Author(s): Robert H. Meade
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Keywords: Floods; Levee breaks; Sediment; Dissolved solids; Contaminants
Abstract: Excessive precipitation produced severe flooding in the upper Mississippi River basin during spring and summer 1993. The flood began in June near the upriver city of Minneapolis and crested near St. Louis, 1,000 km downriver, about the first of August. Levees, which had not been designed or built to withstand such large-magnitude flooding, gave way along the mainstem rivers. Large scour holes were made by rapidly overflowing floodwaters, and masses of new sediment were deposited on floodplains downriver of the levee breaks. The quantities of water that flowed through broken levees, out of the main channels and onto the floodplains, were sufficiently large to lower the heights of flood peaks measured farther downstream. Concentrations of water-soluble agricultural chemicals remained high throughout the flood, even though it was anticipated that the massive streamflows would dilute the concentrations of these chemicals. Loads of major ions and trace elements transported by the rivers also remained large during the flood of 1993.
Year: 2002