rivers 1 (updated 310310)
TRANSCRIPT
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Can you identify this physical feature?
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What about this?
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If your idea of a river is like this…
Then what is this?
Vita StatisticsSingapore RiverLength: 11km
Vita StatisticsRiver MekongLength: 4200km
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Can you imagine catching this in
Singapore River?
This was caught by a fisherman in Mekong River
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It runs through
China, Burma,
Thailand, Laos,
Cambodia &
finally Vietnam.
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Lancang
River (China)
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Hydrologic
Cycle
Key terms:
Transpiration Evaporation
Condensation Precipitation
Infiltration Surface Runoff
River
System
Drainage Basin
Watershed
Parts of a River
‐River Source
‐Tributaries
‐River Mouth
‐Distributaries
Courses of a River
‐Upper
‐Middle
‐Lower
River
Energy
Speed of Flow
‐ Gradient
‐
Roughness of
river bed and
bank
‐ Depth of river
‐
Wetted
perimeter
Volume of Flow
‐Duration of
Rainfall
‐Amount of
Rainfall
‐
Size of drainage
basin
‐Type of soil
‐ vegetation cover
River
Processes
Erosion Transportation Deposition
Hydraulic
action
Attrition
Abrasion
Solution
Traction
Saltation
Suspension
Solution
Loses energy deposit
load (heavier first, then lighter load)
Channelisation
Re‐alignment
Re‐sectioning
Bank Protection
E.g. Dyes
Vegetation Planting
Upper
Waterfall, Gorge
Valley
Middle
Meanders
Lower
Meanders,
Floodplains, Deltas
Rivers
1.
Uses
2.
E.gs
3.
Ltms
Ways to
manage
rivers
Formation of
River features
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1.River System
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1.1 Parts of a RiverUpper Course Middle Course Lower Course
Keywords:River Source River Mouth Tributaries Distributaries Watershed Drainage Basin
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1.1 Shape of River ChannelUpper Course Middle Course Lower Course
Steep GradientNarrow channel Shallow
Gradient less steepWider channel
Very gentle gradientWidest channel
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1.1 River landforms foundUpper Course Middle Course Lower Course
WaterfallGorgesValleys
Meanders MeandersFloodplainsDeltas
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1.2 River Processes• Erosion
1.
Hydraulic action
2.
Abrasion/ Corrasion
3.
Attrition
4.
Solution
• Transportation1.
Traction
2.
Saltation
3.
Suspension
4.
Solution
• Deposition
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• Erosion (Vertical Erosion)
1.2 River Processes
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• Erosion
(Lateral Erosion)
1.2 River Processes
Lateral erosion
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1.2 River Processes
• Erosion
Lateral erosion
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1.2 River Processes (Erosion)• Erosion (Hydraulic Action)
Force of fast‐moving water surges into cracks & joints & breaks and
loosens
pieces
of
rocks
and
soil
along
river
bed
and
banks.
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1.2 River Processes (Erosion)• Erosion (Corrasion/ Abrasion)
Rock fragments dragged along river bed or against river banks grind
against
channel
walls.
As
a
result,
the
river
channel
widens and deepens.
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1.2 River Processes (Erosion)
• Erosion (Attrition)
Rock
fragments
and
other
materials
carried
by
water
collide with
one
another
and
break
down
into
smaller
pieces
over
time. Rough edges of large rocks get smoothened out.
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1.2 River Processes (Erosion)• Erosion (Solution)
Rainwater
dissolve
carbon
dioxide
in
the
atmosphere
forming carbonic
acid.
As
rainwater
falls
into
rivers,
the
carbonic
acid
dissolves
minerals
in
rocks
on
river
beds
and
banks
to form a solution. E.g. Limestone areas
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1.4 River Processes (Transportation)
• Transportation (Traction)
Larger‐sized
materials
such
as
boulders,
pebbles
&
gravel roll
and
slide
along
the
river
bed
as
they
are
too
heavy
to be lifted by river water.
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1.4 River Processes (Transportation)• Transportation (Saltation)
Smaller
materials
such
as
coarse
sand
particles,
get
lifted up and dropped onto the river bed over and over again as they are too heavy to be suspended all the time.
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• Transportation (Suspension)
Finer particles such as silt, clay & sand are carried along the river without touching the river bed by the turbulent flow of
water.
These
form
the
greatest
proportion
of
the
river’s load & gives the river a murky appearance.
1.4 River Processes (Transportation)
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• Transportation (Solution)
Minerals found in the rocks are dissolved by river water and carried downstream.
1.4 River Processes (Transportation)
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• Deposition– When a river does not have enough energy to either
erode or transport its load put down/ deposit its load.
– Factors causing Deposition:1.
Period with low precipitation Reduced River Volume
2.
A river enters a lake or sea Reduced River Speed
3.
A river flows along shallower side of river channel increased friction reduced River Speed
4.
Sudden increase in load
due to landslide, etc.
5.
River channel is obstructed by aquatic plants or
protruding bed rocks Reduced River Speed
1.4 River Processes (Deposition)
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1.5 River Energy
River Energy
Volume (m3)
As a river’s speed increases, its energy increases.As a river’s volume increases, its energy increases too.
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1.5 River Energy
Factors affecting River Speed
1.
Gradient of channel
2.
Roughness of channel
3.
Wetted perimeter
Factors affecting River Volume
1.
Size of drainage basin
2.
Presence of vegetation
3.
Permeability of rocks
4.
Climate
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1.5 River Processes Factors affecting River Speed
1.
Gradient of Channel
• Steep
river gradient Greater gravitational pull Increased speed
• Gentle
river gradient Lesser gravitational pull Decreased speed
Steep Gradient
Gentle Gradient
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2. Roughness of Channel
• Rough river channel more obstacles Morefriction Decreased speed
• Gentle
river channel less obstacles Less friction Increased speed
1.5 River Processes Factors affecting River Speed
Rough Channel Gentle Channel
Rocks, boulders, vegetation
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3. Wetted Perimeter: Part of river channel that is in contact with river water
• Large
wetted perimeter More channel area in contact with water More friction Decreased speed
• Small
wetted perimeter Less channel area in contact with water Less friction Increased speed
1.5 River Processes Factors affecting River Speed
Small wetted perimeter Large wetted perimeter
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1.5 River Processes Factors affecting River Volume
1.
Size of drainage basin
• Large
drainage area More surface area to collect rainwater Increased volume
• Small drainage area Less surface area to collect rainwater Decreased volume
Large Small
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1.5 River Processes Factors affecting River Volume
2. Presence of Vegetation
• Dense vegetation increases interception of rain less surface runoff & more infiltration Smaller volume
• Sparse vegetation decreases interception of rain more surface runoff Larger volume
Dense vegetation Sparse vegetation
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1.5 River Processes Factors affecting River Volume
3. Permeability of rocks
• Area of permeable
rocks higher infiltration less surface runoff Lower volume
• Area of less
permeable rocks lower infiltration more surface runoff Higher volume
Permeable rocks Less permeable rocks
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1.5 River Processes Factors affecting River Volume
4. Climate– Area with distinct wet and dry seasons
• River volume fluctuates
– Dry areas• Low river volume throughout the year
– Hot and wet equatorial areas• High river volume throughout the year
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Stages of stream development: a youthful stream, mature stream, and old age stream .
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The Life of A River
Every river has its way,From Upper, Middle, and all the way,
To the Lower courses of its end,It Erodes, Transports, then Deposits,Forming beautiful river landforms,Waterfalls, Valleys and Gorges,
Meanders, Floodplains, along the way,Finally, ending its journey in a delta
way.