river and environment
TRANSCRIPT
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Chapter 10
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o TheHydrological cycleo The River System
o The Drainage Basin
o Features formed by Rivers
o Identifying River features on topo maps
o How do rivers affect people?
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Distribution of Water on the EarthSalt water (97%)Fresh water (3%)
Fresh water
Groundwater (29%)
Glaciers, ice sheets (70%)
Seas, lakes, rivers (1%)
Almost three-quarters of theEarths surface is covered with
water
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The Hydrologic Cycle
Evaporation:Heat from theSun causeswater tochange towater vapour
Transpiration: Watervapour given out byplants
Condensation Rainfall
Continuous movement of water from the Earthssurface into the air, and back onto the Earth
Water changes state at each stage of the cycle Processes occur at the same time
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The Hydrologic Cycle Condensation: Water
vapour cools and changesinto water droplets
1 Clouds form when watervapour condenses to formwater droplets
2 Water dropletscombine to form
bigger water droplets
3 Water dropletsget bigger andheavier
4 When the waterdroplets become tooheavy to float, they fallas rain or snow
Rainfall:Water droplets fallas rain or snow
Rain flows on the Earths
surface as runoff or seepsinto the Earth to be storedas groundwater
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A River is a body of water flowing in achannel.
The place where a river begins is called a
river source. Due to gravity a river flows downhill from its
source
The streams and rivers that join a main riverare known as its tributaries.
The river ends when it flows into a lake or
sea. This is known as the river mouth.
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A river is a body of water that flows in a channel.Aided by gravity, it always flows downhill from itssource. A river can be divided into three sections the upper, middle and lower courses.
River sourceTributaries
River mouth
Upper course Middle course Lower course
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1. Rivers drain the surrounding land bycollecting the surface runoff and directing it
to the lakes and seas.2. The area that is drained by a river and its
tributaries is called the drainage basin.
3. Watershed is an imaginary line thatseparates one drainage basin from another.
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The Drainage Basin
The area drained by a river and its tributaries
River
River source Tributary
River mouth
Drainage basin
Watershed
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River System
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Refer to the low area between hills or mountains The shape of a valley depends on how the river
cuts into the land
Rivers Features: 1. Valleys
A river cutting through a valley
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A waterfall is formed when a river flows over alternatingbands of rocks of differing resistance
As the river flows, the less resistant or softer rock
is eroded much faster than the more
resistant or harder rock This results in a steep change in gradient
resulting in a vertical drop of water
known as a waterfall
The force of the water is so great that it
cuts a depression or plunge
pool at the base of the water fall
Rivers Features: 2. Waterfalls
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NIAGARA
FALLS
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3. Meanders
As a river flows over flat land, it forms curves andbends which become more and more noticeable alongthe river course.
These bends are called meanders
Meanders are formed when the river erodes sideways
and deposits the sediments it is carrying on the oppside.
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Meandering System of Rivers
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TB PG 120
4. Floodplains
As a river flows through a flat valley, it deposits mostof the sediments it is carrying.
As a result, the bottom of the river bed is raised
Whenever it rains heavily, the river will overflow itsbanks and flood the surrounding low-lying land. This
land is called a floodplain
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TB PG 120
5. Deltas
At the river mouth, the river deposits its sedimentsinto a lake or sea.
There, the sediments build up slowly and obstruct theflow of the river to the sea.
When this happens. The river has to flow along
alternative channels called distributaries. Tributaries join a river but distributaries branch out
from a river.
When layers of sediments have been deposited at theriver mouth, a delta is formed.
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Diagram of Delta
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Delta
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Positive Impact of Rivers
Water supply for farmingRivers are a important source of water for
growing crops.
Fertile soil for farmingWhen a river floods its banks, it helps to
deposit sediments that help increase the
fertility of the soil
Farmers plant their crops along the river course
Source of drinking water and food
How do Rivers Affect People?
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Production of hydroelectric powerRivers are a source of electricityA lot of energy is produced when water moves
quickly in a river
This energy can be converted into electricity
Means of transport
Water supply for industry
23% of all water drawn by people is usedin industries
Recreation and tourismSwimming, fishing, sailing, etc
How do Rivers Affect People?
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Negative Impact of Rivers Floods can cause the loss of lives and property Flooding happens when the water in a river
overflows its banks
How do Rivers Affect People?
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Photo 10-3 The satellite image captures a stretch of theYangtze River and its tributaries. The red portions indicateareas with vegetation. Inset (yellow box) shows theconstruction site of the Three Gorges Dam.