The Corps' latest reservoir regulation studies indicate additional drought conservation measures will be enacted for the Missouri River Mainstem System as the navigation season is set to begin.
Minimum navigation flow support will likely be provided for the first half of the Missouri River navigation season based on the anticipated storage check results, which are expected to show system storage below levels required to support full service navigation flow support.
The navigation season will open on April 1 at the mouth near St. Louis.
Releases from Gavins Point will be stepped up beginning around March 18 to provide flow support for the 2013 navigation season. The level of flow support for the second half of the navigation season and the season length will be made following the system storage check on July 1. Minimum-service flow targets range from 25,000 cfs at Sioux City, Iowa to 35,000 cfs at Kansas City, Mo. and are designed to provide a navigation channel that is 8 feet deep by 200 feet wide. This may require barge operators to carry lighter loads. Full service navigation flows provide a 9-foot by 300-foot channel.
The navigation season opening dates are as follows: locations are:
• March 23 – Sioux City, Iowa
• March 25 – Omaha, Nebraska
• March 26 – Nebraska City, Nebraska
• March 28 – Kansas City, Missouri
• April 1 – Mouth near St. Louis, Missouri
The continuing drought conditions in the upper Missouri River basin indicate less-than-normal runoff in 2013. Based on the current soil moisture and snowpack conditions, 2013 runoff in the Missouri River basin above Sioux City, Iowa is forecast to be 20.0 million acre feet (MAF), 81% of normal for the calendar year.
"The total volume of water stored in the mainstem reservoir system on March 1, the approximate start of the 2013 runoff season, was 8.3 MAF below the top of the Carryover Multiple Use Zone," said Jody Farhat, Chief of the Missouri River Water Management Division. The Carryover Multiple Use Zone is designed to provide service to the eight Congressionally authorized purposes, though at reduced levels, through a 12-year drought like that of the 1930s and early 1940s. "Because we are starting the season below the top of that zone, we will continue implementing drought conservation measures."
Drought conservation measures are enacted based on storage checks included in the Master Manual. The first drought conservation measure, minimum winter releases, was based on the September 1, 2012 storage check. In addition to providing only minimum navigation flow support, the Corps will also conserve water throughout the navigation season by not providing flow support in river reaches where there is no commercial navigation traffic, said Farhat.
Steady to rising reservoir levels during the forage fish spawn at the three large upper reservoirs (Fort Peck, Garrison and Oahe) are preferred and could be accomplished this spring. The forage fish spawn generally occurs from early April through mid-June. Maintaining a steady to rising reservoir level during this period is beneficial for successful spawning and hatching of the forage fish, which are an important food source for walleye and other game fish. Fish and wildlife is one of the eight congressionally authorized purposes for which the Missouri River Mainstem system is operated.
If runoff is less than forecast the Corps will set releases to result in steady to rising pools at Fort Peck and Oahe, to the extent possible.
Mountain snowpack is currently 94% of normal in the reach above Fort Peck and 86% in the reach between the Fort Peck and Garrison. Typically 79% of the peak mountain snowpack accumulation has occurred by March 1.
"The Corps will continue to monitor mountain snowpack, rainfall runoff and basin soil conditions to fine tune the regulation of the reservoir system based on the most up-to-date information," said Farhat.
Source: U.S. Army Corps of Engineers