Geoscience Reference
In-Depth Information
Watershed
(a)
Catchment
(sediment
production)
Channel
(sediment transfer)
Fan apex
Alluvial fan
(sediment
accumulation)
Fan toe
(b)
Fig. 5.12
(a) Schematic representation of an alluvial fan system showing the sediment production (catchment), sediment transfer
(channel) and sediment accumulation (fan) elements and (b) a view from the toe to apex of a typical alluvial fan in northern Chile. Note
the recent debris flow down the right-hand side of the fan.
areas of flow, sediment movement will be pre-
dominantly as diffuse gravel sheets or longi-
tudinal bars (Smith 1974). Fluvial processes will
be encouraged where the supply of fine material
is limited, typically in larger catchments where
stream-side supply of sediment dominates.
Hyperconcentrated streamflows are common
on alluvial fans (Fig. 5.11). These flows may
have some shear strength although there is
some controversy as to their exact nature (Reid
& Frostick 1994). Resulting sediments may
contain weak internal stratification, normal and
