Environmental Engineering Reference
In-Depth Information
FIGURE 7.17
The stages in the fluvial cycle of a river illustrated by stereo-pairs of a 5-km-long stretch of river flowing from
mountains to the sea: (a) early stage or boulder zone; (b) middle stage or floodway zone; (c) late stage or
pastoral zone, and estuarine zone (see Figur e 7.16, scale 1:20,000).
Stream gradients range from 0 to 2 ft/mi (1 m/km). The river is still side-cutting
its channel and building up the valley floodplain, but the channel does not extend by mean-
dering to the valley sides. Sediment loads are usually balanced with the transporting capac-
ity of the stream. Fine bedload materials (silt and sand) form banks. The channel meanders,
changing course frequently, building point bars and isolating oxbow lakes. The valley floor
is broad and periodically subject to floods during which the oxbow lakes are filled, and nat-
ural levees and backswamps are formed. Stratification and interbedding are common.
 
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