Farhat has said repeatedly during the daily briefings there would be inter-system adjustments to maintain pool levels and to ease upstream or downstream pressure. "We expect these releases well into August,” she adds.
The flooding is along the Missouri River and its tributaries in Montana, North Dakota, South Dakota, Nebraska, Kansas and Missouri.
The Missouri flow where it meets the Mississippi will be 200,000 cfs to 225,000 cfs for at least three more weeks. That compares with the Mississippi’s 1.98 million cfs flow when it crested at Memphis in early May.
The Corps began opening the Missouri Basin spillways in early June with plans to reach peak outflows by mid-month.
It was a historic opening June 3 at Big Bend Dam, near Ft. Thompson, S.D., when the spillways were opened for floodwaters for the first time since the dam was completed in 1963. The dam powerhouse discharges 85,000 cfs, so spillways at peak released 65,000 cfs for a total of 150,000 cfs.
Spillways are opened for two reasons, Farhat said. “One is when you need to release more water than can pass through the power plants, and to avoid flow over the top of the [spillway] gates, which would damage them.”
“When the gates are raised, allowing water to pass beneath, it also has the effect of raising the top of the reservoir, allowing us to hold more in the reservoir,” she said.
The higher output levels are being felt downstream.
At Pierre, S.D., the river was almost 6 ft over flood stage on June 13, at Omaha it was at 32.28 ft., more than 3 ft past flood stage with predictions for another foot by June 18, and at St. Joseph, Mo., it was 6 ft past flood stage with another 2 ft predicted.
“We do build in high hazard areas,” said Larry Larson, executive director of the Association of State Floodplain Managers Inc. “There is a whole series of policies that don’t prevent or almost encourage” building in a flood plain – and risk being flooded, he said.
Some cities, in recent years, have relocated housing in particular, turning the land into a parks or open space, Larson said.
Cities have used Federal Emergency Management Agency grant funds to buy out owners of flood-prone properties, giving a river room to expand without causing as much damage, said Jim Schwab, manager of the American Planning Association’s Hazards Planning Research Center.
