Pure Geography SA2 Overall Revision Notes
Chapter 4: Rivers and Coasts
The River System
1.
2.
3.
4.
5.
6.
7.
8.
3 Courses: Lower, Middle, Upper.
Watershed: A stretch of land that surrounds drainage basin (a.k.a. boundary)
Drainage Basin: A river system that collects rainwater and comprises of streams and rivers
Tributaries: Streams that flow in the river which is mainly found in the upper course.
Distributaries: Branch out from the river which is mainly found in the river delta.
Confluence: Area where the stream meets the river
River Mouth: Place where the river meets the ocean
River Delta: Landform created at the mouth of the sea where the river flows into. It is formed by the deposition
of the sediment carried by the river as it flows into the sea.
Upper
Middle
Lower
3 Courses of a River
Place where the river begins
Many tributaries join up to form larger streams which in turn join to create a river
River starts to meander (curve)
Many tributaries join the river
Meanders are common
Many distributaries
River flows towards the river mouth and enters the sea
Delta (land formed by sediments) may form at river mouth
Pure Geography SA2 Overall Revision Notes
Chapter 4: Rivers and Coasts
Factors affecting River Speed and Volume
Gradient
Roughness
of River
Channel
Wetted
Perimeter
Factors affecting Speed of water in River
Definition
High Speed / Volume
Low Speed / Volume
How steep a river is.
River is steeper (usually at River is gentler (lower course)
upper course)
How rough a river channel is
Fewer obstacles
More obstacles  More friction 
(affected by obstacles in river)
Smoother channel
Reduced speed
Faster
Area in contact with the river.
Shape of river channel affects
the wetted perimeter (Length
and Breadth in contact with the
river)
Factor
Permeability
of Rocks
Vegetation
Cover
Climate
Size of
Drainage Basin
A smaller wetted
perimeter Lesser
friction  Faster
A larger wetted perimeter More
water  More friction  Slower
Factors affecting Volume of water in River
Definition
High Speed / Volume
Permeability is the ability of Permeable rocks (holds more
rocks being able to hold
water)  Lesser surface runoff
water
Vegetation: Plants at the
Sparse vegetation  Less
side of the river
rainwater infiltrate ground 
More surface runoff  Large
volume
How rainfall / temperature
Hot / Wet (High Evaporation) 
affects the river
High volume of water
Wet/dry weather  Water
level fluctuates
(drop/unstable)
Drainage Basin: An area
Bigger Drainage Basin Larger
which collects water
Surface area  Higher volume
(comprises of rivers)
of water
High Speed +
High Volume =
High Energy!
Low Speed / Volume
Less Permeable rocks More
surface runoff (more volume of
water)
More vegetation More
rainwater infiltrate ground
Lesser surface run off
Smaller Volume
Dry Low volume of water
throughout the year
Smaller drainage basin
Smaller surface area
Smaller volume of water
Pure Geography SA2 Overall Revision Notes
Chapter 4: Rivers and Coasts
Erosion, Transportation and Depositional Processes
Pure Geography SA2 Overall Revision Notes
Chapter 4: Rivers and Coasts
River Landforms
Author Comments: This is a very important
and crucial part of the chapter. Remember to
know how to draw the various river landforms.
Floodplains and Leeves (Example: Floodplain of River Wyre, England)
1. Floodplains are found at the lower course of a river.
2. When river overflows due to heavy rain, flooding occurs and water spreads over a larger area,
losing speed.
3. When water recedes, river deposits material carrying on the land, leaving behind sediments on
river banks and beds.
4. Coarser sediments are deposited closer to river edges and fine particles are deposited away
from river. The deposited materials build up on both sides of river due to flooding.
5. Over time, the accumulation of sediments at the flat plains called floodplains is formed. Coarser and
heavier materials accumulated nearer to the river form raised banks called levees.
Valleys and Gorges (Example:
1. Valleys and gorges are usually found in the upper course
where vertical erosion is prominent.
2. In the upper course, the volume of water is small but the
gradient is steep.
3. The swift flowing water exerts a powerful force on the river
bed, forming a V-shaped valley through hydraulic action,
abrasion and solution.
4. A gorge is an exceptionally deep and narrow valley formed
when the river erodes vertically through resistant rocks
leaving very steep valley walls.
Waterfalls (Example: Iguazu Falls, border of Argentina and Brazil)
1. River flows through across rocks of different
resistance,
2. eroding the less resistant rocks more rapidly,
3. causing a change of gradient in river course.
4. Over time, river plunges from great height to hit river
bed below with tremendous force, forming a waterfall.
6.
7.
8.
9.
5. Waterfall can also be formed by faulting,
where rocks are uplifted, causing
displacement of rocks where 1 layer is
higher than the other. When the river flows
across an area where faulting occurred,
gradient drops suddenly.
Repeated pounding of river bed leaves a depression at base of waterfall.
Depression is further deepened by rocks and boulders swirling around, forming a plunge pool.
Over time, as the harder rock is undercut it produces an overhang which will eventually collapse.
As the rock collapses the waterfall retreats upstream, leaving a gorge.
Meanders and Oxbow Lakes
1. Meanders can occur anywhere along the course of the river,
however they are more prominent in the middle/ lower course.
2. As the river travels downstream, it tends to find the easiest route,
thus it will bend.
3. Therefore, bends of the river at middle/lower course allows
erosion to occur at the outer bank of a river.
4. Eroded materials are deposited at the inner bank where water
moves in a spiral fashion. Along the outer bank, speed of river is
high due to less friction and greater volume.
5. Over time, the concave bank gets undercut1 and a steep-sided
cliff known as a river cliff is formed.
6. As the bends become more obvious, a meander is formed.
Formation of Oxbow Lakes
7. Constant erosion at 2 consecutive concave banks will cause the
2 meanders to more closer, forming a loop. Over time, it becomes
more distinct, separated by land.
8. As deposition and erosion continues, the 2 meanders eventually
meet.
9. Sediments deposited at convex banks will dam up the river,
forming an oxbow lake which will be separated from the main
river. The main river will flow in a straight path.
10. Due to deposition the old meander bend is left isolated from the
main channel as an ox-bow lake.
1
The process in which material at the bottom of the cliff or river bank is eroded away. This may cause the upper portion of the
cliff river bank to collapse.
Formation of Deltas
1. Deltas are found at the lower course of the river.
2. As a river approaches sea/lake, speed
decreases, thus deposition occurs.
3. Although sediments can be removed by tides, if
rate of deposition is faster than removal,
sediments will build up at mouth.
4. Over time, more sediment is deposited and
delta extends outwards into the sea.
Sediments carried will block flow of main river.
5. As a result, smaller channels known as
distributaries are formed to find their way out to
reach the sea or lake.
6. Deltas only form under certain conditions
a. The river must be transporting a large
amount of sediment
b. The sea must have a small tidal range and
weak currents
c. The sea must be shallow at the river mouth
Pure Geography SA2 Overall Revision Notes
Chapter 4: Rivers and Coasts
River Management Strategies
1. Key Principles:
a. Aimed to improve the speed of flow (take note: This can increase the amount of erosion, reducing
the ability of the river to hold water).
b. Increase the capacity of the river. (N.B. By increasing the volume of water, more water will flow
downstream, causing flooding there)
River Channelization
Processes such as resectioning is the widening or deepening of a river to let it carry more water,
whereas
Realignment deals with straightening the river channel to increase the speed of flow.
Although this can solve the problem upstream, however it will increase the chances of flooding
downstream.
This is because when there is greater speed and volume of the water in the river, more erosion will
occur and thus more sediment will be deposited at the river bed downstream, reducing the capacity of
the river to hold water.
When the huge volume of water reaches downstream, it will eventually cause flooding.
Pure Geography SA2 Overall Revision Notes
Chapter 4: Rivers and Coasts
Introduction
Chapter 7.1: Wave Energy
1. It is the energy produced by movement
of waves
2. Factors that can affect wave energy:
Wind Energy: Wind is air moving
from region of high to low pressure.
The faster wind speed, the greater
wave energy.
Duration of wind: The longer wind
blows, the larger the waves.
Fetch: Distance of sea over which
winds blow to generate waves. The
longer the distance, the more
energy the waves have.
3. The wave energy determines what kind
of coastal processes the waves
possesses.
Chapter 7.3: Constructive and Destructive Waves
Wave Height
Wave length
Wave Frequency
Breakers
Powerful Swash or
backwash
Place of
occurrence
Prominent Process
Constructive Waves
Low
Long
6-8 per minute
Spilling
Swash
Destructive Waves
High
Short
10-14 per minute
Plunging
Backwash
Gentle costal slope,
sheltered coast
Deposition
Steep slope, open
coast
Erosion
Chapter 7.2: Wave Movement
4. Waves move in a series of circular looplike motions. As the waves approach the
shore, the water becomes shallower; the
friction of the waves against the sea
floor slows down wave movement. The
frictional force cause the waves to rise
and bend forward, and eventually
collapse to foaming water.
Swash is the forward movement of
waves to the shore. It carries
sediments to the shore.
Backwash is the flow back to the sea
due to gravity. It carries sediments
back to the sea.
Chapter 7.4: Tides
Refers to the daily alternate rising and falling of sea level
seen along coasts.
Mainly caused by gravity of the Moon.
The pull produces high tides on opposite sides of the
Earth.
Each costal area receives 2 high tides and 2 low tides daily.
The difference in water level between the 2 tides is known
as tidal range.
The rise and fall of sea level affects erosion and
transportation.
Areas located between low and high tides will experience
more weathering and erosion as it have continuous drying
and wetting.
Chapter 7.5: Currents
Refers to the large-scale and persistent
movements of water in the ocean.
Driven mainly by winds.
Longshore currents is a ocean current that
flow parallel to a coast and are formed by
waves that approach the coast at an oblique
angle.
Pure Geography
Chapter 7: Coastal System and Processes
Coastal Processes
Coastal Erosion
Coastal Transportation
1. Corrasion (Abrasion): Rock fragments
are hurled at cliffs by breaking waves,
gradually scraping away at the cliff face.
2. Attrition: Rock fragments carried by the
waves hit each other and wear down to
form sand and silt.
3. Solution (Corrosion): Occurs when the
salt water can dissolve some chemicals
in the rocks.
4. Hydraulic Action: Waves break against
the cliff face, the pressure of the
breaking wave compresses air in the
cracks, which gradually forces open the
crack in the rock. It becomes weakened
as the process continues.
5. Scouring: This occurs at the base of the
cliff as the waves break and swirl
around, gradually removing loose rock.
6. Wave Pounding: The sheer force of
waves hitting against the cliff face.
1. Waves usually approach the coast at an angle in the
direction of the prevailing wind.
2. This causes the waves to break on the beach.
3. The swash then carries materials up the beach at an angle.
The backwash then flows back to the sea in a straight line
at 90o due to gravity.
4. This movement of material is called transportation.
5. The combined effect causes material to be transported
sideways along the coast known as longshore drift.
6. The 4 ways that waves can transport sediment (solution,
suspension, saltation, traction applies here too!)
Coastal Deposition
1.
2.
3.
4.
Deposition occurs when the material is too heavy to be transported is left behind, building up the beach.
The largest material is deposited first.
Distinctive features may form due to deposition.
Factors: Deposition of sediment along the coast is dependent on:
 Supply of sediment: Most sediment is transported down to the coast by rivers, from coastal erosion or
from coasts. When the waves cannot carry their load of sediment, deposition takes place.
 Gradient of slope: On gentle slopes, the wave energy is spreaded out and reduced due to the friction
with the shore and gravity, resulting in constructive waves as they deposit materials more than eroding
them.
 Position of the coast: Coasts that are sheltered from strong winds and the calm coastal condition allow
deposition to take place.
 It also occurs when waves enter a region of shallow water.
Pure Geography
Chapter 7: Coastal System and Processes
Coastal Landforms
Cliffs and Wave – cut platforms
1. Cliffs are produced by the action of waves undercutting a steep rocky
coast.
2. Hydraulic action and abrasion may erode a crack on the rock surface.
3. The crack can enlarge to form a notch, which is further deepened to
produce a cave. Further undercutting by the waves will cause the roof of
the cave to collapse.
4. An overhanging cliff is formed, which will eventually collapse and its
sediments deposited at the foot of the cliff.
5. Those sediments might be picked by crashing waves and thrown against
the base of the cliff, causing further erosion. A cliff is formed.
6. Continuous erosion may cause the cliff to retreat further inland and over
time, a wave-cut platform is formed at the foot of the cliff.
Headlands and Bays
1. A headland is made of resistant rocks which extend
outwards into the sea and formed due to differential
erosion of coastal rocks.
2. Coasts with alternate strips of resistant hard rock and
less resistant soft rock will cause the soft rock to be
eroded faster than the hard rock.
3. The result is the formation of an indented coast with
the remaining hard rocks forming headlands
extending into the sea and soft rocks forming bays.
Beach
1. A beach is a zone of deposition along the coast. It is formed when
materials carried by waves and currents is deposited on gentle slopes and
constructive waves which allows materials to be deposited by the strong
swash.
2. They are formed at protected bays along an indented coast due to wave
refraction, where waves approach the shallow sea in front of the headland
first.
3. As wave energy tends to concentrate at the headlands, erosion takes place
there.
4. Along the bays, waves are diverged, thus their energy is spread out and
weakened. Deposition occurs, and over time beaches are formed.
Spit and
Tombolo
1. Spits are beaches joined to the coast at just one end.
2. Formed by longshore drift.
3. When the direction of the coastline changes, it continues to deposit materials in the original
direction which accumulate in the sea forming a spit.
4. The spit continues to grow as materials are continuously deposited, joining a nearby island
to the mainland, forming a tombolo.
Pure Geography
Chapter 7: Coastal System and Processes
Coastal Protection Measures
1.
2.
3.
4.
The rationale and principle for coastal protection usually rest on the economic values of these coastal areas.
Often, the implementation of these measures led to more problems rather than solving the threats from coastal processes.
The 2 underlying principles are to reduce the energy of waves and/or retain coastal materials.
Types of Approaches:
Hard engineering: Construction of physical structures to defend against the erosive power of waves.
Soft engineering: Focuses on planning, management and changing individual attitudes towards coastal protection.
Measure
Seawalls (e.g.
Kallang River in
Singapore)
Advantages
Disadvantages
They are built along the coast which absorbs the
energy of waves before they can erode away
loose materials.
1.
Breakwaters
1.
Groynes
They help protect the coast and harbour by
reducing the force of high energy waves
before they reach the waves.
2. They create a zone of calm water behind
them.
1. They are built at right angles to the shore to
prevent longshore drift.
2. They absorb/reduce the energy of the waves
and cause materials to be deposited on the
side of the groyne facing the longshore drift.
Gabions
1.
Beach
Nourishment
Planting of
Mangroves
Refers to the constant replenishment of large
quantities of sand to the beach system, which
leads to the improvement of beach quality and
storm protection.
1. Coastal planners are trying to protect manmade structures by relocating them and let
nature reclaim the beach slowly.
2. No building of new structures is allowed in
coastal areas vulnerable to coastal erosion.
1. Mangroves can help to trap sediments and
reduce coastal erosion.
Coastal Dunes
1.
Relocation of
Property
Growth of
Coral Reefs
They are wire cages filled with crushed rocks
that are piled up along the shore to reduce
coastal erosion by weakening wave energy.
However, they do not prevent the powerful
backsplash of refracted waves from washing away
the beach materials between the walls.
2. The backsplashes will eventually undermine the base
of the seawall and eventually it collapses.
3. They are costly to build and maintain as repairs have
to be made to prevent their collapse.
However materials deposited in the zones behind the
breakwater are protected but the zones located away
from the breakwater are not, and will be eroded away.
3. As no fresh materials are deposited on the downdrift
side, that part will gradually be eroded.
4. To prevent this, the tips of groynes are sometimes
angled about 5 to 10°, but if failed, erosion can still
take place on unprotected areas.
2. They need to be maintained as they are easily
corroded.
3. If not properly maintained, the wire baskets become
unsightly and pose a threat.
However it is expensive to constantly transport sand to fill
up the beach as it is continuously eroded. Coral reefs may
be in danger as the sand covers the corals. It can also led
to muddy and polluted water.
This approach is likely to be opposed by people who want
to invest in the coastal areas.
2.
3.
1.
2.
Coastal dunes can be found along the shore
where lots of sand and strong winds exist.
The winds carry and deposit the land on the
coast further inland, forming coastal dunes
gradually which help defend the coast from
the sea.
They can weaken wave energy.
Artificial reefs are created along the coast to
help enhance fishing opportunities, serve as
undersea barriers and replace damaged
coral reefs.
2.
4.
3.
However some areas with violent destructive waves
may not support mangroves.
The depth of the coast may also become shallower,
affecting coastal transportation and port activities.
However they are very fragile and thus access points
to the beach are controlled and designated.
Shrubs and trees are planted to stabilise the dunes to
anchor the sand.
Tourists can damage these coral reefs.