Missouri River to be high but manageable all summer, barring torrents of rain
June 16, 2011
ST. LOUIS • The rush of water coming down the Missouri River from swollen reservoirs in the Great Plains will keep the river slightly above flood stage here all summer.
Normally, no big deal. But widespread heavy rainfall is likely to top some of the smaller agricultural levees along the river in eastern Missouri.
That was the picture offered today by the National Weather Service and the Army Corps of Engineers during a press conference downtown. It was called in part to calm doomsday fears inspired by television footage of levees breaking in Iowa and northwestern Missouri.
But spokesmen also warned of major flooding if the wide Missouri River basin, or even large areas of the state of Missouri, get heavy rainfall this summer.
On Tuesday, the corps opened the spillways at the Gavins Point Dam, near Yankton, S.D., to five times normal flow because the massive flood-control reservoirs on the upper Missouri are at brimful, compliments of heavy snow melt and record rains across Montana and the Dakotas. Gavins Point is the last of five reservoirs on the river.
The first of that water is expected to reach the St. Charles area late next week. That flow will be enough to keep the river about three feet over flood stage there through the summer.
Normally, it takes about 10 days for water spilling from the Gavins Point Dam to reach the St. Louis area.
"Because of that flow coming down the river, we will be close to flood stage all summer. That's then new normal," said Wes Browning, chief of the local Weather Service office in Weldon Spring. "But if we get much above normal rainfall, or big bursts of rain, there's likely to be trouble."
Browning's "new normal" of three feet over flood stage at St. Charles is considered minor flooding, but is nine to 14 feet above the normal summertime levels on the lower Missouri.
Browning and Col. Tom O'Hara, commander of the corps' St. Louis district, showed reporters maps of the potential flooding on the lower Missouri and Mississippi, depending upon rain-induced flow from the Missouri's many tributaries. The summer forecast suggests a range from three feet over flood at St. Charles to 12 feet over flood stage there.
That higher amount would be only three feet below the crest during the Great Flood of 1993 and would break through most of the agricultural levees from Washington, Mo., downstream. That higher level still would spare Chesterfield Valley, Maryland Heights, Earth City and other major suburban bottomlands protected by high levees.
"With normal, even rainfall, we do not anticipate river elevations that will cause overtoppings of any levees," O'Hara said. "The water from the reservoirs have not produced, and will not produce, overtoppings in the St. Louis area. The driving force for that would be concentrated additional rainfall.
"If we get that much rainfall, we could have issues with some of the levees," O'Hara said.
He said the high water on the Missouri that has broken some levees in Iowa won't have the same effect here because the lower Missouri "has more capacity to absorb that flow."
Browning said the five-day forecast calls for heavy rain in the upper Missouri and upper Mississippi river basins.
"The good news is that we don't have strong signals for abnormal rain this summer in the (Missouri) basin," he said.
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