WATER AS A RESOURCE

BY THE END OF THE LESSON…

We will be able to,1. Describe the distribution of water on

Earth.2. Describe the hydrological cycle.

WATER DISTRIBUTION

The Hydrologic Cycle

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.

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.

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).

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.

RIVERS

Lower Lewis River Falls, Washington

Unnamed river

Horseshoe Bend, Colorado River, Arizona

Lake Powell, Colorado River, Utah

Rio Negro, Brazil

Ganges, India

Mississippi, New Orleans

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.

Parts of a River System

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.

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

DRAINAGE BASIN, WATERSHED

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

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.

Yosemite Valley, USA

VALLEYS

• A low area between hills and mountains.

• Formed by the erosive action of a river.

• E.g. Grand Canyon, Arizona, USA.

WATERFALLS

• A vertical flow of fast-moving water falling from a great height.

• E.g. Iguazu Falls, Niagara Falls

Greenland Creek FallsNantahala National Forest,

USA

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.

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.

Iguazu Falls, Brazil

MEANDER

• A river that follows a winding course, usually forming hoop-like bends.

CONCAVE & CONVEX BANKS

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.

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.

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.

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.

Atchafalaya Delta, Louisiana, USA

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.

DELTAS

• Overtime, the accumulation of sediments eventually forms an extensive platform at the river mouth.

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.

BY THE END OF THE LESSON…

We will be able to,1. Describe the positive impact of rivers

on people.

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

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.

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.

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.

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.

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.

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.

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.

BY THE END OF THE LESSON…

We will be able to,1. Describe the negative impact of

rivers on people.

DISCUSSION

• What are the negative impact of of rivers on people?

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.

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?

NEGATIVE IMPACT OF RIVERS

1. Destruction of properties2. Loss of lives

END