The great flood of summer 1993: Mississippi River discharge studied.

Walker, N.D., Fargion, G., Rouse, L.J., and Biggs, D.

In the summer of 1993, the Mississippi River basin in the midwestern United States experienced anomalously high rainfall. Record flooding resulted from an abnormally persistent atmospheric weather pattern consisting of a quasi-stationary jet stream positioned over the central part of the nation, where moist, unstable air flowing north from the Gulf of Mexico converged with unseasonably cool, dry air moving south from Canada.

In concert with the persistent weather pattern over the United States, highly anomalous circulation patterns were observed over much of the Northern Hemisphere [Richards, 1994]. The rainfall anomalies over the central United States produced abnormally high river discharges along the Louisiana coastline from the Mississippi and Atchfalaya Rivers during July and August, traditionally months of low river water discharge. Some of the river water discharged into the northern Gulf of Mexico reached the Straits of Florida by September 1993 [Lee et al., 1994].

The Mississippi River is the sixth largest river in the world in terms of discharge with an annual average flow rate of 14,000 m3/s and a freshwater discharge onto the continental shelf of 580 km3/yr. River discharge into the Gulf of Mexico is distinctly seasonal, with highest flow occuring between March and May and lowest flow occuring between August and October. Approximately 70% of the Mississippi River flow enters the northern Gulf of Mexico through the bird-foot delta. The remaining 30% of the flow is discharged into the Gulf of Mexico by the Atchafalaya River through Atchafalaya Bay, further west.

Ref: EOS Transactions, Vol. 75, No. 36, pp. 409-415, Sept. 6, 1994

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