Geomorphology
Ms HL Benjamin
Geography Co-Ordinator FET
Northern Cape
2021
Table of Contents
Ms HL Benjamin
Glossary List
Slides 02-08
Lesson 1
Drainage Systems in South-Africa
Slides 09-29
Lesson 2
Fluvial Processes
Slides 30-68
Lesson 3
Catchment Management
Slides 69-78
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Glossary List
Drainage Basin
The entire area drained by a river system including the
mainstream and its tributaries.
One drainage basin is separated from another by a major
watershed.
Catchment area
The area from which any rainfall will drain into the river
system through surface flow
River system
A mainstream and all its tributaries
Tributary
Smaller streams that flow to the mainstream of a river
Confluence
The place in the river where two tributaries meet
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Glossary List…Continue
Permeable
Rock or soil that allow water to move through it quickly
e.g., sand
Porosity
Rock or soil with pores where water can be stored
Watershed
High lying areas separating different drainage basins.
Interfluve
The higher (dry) areas between different tributaries
Source
The beginning of all streams
(in the higher lying areas – 1 river has many sources)
River mouth
where the river ends in the Sea. The river mouths out in
the ocean and deposits all its water in the ocean
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Glossary List…Continue
Water that runs over the surface of the Earth during
and after precipitation and lands up in rivers.
Surface run-off
Run-off can be divided in direct run- off and indirect
run-off.
Direct run-off
Is the water that runs over the surface of the Earth
during and directly after precipitation and lands up in
rivers
Indirect run-off
Is the water that first infiltrates into the soil and is
later released into to streams through base flow.
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Glossary List…Continue
Base flow
Refers to the groundwater that seeps into streams
Groundwater
Water stored in porous soil and rock masses
Water Table
The top level of groundwater; beneath the water
table the soil is saturated
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Allocate concept into correct block
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Identify Concepts on Diagram
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Glossary List…Continue
Laminar Flow
Smooth flow of water in a river
Permanent Base level
The sea, the lowest level to which a river can
erode the landmass
Permanent River
River flowing all year
Periodic River
A river that receives groundwater only in the
rainy season
Episodic River
A river that flows only after heavy rain
Base Level
The level to which a river erodes the land
Captor Stream
Stream that captures another stream
Braided River
River with islands of alluvium deposits
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Ms HL Benjamin
Lesson 1
Drainage Systems in South-Africa
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Features of a Drainage Basin
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How does water enter a Drainage Basin
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Factors that influence Infiltration and
the effect on the Water Table
Factor
Explain / Describe
Precipitation
With soft rains more water will be able to infiltrate the
ground…the water table will rise
Heavy rains will cause run-off…the water table will rise
slower
Rate of Evaporation
Dry, warm, windy air causes the surface moisture to
evaporate rapidly, this reduces the amount of moisture that
can penetrate the ground…the water table will be low
Slope of the land surface
Steep gradients lead to rapid run-off…water table will be
low
Level surface make it easier for infiltration to take
place…the water table will rise
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Factors that influence Infiltration and the
effect on the Water Table…Continue
Factor
Explain / Describe
Vegetation
A thick cover increases surface retention and protects the
surface against evaporation. This leads to greater
infiltration…the water table will be high
Amount of moisture in the
ground
Dry ground will absorb moisture than ground that is
saturated
Porosity and Permeability
The ability of rocks to absorb, store water or allow it to filter
through them
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Position of the Water Table
• No infiltration can happen in the paved
area, therefor the water table will be
extremely low
• After infiltration the water table will lift a
little where grass is between the paving
• After infiltration the water table will be
high where the grass is
• Think twice before removing
grass
• Underground water will be compromised
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Height of Water Table after Seasonal Rain
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Different types of Rivers
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Different types of Rivers
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Different types of Rivers
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Different types of Rivers
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Drainage Patterns
❖The way in which the rivers within a river
system or network are arranged
❖Rock structures underlying determine the
drainage pattern
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Drainage Patterns…Continue
MUST KNOW THE
FOLLOWING
What does it look like
Description
Underlying structures
RADIAL
From highest
central point
(butte/conical
hill)
RECTANGULA
R
Bends 90°
Tributaries 90°
Joints and faults
DENDRITIC
Tree
Uniform rocks
TRELLIS
Alternating layers of
hard and soft rock
Parallel streams
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Drainage Patterns on Topographical Maps
Trellis
Dendritic
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Drainage Patterns on Topographical Maps
Rectangular
Radial
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Drainage Density
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Drainage Density…Continue
•
•
•
•
•
High rainfall
Hard rocks
Steep slopes
Less vegetation
Less infiltration
•
•
•
•
Low rainfall
Softer rocks
Gentle slope
Lots of
vegetation
• More infiltration
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Stream Orders
❶
❶ ❶ ❶❶
❷
❷
❶
❷
❷
❶
❸
❷
❶
❸
❶
❶ ❷
❶
❶
❶
❶
❹
1+1=2
2+2=3
3+1=3
3+2=3
3+3=4
4+1=4
4+2=4
4+3=4
4+4=5
etc
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How to determine Stream Order
❖Stream order 1 - Where streams originate
❖Stream order 2 – Where two stream order 1 meet
Remain stream order 2 where stream order 1 and 2
meet
❖Stream order 3 – Where two second stream orders
meet
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River Discharge
Volume of water that flows down a river. River
flow can either be laminar or turbulent.
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Laminar and Turbulent Flow
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Ms HL Benjamin
Lesson 2
Fluvial Processes
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Longitudinal Profile of a River
Longitudinal Profile
Side view of a river from source to mouth
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Longitudinal Profile of a River…Continue
❖Perfect concave shape
❖Concave shape – Steep gradient in the upper
course and gradual gradient at the lower
course
❖No knick points along the profile
❖Balance between erosion and deposition
❖Permanent base level – lowest level to which a
river can erode its valley eg. sea
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Longitudinal Profile of a River…Continue
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Longitudinal Profile of a River…Continue
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Transverse (Cross) Profile
Transverse (Cross) Profile
Shape of river valley from one bank to the opposite bank
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Three stages of a River
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Upper Course (Young Stage)
UPPER COURSE
• Steep
• Fast flowing
• Downward erosion
• Turbulent flow
• Waterfalls, rapids, interlocking spurs
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Landforms in the Upper Course
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Upper Course on a Topgraphical Map
Upper Course
❖Steep
❖Fast flowing
❖Downward erosion
❖Turbulent flow
❖Waterfalls,
❖Rapids
❖interlocking spurs
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Middle Course (Mature Stage)
Middle Course
❖Gradual
❖Slower flow
❖Lateral erosion
❖Meanders, spurs
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Landforms in the Middle Course
Spur
Meander
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Middle Course on a Topographical Map
Middle Course
❖Gradual
❖Slower flow
❖Lateral erosion
❖Meanders, spurs
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Lower Course (Old stage)
Lower Course
❖Almost flat
❖Flows very slowly
❖Deposition
❖Oxbow lakes
❖ deltas
❖Meanders
❖Marshes
❖Braided streams
❖Sand banks
❖Natural Levee
Deposition
Refer to the deposit of material
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Landforms in the Lower Course
Sandbanks
Braided Streams
Marshes
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Landforms in the Lower Course…Continue
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Lower Course on a Topographical Map
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Identify the Landforms in Lower Course
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CROSS PROFILE ROUND A BEND
Y
X
Deposition
Undercut
Erosion
Slower
flow
Slipoff
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River Grading
Temporary base level erosion
Waterfall, dam, lake, rapids
Permanent base level erosion
Permanent baseSea
level erosion
Sea
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River Rejuvenation
River Rejuvenation
Occurs when the rivers speed and erosive power increases
resulting in an increase in downward erosion (vertical erosion)
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Reasons for Rejuvenation
❖ When the sea level is lowered
❖ When land is uplifted e.g., due to tectonic processes
❖ Increase in volume of water e.g., due to rainfall
❖ River capture
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Features of River Rejuvenation
Knickpoint
❖Knickpoint is part of a river or channel where there is a
sharp change in channel slope (gradient)
❖This can result from an increase in downward (vertical
erosion) due to rejuvenation
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Features of River Rejuvenation…Continue
Terrace
❖When a river flowing on the valley floor experiences
rejuvenation it cuts into the valley floor
❖As this process continues it creates steps at different levels
known as terraces
❖They are found on both sides of the river valley
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Features of River Rejuvenation…Continue
Incised/Entrenched Meander
❖It occurs when a meandering river experiences rejuvenation
resulting in more downward (vertical) erosion
❖This causes in deep incisions (cuts) resulting in incised
meanders
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Features of River Rejuvenation…Continue
Valley in a valley
❖The newly formed terrace begins to cut back and form a valley
❖ This valley widens through lateral erosion
❖The process continues gradually and if rejuvenation occurs repeatedly
new terraces form as well due to increase in vertical erosion
❖This creates a smaller valley
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River Rejuvenation took place if you see the following
Waterfalls
Augrabies Waterfall: NC
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River Rejuvenation took place if you see the following
Ox-bow lakes
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River Rejuvenation took place if you see the following
River Capture
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River Rejuvenation took place if you see the following
Incised Meanders
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River Rejuvenation took place if you see the following
River Terraces
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River Capture/ Stream Piracy
River Capture
Caused by “headward erosion” as the river erodes back from its
source until it reaches another river and “captures” it
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River Capture
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Explain why one river will capture another river
of its headwaters
It occurs when
❖One river has a steeper gradient than the other river
❖One river has a less resistant underlying rock than the other
river
❖One river has a greater volume of water than the other river
❖More energetic river capture the water of a slower stream
❖River cuts through the watershed and capture the flow of the
other stream
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Discuss the features of Stream Piracy
Captured stream
❖The part of the river that is diverted by the captor stream
Captor stream/ Pirate Stream
❖This is the energetic stream that cuts back and intercepts the other
river
Misfit Stream/ Beheaded Stream
❖The river that has lost its headwaters as a result of capture
Elbow of capture
❖This is the point of capture where the change of flow direction occurs
Windgap
❖This the area between the elbow of capture and the misfit stream
where the water stops flowing and river gravels are deposited
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Identify features of Stream Piracy
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River Capture…Continue
Advantages of River Capture to the Captor Stream
❖ Fertile soil
❖ Farming
❖ Economy
Disadvantages of River Capture to the Captor Stream
❖ Flooding
❖ Erosion
Disadvantages of River Capture to the Misfit Stream
❖
❖
❖
❖
❖
Water Shortage has a negative impact on:
Farming
Fishing
Recreation
Industries
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Superimposed Stream
❖ River runs over an old landscape/The rivers are formed over
already present underlying rock structures
❖ River erode the original surface to reach the underlying rocks
❖ River change its patterns to flow on newly exposed rocks
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Antecedent Stream
❖ The rivers are formed even before their underlying rock
topography
❖ River develop its course over a young landscape that was
later uplifted due to tectonic activities
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Ms HL Benjamin
Lesson 3
Catchment Management
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Importance of River Management
❖ South Africa is not a water rich country
❖ Our river systems are a resource
❖ Like all other natural resources, rivers are shared
❖ Water is essential for our survival and well-being, as well
as for social and economic development
❖ River systems are part of the water cycle
❖ The way we use the land has a dramatic impact on the
water cycle
❖ Water resources are used for agriculture, industry,
domestic use, hydro electric power and recreation
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Importance of River Management…Continue
❖Primary water sources for activities
❖Valleys and floodplains are used to built
infrastructure
❖Ensure the possibility of trade and transport
❖Act as boundaries between countries
❖Fishing – food source- food security
❖Floodplains have fertile soil for farming
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Importance of River Management…Continue
Fishing – food source- food security
Primary water sources for activities
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Impact of People on Drainage Systems
❖Landfills, mining and agriculture pollute
groundwater
❖Industries and sewage works discharge water
waste into rivers
❖Agricultural run-off contains fertilizers and
pesticides, which pollute rivers
❖Domestic use of rivers in informal settlements
pollutes and litters rivers
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Impact of People on Drainage Systems…Continue
❖ Boreholes reduce the amount of groundwater that feeds
rivers
❖ Alien vegetation consumes large quantities of water very
quickly in the river zone
❖ Overgrazing and removal of vegetation reduce
groundwater and increase run-off
❖ Dams change the flow of a river
❖ Draining of wetlands causes increased flooding
❖ Flood control methods restrict the path of a river
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Impact of People on Drainage Systems…Continue
Sewage in the Vaal River
Pollution of water
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Impact of People on Drainage Systems…Continue
Pollution in the Vaal River
Pollution of water
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Management Strategies
❖Water should be monitored and managed
❖Legislation: should regulate what is
discharged into rivers and regulate the use of
groundwater
❖Education: people must be educated to use
water wisely
❖Flood control should be practised with artificial
surfaces like storm drains
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Management Strategies
Time to protect our water
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Safe it
for our
childre
n
HL Benjamin
and their
children
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Ms HL Benjamin
Thank
you
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