Isaac’s rain throws temporary rise to Mississippi

Published 11:20 am Wednesday, September 5, 2012

Rain dumped on the Lower Mississippi River and Ohio River valleys during Hurricane and Tropical Storm Isaac has lifted near-historic low stages between Memphis and Vicksburg, but only temporarily, a key hydrologist said.

Isaac’s remnants produced 2 to 5 inches across Southern Illinois and Missouri and about a half-inch to 2 inches in Indiana and Ohio, said Marty Pope, senior service hydrologist with the National Weather Service in Jackson.

The rain raised stages, but much of it went straight into the ground, Pope said.

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“East Arkansas had 2 to 6 inches,” he said. “There was not much runoff from the storm. Soils soaked up a lot.”

A rising Mississippi River north of Arkansas City is expected to spread into low-lying streams and won’t raise the gauge there much, he said.

“We should see some relief from Arkansas City to Natchez — not much considering how much rainfall occurred,” he said.

Persistent drought this summer, particularly in the Midwest, contributed to low levels on rivers and lakes nationwide. The stage at Vicksburg were 0.7 feet this morning, up four-tenths of a foot. The record low is minus 7 feet, set in 1940. In Greenville, where the river was closed to barge traffic intermittently in August due to low water, stood at 8.42 feet, up half a foot. In Memphis, where the stage has shown negative since July, the river was minus 7.38 feet this morning, up four-tenths of a foot.

A forecast Tuesday dialed back the projected lows in early October for several river stations. Memphis could reach minus 9.9 feet by that time, farther off the 1988 record low of minus 10.7 feet than previous forecasts. The projection for Vicksburg by October is minus 0.8 feet, off half a foot from estimates last week.

Rainfall in Vicksburg totaled 3.84 inches Wednesday and Thursday as Isaac brushed past West Central Mississippi.

Barges have moved freely north and south since a bottleneck south of Greenville cleared early last week. The Coast Guard has limited the flow to one tow at a time through a 2-mile safety zone, Petty Officer Bill Colclough said.