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Flooded Main Street in Hamburg, Iowa, on March 20.

A surge in snowmelt on the upper Missouri River is putting the squeeze on efforts by the Army Corps of Engineers to moderate releases from the dams that feed water downstream.

As a result, the corps has increased releases from Gavins Point Dam, the farthest downstream of six massive dams. Flows from that dam affect river levels in downstream communities such as Omaha; Plattsmouth, Nebraska; Hamburg, Iowa; and St. Joseph, Missouri.

More water flowing into the river isn’t what downstream communities want as they struggle to recover from historic flooding. But John Remus, who oversees the corps’ management of the Missouri River system, said the corps has to increase releases from the dams to save room for runoff and prevent potentially worse problems later in the season.

The releases by themselves won’t trigger significant flooding downstream, Remus said. The bigger problem for the lower basin will be spring rains.

Remus said the agency is reacting to a substantial amount of runoff from Plains snowpack. The amount of snow itself is not extraordinary, according to the corps. Instead, the problem is that warm weather is causing it to melt faster and in a greater volume.

Additionally, the ground in South Dakota is frozen, so snowmelt is simply flushing into the reservoirs as if the state were one large “parking lot,” he said.

Although releases have increased, the corps is holding back substantially more water than it is letting out because the reservoirs still have room. On Tuesday, the reservoirs still had more than 80 percent of their designated capacity for storing runoff.

On Tuesday, releases from Gavins Point Dam were targeted for 30,000 cubic feet per second. The corps plans to increase that to at least 36,000 cfs. The winter baseline amount was 20,000 cfs.

Rain isn’t forecast in the upper basin for the next several days, Remus noted. That takes some pressure off the corps. During the historic flooding of 2011, heavy rains combined with extraordinary snowmelt to generate a summerlong flood along the Missouri River.

Gavins Point is also the dam that handles water from the Niobrara River, where devastating ice jams and flooding occurred. At the peak of the flooding, flows from the Niobrara River were estimated between 170,000 and 200,000 cubic feet per second. Those flows are now down to about 23,000 cfs, but there remains “a lot of water” stored in the Niobrara flood plain and in the snowpack in the upper reaches of the Niobrara basin, Remus said. As a result, declines in the Niobrara are expected to be slow.

Rain is forecast later this week in the lower basin. Southeast Nebraska, southern Iowa and points south could see 1.5 inches of rain, said Kevin Low, a hydrologist at the National Weather Service. Along the Missouri-Iowa border, 2.5 inches of rain is possible, Low said.

Preliminary simulations indicate that the Missouri River could reach moderate flood stage along the southern stretch of the Nebraska-Iowa border. Worse runoff problems are expected near St. Joseph.

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Nancy Gaarder helps cover public safety and weather events as an editor on The World-Herald's breaking news desk. Follow her on Twitter @gaarder. Phone: 402-444-1102.

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