03 Sec 1 Cht 10 Rivers 08

Chapter 10

o The Hydrological cycleo The River Systemo The Drainage Basino Features formed by Riverso Identifying River features on topo mapso How do rivers affect people?

Distribution of Water on the Distribution of Water on the EarthEarth

Salt water (97%)Fresh water (3%)

Fresh water

Groundwater (29%)

Glaciers, ice sheets (70%)

Seas, lakes, rivers (1%)

Almost three-quarters of theEarth’s surface is covered withwater

The Hydrologic CycleThe Hydrologic Cycle

Evaporation: Heat from the Sun causes water to change to water vapour

Transpiration: Water vapour given out by plants

Condensation Rainfall

• Continuous movement of water from the Earth’s surface into the air, and back onto the Earth

• Water changes state at each stage of the cycle• Processes occur at the same time

The Hydrologic CycleThe Hydrologic Cycle

Condensation: Water vapour cools and changes into water droplets

1 Clouds form when water vapour condenses to form water droplets

2 Water droplets combine to form bigger water droplets

3 Water droplets get bigger and heavier

4 When the water droplets become too heavy to float, they fall as rain or snow

Rainfall: Water droplets fall as rain or snow

Rain flows on the Earth’s surface as runoff or seeps into the Earth to be stored as groundwater

• A River is a body of water flowing in a channel.

• 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 river are known as its tributaries.

• The river ends when it flows into a lake or sea. This is known as the river mouth.

A river is a body of water that flows in a channel. Aided by gravity, it always flows downhill from its source. A river can be divided into three sections — the upper, middle and lower courses.

River sourceTributaries

River mouth

Upper course Middle course Lower course

1. Rivers ‘drain’ the surrounding land by collecting 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 that separates one drainage basin from another.

The Drainage BasinThe Drainage BasinThe area drained by a river and its tributaries

River

River source Tributary

River mouth

Drainage basin

Watershed

River System

• 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. ValleysRivers Features: 1. Valleys

A river cutting through a valley

• A waterfall is formed when a river flows over alternating bands 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. WaterfallsRivers Features: 2. Waterfalls

NIAGARA FALLS

3. Meanders• As a river flows over flat land, it forms curves

and bends which become more and more noticeable along the river course.

• These bends are called meanders• Meanders are formed when the river erodes

sideways and deposits the sediments it is carrying on the opp side.

Meandering System of Rivers

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4. Floodplains• As a river flows through a flat valley, it

deposits most of the sediments it is carrying.• As a result, the bottom of the river bed is

raised• Whenever it rains heavily, the river will

overflow its banks and flood the surrounding low-lying land. This land is called a floodplain

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5. Deltas• At the river mouth, the river deposits its

sediments into a lake or sea.• There, the sediments build up slowly and

obstruct the flow 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 the river mouth, a delta is formed.

Diagram of Delta

Delta

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 soilFarmers plant their crops along the river course

Source of drinking water and food

How do Rivers Affect People?How do Rivers Affect People?

Production of hydroelectric powerRivers are a source of electricityA lot of energy is produced when water moves quickly in a riverThis energy can be converted into electricity

Means of transport

Water supply for industry23% of all water drawn by people is used in industries

Recreation and tourismSwimming, fishing, sailing, etc…

How do Rivers Affect People?How do Rivers Affect People?

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?How do Rivers Affect People?

Photo 10-3 The satellite image captures a stretch of the Yangtze River and its tributaries. The red portions indicate areas with vegetation. Inset (yellow box) shows the construction site of the Three Gorges Dam.