POSSIBLE EVOLUTION OF THE WHITE RIVER IN RESPONSE TO A MISSISSIPPI RIVER AVULSION

The Mississippi River has a complex Holocene history in the alluvial valley and has occupied six different meander belts (Saucier, 1994). Near Greenville, Mississippi, the present Mississippi River is in the central portion of its valley and abandoned meander belts 2, 3, and 4 are along the eastern edge of the valley. Initiation of meander belt 1 has been dated approximately 2.5 kya by Saucier (1994) and this age is consistent with dates from some of the older meanders in meander belt 1 of 2.1 kya (Guccione et al., 2004). As the Mississippi River has avulsed from the east side of its valley to the central valley 2.5 kya, any tributary confluence between the original and later channel positions must respond to the avulsion. For example, if the avulsed channel moves to the east, any tributaries on the western side of the basin must extend their valleys. Conversely, if the avulsion is to the west (as near Greenville, Mississippi), any tributaries on the western side of the valley will become shortened and the lower part of these tributary valleys will be beheaded and abandoned as is demonstrated by the abandoned White River channel (now the Black Bayou in MS).

The Black Bayou, a meandering paleochannel located east of Greenville, MS, is thought to be a beheaded section of the White River, the Arkansas River, or the combined White and Arkansas River, or a Mississippi River distributary. Due to their geographic proximity, the Arkansas and White Rivers are two obvious choices to have occupied the paleochannel of the Black Bayou. However, the Black Bayou is more similar in sinuosity and channel size to the White River whereas the Arkansas River is a significantly larger fluvial system. In addition, both paleochannel of the Black Bayou and the paleochannels and active channel of the White River are buried by approximately 7-9 m of overbank clay.