managing river and coastal environments: a continuing challenge 2010 china floods duration10 may -...

Managing river and coastal environments: A continuing challenge

2010 China floods2010 China floods Duration 10 May - Present

Damage 41 billion US$

Fatalities2746+ dead, 11,800+ missing or buried

Area affected28 provinces, autonomous regions and municipalities

Source: Wikipedia


Why?Why?• Heavy downpour in summer

• Summer monsoon

• Onshore winds

• Low pressure centre over Asia

• Mudflow / landslide

• Overflow of rivers


22 Managing river andManaging river and coastal environments: coastal environments: A continuing challenge A continuing challenge

22 Managing river andManaging river and coastal environments: coastal environments: A continuing challenge A continuing challenge


2.12.1 How does water shapeHow does water shape our rivers and coasts? our rivers and coasts?


A large crack along the coast at Cheung Chau(Credit: Liang Wing Hang Yanchap)

crack

A narrow ridge of sand in Greece(Credit: Corbis)

A lake in New Zealand(Credit: NSIL)

Cheung Chau Islands

(Credit: The Government of Hong Kong Special Administrative Region)


Do you know what agents shape these landscape?

Do you know what agents shape these landscape?

They are shaped by rivers and

waves.

Let’s study some basic knowledge about river and coast before we learn how rivers and

waves shape the land.


How does water move on our earth?

Main storages of water

Atmosphere Land Ocean

Soil and rocksRivers and

lakesVegetation

cover

Water moves among the storage areas on the earth.

The main storages are:

Ice caps



condensation

surface run-offinfiltrationsubsurface run-off

transpiration

evapotranspiration

evaporation

evaporation

atmosphere

rivers and lakes

ocean

soil and rocks

vegetation cover

precipitation

precipitation



interception

precipitation transpiration

evaporation

stem flow

drip flow

Vegetation cover


Surface run-off

evaporationprecipitation

overland flow

channel flow

surface run-off



Water movement underground

unsaturated rock and soil

water table

saturated rockimpermeable rock

surface storage

soil moisture storage

infiltration

absorption

ground water storage

percolation

evaporation

throughflow

base flowsubsurface run-off



If trees are cut down, how will the water cycle

change?

If trees are cut down, how will the water cycle

change?

If there is deforestation …Test yourself!

Interception will ( increase / decrease );

surface run-off will ( increase / decrease );

infiltration will ( increase / decrease ).

Some map skills about rivers


The running water of the Jinsha Jiang(Credit: Tsui Chung Pong David)

How does a river shape the land?

Rivers can• split rocks and cut into land;• carry stones and sand along;• drop the carrying stones and sand in places where their energy drops.

Rivers are a significant agent that shape the landscape.

Erosion

Transportation

Deposition


How does seawater shape our coast?

An isolated mass of rock near Jeju Island, Republic of Korea(Credit: Liang Wing Hang Yanchap)

Tides and waves are also agents that shape the coast.

Waves can be either erode the land or deposit sediment there.

Tides have significant impact on the formation of coastal landform.



Tidalrange

There are two high tides and low tides every day.

High tide – Low tide = Tidal range

Active zone of wave action

The larger the tidal range, the larger the zone of active wave action.



Lowest water level

Highest water level where storm waves can reach

Zone of wave attack



Foreshore

Lowest water level

Shore

High tide level



Backshore

Foreshore

Lowest water level

Shore

High tide level

Highest water level

Offshore


1 Defining the area of a drainage basin

Can you identify the watershed of River basin A on

the map?

Can you identify the watershed of River basin A on

the map?

First, identify the ridge that separates the basin from adjacent ones.

Second, use a curved line to join the ridge and the highest parts down the spurs.

Cut every contour line at right angle on its way.

Last, close the watershed at the mouth of the river.

River basin A


2 Drainage density of a river

Scale: 1:100,000

Drainage basin

ChannelsDrainage density of the river

= ___________________________Total length of the channels in

a drainage basin

Total area of the drainage basin

Total length of the channels

= 21 cm 100,000

= 2,100,000 cm

= 21 km


8

1

20

3 4 5 6 7

9 10 11 12 13

14 15 16 17 18 19

2721 22 23 24 25 26

2

28 29 30 31 32 33 34

35 36 37 38 39 40 41

42 43 44 45 46 47

48 49 59 51 52

53 54 55


Scale: 1:100,000

Drainage density of the river

= ___________________________

Total length of the channels in a drainage basin

Total area of the drainage basin

0.5cm

0.5cm

Complete squares

= 55 squares


Scale: 1:100,000

55


12

13

26

1815

21

23

25

8

7

5

3

35 34 33

31

30

2

4

6

9

10

11

14

16 17 19

20

22

24

27

28

29

32

1

Incomplete squares=35 0.5= 17.5 squares

Complete squares +Incomplete squares

=55 + 17.5= 72.5



On the map,1 cm = 100,000 cm (1 km) in actual;0.5 cm = 50,000 cm (0.5 km) in actual

The actual area of each square= 0.5 km 0.5 km= 0.25 km2

The total area of the drainage basin= 0.25 km2 72.5 complete squares= 18.125 km2



Drainage density of the river

Total length of the channels in a drainage basin= Total area of the drainage basin

21 km= 18.125 km2

= 1.16 km/km2

The higher the drainage density, the more ( active / inactive ) the erosional force in the basin.

Discussion : How will deforestation affect drainage density?


3 Identifying different features of a river

River A

River source

Confluence point

Main river

Tributaries


4 Finding out the stream order

River A

11

1

1

1

1

1

111

22

223

3

3

4

4

Stream order = stream hierachy

1 First order streams

2 Second order streams

3 Third order streams

4 Fourth order streams

This is a fourth order basin.

Discussion:

What is the difference in stream order between a river basin in TRF and a river basin in desert?


Identifying the ridges on a contour map

800700 600 500

A ridge

A ridge is an elongated area of relatively high ground.


Is this a spur?Is this a spur?

100

200

300

BA

Height (m)

100

200

300

A B

The cross-section of AB

Identifying the spurs on a contour map

managing river and coastal environments: a continuing challenge 2010 china floods duration10 may -...

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