FORT PIERRE — As the rain fell outside, there was no need to show drought-severity maps to the representatives of state, tribal and federal governments gathered Thursday to discuss management of the Missouri River.

Instead, those at the meeting of the Missouri River Association of States and Tribes identified a new reason for caution — the prospect of spring flooding, which could be made worse by sediment built up during the drought.

The low flows during dry years meant water often moved slower than normal. That caused more silt than usual to be dropped in the Missouri’s narrow reaches and at the mouths of many of its tributaries. Now the reservoirs behind the six big dams are full again, and the combination of conditions may be a recipe for trouble next spring.

Advertisement

The situation especially concerns some state and tribal officials in North Dakota and South Dakota. They foresee a potential for flooding problems in 2010 that could be made worse if runoff from snowmelt and spring rains is higher than normal and backs up behind blockages from the additional sediment.

The matter came up several times during Thursday’s meeting.

Severe flooding occurred late last winter and spring in the Bismarck, N.D., stretch of the main river and along parts of the Cheyenne and Moreau rivers that feed into the Missouri. Oahe reservoir rose 16 feet in March and April, and a total of 21 feet from Jan. 1 to its crest last summer. The level has dropped about seven feet in the past three months.

Oahe’s surface elevation as of Thursday was 1,606.9 feet above sea level. The U.S. Army Corps of Engineers, which manages the river’s flows, plans to drop Oahe about two feet for the winter. Todd Sando, an assistant engineer for the North Dakota Water Commission, said suggestions from some in South Dakota that Oahe’s elevation remain above 1,605 over the winter makes people in the Bismarck area nervous.

 “Holding Oahe high when it is already is basically full makes us very nervous,” Sando said. “We’re very concerned about flooding again next year.”

Cheyenne River Sioux tribal council member Bob Walters said flooding along tributaries has been a problem for people living along them on the reservation.

Walters explained that the mouths of the Cheyenne and Moreau are silting in as they meet the Missouri, and water can’t flow out fast enough. That causes water to back up and flood bottomlands. He said roads have been inundated and evacuations of residents became necessary. He said cemeteries have been damaged and stretches of land no longer produce much more than cockleburs.

The reservoirs are now sufficiently full to allow a full navigation season in 2010 for the barge industry below Sioux City, Iowa, and for the hydropower dams to return to 90 percent of their normal generation of electricity, an official for the U.S. Army Corps of Engineers told the gathering.

Hydropower production ran about 70 percent of average in 2009, up from about 50 percent the two prior years.

“That is good news,” Jody Farhut, the Corps chief of water management for the Missouri River, said. “We are working our way back to normal generation.”

Based on current conditions, total runoff in the Missouri River basin will be 133 percent of normal this year. Questioned how much flexibility the corps has for adjusting Oahe during the winter period. Farhut replied that moving three feet of water from one reservoir to another is very difficult, especially if the river is already frozen.

“It is hard to make adjustments. Quite frankly, this year we were not expecting that kind of runoff into Oahe,” she said. “We knew we had good snowpack out there, but we were not expecting a huge runoff into Oahe.”