2e rivers
DESCRIPTION
TRANSCRIPT
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WATER AS A RESOURCE
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BY THE END OF THE LESSON…
We will be able to,1. Describe the distribution of water on
Earth.2. Describe the hydrological cycle.
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WATER DISTRIBUTION
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The Hydrologic Cycle
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HYDROLOGIC CYCLE
• Refers to the continuous movement of water on, above and below the Earth’s surface.
• Water goes through the 3 states of solid, liquid and gas in the hydrologic cycle.
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HYDROLOGIC CYCLE
• During the day, the Sun heats up the Earth and changes some of the water from the oceans and rivers into water vapour through the process of evaporation.
• Plants also give out water vapour through their leaves through the process of transpiration.
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HYDROLOGIC CYCLE
• As the warm air rises, the water vapour cools and changes into very small water droplets in the process known as condensation.
• When billions of water droplets gather together, clouds are formed.
• As the water droplets became to large and heavy, they fall back to the surface in the form of precipitation (rain, snow, hail).
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HYDROLOGIC CYCLE
• The precipitation may fall back onto water bodies such as seas, lakes and rivers.
• Or seep into the ground to become groundwater which may eventually flow back to various water bodies.
• Some water may fall on the highlands and travel to the lowlands as runoff.
• The cycle then repeats itself as water evaporates or given out by plants through transpiration.
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RIVERS
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Lower Lewis River Falls, Washington
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Unnamed river
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Horseshoe Bend, Colorado River, Arizona
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Lake Powell, Colorado River, Utah
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Rio Negro, Brazil
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Ganges, India
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Mississippi, New Orleans
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BY THE END OF THE LESSON…
We will be able to,1. Describe the river system.2. Identify and describe the 3 courses of
a river.
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Parts of a River System
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PARTS OF A RIVER
• River source– Where the river begins, usually found in
mountainous areas or highlands.• Tributaries
– The streams and rivers that join a main river.• Distributaries
– The streams and rivers that does not return to the main river.
• River mouth– Where the river ends, normally a lake or a
sea.
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PARTS OF A RIVER
• Drainage basin– Area drained by a river and its
tributaries• Watershed
– Boundary of a drainage basin– Imaginary line that separates one
drainage basin from another
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DRAINAGE BASIN, WATERSHED
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RIVER COURSES
• Upper course– Steep gradient– River flows at high speed– Steep v-shaped river channel
• Middle course– Relatively steep to gentle gradient– Wider v-shaped river channel
• Lower course– Almost flat gradient– High volume of water in river– Almost u-shaped river channel
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BY THE END OF THE LESSON…
We will be able to,1. Describe various landforms formed
by rivers with the use of examples.2. Explain the formation of waterfalls,
meanders and deltas.
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Yosemite Valley, USA
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VALLEYS
• A low area between hills and mountains.
• Formed by the erosive action of a river.
• E.g. Grand Canyon, Arizona, USA.
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WATERFALLS
• A vertical flow of fast-moving water falling from a great height.
• E.g. Iguazu Falls, Niagara Falls
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Greenland Creek FallsNantahala National Forest,
USA
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WATERFALL
• River flows across rocks of unequal resistance.
• The less resistant rocks are eroded faster than the more resistant rocks, causing a slight depression at the boundary between the hard and soft rocks.
• This further increases the rate of erosion as turbulence is created at the depression.
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WATERFALL
• Overtime, this results in a sudden change in gradient of the riverbed and causes the river to plunge from a great height, forming a waterfall.
• The hydraulic action of the plunging water and the abrasive action of the swirling rocks erode the riverbed to form a depression known as a plunge pool.
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Iguazu Falls, Brazil
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MEANDER
• A river that follows a winding course, usually forming hoop-like bends.
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CONCAVE & CONVEX BANKS
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RIVER CLIFF
• Speed of river flow is fastest at the concave/outer banks of a meander hence erosion is most dominant.
• This leads to constant undercutting of the concave/outer bank which overtime, forms an overhanging cliff known as a river cliff.
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RIVER SLOPE / SLIP-OFF SLOPE
• Speed of river flow is slowest at the convex/inner banks of a meander hence deposition is most dominant.
• This leads to constant deposition of sediments which accumulates overtime and rise up above the water to form a gently undulating slope also known as a river slope / slip-off slope.
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FLOODPLAINS
• A wide and low-lying plain found on both sides of a river covered with alluvium deposited by the river.
• Formed by repeated overflowing of the river onto the surrounding land.
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DELTAS
• An extensive platform commonly found at the river's mouth.
• Formed by the accumulation of layers of sediments build up over a period of time.
• E.g. Nile Delta, Egypt.
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Atchafalaya Delta, Louisiana, USA
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DELTAS
• River loses energy as it enters a lake or sea leading to the deposition of sediments.
• Larger sediments such as sand are deposited closer to the shore, while fine silt and clay are carried farther out.
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DELTAS
• Overtime, the accumulation of sediments eventually forms an extensive platform at the river mouth.
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DELTAS
• Conditions for a delta to formed– River must be carrying a large amount
of sediments.– Waves along the coasts must not be
too strong that they remove the sediments faster than the river can deposit them.
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BY THE END OF THE LESSON…
We will be able to,1. Describe the positive impact of rivers
on people.
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POSITIVE IMPACT OF RIVERS
1. Water supply for farming2. Fertile soil for farming3. Water supply for industry4. Recreation and tourism5. Source of drinking water & food6. Production of hydroelectric power7. Means of transport
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WATER SUPPLY FOR FARMING
• Rivers are an important source of water for growing crops, especially in areas which receive little rain, as water can be supplied to farms through man-made canals known as irrigation.
• The Chao Phraya River in Thailand is an example of a river that enabled the the growing of rice on a large scale.
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FERTILE SOIL FOR FARMING
• When a river floods its banks, sediments are deposited that help to increase the fertility of the soil.
• This explains why deltas such as the Ganges Delta and Nile Delta are heavily farmed.
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WATER SUPPLY FOR INDUSTRY
• Water from rivers can be used for industrial purposes, such as for cooling machines and for the manufacture of certain food products.
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RECREATION AND TOURISM
• Rivers can be used for recreational activities such as rafting, canoeing and fishing and are scenic sites for tourism.
• For example, the Singapore River is a popular tourist attraction and recreational activities such as boat races and river cruise are held frequently.
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SOURCE OF DRINKING WATER & FOOD
• Rivers are a important source of drinking water especially in places where piped water is not available.
• Rivers is also a source of food as many edible creatures can be found in rivers.
• For example, 73 million living along the Mekong River depend on it for water and food.
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PRODUCTION OF HYDROELECTRIC
POWER• A lot of energy is produced when
water moves quickly in a river.• This energy can be converted into
electricity by building dams across rivers to trap large volumes of water before releasing it to turn turbines to generate electricity.
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MEANS OF TRANSPORT
• Rivers can serve as an effective mean of transport, especially in areas where it is difficult to travel on land.
• For example, goods and people are transported by large ships and boats along the Amazon River as the land is heavily forested.
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BY THE END OF THE LESSON…
We will be able to,1. Describe the negative impact of
rivers on people.
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DISCUSSION
• What are the negative impact of of rivers on people?
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SCENARIO
• Around 140 million people live on the Ganges delta, despite risks from floods.
• It is believed that upwards of 300 million people are supported by the Ganges Delta, making it the most populous river basin in the world.
• Most of the Ganges Delta has a population density of more than 200 people per km2, making it one of the most densely populated regions in the world.
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SCENARIO
• Each year, the flooding of the delta takes away lives and destroys property.
• In 1998, the Ganges flooded the delta, killing about 1,000 people and leaving more than 30 million people homeless.
• You are a team of river specialists and city planners. What would you suggest to alleviate the problem?
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NEGATIVE IMPACT OF RIVERS
1. Destruction of properties2. Loss of lives
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