Physical Changes in Cutoff Bends Along the Tennessee-Tombigbee Waterway
1989
Shields, Jr | F. D. | Gibson, Anthony C.
Historical and future physical changes in 38 cutoff meander bends (bendways) along the river section of the Tennessee-Tombigbee Waterway(TTW) are examined. These major physical features of the TTW furnish an important biological and recreational resource. Historical changes are described by analysing results of annual hydrographic surveys of sedimentation ranges located in 14 bendways. Data analyzed were collected 1977-1987. The volume of deposition below normal pool elevation in the 30 bendways downstream of Aberdeen Lock and Dam is estimated to be 14,400,000 million cu. yds. Mean depth in the monitored bendways decreased 3 ft, but only 3 of the 14 bendways experienced significant reductions in surface area. Deposition rates were greatest 1981-1983 and slowed between 1985 and 1986 due to low discharges. The long-term outlook for the bendways was examined by measuring the perimeter and enclosed area of tree lines depicted on repetitive aerial photographs of 26 floodplain water bodies located along 7 alluvial rivers in the S.E. U.S. Tree line enclosed area declined 1-9%/ year for sites located along free-flowing rivers, with average suspended sediment concentrations of approx. 200 ppm or greater. Bendways with higher ratios of bend length to cut channel length tended to decline most slowly. Sites along canalized rivers had rates of change too low for detection with the method employed. Tree line perimeters tended to be rather stable with time relative to tree line enclosed areas. Shorelines became more complex as lakes grew smaller. Based on these results, TTW bendways that receive little sediment from local drainage should decline in size very slowly after blockage of upstream entrances to top-bank elevation.
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