S2 GE Slides - Floods (Part 2)

Chapter 5
A natural occurrence

1)  Types & Causes of floods:
https://www.floodsmart.gov/floodsmart/pages/
flooding_flood_risks/flood_scenarios.jsp
https://www.floodsmart.gov/floodsmart/pages/
flooding_flood_risks/levee_simulator.jsp
2) Factors that increase flood risks
Recap:

1. What are floods? What causes floods?
2. Which cities are prone to floods?
Why are these cities more prone?
3. How do floods affect city dwellers?
We want to learn about…

Impacts of floods
Social
impacts
(a) Economic
impacts
(B)

Social
impacts
(a)
1. Injuries and loss of lives
Fast-‐ﬂowing
ﬂood

waters
cause

buildings
to
collapse

Sweep
people
&

livestock
away;

causes
injuries
&

deaths;

Objects
and
debris

are
washed
along
by

fast-‐moving
water

Social
impacts
(a)
2. Affects physical health
People
may

get
caught
in

the
ﬂood
for

too
long

Cause
people
to

suﬀer

from
hypothermia

(constant
shivering,

confusion,
loss
of

coordina4on)

Social
impacts
(a)
3. Affects emotional & mental health
loss
of
homes

or
livestock

loss
of
loved

ones
/
family

Cause
mental
stress

Cause
emo2onal

distress

Social impacts(a)
4. Spread of diseases
During
a
ﬂood,

water
supplies

may
be

contaminated

by
chemical

spills

People
may
be

exposed
to

contaminated

drinking
water

Results
in

the
spread

of
cholera

and

dysentery

More
cases
of

malaria
&

dengue
fever

Social impacts(a)
4. Spread of diseases
Stagnant
pools
of

ﬂoodwater
encourage

mosquitoes
to
breed

Social
impacts
(a)
5. Homelessness
Floodwaters
can

damage
property
&

sweep
houses
away

People
lose
a
roof

over
their
heads;

People
may
have
to

evacuate
to

emergency
shelters

Social
impacts
(a)
6. Disruption to clean water supply
Floodwaters

can
damage

water
pipes

Cause
disrupIon
to
water
supply

Water
supply
may
also
be

contaminated
due
to
burst

sewage
pipes

Economic
impacts
(B)
Machinery
&
equipment
may
be

submerged
or
damaged
by
floodwaters

Companies
may
lose
profits
&

have
to
spend
money
to
buy
new
equipment

Factories
unable
to
operate

à
suffer
economic
losses

1. Damage to machinery & equipment

Tourism
declines

Economic
impacts
(B)
Transport
infrastructure

submerged
or
damaged
by
ﬂoodwaters

Overall
reducIon

in
produc2vity,

employment
&

proﬁts

People
unable
to

travel
to
work

2. Damage to transport infrastructure

Loss
of

employment
&
income
for

individuals
&
companies

Companies
&
factories

are
unable
to
operate

Economic
impacts
(B)
During
a
ﬂood,
power
lines
may
be
damaged

Causes
power
outages
to
occur,

and
leads
to
the
lack
of
electricity

3. Disruption to energy supply

1. What are floods? What causes floods?
2. Which cities are prone to floods?
Why are these cities more prone?
4. How should cities prepare for floods?
We want to learn about…

(A)
Regula2on
(B)
Investment
in

infrastructure

(C)
Disaster

preparedness

Zoning
Levees
and

ﬂoodwalls

ForecasIng
and

warning
system

Elevated

properIes

Channel

improvement

EvacuaIon
drills

Mitigation measures are implemented to:
•  reduce the impact of floods
•  help prevent floods from occurring

Regulation(a)
(1) Zoning
By using zoning laws:
Specifies the areas where residential,
industrial, commercial or recreational
development may take place.
Government plans the physical
development of the land & its uses

Regulation(a)
(1) Zoning
•  Flood-prone areas are often zoned as
low-value developments (eg. parks
& fields for recreational activities).
•  Low-value development usually
does not cost much to develop à
fewer economic losses during floods.

Regulation(a)
(1) Zoning
map
Eg. Eagan City in
Minnesota, USA

BENEFITS
•  Zoning
creates
spaces
of

green
areas,
such
as
parks

and
fields,
which
help
to

reduce
the
impact
of
flood

damage.

Regulation(a)
(1) Zoning
CHALLENGES
•  Zoning
may
limit
the

development
of
available
land

because
only
certain
land
uses

are
permiRed.

•  Zoning
is
difficult
to
carry
out

because
of
compe2ng
land

uses.
People
may
also
not

abide
by
the
recommended

land
use.

Regulation(a)
(2) Elevated properties
SG – Minimum platform level (MPL):
•  Minimum ground level for any
development (eg. building)
•  Imposed on new & existing developments
Properties are elevated or
raised to a certain height.

Regulation(a)
Area with flood history and minimum platform level
SG – Minimum platform level (MPL):
Area with flood history and
minimum platform level
Areas with NO
flood history
MPL is 300mm
above the
adjacent road
or ground
level
Areas with
flood history
MPL is 600mm
above the
highest
recorded
flood level

Regulation(a)
(ii) Elevated properties
A series of slopes or steps are built to
meet the MPL requirements

BENEFITS
•  Development
is

protected
against

ﬂoods
up
to
the
height

of
the
MPL.

Regulation(a)
CHALLENGES
•  It
is
challenging
to

implement
MPL
because

of
the
increased
cost
of

development.

Investment in infrastructure(B)
Barriers that are built higher than
floodplains / rivers / canals
(3) Levees & floodwalls

To keep out
floodwater &
protect
developments
from flooding

Barriers that are built higher than
floodplains / rivers / canals

Levees: raised banks
Natural banks
(made of mud)
Man-made banks
(made of concrete)

Levees: raised banks
Bishan park, SG:
man-made but
natural looking

Floodwalls:
Man-made structure
(made of concrete)
Austria’s
ﬂood
walls:
hRps://
www.youtube.com/watch?v=hzQyTOaBHzI

Investment in infrastructure
(3) Levees &
floodwalls
BENEFITS
•  It
is
cheaper
to
build

levees
and
floodwalls

than
to
raise
the
height

of
the
land
surrounding

the
river.

CHALLENGES
•  Regular
maintenance
is

required
to
ensure
that

the
levees
and
floodwalls

are
strong
enough
to
hold

back
floodwater.

•  They
are
unable
to

prevent
floods
beyond
a

certain
level.

(B)

(4) Channel improvement
To increase its capacity to hold water
or to carry more storm water away.

River channels and canals can be
widened, deepened or straightened
Prevents water in the river
channels & canal from overflowing.

Investment in infrastructure
(4) Channel
improvement
BENEFITS
•  Moderate-‐value
&
high-‐
value
developments
can

now
take
place
on
the
land

next
to
river
channels
or

canals.

CHALLENGES
•  Is
diﬃcult
to
carry
out
if
the

land
next
to
the
river
channels

&
canals
is
already
used
for

other
purposes.

•  May
create
problems
for
areas

upstream
or
downstream
of

the
improved
area.

(B)

Disaster preparedness(c)
(5) Forecasting & warning system
2. The information collected is then
analysed to make a flood forecast on the
areas that are likely to be flooded
3. Flood warnings are issued to the public
1. Water levels in river channels and canals,
tide levels in seas & surrounding
weather conditions are monitored regularly.

(i) Manual
monitoring systems
(ii)
Technology
using:

1. Water levels in river channels and canals,
tide levels in seas & surrounding
weather conditions are monitored regularly.

Water level
sensor used in SG
Weather
instruments
used to collect
information
on weather
conditions
(i) Manual flood monitoring systems:

(ii) Technology:
Map out
flood-prone
areas 
make more
accurate
flood
forecasts
Remote sensing
techniques
+
Geographical
information
systems (GIS)

Disaster preparedness
BENEFITS
•  Provides
useful

informaIon
so
that

there
is
2me
for
people

to
take
ac2on
to

minimise
ﬂood
damage

CHALLENGES
•  Some
ci2es
may
not
have

the
exper2se
and

technology
to
collect

accurate
data
and
make

accurate
ﬂood
forecasts.

(C)

A form of preparedness measure where
people practise the steps to leave a place in a
safe and orderly manner during an emergency.
(6) Evacuation drills
Involves:
•  People moving to safe locations by
following instructions given by
trained personnel.
•  Practising first aid

(6) Evacuation drills
Disaster preparedness
BENEFITS
•  People
are
educated
on

what
to
do
when
a
flood

warning
is
issued
and
this

would
thus
reduce
panic

during
a
flood
event.

CHALLENGES
•  Limited
par2cipa2on

from
the
public
will

reduce
the
effec2veness

of
the
city’s
evacuaIon

plan.

(C)

S2 GE Slides - Floods (Part 2)

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S2 GE Slides - Floods (Part 2)