Post on 12-Jan-2016
description
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
Managing river and coastal environments: A continuing challenge
Why?Why?• Heavy downpour in summer
• Summer monsoon
• Onshore winds
• Low pressure centre over Asia
• Mudflow / landslide
• Overflow of rivers
Managing river and coastal environments: A continuing challenge
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
Managing river and coastal environments: A continuing challenge
2.12.1 How does water shapeHow does water shape our rivers and coasts? our rivers and coasts?
Managing river and coastal environments: A continuing challenge
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)
Managing river and coastal environments: A continuing challenge
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.
Managing river and coastal environments: A continuing challenge
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
Managing river and coastal environments: A continuing challenge
How does water move on our earth?
condensation
surface run-offinfiltrationsubsurface run-off
transpiration
evapotranspiration
evaporation
evaporation
atmosphere
rivers and lakes
ocean
soil and rocks
vegetation cover
precipitation
precipitation
Managing river and coastal environments: A continuing challenge
How does water move on our earth?
interception
precipitation transpiration
evaporation
stem flow
drip flow
Vegetation cover
Managing river and coastal environments: A continuing challenge
Surface run-off
evaporationprecipitation
overland flow
channel flow
surface run-off
How does water move on our earth?
Managing river and coastal environments: A continuing challenge
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
How does water move on our earth?
Managing river and coastal environments: A continuing challenge
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
Managing river and coastal environments: A continuing challenge
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
Managing river and coastal environments: A continuing challenge
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.
Managing river and coastal environments: A continuing challenge
How does seawater shape our coast?
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.
Managing river and coastal environments: A continuing challenge
How does seawater shape our coast?
Lowest water level
Highest water level where storm waves can reach
Zone of wave attack
Managing river and coastal environments: A continuing challenge
How does seawater shape our coast?
Foreshore
Lowest water level
Shore
High tide level
Managing river and coastal environments: A continuing challenge
How does seawater shape our coast?
Backshore
Foreshore
Lowest water level
Shore
High tide level
Highest water level
Offshore
Managing river and coastal environments: A continuing challenge
Managing river and coastal environments: A continuing challenge
Managing river and coastal environments: A continuing challenge
Managing river and coastal environments: A continuing challenge
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
Managing river and coastal environments: A continuing challenge
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
Managing river and coastal environments: A continuing challenge
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
2 Drainage density of a river
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
Managing river and coastal environments: A continuing challenge
Scale: 1:100,000
55
2 Drainage density of a river
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
Managing river and coastal environments: A continuing challenge
2 Drainage density of a river
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
Managing river and coastal environments: A continuing challenge
2 Drainage density of a river
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?
Managing river and coastal environments: A continuing challenge
3 Identifying different features of a river
River A
River source
Confluence point
Main river
Tributaries
Managing river and coastal environments: A continuing challenge
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?
Managing river and coastal environments: A continuing challenge
Identifying the ridges on a contour map
800700 600 500
A ridge
A ridge is an elongated area of relatively high ground.
Managing river and coastal environments: A continuing challenge
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