Sakakawea to be at 1,831.9 feet in Feb. 2022.
“It’s low and the basin is dry and continues to get dry,” said Todd Lindquist, Corps project manager, Riverdale. “Our plains snowpack runoff was essentially zero and we haven’t got any spring precipitation.”
In creating the runoff outlooks for the Missouri River Basin the basic formula used is that 50% of runoff comes from mountain snowmelt, 25% from Plains snowpack, and 25% from annual rainfall. Plains snowpack this year was extremely minimal, as was rainfall with long-term forecasts favoring a worsening of drought conditions.
Sakakawea’s lowest elevation since construction on Garrison Dam was completed in 1955 was 1,807.1 feet in Feb. 2007. Peak elevation that year was 1,818.3 feet. Sakakawea experienced very low water levels from 2005-2008, a period when many additional “low water” boat ramps were constructed throughout the reservoir. Most of those boat ramps have been under water for several years.
Lake Sakakawea was at 1,835.08 feet Tuesday with an inflow of 15,000 cubic feet per second and an outflow of 21,800 cfs.