Page 258 - Fundamentals of Geomorphology

FLUVIAL LANDSCAPES 241

() Convex floodplain Old alluvial terrace
a
River

b
()
Lateral
Braided channels and alluviation planation

c
()
New, flat floodplain

() Fluvial
d
Dissection Abandoned floodplain bench

e
() New alluvial Old terrace
terrace
New convex Lateral
floodplain 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
River sediment increase
conclusion. With the maturation of farmlands world-
In North America, agricultural land-use typically accel- wide, and with the development of better soil conser-
erates erosion tenfold to a hundredfold through fluvial vation practices, it is probable that the human-induced
and aeolian processes. Much of this high sediment yield erosion is less than it was several decades ago (e.g. Trim-
is stored somewhere in the river system, mainly in ble 1999). Overall, however, there has been a significant
channels, behind dams, and as alluvium and colluvium. anthropogenic increase in the mobilization of sediments