Normal Rocky Mtn. Snowpack Good for Missouri River Users

Given that the mountain snowpack is near normal for this time of the year, but the plains snowpack is below normal, the current forecast for runoff in 2009 is 22.3 million acre-feet, about 90 percent of average.

"The snowpack is a good sign, but it's too early to be very optimistic about significant recovery," said Larry Cieslik, chief of the Water Management office in Omaha.

"2008 was the first year since 1999 with runoff above the normal 24.8 million acre-feet," Cieslik said. "The higher inflows helped, but another major contributor to the higher reservoir levels was the weeks of low releases due to good downstream tributary inflow. It remains to be seen if downstream inflow will be good again this year."

Missouri River in Montana (Photo courtesy Montana Fish, Wildlife and Parks)

The longest river in the United States, the Missouri begins at the confluence of the Madison, Jefferson, and Gallatin rivers in Montana, and flows south and east into the Mississippi River north of St. Louis, Missouri. At 2,540 miles in length, it drains about one-sixth of the North American continent.

The Corps' 2009 Annual Operating Plan for the Missouri River was published in late December. It contains a detailed description of continued drought conservation measures because reservoir levels are still below normal.

The Corps report today forecasts reduced navigation support, reduced hydropower generation, and lower than desired reservoir levels.

There will be two "spring pulses" of water released from Gavins Point Dam this year, one in March and one in May. The pulses are required to comply with the 2003 Amended Biological Opinion of the U.S. Fish and Wildlife Service.

The opinion identified pulses of water in the spring from Gavins Point as "reasonable and prudent" to avoid jeopardizing the continued existence of the endangered pallid sturgeon as required by the Endangered Species Act.

The annual operating plan includes "flood control constraints" as described in the Corps' Master Water Control Manual. These are the river levels that act as triggers for reducing releases from Gavins Point during high downstream flows. Both pulses may be reduced or eliminated due to these limits, Cieslik said.

An additional safeguard is the use of observed and anticipated rainfall into the daily river forecast to provide greater assurance that flows will remain below the limits.

Timing of the March pulse will correspond with the annual increases in releases to meet navigation targets at Sioux City, Omaha, Nebraska City and Kansas City.

Cieslik said the water needed for both pulses will be gradually staged in the Fort Randall reservoir before their implementation, further reducing negative impacts to storage in the three large upper reservoirs of Oahe, Garrison and Fort Peck.

The plan anticipates that there will be minimum flows at the start of the navigation season which could be shortened by up to 22 days, depending on runoff this winter and spring. A final determination on length of the season will be made on July 1, 2009.

Steady to rising reservoir levels during the spring fish spawn at the three large upper reservoirs are likely if there is normal or above normal runoff. However, continued drought conditions may not make that possible at all three.

If that is the case, the Corps will set releases at Garrison Dam to result in a steady to rising pool during April and May, to the extent reasonably possible.

The ability to provide such conditions depends on the volume, timing and distribution of the runoff from melting snow on the plains and in the mountains of Montana and Wyoming.

The six main stem power plants on the Missouri River generated 471 million kilowatt hours (kWh) of electricity in January, only 65 percent of normal because of lower pool levels and reduced releases from the dams, the Corps reports.

Total energy production for 2009 is forecast to total 7.1 billion kWh, compared to the average of 10 billion kWh.

Copyright Environment News Service (ENS) 2009. All rights reserved.