Figure 2. Landsat imaae of the floodplain of the Oconee River, GA, showing how large 

 alluvial rivers that drain the Piedmont form extensive tracts of bottomland hardwoods 

 below the fall line, which in this photo runs diagonally from lower left to upper 

 right. Milledgevil le, GA, is marked M. Photo courtesy Georgia Department of Natural 

 Resources. 



tion on the convex bank keeps pace with 

 erosion of the opposite concave bank, the 

 bulk of the sediment remains stored in the 

 floodplain (Leopold and Wolman 1957). 



Though much slower than point bar 

 formation, vertical accretion by overbank 

 deposition also builds most southeastern 

 floodplain surfaces. Overbank deposition 

 results from high water losing its veloc- 

 ity and dropping sediments as it traverses 

 the floodplain, usually by sheetflow or 

 overflow channels. The amount of sediment 

 deposited can vary widely. For example, a 

 single flood in the Atchafalaya River 

 Basin, LA, caused sediment accumulations 

 of up to 46 cm (18 inches) over portions 

 of this vast flood plain. Accumulations 

 ranging from 0.3 cm (.125 inches) to 



3.8 cm (1.5 inches) have been documented 

 for floods in the Potomac River Basin, VA 

 (Sigafoos 1964). Average deposition, how- 

 ever, ranges between 0.3 m (1 ft) and 

 0.6 m (2 ft) in 200 to 400 years (Wolman 

 and Leopold 1957). The bed of the chan- 

 nel, as well as the surface of the flood- 

 plain, accumulates sediment deposits dur- 

 ing floods. Channels are also created and 

 maintained by these overbank flows and 

 accommodate the excess discharge of flood 

 waters. 



On forested floodplains, local ero- 

 sion by overbank flows may produce rapid 

 recycling and overturn of deposited sedi- 

 ments. Surface erosion or scour is fol- 

 lowed by deposition of comparable magni- 

 tude, and the floo'dplain becomes a spatial 



