Geoscience Reference
In-Depth Information
Table 12.2
Examples of natural factors besides climate and hydrology that can influence dryland river characteristics (for more
details see Chapters 1 to 4).
Environmental
factor
Examples of related
factors
Examples of implications for
river character
Examples of contrasting
drylands
Primary subdivision
Active continental
margins (1)
Older orogenic belts
(2)
Interorogenic,
intercratonic areas (3)
Passive continental
margins (4)
Cratons (5)
Rates and amounts of
uplift or subsidence
Degree of neotectonic
warping
Nature and degree of
fault and fold activity
Degree of
continentality
Tectonic and
structural
setting
Tectonic and structural factors
influence:
Absolute and relative local
relief
Catchment hypsometry
Baselevel
stability/instability
Nature and distribution of
sediment sources and sinks
(e.g. patterns, rates,
volumes and calibre of
sediment supply, and the
potential for sediment
accommodation)
Drainage patterns (e.g.
channel orientations)
Valley and channel
gradients
Mediterranean drylands:
dominated by a variety of
tectonically active settings
(including 1, 2 and 3), with
many areas characterised
by seismicity, uplift,
subsidence or faulting.
Most catchments have
coastal outlets with
baselevel instability
commonplace
Australian drylands:
dominated by essentially
tectonically inactive
settings (including 2, 4 and
5), which are characterised
by negligible or slow
long-term uplift or
subsidence. Most
catchments are in
continental settings with
relatively stable baselevels
Lithology
Igneous
Metamorphic
Sedimentary
Igneous and
metamorphic rocks:
Mineralogy and grain
size
Nature of foliation,
folding and faulting
Joint density and
orientation
Sedimentary rocks:
Mineralogy and
nature of cementation
Grain size
Nature of bedding
(e.g. dip/strike),
folding and faulting
Joint density and
orientation
Nature of contacts
between sedimentary
units
Lithological factors influence:
Patterns, rates, volumes and
calibre of sediment supply
Valley width and drainage
patterns (e.g. channel
orientations, channel
planforms)
Valley and channel
gradients
Channel boundary (bed,
bank) strength, either
directly for bedrock rivers
or indirectly through the
calibre of alluvial bank
material
Southwestern Africa (western
South Africa, Namibia):
dominantly igneous and
metamorphic rocks with
varying degrees of
deformation. Most areas
characterised by low to
moderate sediment supply,
with abrupt changes in
valley widths, channel
planforms and gradients
commonly corresponding
with changes in lithology
American southwest
(Colorado Plateau):
dominantly sedimentary
rocks, albeit with exposed
igneous/metamorphic
basement and intrusions.
Sedimentary strata
dominantly horizontal to
gently dipping but with
some deformation (folding
and faulting). Many areas
are characterised by
moderate to high sediment
supply, with abrupt changes
