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()
a
Old alluvial terrace
Convex floodplain
River
()
b
Lateral
planation
Braided channels and alluviation
()
c
New, flat floodplain
()
d
Fluvial
bench
Dissection
Abandoned floodplain
()
e
Old terrace
New alluvial
terrace
New convex
floodplain
Lateral
planation
Figure 9.12 Alluvial terrace formation. (a) An initial convex floodplain. (b) Burial of the initial floodplain by coarser
sediments through rapid alluviation of braided channels. (c) A stable, flat floodplain forms by alluviation and some lateral
planation. (d) Another environmental change leads to dissection of alluvium and the abandonment of the flat floodplain.
(e) A new convex floodplain is established by the alluviation of fine sediments and lateral planation.
Source: After Butzer (1976, 170)
Many other reports in the literature support this
conclusion. With the maturation of farmlands world-
wide, and with the development of better soil conser-
vation practices, it is probable that the human-induced
erosion is less than it was several decades ago (e.g. Trim-
ble 1999). Overall, however, there has been a significant
anthropogenic increase in the mobilization of sediments
River sediment increase
In North America, agricultural land-use typically accel-
erates erosion tenfold to a hundredfold through fluvial
and aeolian processes. Much of this high sediment yield
is stored somewhere in the river system, mainly in
channels, behind dams, and as alluvium and colluvium.
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