Floodwaters Add Pressure To Dam Systems, Flood Lower Basin

Snowpack could lead to more devastating floodwaters for downstream residents and businesses. ( U.S. Army Corps of Engineers )

As rain continues to fall and snow melt looms, the U.S. Army Corps of Engineers is increasing water releases from the Gavins Point Dam, near Yankton, S.D., to 90,000 cubic feet per second. Downstream farmers, business owners and home owners along the Missouri River should take heed to avoid potential damage from floodwaters.

This high release level is nearing levels not seen since the 2011 Missouri River flood, according to Yankton Daily Press and Dakotan.

The water being released is from unregulated tributaries that bring water into Gavins Point Dam’s reservoir, according to the Corps. Currently, 12 of the 14 spillway bays at Gavins Point are open and they’re using the powerhouse to pass flows. The remaining two spillways are partially open, but frozen in place from ice.

“Given the amount of water still expected to come out of the tributaries, we expect we will hold at 90,000 cubic feet per second through Saturday morning, provided the current inflow trends are maintained,” said John Remus, chief of the Corps’ Missouri River Water Management Division in Omaha, in a recent press release. “As that unregulated runoff decreases, we will be able to decrease outflows from Gavins Point.”

The primary flow source for Gavins Point is the Niobrara River basin, which has undergone exceptional challenges and failures this week. The unregulated flow is from a breach in the Spencer Dam, located just south of Spencer, Neb. This dam plays a major role in controlling the Niobrara River flow to the Missouri River.

For residents of Niobrara, Neb., the dam failure could bring catastrophic damage. The Yankton Daily Press and Dakotan is reporting the town of 400 is evacuated and a number of businesses have been destroyed in the western part of the community. In addition, many roads and highways have been rendered impassible.

In addition, citizens in Norfolk, Neb., about 8,000 total, were forced to evacuate earlier this week. Additional evacuations along the Niobrara River are anticipated.

The Corps says it’s doing what it can to reduce risk for additional downstream stakeholders. On March 14, the Corps stopped all releases from the Fort Randall Dam, the next dam upstream on the Missouri River mainstem to reduce water going to the lower Missouri River.

Despite these efforts, there is very little storage capacity behind Gavins Point, and most of what flows into the reservoir has to be released downstream, so communities from Sioux City, Iowa, to St. Louis are flooding.

The mainstem system’s annual base is 56.1-million-acre feet in reservoirs, Remus said. Anything above that, up to 72.4-million-acre feet, is available for flood control storage.

Currently the system storage is at 56.4-million-acre feet, just .3-million-acre feet above the base of the Annual Flood Control and Multiple Use Zone, so 16 to 16.3-million-acre feet of storage is available. Peak hourly inflow for Gavins Point Reservoir was about 180,000 cubic feet per second (CFS).

Here’s what the Corps is forecasting for inflows into Gavin’s Point Reservoir this week:

  • March 13- 21,000 CFS (actual)
  • March 14- 34,000 CFS (actual)
  • March 15- 102,000 CFS (estimate)
  • March 16- 80,000 CFS (estimate)
  • March 17- 44,000 CFS (estimate)

“River levels could remain high in places for several days to a week as conditions in the different basins normalize,” Remus said. Because of the runoff from South Dakota, North Dakota and Montana, the reservoirs at Oahe, Garrison and Fort Peck have been impounded. Because of this, the Missouri River is in a worse position than if the weather system had tracked further north and reduced flow into the river.

Read more about what winter storms and flooding are doing to producers in the Midwest:

Winter Storms Remains Threat to Producers During Calving Season

What's Your Weather Forecast for Planting Season?