3. Types of Rivers
• Rivers are very dependent on climate and
their characteristics are closely related to the
precipitation and evaporation regimes in their
drainage areas.
• Four types:
– Perennial or permanent rivers
– Periodic rivers
– Episodic rivers
– Exotic
www.aquatic.uoguelph.ca/rivers/chintro.htm
4. Permanent / Perennial Rivers
• Rivers that flow all year e.g. Orange (Gariep), Kunene, Zambezi.
• River channel reaches water table throughout the year.
• Orange River used to be non-perennial before the construction of
the Gariep Dam.
5. Periodic / Non-Perennial Rivers
• Only flow during the rainy season e.g. Berg River (seen below)
• Water table must rise enough to feed the river when it is not raining
6. Episodic Rivers
• Only flow for short periods after heavy rain e.g. Nassob (Namibia).
• May have some permanent pools where bed intercepts water table.
• It is an important water source in desert regions.
7. Exotic Rivers
• Rise in humid areas with high rainfall and flow through dry areas.
• Gariep river rises in the Drakensberg moutains (high rainfall) and
flows through the Northern Cape (dry region).
11. Dendritic drainage
pattern
•Occurs in regions
where the rock is
uniform in its
resistance to
erosion.
•Shaped like the
branches of a
tree.
•Consequent and
subsequent streams
meet at acute
angles.
12. Rectangular drainage pattern
• Rectangular drainage patterns
have rt.-angled bends in the
tributaries and the main streams.
• Streams are not parallel to each
other.
Rectangular drainage pattern
13. Trellis drainage pattern
• Occurs in regions the
sedimentary rock is folded or
where there are alternate
layers of hard and soft rock.
• The main stream and tributaries
join at rt. angles.
• Streams are parallel with short
tributaries.
16. Radial drainage pattern
• The stream flows down a
dome shaped feature e.g. an
isolated hill volcanic dome
spitskop.
17. Deranged drainage pattern
• A deranged pattern is found in a
region that is geological young.
• Haphazard shape.
• Streams entering lakes and marshes in
a haphazard pattern.
19. Superimposed (Inherited) Streams / Drainage
A stream establishes its course in rock layers.
The covering rock is removed and the stream imposes its course on
underlying rock of a completely different structure.
River is younger than the structures they flow through.
E.g. The Vaal river in the vicinity of Parys (in the Free State) breaks
through two quartzite hills instead of following a course around them.
23. Antecedent Streams / Drainage
A stream existed on an earlier landscape which was subsequently raised.
The stream was able to maintain its original course in spite of uplift
(or the formation of a mountain or a ridge).
Antecedent streams are therefore older than the structures they
flow through.
e.g. The lower part of the Orange river retained its course and
eroded downwards at the same rate that the mountains of the
escarpment formed.
The stream cut through the obstruction as it formed.
27. Superimposed and
Antecedent Streams
• Superimposed streams is one
whose valley and direction of
flow were developed much later
than the underlying structure,
and the river possessed sufficient
stream power to cut through
these underlying structures.
• An antecedent stream is one
whose path of flow within a
valley was established before the
mountainous structure was
uplifted
34. River Channel Patterns / Stream flow characteristics
Identify the stream flow characteristic of the following river:
Meandering Stream
River winds from side to side
River flows over loose silt
and clay
The banks are fairly stable
The river starts to wind due
to irregularities in the
channel (corkscrew action)
Lateral shifting takes place
(meanders shift downstream)
Fastest flow speeds occur on
the outer bank (undercut
slope) resulting in erosion
Slowest flow occurs on the
inner bank (slip-off) slope
resulting in deposition
41. Identify the stream flow characteristic of the following river:
Braided stream
The velocity of the river is
reduced and this causes the
river to split and rejoin
many times
The river flows over loose
sandy alluvium
The banks of the river are
unstable and lateral erosion
occurs easily
As a result of the wide
channel, the river flows
slowly and large deposits of
alluvium form islands in the
middle of the river.
River Channel Patterns / Stream flow characteristics
42. • Braided Pattern = steep slope + high stream
power + coarse bed materials changes to gentle
gradient and slows down depositing material
Braided channel
earthsci.org/teacher/basicgeol/stream/stream.html#Erosion%20by%20Streams
46. Identify the stream flow characteristic of the following river:
Straight Stream
Rock-controlled channel
o The river flows in straight and
twisting sections
o It is characterized by many rocky
banks, rapids and waterfalls
o The rock barriers on the sides
and riverbed prevent the river
from determining its own channel
pattern
River Channel Patterns / Stream flow characteristics
