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Missouri River Basin runoff second most in history

Latest outlook for Lake Sakakawea

Kim Fundingsland/MDN A tree clings to the shoreline in Lake Sakakawea’s Douglas Bay. The tree’s roots have become exposed due to high water in the reservoir.

The second highest runoff ever recorded in the Missouri River Basin was increased again this week as the U.S. Army Corps of Engineers released their latest projections. Significant rainfall has boosted the September forecast to 54.6 million acre feet of water, an increase of 1.7 maf from a month earlier.

The September outlook issued by the Corps for the Missouri River Basin is 215% of average, exceeded only by the record runoff of 61.0 maf in the historic flood year of 2011. Most of the water entering the system is occurring downstream from North Dakota, limiting the impact on water levels in Lake Sakakawea which has been declining for several weeks.

Lake Sakakawea stood at 1,847.7 feet Wednesday following a peak elevation near 1,852 feet earlier this summer. Inflow into the large reservoir Tuesday was recorded at 32,000 cubic feet per second. Outflow through Garrison Dam was 46,100 cfs, an amount considerably higher than average for the season. The release rate is scheduled to be reduced later this month before reaching an end of month rate of 42,000 cfs.

The Corps says Lake Sakakawea’s elevation at the end of this month should be 1,844.9 feet and continue dropping until reaching the goal of 1,837.5 feet at the end of February, 2020. Spillway level at Lake Sakakawea is 1,854.0 feet, meaning there is storage available should further heavy rainfall downstream necessitate a reduction in flows out of the reservoir.

Some of the inflow downstream, compared to the 121-year average, has reached remarkable numbers. An example is at Sioux City, Iowa where flows in the Missouri River this year have surpassed 500% of average. In comparison, Lake Sakakawea is projected to finish 2019 with inflow approximately 143% of the long-term average.

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