MINOT, N.D. — Too much water in the lower reaches of the Missouri River is leading to very high water in upstream reservoirs, including Lake Sakakawea, where the water level continues to climb.
The U.S. Army Corps of Engineers determined that utilizing upstream storage in Fort Peck, Lake Sakakawea and Lake Oahe is vital to prevent additional water from aggravating already precarious flooding situations at downstream locations. There are limitations to the plan, such as unexpected or substantial rainfall that would increase runoff into Fort Peck in Montana or Lake Sakakawea.
The runoff projection into the Missouri River Basin a month ago was 42.2 million acre feet of water. As of June 1, that number was revised to 50 maf, a whopping increase that would be the second highest runoff total for the Missouri River Basin in the last 121 years and the most since 61 maf of runoff in the historic flood year of 2011.
The projected runoff includes a huge increase in water due to heavy rainfall in the lower reaches of the basin while expected snowmelt runoff from the Rocky Mountain region is beginning to impact the upper basin. Lake Sakakawea had an inflow of approximately 39,000 cubic feet per second last Saturday. That number increased to 55,000 cfs Tuesday, June 4, with releases through Garrison Dam remaining slightly under 15,000 cfs, down from 25,000 cfs early last week.
The May 1 projection had Lake Sakakawea peaking at 1,848.8 feet on June 30. As of Tuesday morning, Lake Sakakawea stood at 1,848.36 feet and calculations are that it will reach 1,851.6 feet by June 20. According to the latest three week forecast issued by the Corps, inflow into Lake Sakakawea will still exceed outflow on June 20 and the water level in the reservoir will continue to climb.
Lake Sakakawea's exclusive flood control zone is the upper four feet of the massive reservoir, from 1850 to 1854 feet, which is overflow level. At Fort Peck, where the exclusive flood control zone is 2,246 to 2,250 feet, Tuesday's water level reached 2,244.4 feet and is expected to climb to nearly 2,247 feet by June 20. Fort Peck inflow was listed at 35,000 cfs Tuesday with outflow at 8,800 cfs.
As of last Saturday, the Corps calculated that total flood control storage in the six Missouri River reservoirs was 33% occupied. That number was reduced to 30% Tuesday. Lake Oahe Dam, which is located in South Dakota but backs up water well into North Dakota, was utilizing 86.4% of its flood control storage as of Tuesday morning. Releases through Oahe Dam were 43,900 cfs Tuesday with inflow of 33,000 cfs. The water level there was listed at 2,244.4 Tuesday. Spillway level is 2,250.0 feet.
Based on current conditions, the Corps expects to begin increasing outflow from Garrison Dam early next week until reaching 42,000 cfs later in the month.