SERVICE REVISES FLOOD RECORD UPWARD

The National Weather Service has revised the level and date of the 1993 record flood crest that occurred last month at Cape Girardeau and other locations along the Mississippi and Missouri rivers.

The new preliminary record flood crest for Cape Girardeau was revised upward to 48.49 feet, nearly one-half foot higher than the 47.9 foot flood crest first announced Aug. 7. The revised flood crest at Cape also occurred one day later, on Aug. 8 instead of Aug. 7.

Meanwhile, the National Weather Service predicts that the Mississippi at Cape Girardeau should drop below flood stage by late this week. In its 30-day river forecast issued last week, the weather service said the Mississippi at Cape is expected to drop to 32.4 feet on Thursday, .2 of a foot above flood stage.

The river is expected to drop to 27.3 on Sept. 22, to 23.9 feet on Sept. 29, and to 22.4 feet on Oct. 6. The forecast is based on the assumption that no significant rainfall will occur north of Cape Girardeau after Sept. 8.

Jack Burns, hydrologist with the National Weather Service at St. Charles, said the revised flood crest figures are based on preliminary data obtained from each river gauge station, and are subject to a final determination by the U.S. Geological Survey.

Burns said there are three steps that determine the official flood crest at each river gauge location. "The first is the highest observed stage of the river at the time of the crest occurs. That's the figure that is most publicized in the news media.

"After the crest has passed and the water is receding, a technician goes to each river gauge station and pulls the punch tape from a recorder that records the river stages every quarter hour, or on the hour," said Burns.

"This data is then used to determine a preliminary flood crest, and the approximate time it occurred at each gauge location."

The third step may occur several weeks or even months after the punch tapes are pulled, when the U.S. Geological Survey sends survey teams to each river gauge location.

The USGS team surveys the actual high-water mark along the riverbank by using a government bench mark located near the gauge. From the survey, the USGS team determines the high-water mark in terms of elevation above sea level. That figure becomes the final flood crest and will go into the record book, Burns said.

It may be some time before the final benchmark surveys are completed, he added.

Burns noted 34 new flood crest records were set in Missouri alone. Each gauge station will have to be surveyed to determine the official flood crest, he said.

Of the 34 new record flood crests that occurred in Missouri this summer, 12 each occurred on the Mississippi and Missouri rivers.

Following are sites and flood stages; preliminary 1993 record flood crests and dates in Missouri; and previous record flood crest and date for each location:

- MISSISSIPPI RIVER

- Quincy (17 feet); 32.2 feet on July 13; 28.9 feet on April 25, 1973.

- Hannibal (16 feet); 31.8 feet on July 15; 28.59 feet on April 25, 1973.

- Grafton, Ill., (18); 38.15 feet on Aug. 1; 33.12 feet on April 28, 1973.

- St. Louis (30 feet); 49.58 feet on Aug. 1; 43.2 feet on April 28, 1973.

- Chester, Ill., (27); 49.69 feet on Aug. 7; 43.3 feet on April 30, 1973.

- Cape Girardeau (32 feet); 48.49 feet on Aug. 8; 45.55 feet on May 1, 1973.

- Thebes, Ill. (33 feet); 45.5 feet on Aug. 7; 44.2 feet on May 6, 1983.

- MISSOURI RIVER

- Kansas City (32 feet); 48.9 feet on July 28; 46.2 feet on April 24, 1973.

- Jefferson City (23 feet); 38.6 feet on July 30; 34.2 feet on July 18, 1951.

- St. Charles (25); 39.6 feet on Aug. 2; 37.5 feet on Oct. 7, 1986.

- MERAMEC RIVER

- Arnold (24 feet); 45.3 feet on Aug. 1; 43.9 feet on Dec. 12, 1982.