(1) INITIAL UNIFORM CHANNEL DIRECTION OF FLOW - 



(2) <illi> m 



<234 -^ 



gg^ 



POOL TO POOL - 5 TIMES WIDTH 



POOL TO POOL - 5 TIMES WIDTH 



^=--RIFFLE 



CUT BANK 



Figure 3. Point bar and meander formation in floodplains. Unstable stream flow in 

 uniform river channels (1) forms pools and riffles (2). A meandering channel (3) 

 develops and eventually exhibits erosion on the concave banks of meanders as well as 

 deposition and point bar formation on the convex banks (4). (After Muller and Ober- 

 lander 1978, courtesy of Random House, Inc.) 



mosaic of erosional and depositional sur- 

 faces superimposed over material deposited 

 earlier by point bar accretion (Sigafoos 

 1964). The features resulting from these 

 processes are detailed in the followinc 

 se.ctions. 



Sediment 



Sediment source is provided by con- 

 tinual erosion of the landscape throughout 

 geological time. In the Piedmont and 

 mountains, this source is igneous and 

 metamorphic rocks (granites, schists, and 

 gneisses) which decay or weather under the 

 influence of rainwater. Released compo- 

 nents are sands, silts, and clays, which 

 are transported by sheet-wash or gully- 

 wash into streams. In the Piedmont this 

 decay produces a soil horizon (vertical 

 layer) of saprolite (decomposed rock) up 

 to 9.2 m (30 ft) thick. 



The weathered Piedmont saprolite 

 little by little washes downstream. Pied- 

 mont sands are transported as bedload 

 rolling along the bottom of stream chan- 



nels, whereas silts and clays are carried 

 as suspended matter in the water column. 

 Silts and clays, the principal components 

 of surface floodplain soils, settle out or 

 form overbank deposits during floods. A 

 reduction of particle size downstream v\h)/ 

 result from the weathering of silt and 

 clay particles that remain in place for 

 long periods of time between episodes of 

 downstream transport (Curry 1972). 



Land uses in uplands profoundly af- 

 fect the quantities of sediment entering a 

 stream. Before the 19C0's, sediment inputs 

 to southeastern river systems were minimal 

 according to some observers. River pilots 

 recalled that as late as 1912 the Tennes- 

 see River was relatively clear even after 

 heavy rains (Ellis 1936). According to 

 one report, the turbid Altamaha River of 

 coastal Georgia was once a relatively 

 clear stream, and as late as the 1840's it 

 was possible to determine on which tribu- 

 tary (Ocmulgee or Oconee) rains were fall- 

 ing since much of the Oconee drainage was 

 in agriculture (Lyell 1849). 



