River and Environment

8/2/2019 River and Environment

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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



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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



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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.

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River and Environment