notes sect2 eng

8/12/2019 Notes Sect2 Eng

1/62

HKDSE

Interactive Geography

Notes

Section 2

Managing river and coastal environments:

A continuing challenge

HKDSE Interactive Geography

Aristo Educational Press Ltd. @ 2009


2/62

Section 2Managing river and coastal environments: A continuing challenge

2

Unit 1 How does water shape our r ivers and coasts?

The work of water creates a variety of ____________ and ____________

environments. There are various physical and human factors that shape the Earths

surface.

From source to mouth, a river develops distinct landform features. Most rivers consist

of ____________ courses, namely the upper course, middle course and lower course.

But in Hong Kong, most rivers are ____________ due to compact land profiles and

steep slopes. They typically have only _______ courses, upper and lower.

Coasts have various landform features formed by the wearing away of rocks or

transporting sediments by the waves to a new location. In Hong Kong, there are more

than 260 ____________ islands with magnificent coastlines and coastal features.

Example of r iver in China-Chang J iang Refer to Fig.1.2 in Section 2 p.7 Refer to Fig.1.3 in Section 2 p.8-9

The Chang Jiang is the ____________ and largest river in China. It is 6 300 km long,

the third longest river in the world.

Originates from the _____________ Gaoyuan.

Flows through 11 _____________ and autonomous regions.

A huge _____________ network, with a total drainage area of 1.8 million km 2, one-fifth

of China's total land area.

The huge _____________ produces a large sediment load, amounting to 486 million

tons each year.


3/62


3

Coastal features in the United Kingdom Refer to Fig.1.4 in Section 2 p.11-12

The coastline of the United Kingdom is very _________ with a length about 12 500 km. In the south and west, the coast is _________ with steep cliffs.

The east coast is often _________ and low-lying, with beaches and mud-flats.

In the southeast, there are dramatic _________ cliffs.

In the southwest, a long peninsula with rocky outcrops of _________, sea arches and

stacks can be found.


4/62


4

Unit 2 The river basin and coast

The water cycle Water on the Earths surface is returned to the atmosphere through the process of

____________.

The water vapour will later ____________ into liquid or solids that fall to the ground

again. This ____________ process is known as the water cycle.

The operation of water cycle

Water has three physical states: 1. solid (_________), 2. liquid (_________) and 3. gas

(__________________).

Refer to Fig.2.1 in Section 2 p.17

Input:

1 Precipitation

When air is saturated with water vapour, water vapour condenses to form ____________.

When water droplets become larger and are too heavy to remain suspended in the air, they

fall to the ground as precipitation.

Transfer:

1. Interception Precipitation falls on _______________ and is caught there.

2. Throughfall &

stem flow

Some water reaches the ground by dripping off ____________

(throughfall) or flowing down the ____________ (stem flow).

3. Infiltration Some water ____________ into the soil, forming soil storage.

4. Throughflow Some water ____________ in soil flows along the slope as

throughflow.


5/62


5

5. Percolation Some soil water flows downward as percolation until it reaches

the _____________________.

6. Ground water

flow

Some ground water remains deep in the ____________, while

some flows to the surface and into rivers or oceans.

7. Surface

runoff

Water flows on the surface as surface runoff. It includes

____________ flow and ____________ flow.

8. Channel flow Surface runoff following river channels is called channel flow.

9. Overland flow The _______________ surface runoff, flowing on the ground

surface.

Outputs:

1. Evaporation Water in soil, on the ground or in rivers and sea will absorb heat

energy from the sun. It will change into water ____________

and return to the atmosphere through the process of

evaporation.

2. Transpiration Water in _______________ is released into the atmosphere

through transpiration.

A river bas in Refer to Fig.2.2a and b in Section 2 p.19

It is a _______________ area of a river and its tributaries. It is also known as the river

_______________ area.

The main stream and its _____________ form a drainage network or drainage system.

Adjacent river basins are separated by a _______________.


6/62


6

A coast

It is the ____________ of the land where it meets the sea or ocean.

It is the area between the _______________ (marks the highest level reached by the

sea and shoreline), the outer margin of the wave-cut terrace.

The coast can be generally divided int o several parts:


1. Shore - the area between the _______________ and the low water level.

- It includes two parts _______________ and _______________.

2. Nearshore - the area between the low water level and the _______________

(lowest water level).

3. Offshore - extends seawards from the ____________ water level.

A coast is a ____________.

Inputs: energy from wind, sediments from the sea

Outputs: sediments deposited on shores, energy dissipated by waves. Sometimes

beautiful coastal features can be regarded as another output.

The coast contributes to the ________________ of an area because it serves the

functions of defense, fishing, recreation and overseas trading.

In Hong Kong, much of our urban land has been modified and _______________ from

coastal areas. As a result, many parts of the coastline have been ________________.


7/62


7

Unit 3 How do fluvial processes shape the land?

The fluvial processes Fluvial processes are _______________ processes that occur at or near the Earths

surface.

Different fluvial processes create various _______________ features within a drainage

basin.

River flows lead to fluvial _______________, _______________ and

_______________ that occur in all parts of a river.

The strength of the fluvial processes is determined by the amount of

________________________.

The river energy

Rivers flow from high altitude (higher potential energy) to low altitude (lower potential

energy) under the force of _____________.

Potential energy is converted into _____________ energy, which becomes the energy

of a river that causes erosion and deposition, forming various fluvial landscapes.

Factors determine river energy

River energy is _______________ to river discharge, which depends upon the amount

of water and the _____________ of river flow.

______________ refers to a measured volume of water (usually in cubic metres or in

cubic kilometres) flowing past a given point in a specified period of time (usually one

second).


8/62


8

1. Volume of flow

The higher the volume of flow of a river, the ___________ the rivers energy and

the more intense its fluvial _______________ and _______________. _____________________ determines the volume of flow. Therefore, factors

affecting channel capacity also affect the volume of flow.

a. Precipitation

The _______ precipitation, the

_______ surface runoff.

Volume of flow of the river will

___________.

b. Vegetation cover

The _______ vegetation cover,

the ___________ the rate of

infiltration and ___________

surface runoff.


___________.

c.Evapotranspiration

rate

The ___________ the rate of

evapotranspiration, the

_______ the surface runoff.


___________.


9/62


9

d. Permeability of river

basin

The ___________ the

permeability of bed rock, the

___________ the rate of

infiltration.


___________.

e.Slope gradient of

the river basin

The ___________ the

gradient, the _______ the

surface runoff. This permits

_______ infiltration.


___________.

f. Human activities

Urbanisation increases surface runoff as more land surface

is covered by impermeable concrete.

Volume of flow of the river will ___________.

2. River veloci ty

The higher the river velocity, the ___________ the energy of the river.


10/62


10

Factors affecting river velocity

a. Channel

gradient

If the channel gradient is steep, _____________ energy can be

converted into ___________ energy at a faster rate, so river

velocity will ___________.

b. Channel frictionMuch of a rivers energy is used to overcome channel friction, which

depends on the following factors:

i. Channel roughness Channel roughness depends on the materials that form

the river ________ and ________.

The ___________ the materials, the greater the channel

roughness.

A rough channel causes greater ___________, which

depletes river energy as water passes the channel

surface.

ii. Channel shape River channels vary greatly in __________ which affects

channel friction.

The greater the ______________ of the channel, the

longer the channel is. The total contact surface between

water and the river banks and bed ____________, thus

friction increases.

iii. Wetted perimeter

of the channel

River channels also vary in their cross sectional profile.

This determines the contact surface area between water

and the channel, which is known as

_______________________________.

In general, the larger the wetted perimeter, the

____________ the channel friction.


11/62


11

Fluvial erosion

Fluvial erosion is the ____________ down of rocks and minerals along the river bed

and banks.

When river energy ____________, or when there is a decrease in energy loss, more

energy is available to carry out ____________.

Flowing water removes __________ materials from the river source, the river bed and

river banks. The transported loads will also cause abrasion, by which the sides and

bed of the river channel are eroded.


12/62


13/62


13

Types of f luvial erosion Refer to Fig.3.4 in Section 2 p.33

1. Hydraulic action Running water produces a great __________ which erodes the bed and walls of a river

channel.

This force also widens __________ and __________ in rocks, and removes loose

materials.

2. Solution/Corrosion

Water dissolves and removes __________ minerals in rocks. An example of such a

mineral is __________ in limestone.

As minerals are removed, the rocks are weakened and are more easily eroded by

other erosive processes.

3. Abrasion/Corrasion

The load of rock fragments carried by the river scrapes against the bottom and sides of

the river channel.

__________ often occur in a rough channel of pebbles and boulders. These eddies

twist rock fragments which drill into the river bed, carving out __________. Such

hollows are called potholes.

Both abrasion and hydraulic action are intense beneath a _____________. The river

bed is eroded and deepened, forming a depression or ____________________.

4. Attri tion

Rock fragments in the load carried by the river __________ against one another.

The rock fragments are then broken down into __________ and more __________pieces.


14/62


14

Fluvial transportation

Fluvial transportation is the _______________ of loads downstream.

A river carries eroded materials to its lower course for deposition, so that the inputs of

the whole system can be transformed to outputs. Land is re-shaped throughout the

entire course of the river.

The load of a river

The load of a river refers to materials it carries. These are mainly weathered materials

in the drainage basin, such as ______________________, sand and clay.

Some are materials produced by fluvial _____________ and others come from

_______________ of river banks. The larger the load, the greater the amount of

energy needed to transport it.

Types of load

There are three different types of river load, classified according to the particle

_________ and _________ of transportation.

1. _________ load consists of large rock fragments transported on the river bed by

_____________ or _____________.

2. _____________ load is made up of tiny silt and clay particles transported in

_____________.

3. _____________ load consists of ions of minerals dissolved in the water.


15/62


15

Major fluvial t ransportation processes Refer to Fig.3.5 in Section 2 p.35

Mode Characteris tics of

load

Where

transported?

How does it take place?

Solution _________ of

different minerals

(dissolved load)

In flowing water Icons are dissolved in the water

Suspension _________ silt and

clay (suspended

load)

In flowing water Silt and clay particles are so

small that they remain

suspended in water

Saltation _________ rock

fragments

(bed load)

River bed and

flowing water

Rock fragments undergo

saltation when they regain

energy bouncing on the river

bed

Traction _________ rock

fragments

(bed load)

River bed The fragments are so large that

they can only be dragged by

water along the river bed

Fluvial deposition Fluvial deposition is the ______________ of materials of a river.

It takes place when a river loses its ___________ and its load becomes too heavy for it

to carry, i.e. the amount of load ___________ the rivers carrying capacity.


16/62


16

Process of fluvial deposition

When velocity or discharge ______________, river energy is gradually reduced.

______________ particles remain suspended in the water until there is a further

reduction of river energy.

Therefore, along the course of a river, the __________ particles are deposited first.

Smaller ones are carried further downstream before they are deposited.

As deposition takes place in sequence according to particle __________, it occurs at

different times and locations. This process is called ______________.

Sediments are deposited on a sea, river or lakes bed in sequence. __________ of

sediment are formed. This is called __________________.


17/62


17

The characteristics of the different courses of a river

Upper course Middle course Lower course

Stream order Low Medium High

Slope gradient Steep Medium Gentle

Size of load Large Medium Small

Shape of load Angular Mixed Rounded

Amount of load Small Medium Large

Cross section of

valley

Shape of valley Deep, narrow

V-shaped

Wider V-shaped Flat and broad

V-shaped

Channel shape Relatively _________,

sometimes bends

along interlocking

spurs

Meander-formed,

__________ course

along the valley

Well-developed

__________, winding

course on the

floodplain

Channel

roughness

__________

(mainly boulders)

Medium __________ (mainly

fine sand and silt)

Wetted perimeter Medium

Average velocity Medium

Discharge Medium

River energy Medium

Main fluvial

process

More __________ and

__________ erosion

than lateral erosion

More

______________ and

__________ erosion

than vertical erosion

Dominantly

______________,

______________ and

lateral erosion


18/62


18

The veloci ty, discharge and channel shape change downstream and the factorsinfluencing these changes

Characteristics Reason

Velocity

River bed and banks become increasingly smooth towards the

__________ course as the materials are finer. Less energy is used

for overcoming friction, thus allowing the river to flow faster.

As discharge _____________ downstream, so does the velocity.

Discharge The number of tributaries ___________ from the source. Thus the

discharge ___________ as flow proceeds towards the main stream.

Efficiency

River efficiency is determined by __________ and __________.

In the upper course, the channel tends to be __________ in shape

with protruding rocks. The loads carried are angular and consist of

large boulders and rocks. All these contribute to the increase in

channel roughness, leading to greater friction and __________

efficiency in the upper course.

When moving downstream, the channel becomes __________ and

the loads become smaller, leading to a reduction in friction, so

efficiency ____________.

Channel

gradient

Valley shape

In the upper course, ____________ erosion is greater than

__________ erosion, forming a deeply cut, narrow and steep,V-shaped valley.

____________ erosion becomes more dominant in the middle

course. The valley is gradually ____________.

In the lower course, there is simultaneous __________ erosion and

________________. The meander keeps changing course, thus

further widening the valley. The slope is gentle.


19/62


19

Landform features in the upper course of a river

1. Waterfalls and rapids


When a river flows over a very _________ portion of its channel with a sudden

increase in ____________, it is called a waterfall.

A waterfall usually occurs when a layer of _____________ hard rock rises vertically

across the river bed, dips upstream or lies horizontally. The _________ rock lying

beneath is more rapidly eroded by the river, resulting in a vertical drop.

Cross

section

of a

waterfall

Condition Vertical, resistant rocklayers such as porphyry

dykes are exposed afteroverlying rock is eroded.The surrounding, lessresistant granite iseroded by the river,forming a waterfall.

The more resistant layerof rock such as

conglomerate lyingacross the river coursedips upstream, while theunderlying volcanic rockis less resistant andsubject to erosion,forming a waterfall.

At the top lies a layer ofhard rock, such as

dolomite, with lessresistant rock, such asshale or sandstone lyingunderneath it. The watertumbles over the highcliff into the plunge poolbelow.

Example Waterfall on River Silver

near Silver Mine Bay

Brides Pool Falls Niagara Falls, border of

the USA and Canada


20/62


20


____________ may also cause a

waterfall or rapid to form. Faulting can

cause the block of crust on the

downstream side to ____________.

The displacement results in a sudden

____________ drop. The channel

gradient becomes much

____________, forming a waterfall or

rapid.


__________ occur where the flow of the river is very swift and ________________

develops as a result of a sudden increase in steepness of the river channel.

A river plunging over a waterfall erodes the river bed below by ___________________

while its load erodes by ____________.

The river bed below the waterfall is deepened, forming a ____________________,

such as the Brides Pool and Mirror Pool in Hong Kong.


21/62


21

2. Gorges

a. Gorge formed by waterfall retreat


The __________ of a waterfall leads to the formation of a gorge.

The resistant rock underneath the waterfall is gradually _____________ by erosion, so

pieces of rock break free and fall away.

The waterfall then retreats upstream and a __________ may develop on the

downstream side of the waterfall.

Refer to Fig.3.14a and b in Section 2 p.47

Example: _____________________ at the border of the USA and Canada has

retreated upstream for 11.4 km because the river bed shale has been constantly

eroded by River _____________.


22/62


22

b. Gorge formed by downcutt ing


During a tectonic _________ of landmass, or under intense vertical erosion caused by

an abrupt increase in river discharge, a gorge is developed.

Example: The _________________________________ in China and the

_______________________ in the USA are famous examples of this kind of gorge.

Landform features in the middle course of a river

1. Bluffs and slip off sl opes

Refer to Fig.3.19 and 3.20 in Section 2 p.50

In the middle course, __________ erosion is dominant. Swing of waterflow, rugged

river bed and the nature of the loads contribute to the development of a winding river

course, which __________ the valley.

Lateral erosion cuts into the __________ bank (outer bank) of a river bend, forming

__________ slopes bordering the rivers. Such steep slopes are known as

__________.


23/62


23

The water flow at the ___________________ (inner bank) of a river bend is slower.

___________________ instead of lateral erosion takes place as river energy falls.

Sediments carried by the river are gradually dropped, and a __________ slope is

formed as a _____________ slope.

2. Meanders

Refer to Fig.3.19 and 3.20 in Section 2 p.50

In its middle course, a river begins to flow in a __________ course and its valley

widens.

Water undercuts the __________ (outer) banks and slow-flowing water deposits

sediments on the __________ (inner) banks. These curves or bends of a river are

called ________________.


24/62


24

Landform features in the lower course of a river

When a river enters its lower course, its winding course forms _________________.

Sand bars in the channel lead to the formation of _________.

Sediments are also deposited at the river mouth to form a _________.

1. Meanders

The flat and smooth river bed in the lower course favours __________ erosion. This

leads to further __________ of the river channel and meanders are formed.

Meanders in the lower course are generally more maturely formed than those in the

__________ course.

2. Oxbow lakes


As erosion is intense along the ______________________ (outer bank) of the

meander, the bank gradually __________.

Deposition along the ______________________ (inner bank) causes the bank to

extend outwards. The bend becomes more ________.

When two adjacent __________ banks continue to be undercut, only a narrow

________ of meander is left between them. The neck is eventually cut through by

further lateral erosion to form a __________.

As the water flows along the new straight channel, the abandoned meander will be

closed off by deposition and separated from the main channel. This cutoff meander

has a crescent shape and is usually filled with water. It is called an oxbow lake.


25/62


25

The neck of a meander

separates two concave

banks which are being

undercut.

3. Floodplains


__________ of the concave bank (outer bank) and ______________ on the convex

bank (inner bank) cause a meander to expand. Flat land is thus developed in the lower

river course.

Due to its gentle gradient, high discharge and shallow river bed, the river easily

______________ banks during flooding, and deposits large amounts of

______________ on the valley floor. An extensive, flat plain known as a

______________ is thus formed.

Examples: ______________ and ______________ floodplain.


26/62


26

4. Levees


During a flood, large amounts of sediment are carried onto the ______________ by

floodwaters.

The ______________ are deposited when the river slows and loses its energy after

the flood.

___________ and ___________ materials are first deposited on the channel banks,

while ___________ particles and silt are carried further onto the floodplain before

being deposited.

Repeated flooding causes a raised bank which forms ___________. They often flank

the river as far as the river ___________.


27/62


27

5. Braided stream

The river channel in the lower course of a river is wider.

______________ of a large number of loads will form sandbars within the channel.

These ______________ divide the river into many smaller channels which rejoin

downstream to form braided stream.

6. Deltas


Sediments accumulate at the shallow river __________. Due to __________ currents

in the area, the deposition rate is faster than the natural removal rate.

Gradually sediments build up from the coarsest to the finest in a seaward direction to

form a flat, gentle ______________ feature known as a delta.


28/62


28

Types of delta

Refer to Table 3.8 in Section 2 p.55-56

Types of delta Formation process Example

Estuarine delta

Most of the ______________ settle around the

main river and distributaries.

As the shallow sea floor at the river mouth

receives added ______________, the delta

extends along _______ sides of the mouth.

Chang Jiang

Delta

Arcuate delta

Sediments deposit at the river mouth, forming

______________.

Numerous distributaries develop and the delta is

______________ in shape.

Nile River

Delta

Birds foot delta

The delta extends into the sea with an

______________ shape which looks like a

______________.

The distributaries carry sediments and deposit

them over a wide area along the courses of the

______________.

Mississippi

River Delta


29/62


29

Unit 4 How do coastal processes shape the land?

Wave generation Refer to Fig 4.1 in Section 2 p.64

Waves get energy and motion from _________, and they are generated when wind

blows over the sea surface.

Wind action produces tiny ___________ in the water. These ripples combine and

increase in size to form _________.

The wind then causes the water particles to ___________ in a vertical, circular orbit,

moving the waves forward in the direction of the wind.

Parts of a wave

Refer to Fig 4.2 in Section 2 p.65

A wave ___________ is the curved top or ridge of a moving wave.

A wave ___________ is the lowest part of the moving wave.

Wave ___________ is the distance between the trough and the crest.

Wave ___________ is the distance between two consecutive crests or troughs.

Characterist ics of wave generation

1. Fetch


Fetch is the _______________ distance in one direction across an open body of water

that wind can blow, or simply, the maximum distance a wave can travel.

The longer the fetch, the ___________ the wave. So areas with longest fetch potentially receive the highest ___________ waves.


30/62


30

For example, Cornish Coast in the southwestern part of England receives maximum

fetch because it is exposed to the _____________ Ocean.

2. Energy

The size and energy of waves are affected by the following four factors:

a. How long the wind has been blowing The ___________ the time, the stronger the

wave

b. The strength of the windThe ___________ the wind, the stronger the waves

c. The fetchThe ___________ the fetch, the stronger the waves

d. Wave heightThe ___________ the wave, the greater the wave energy

Refer to the case of Hong Kong coastal areas in Section 2 p.66

Constructive waves and destructives waves


As a wave approaches the coast and comes in contact with the sea bed, its bottom part

is held back by _____________ drag.

This _____________ the velocity and length of the wave, while the height and

steepness of the wave _____________. Then, the top of the wave is thrown forward,

resulting in a ___________.

When a wave breaks, its ___________ is released. Water is washed up the beach.

Such a water movement is called ___________. After that the water drains back down

the beach as _____________.


31/62


31

Constructi ve wave Destructive wave

Wave height

Wave length

Wave size

Swash

Backwash

Relationshipbetween swashand backwash

Wave frequency

Offshore gradient

Coastal process

Cross section

Erosion processes along coasts Refer to Fig 4.8 in Section 2 p.70

1. Hydraulic action Sea cliffs and rocks contain lines of weakness such as __________ or __________.

When water is thrown against these lines of weakness, air may be _____________ or

________________ within, leading to an increase in ________________.

When the wave retreats, the compressed air rushes out of the gap.

The sea cliffs and the rocks will be ________________ or cracked as this process is

repeated.


32/62


32

2. Abrasion/corrasion

Waves carry materials such as __________, shingles, __________ and boulders.

These materials scrape against the bases of sea cliffs through wave __________,

gradually wearing them away.

3. Attri tion

This is the process by which waves drive eroded rocks and pebbles into each other,

causing them to __________ into smaller sizes and become more rounded in shape.

4. Solution/corrosion

Solution is the process of dissolving _____________ loads. Sea water contains

chemicals like _____________ acid, which can dissolve _____________ and

_____________.

________________ of sea water leaves behind salt crystals, which may cause the

________________ of rocks.

Transportation processes along coasts Refer to Fig 4.9 in Section 2 p.71

Along the coast, there are _______ major transportation processes.

1. _____________ large boulders and materials that are rolled along the sea floor by

waves.

2. _____________ slightly lighter pebbles and materials are bounced along the sea floor

by waves.

3. _____________ small materials such as sand and silt are carried by moving water.

4. _____________ fine materials such as calcium carbonate and salts are dissolved andcarried by the water.


33/62


33

5. Longshore drift Refer to Fig 4.10 in Section 2 p.72

Longshore drift is a transportation process that _________ rock particles eroded from

one part of a coastline to a place of deposition elsewhere. Wind causes waves to break on the beach at an _________. The swash carries

materials up the beach at an ___________ angle, but the backwash carries materials

down the beach at a _________ angle under the force of ___________.

The drift moves materials and sand along the beach downward in a _________ pattern

parallel to the shore along the sea floor. This movement is known as

________________.

Waves continuously approach the shore at an angle. When a wave meets the shore

and breaks, another _________ is right behind it. This prevents the broken wave from

flowing backward and causes a slight raise in the _________ level.

A _______________________ flowing parallel to the shore is formed. Both water and

sediments are moving along with it.Longshore drift = _______________________ + _______________________

Deposition processes along the coasts

When waves lose their _________, they will drop the materials they are carrying such

as sand, rock particles and pebbles. This process is called ________________.

It occurs when swash is ________________ than backwash.

Deposition takes place in ________________ areas with low-energy waves or where

rapid coastal erosion nearby along the coast provides an abundant supply of materials.


34/62


34

Factors affecting coastal processes change over space

Coastal erosion, transportation and deposition processes change over space due to

different coastal energy that is affected by ________________, ________________

and ________________ factors.

2.1 Atmospheric factors

1. Strength of wind (velocity)

Wind _____________ affects the energy of waves.

With a _____________ wind velocity, wave energy is _____________ and is capable

of overcoming _____________, contributing to a _____________ rate of erosion and

transportation.

On the contrary, a ___________ wind velocity means waves have less energy to carry

their loads, thus ________________ will occur.

2. Duration of wind

The ___________ distance the wind blows (fetch), the more time that is available for

waves to gather energy from the wind.

Stronger wave energy means the rate of erosion is ___________. A shorter fetch

means less wave energy, which favours ________________.

2.2 Marine factors Refer to Fig 4.12 a and b in Section 2 p.73

1. Depth of the sea

________ water provides a favourable condition for coastal erosion and transportation

processes.


35/62


35

There is ________ wave energy and less friction in deep water, so the rate of erosion

will ___________.

However, when waves enter an area of shallow water, they begin to break

___________.

As waves lose their energy, the rate of ________________ will increase.

2. Gradient of offshore slope

Refer to Fig 4.13 a and b in Section 2 p.74

A ________ offshore slope such as the foot of a sea cliff contributes to a ________

rate of coastal erosion.

When a wave strikes a steep offshore slope, most energy is released and causes

___________.

A ___________ offshore slope can increase the rate of deposition.

Wave ___________ and ___________ are reduced when entering a gentle offshoreslope, and waves will release and deposit their loads.

3. Type of wave


________________ waves favour the deposition of loads. When swash is

___________ than backwash, sediments are washed onto the coast and the rate of

deposition increases.

________________ waves increase the rate of erosion. When backwash is

___________ than swash, waves can remove materials from the coasts.

4. Longshore current

Longshore current is the current of water flowing ______________ to the shore.


36/62


36

The ___________ the longshore current, the greater the rate of sediment

________________. Sediment loads resulting from erosion can thus be easily

transported. This will expose the coast to further ___________. The ___________ the longshore current, the less efficiently sediment loads can be

transported. This protects the coast against further erosion.

5. Tidal range


________________ is the difference in height between a high and a low tide in an

area.

The ___________ the tidal range, the stronger the tidal current which can remove

sediment loads effectively, which exposes the coast to further erosion.

A _________ tidal current can protect the coast against erosion because it is

_________ efficient in removing sediment loads.

2.3 Geological factors

1. Type and structure of rock

Refer to the case in Section 2 p.76

The type, structure and ______ of rocks can affect their resistance to coastal erosion.

Less resistant rocks usually possess lines of weaknesses or are composed of soluble

materials, which are more prone to ___________.

Rocks of ___________ resistance overlie one another, increasing the susceptibility to

erosion.

Rock dipping upward from the sea forms the ____________ sea cliffs but horizontal or

vertical dip forms the ____________ sea cliffs.


37/62


37

2. Amount of load

_________ weathering and erosion can produce excessive amounts of sediments.

They are brought by rivers or ____________________ to the coastal area. When a load becomes too heavy for waves to transport, ________________ takes

place. Deposited sediments can protect against coastal erosion by dissipating and

absorbing wave energy.

The more the amount of deposited beach materials, the deeper the beach extends

inland, hence offering more ________________ for coastal features like sea cliffs.

3. Size of load

Large loads require strong waves for ________________. If the average size of loads

is smaller, the rate of transportation will be _________.

If the size is large, the loads can be transported only by ________________ and

________________ in the offshore region, while smaller loads can be carried closer to

the backshore by ________________ and ________________.

2.4 Other factors

1. Coastal obstacles

Coastal landscape features and ______________ structures along the coast affect

coastal erosion and transportation processes.

______________ like mangroves and coral reefs in a coastal area can __________ it

from erosion and transportation processes.

Coastal ________________strategies such as building groynes and other artificial

wave breakers may slow down the ________________ of sediments by longshore drift,

so that orderly ________________ occurs.


38/62


38

2. Location of coast

Erosion tends to concentrate on _____________ coastal locations, for instance around

headlands. If the coast is located in a _____________ area or a bay, wave energy will be _______

and this _____________ the rate of deposition.

Features of coastal erosion Refer to Fig 4.32 and Fig 4.33 in Section 2 p.83

1. Sea clif f and wave-cut platform


A sea cliff is a high _______ rock face and a __________________________ is a

gently sloping rock surface extending from the base of the sea cliff.

A wave-cut platform is covered by water at __________ and exposed at __________.

Destructive waves cut out a

_______ just above low tide level

through ___________________

and _____________.

The base of the notch is

_____________ after prolonged

wave erosion.

The upper part of the notch

eventually _____________ by

weathering and mass wasting.


39/62


39

Waves break the fallen debris and carry it

away. A steep sea cliff is formed.

Further undercutting causes the sea cliff to

_____________ and a _____________ is

left. As the wave-cut platform widens, the

sea covering it becomes shallower.

The cliff will be attacked less frequently

and less vigorously by waves.

Refer to Fig 4.21 and Fig 4.22 in Section 2 p.80

Example: The steepest sea cliffs- ________________ near High Island at Sai Kung.They are formed by resistant ___________.

Cliffs formed by less resistant granite are typically much less ________. As the tidal

range is small and coasts are often steep, wave-cut platforms in Hong Kong are

typically not _______. As long fetch can be found on ______________ coasts, most of

the platforms are formed there.

2. Sea cave


A sea cave is a ___________ or ___________ formed by waves on a coast.

When waves attack a sea cliff, they first erode rocks with lines of ______________

such as joints, cracks and bedding planes, and areas of weakness composed of lessresistant rocks.


40/62


40

_____________ and _____________ erode rock layers. ____________________ and

_________ caused by waves also erode weak areas between high and low tide levels.

The sea cliff is thus opened up and sea caves are formed.

3. Geo


The waves gradually wear away the ____________ of the sea cave and enlarges it.

Later mass wasting of the roof leads to its ____________ due to a lack of support.

The sea cave is exposed and the narrow, steep-sided ________ is called a geo.

4. Sea arch and stack

Refer to Fig 4.27 and Fig4.28 in Section 2 p.81-82

Since wave energy is concentrated on a ____________, both sides of the headland

are subjected to wave ____________. When a line of weakness lies across a headland, sea caves will develop on both sides

of the headland. A cave may cut through a narrow headland, or back-to-back

_________ may eventually meet, forming a __________ through the headland.

Further erosion will widen the tunnel, eventually leaving only a rock __________ above

it, which is called a ____________.

When the roof of the arch ____________ under denudation, leaving part of the

headland isolated in the sea, a ________ is formed.

It may also be formed when two ________________ geos join together. Both arches

and stacks are features which will eventually disappear under continued wave erosion.


41/62


41

Features of coastal deposition Refer to Fig 4.41 in Section 2 p.87

When wave energy ____________, sediments are deposited instead of transported.

Examples of deposition featuresbeach, spit, bar and tombolo

1. Beach


A beach is a strip of land bordering the sea, normally consists of ____________,

____________ or ________.

It lies between _______ and _______ tides, accumulating sediments above and below

the waterline.


When sediments are deposited to form a beach, the ____________ materials are

usually pushed by swash and deposited near the top of the beach, while the _______

materials are dragged by backwash and deposited on the seaward side.

A beach also shows differences according to different climatic conditions. Typhoon and

__________ backwash of storm waves can remove large amounts of ____________

from the beach, while mild winds push the sediments back onto the beach, forming a

longer and wider beach.

Example: Sandy beach at ____________


42/62


42

2. Offshore bar

Refer to Fig 4.36a, b and c in Section 2 p.85

Along a gently sloping beach, waves break at or near the ____________ as the water

is shallow.

The waves ____________ sediments and a narrow _________-like feature called an

offshore bar is formed.

It is ____________ to the coast and both ends are not attached to the _______.

Formation processes of an offshore bar:

3. Spit


A spit is a long, narrow accumulation of sand with one end linked to the ____________

and the other projected into the _______ or across an ____________.

It is formed by a combination of ___________________, tides, river or ocean currents,

and a bend of the ____________.


43/62


43

When a longshore drift travels along a coast, the water becomes shallow and calm.

Wave energy ____________, the drift cannot be maintained and materials being

transported are deposited. A _________ sand spit that points in the direction of the longshore drift is then formed.

Example: _________ of Lantau Island

Formation processes of a spit:

Beach material is transported

along the coast by longshore

drift.

4. Bay-bar


If longshore drift deposits sediments in a _______, a bay-bar may be formed by linking

the ends of two ____________.

A bay-bar is a long _________ of sand or pebbles running ____________ to the

coastline across a bay, which straightens coastlines and traps water in a

____________ on the landward side.

Formation processes of a bay-bar:


44/62


44

A spit extends from the endof headland

5. Tombolo


A tombolo is formed when a spit or bar is extended between an ____________ island

and the ____________, or between two __________.

Sediments brought by ______________________ from each direction are deposited,

thus the original separated landmasses eventually _____________ by the extension of

the spit or bar, and a narrow piece of land named a tombolo is formed.

Example: the tombolo at ___________________.

Formation processes of a tombolo:

Two seperate islands existed.Longshore drifts broughtsediments to the areas.

Refer to the case of coastal features in Holderness, England in Section 2 p.90-91


45/62


45

Unit 5 How do human activities influence and alter river and

coastal environments?

Human activit ies and their consequences for river and coastal

environments

1.1 Reclamation

Reclamation is the usual method of acquiring land by dumping materials into the sea to

_________ the level of the sea bed or areas of land that were once _________ the sea

until they become ______ land.

Reclamation is commonly practised in Hong Kong as there is little ____________.

More than ______ of Hong Kong developed land area is reclaimed from the sea,

especially the area along both sides of _______________________, which has

provided valuable flat land for economic development.


Consequences:

Reclamation can change the ground _________________ and cause ____________

flow of ground water.

It also reduces the __________________ capacity of a lake by reducing its size.

All these may lead to more frequent ____________.

Dumping of pebbles and sand into water bodies and intensive development of the

reclaimed site may ____________ the water in nearby areas.

Water also becomes more ___________ and affects photosynthesis of water plants.

______________ of the harbour and water courses results in higher waves and

stronger currents, which threaten marine safety for ______________ and other water

activities.


46/62


46

The natural coastline, river banks and river bed are altered by reclamation that leads to

the removal of wildlife ___________.

Local ______________, feeding grounds of various organisms and the original

ecosystem cannot be maintained.

1.2 Dredging

Dredging is the process of ____________ sediment and accumulated debris from

water bodies and placing the materials in particular locations.

Dredging is practised to keep harbours and rivers from __________ up or as a method

of collecting sand for ______________.

It is an important process used to _____________ ports, fairways, typhoon shelters,

drainage and flood protection schemes.


Consequences:

Dredging disturbs the natural sediment _____________ pattern of water currents of

rivers and sea directly.

It also pollutes the water bodies by stirring up highly _______________ mud at the

bottom of the harbour, _______________ and burying aquatic life.

Removal of sediments from the sea bed and river bed destroys __________. For

example, large areas of coral reefs and sea grasses are damaged due to dredging.

Food supplies for animals higher up the _______________ such as fish and dolphins

will be reduced.


47/62


47

1.3 Destabilisation and erosion

1. Coastal mining

Coastal mining is the process of _____________ sand or minerals from the sea bed

and beaches.

It includes the exploitation of rare _____________ and _____________ like diamonds

and titanium found in coastal waters.

Mining of ________ and gravel is concentrated in estuaries, beaches, dunes and

near-shore areas. Large-scale mining of sand and gravel is also conducted in offshore

areas and in river beds

2. Urban development

River and coastal regions provide good ________________ and beautiful scenery

which attract many people to live there.

Urban development of cities and towns along rivers and coasts always involves

large-scale ________________ projects for commercial, industrial and residential

facilities.

3. Deforestation


Deforestation refers to ________________ removal of forests or vegetation. It is

commonly practised along rivers and coastal areas.

The spread of agriculture, firewood collection, and unregulated timber _____________

activities are the principal causes of deforestation.


48/62


48

Consequences:

Coastal mining, urban development and deforestation remove the vegetation and

expose the soil to severe ____________, which will cause the ____________ up of

rivers and reduce their natural flood storage.

Impervious areas in cities such as roads and roofs lower _________________ and

increase the risk of ____________.

Mining activities and urban development also cause pollution and bring serious

damage to the ecosystem. _________________ and toxic substances from mining,

____________ from industries and households pollutes groundwater and surface

runoff.

Nutritive pollutants stimulate the growth of ________. Together with _______________

particles in the water, they will cover filter-feeding corals and hinder their ability to

survive.

1.4 Agriculture

1. Farming

The relatively flat land on either side of a river provides __________ soil for agricultural

activities. Annual floods deposit a fresh layer of _____________ that rejuvenates the

soil of the floodplain, saving the costs of _____________.

Farmers can take advantage of the nearby river by drawing water from the river for

_____________.

They can also have access to __________ water transportation for delivering the

crops to markets.


49/62


49

2. Aquacul ture

Aquaculture is the cultivation of __________ organisms such as fish, shellfish, algae

and other aquatic plants in ponds near or along rivers and coasts.

This practice helps to form a _________ zone to protect the coast from life-threatening

erosion and _____________ problems.

Consequences:

Clearing land for farming will leave the land barren and result in

__________________.

Chemical fertilisers from agriculture may stimulate the growth of _________ and other

marine organisms. When they die and decompose, they will consume a lot of

____________ and make a lake or river ____________. Aquatic plants and fish may

die because of a lack of oxygen.

Pesticides and other toxic substances can also enter and accumulate throughout local

__________________, and may eventually affect human health. For example, excess ____________ in drinking water may lead to blue baby syndrome

and stomach cancer.

1.5 Recreation

Rivers and coasts are areas many people visit to enjoy their _______________. They

take advantage of the multitude of recreational activities available there, from

swimming or fishing to simply lying on the beach to enjoy sunbathing.


50/62


50

Consequences:

Undesirable visitors behaviour, however, could cause direct _______________ of

ecosystems.

The development of recreational facilities along the coast is the prime contributor to

coastal erosion and _______________. It involves sand mining, beach and sand dune

erosion, soil erosion and extensive paving of ground surfaces.

Recreation also contributes to ____________ and solid wastes, which ____________

rivers, seas and lakes.

1.6 Power generation

1. Hydro-electr ic power (HEP)


Hydro-electric power requires a _______ and ____________ on a large river that has

a dramatic drop in ____________.

The falling water spins turbines that generate electricity. Hydro-electric power is a

clean, inexpensive and ________________ power resource.

2. Tidal power

Refer to Fig 5.14a and b in Section 2 p.102

Tidal power is also a ________________ power resource.

It involves the building of a dam across a river mouth or _______.

The incoming and outgoing _______ of the sea drive the air turbines to generate

electricity.


51/62


51

3. Nuclear power

Many nuclear power stations are located along rivers and coastal areas. These

locations can provide an adequate supply of ____________ water for the reactors.

Consequences:

Power generation requires _________________ construction projects like the building

of dams, reservoirs and power plants, resulting in many problems such as

____________ and _________________.

Soil erosion increases the amount of sediments which silt up the _____________

capacity of reservoirs and increase the risk of ____________.

The reservoir for HEP generation, for example, changes ____________ conditions in

the surrounding area. The temperature in the region will ________, which may affect

the aquatic environment and wildlife habitats.

____________ pollution caused by the discharge of hot water from the power plant will

lead to the ______________ of coral reefs and killing of marine organisms.

The management of river and coastal systems

Rivers and coastal shorelines are ______________.

Humans have significantly ______________ rivers and coasts by different

management strategies such as constructing dykes and groynes, beach nourishment

and land use zoning.


52/62


52

Hard engineering st rategies

Hard engineering are traditional _________________ responses which aim at

resisting the energy of waves and tides.

These projects involve the construction of ______________ structures that can stop

wave energy reaching the shore, or absorb and reflect the energy at the shore.

1. Dykes

A dyke, an _____________ wall built along the edge of a water body onto an adjacent

lowland, can solve the problem of ______________.

The ________________ has been successful with the dyke system.

With careful design and management of the _______ system, the flood problem in the

Netherlands has been turned into an economic opportunity, as shown by a prosperous

development of __________________________ which requires a high input of

irrigation water.

2. Groynes


A groyne is one of the most common methods of countering ___________ erosion in

an outer bank.

Structures of stone, timber, concrete and steel extend from the river ________ into the

water so that high ___________ currents are diverted away from the banks to prevent

or minimise erosion.

Along many coasts, ________________________ causes the beach to thin out in

places where erosion of land behind the beach becomes a problem.

Groynes are built at ________ angles to the coastline to reduce the power of the

longshore drift and ________ sediments, so that beaches will not be eroded.


53/62


53

Groynes are commonly constructed along the coasts in the United Kingdom because

they are __________ to build. The building costs are comparatively

________________ and maintenance costs decrease with time. They are also efficient

in trapping sediments.

Groynes have a significant impact on the landscape as they destroy the beautiful

coastal _____________ and create _____________ to the recreational use of the

beach.

Local _____________ around groynes and downdrift erosion may happen if beaches

are not well-managed.

3. Other examples of hard engineering s trategies

Refer to Table 5.2 in Section 2 p.109

Sea wall

Sea walls are placed ____________ to the shore, often along the base

of a cliff.

They can be __________ and have a __________ top which breaks

up the energy of the waves and prevents water from going over the top

of the wall during heavy storms.

Gabion

A gabion is a metal ________ filled with rocks.

They are stacked to form a simple ________ or placed at the foot of an

eroding cliff.

They are relatively _________, easy to use and are especially quick to

install.

Breakwater

Breakwaters are built ____________ or at an __________ to the

coastline as an obstacle to break the waves further onshore.

They are usually made of ________, blocks of stone and rubber tyres.


54/62


54

Revetment

Revetments are placed ____________ to the coastline.

They are ________________ and let water pass through, protecting

the cliff from wave erosion.

Timber slats, concrete or __________ are the major materials.

Riprap / rock

armour

Riprap are large _____________ piled up along the ____________

or placed at the foot of the cliff to form a protective wall.

Riprap dissipates wave energy and traps _______________. So

energy of the waves is dispersed and ____________ is reduced.

Dam and

reservoir

Dams and reservoirs are constructed along rivers to limit

____________ and protect existing land uses.

A dam can help ____________ water flow as well.

Refer to the case of coastal hard engineering used in Happisburgh in Section 2 p.115

Soft engineering strategies

Since hard engineering often causes problems, soft engineering has become more

popular. Soft engineering tries to work with natural processes to ____________, rather

than ____________ erosion.

These techniques involve promoting ____________ systems such as beaches to

protect the coast.

They are usually less _______________ to construct and maintain than hard

engineering techniques and are more _______________________.


55/62


55

1. Beach nourishment

Beach nourishment is the process of placing sand that has been removed by

longshore drift or erosion in order to provide a ___________ against waves.

Sand is either brought in from elsewhere, or transported back along a beach, usually

_________ a year.

This strategy is widely adopted because it restores and improves the

_________________ value of the beach.

When compared with other hard strategies, beach nourishment does not leave

_________ on the beach if erosion continues and no costly construction is involved.

The beach turns into a _________________ zone during its nourishment and the

coastal ecology of the beach will be damaged. A variety of plants, insects and other

animals become _________________ or endangered.

Beach nourishment does not stop erosion and periodic nourishment is needed, which

is known as ______________________________.

In fact, beach nourishment is an ________________ management option because of

its uncertain ________________ and continuing maintenance cost.

2. Land use zoning

Land use zoning aims to _______________ land use for meeting specified intentions

for individual areas. It is used as a conservation tool to conserve the natural

environment and _______________ heritage.

It is particularly effective in preventing the occurrence of coastal problems in

_________________ and _______ populated coastal areas.

Land use zoning can be achieved primarily by the designation of _________________

__________________________________________ (SSSIs), ___________________

_________________________ and _______________________________________.


56/62


56

a. Site of Special Scient ifi c Interests (SSSIs)

SSSIs are designated to conserve areas of ______________ interest with rare fauna

or flora species in Hong Kong.

Generally, no new _________________ or change in land use can be carried out in

the area.

The north shore of Tolo Harbour and the _____________ Marshes are examples of

SSSIs.

b. Coastal protection areas

Coastal protection areas are planned to conserve, protect and retain the natural

coastline and preserve the coastal environment. These include places with attractive

_______________ features, physical landforms or areas of natural landscape with

scenic or _______________ value.

Only development which _____________ the existing natural landscape or essential

infrastructure projects are permitted. The estuary of _______________ river is an example of coastal protection area.

c. Marine parks / reserves

Marine parks / reserves are set up to protect and _____________ ecologically

important marine environments and resources.

These parks / reserves can facilitate _________________, recreation,

_________________ and research activities for the public.

There are _________ marine parks and _________ marine reserve in Hong Kong,

covering a total marine area of 2 430 ha.


57/62


57

3. Managed retreat (doing nothing)

With the approach of managed retreat, the coast is allowed to evolve naturally by

____________, deposition and flooding. The government takes ______________ other than to monitor the situation.

This approach is applied to land of ______ value with no significant risks to people.

As nothing is done, this is a very _________________ method in the short term.

Nevertheless, if erosion continues, there may be a need to _________________

people for the loss of business, land or home.

Evaluation of methods and st rategies used for r iver and coastalmanagement

1. Effectiveness of the strategy

Some of the strategies taken are not as ______________ as expected.

2. Durabili ty of the str ategy

Some of the strategies are not _____________ and cannot withstand strong ocean waves.

Strategies Advantages Disadvantages

Dyke /

sea wall

Provides

______________

protection against

flooding or erosion

May ______________ beach erosion

Limits ______________ to the beaches

_____________ wave may erode the

materials under the sea wall

Disrupts the natural interaction

between the coast and the sea

Very ______________


58/62


58

Groynes

Protect the beaches / banks

from erosion

Maintain beach

____________

Shift the coastal erosion problems to

the downdrift location

__________ impact unsightly

Beach

nourishment

Increases sand in the

_______________ to protect

the beach

_______________ the

beach to an optimal profile

against erosion

Relatively ______________

Requires ________________

maintenance

Must be carefully designed as they

may alter the ________ on the

beach and dredging site

Land use

zoning

______ cost

Prevents / reduces

_________ damage

effectively

____________ reduce existing

damage

Reduces _______________

Land use _______________ is

costly

Managed

retreat

Limits the damage of erosion

or flooding

Maintains the _________

operation

Expensive _______________ to

relocate residents

Affects _____________ human

activities along the river course or

coast


59/62


59

Costs and benefits

Costs Benefits

1. Economic

a. Construction costs

Most ________ engineering incur

construction costs which

________ countries may not be

able to afford.

For instance, construction of

large-scale ________ and

_____________ is a costly and

lengthy process which incurs

huge costs.

In contrast, groyne construction

requires relatively less

_____________ cost.

b. Maintenance costs

All strategies have a limited

_____________ and require

regular _____________ work.

After dam construction, regular

_____________ and

_____________ must be

conducted to maintain the

reservoir capacity and strength of

Human ________ and

_____________ are

protected from floods and

erosion by effective

management strategies.

Values of properties and

the cost of _____________

can be maintained.


60/62


60

the dam.

Wooden groynes are _________

to build but have a _________

lifespan that requires constant

repair after installation.

2. Ecological

Some of the strategies, especially

those related to _________

engineering strategies such as

river channelisation, building sea

walls and dykes, may destroy the

__________ beauty along the

coastline or river.

Management works cause the

displacement of large areas of

wetland habitat and can act as a

sink for trapping marine or

river-borne _____________ that

would otherwise be flushed away

by natural flows. These ecological

costs should not be neglected.

Some areas with high

_____________ value can

be protected from erosion

and flooding through

different river and coastal

management strategies.

Plants and animals living

along rivers and the coast

can continue to flourish and

their __________ can be

preserved.


61/62


61

3. Social

Constructing reservoirs or

managing retreat strategies

along hazardous coasts

requires _____________ local

residents and economic

activities.

Compensation and relocation

are costly and may cause

__________ unrest.

The ________ of

submergence or collapse of

historic sites, tourist spots and

unique heritage areas cannot

be measured.

Coastal and river management

can effectively prevent

_____________. This can help

minimise worries of people

who were once threatened by

the hazards, therefore

promoting social

_____________.

These management strategies

are intended to strike a

______________ between

resource protection and

economic development,

therefore balancing and

settling ____________ among

different interest groups.

Certain measures such as

beach nourishment can help

protect ______________

areas for different groups of the

society such as surfers,

swimmers and sunbathers.


62/62


Problems may be encountered after all the costs and benefits have been

analysed

1. Enforcement issue

There are often criticisms about the ________________ of existing strategies for

conserving ecologically important sites under _____________ ownership.

As long as land use complies with zoning control, the government cannot prohibit

activities carried out on _____________ lands even though they may not be

compatible with conservation objectives or may cause adverse impacts on natural

habitats.

It is evident that conservation of important habitats involving private lands cannot

succeed without the support and cooperation of the landowners and other local

________________.

The level of __________________ is still low and this limits the effectiveness of the

measures.

Although there are four marine parks and one marine reserve in Hong Kong, they

protect less than 2% of local coastal waters.

2. Divided opin ions

From time to time, there are _____________ on whether a site should be conserved,

especially when the nature conservation objective _____________ with development

proposals.

Nature conservation is essentially the conservation of biodiversity. Different people

notes sect2 eng

Documents