The University of the West Indies

swedishstreakMechanics

Feb 22, 2014 (3 years and 8 months ago)

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By

Jacob
Opadeyi

Phd
, Leah Fouchong BSc, Gabrielle Thongs MSc, and
Roxann

Smith BSc

Department of
Geomatics

Engineering and Land Management

The University of the West Indies

St. Augustine

Trinidad


Background


Trinidad

and

Tobago

faces

a

number

of

natural

disaster

issues
.




Although

the

islands

are

located

to

the

south

of

the

Caribbean,

where

there

is

very

little

threat

from

hurricanes

,

the

islands

are

still

subject

to

tropical

storms

and

the

associated

heavy

showers

that

result

in

flooding

and

landslides
.




The

Northern

Range

and

Central

range

,often

referred

to

as

the

Caroni

Basin

is

considered

most

vulnerable

to

the

impacts

of

these

heavy

showers
.




Furthermore

the

Caroni

Basin

is

under

threat

from

poor

landuse

practices

which

include

deforestation

of

the

Northern

Range,

which

results

in

landslides

and

perennial

flooding

of

the

lower

regions

of

the

basin
.


Background


Greater

Port

of

Spain

,

the

capital

is

estimated

to

have

a

current

population

of

130
,
000
,

with

the

city

itself

having

some

40
-
45
,
000

inhabitants
.



Despite

this

POS

is

considered

one

of

the

main

areas

for

future

development

regardless

of

the

fact

that

it

is

physically

constrained

and

can

only

handle

so

much

infrastructure

and

population



The

historical

growth

of

the

city

gives

an

indication

of

the

urban

sprawl,

now

being

experienced

in

the

main

urban

areas

of

Trinidad

and

Tobago
.




Physical

planning

constraints

for

the

city

include

flooding

problems

where

drainage

channel

capacity

is

undermined

through

the

presence

of

high

sedimentation

and

high

amounts

of

debris
.




This

is

compounded

by

the

areas

of

informal

and

formal

developments

on

steep

slopes


Background


Flooding

has

continued

perennially

throughout

Trinidad,

particularly

flash

flooding

along

the

east

west

corridor

at

the

foothills

of

the

Northern

Range
.




This

flooding

often

results

in

landslides

on

the

hillsides
.



Floods

and

Landslides

are

annual

events

associated

with

the

rainy

season

in

Trinidad

and

Tobago
.

They

have

caused

millions

of

dollars

damage

to

infrastructure,

agriculture

and

households,

floods

in

particular

have

even

taken

lives
.



Landslides

are

a

common

occurrence

in

hilly

areas

on

both

islands
.



Vulnerable

communities

for

floods

are

generally

low
-
lying

areas

,

in

particular
:



Port

of

Spain,



San

Juan,



Caroni,



Sangre

Grande,



Caparo
,




Wrightson

Road,



Western

Main

Road

in

Cocorite
,



South

Quay,



Maraval
River

Flood Events in Trinidad


Eastern Main Road

Trinidad Guardian 1 Nov 2010

Landslide Events in Trinidad

Introduction



Hazard
=

Probability

of

event

with

a

certain

magnitude


Triggering

mechanism


Type

of

event




Magnitude
:

Volume,

domino

effect,

distance,

duration,

speed

etc



Vulnerability
=

Degree

of

damage
.

Function

of
:


magnitude

of

event,

and



type

of

elements

at

risk



Amount
=

Quantification

of

the

elements

at

risk

e
.
g
.


Replacement

costs

of

buildings,

infrastructure

etc
.


Loss

of

function

or

economic

activities


Number

of

people



Source
:

van

Westen,

2005


What is
S
usceptibility
M
apping?





Susceptibility mapping depicts division of land surface into zones of varying
degree of stability based on the estimated significance of the causative
factors in including the instability (
Anabalagan

1992).



Thus susceptibility should be examined as the likelihood that such
phenomena occur under the given terrain conditions regardless of the time
scale within which a particular event is likely to take place (van Westen et
al. 1997, Atkinson &
Massari

1998).



The susceptibility term also does not depend on impact factors such as
rainfall, earthquake and human activity (Lee & Min 2001).


What is a landslide and flood susceptibility
maps?



The

landslide

and

flood

susceptibility

maps

shows

areas

vulnerable

to

landsliding

based

on

an

estimated

significance

of

causative

factors

in

inducing

the

instability
.



The

purpose

of

the

susceptibility

map

is

to

convey

the

relative

likelihood

of

landsliding

and

flooding

using

susceptibility

categories
.






Many

susceptibility

maps

use

a

color

scheme

that

relates

warm

colors

(red,

orange,

and

yellow)

to

unstable

and

marginally

unstable

areas,

and

cool

colors

(blue

and

green)

to

stable

areas

(USGS)
.


Methodology


The selected instability factors were supported by literature, local
knowledge and the availability of input data. The factors considered
are :



Lithological Formation


Tectonic Features


Slope Angle


Road Network


Drainage Network


Land Cover


Rainfall


Instability Factors


Lithology
-

rock

characteristics

are

strongly

related

to

the

geomorphologic

and

geologic

units

of

the

study

area
.

This

is

important

for

landsliding

as

it

is

strongly

correlated

to

the

nature

of

the

material

,

steepness

of

the

slope

,

and

its

stability

.

Unconsolidated

and

less

cohesive

steep

slopes

increases

the

susceptibility

to

landsliding
.




Tectonic

Features



landslides

are

known

to

be

more

frequent

in

areas

that

are

in

close

proximity

to

tectonic

features

such

as

strikes

and

dip

faults
.

As

the

distance

away

to

tectonic

features

increases,

the

susceptibility

to

landslides

is

likely

to

decrease
.

Consequently

,

areas

that

are

close

to

tectonic

features

are

more

prone

than

areas

far

away
.



Slope

Angle



contributes

to

mass

movements

in

terms

of

acceleration
.

Steeper

slopes

are

more

susceptible

than

gentle

slopes



Road

Network
-

changes

in

land

natural

gradient

cause

by

road

construction

are

noted

to

sometimes

influence

the

occurrence

of

landslides

as

a

result

of

ground

subsidence

activities



Drainage

network



areas

that

are

closer

to

rivers

and

streams

are

more

susceptible

to

landslides

because

of

their

ability

to

have

higher

moisture

contents

than

areas

farther

away
.

Instability

Factors

(
Con’t
)


Land Cover


is a well known trigger to landslides. Disturbed
vegetation, agriculture on hilly slopes and building construction on
unstable slope geological features are examples of landuse activities
likely to cause landslides



Rainfall



landslides are more likely to occur in the wet season than
in the dry season. They are often associated with heavy rainfall
events. Areas with high rainfall are more susceptible to landslides
than areas with low rainfall.

Instability

Factors

(
Con’t
)

Instability
Factors

Classifications

Susceptibility
Level

Rank

Lithological


Formation

Formations

Alluvium,

Navet,

Palmiste

Very High

5

Moruga
,
Lengua
,
Brasso
,
Manzanilla
,
Maracas,
Galera

High

4

Toco
,
Maraval
, Rio
Seco
, Springvale,
Nariva
,
Chaudiere
,
Cipero
,
Morne

L'Enfer,Mud

Volcanoes Cones
&
Flows,Gros

Morne
,
Karamat
,
Mayaro
, San
Fernando

Moderate

3

Cedros
,

Diorite,

Laventille
,

Guayamara
,
Tompire
,
Chancellor,
Guayamara
,
Talparo
,
Lopinot
,
Cushe
,
Cunapo
,
Concord, Gautier
,
Naparima
,
Lizard Springs,

Chaudiere

Low

2

Sans

Souci,

Arima
,

Water,

Pointe
-
a
-
Pierre,

Cruse,

Erin

Very Low

1

Classification and Landslide Factor Ranking


Classification and Landslide Factor Ranking

Instability
Factors

Classifications

Susceptibility
Level

Rank

Tectonic
Features

Proximity (m)

0
-
100

Very High

5

100
-
200

High

4

200
-
300

Moderate

3

300
-
400

Moderate

3

400
-
500

Low

2

500
-
600

Low

2

> 600

Very Low

1

Slope Angle

Angles
(degrees)

48

-

87

Very

high

5

27
-

48

High

4

15

-

27

Moderate

3

5

-

15

Low

2

0

-

5

Very

Low

1


Tectonic
Features


Classification and Landslide Factor Ranking

Instability
Factors

Classification

Susceptibility
Level

Rank

Road Network

Proximity (m)

0
-
100
m

Very

high

5

101
-
200
m

Very

high

4

201
-
300
m

High

3

301
-
400
m

High

3

401
-
500
m

Moderate

2

501
-
600
m

Moderate

2

>
600
m

Low

1


Classification and Landslide Factor Ranking

Instability
Factors

Weight

Classifications

Susceptibility
Level

Rank

Drainage
Network

0.06

Proximity (m)

0
-
100
m

Very

high

5

101
-
200
m

Very

high

4

201
-
300
m

High

3

301
-
400
m

High

3

401
-
500
m

Moderate

2

501
-
600
m

Moderate

2

601
-
700
m

Moderate

2

>
700
m

Low

1


Classification and Landslide Factor
Ranking

Instability
Factors

Classifications

Susceptibility
Level

Rank

Land

Use

Classes

Barren land

Very High

5

Urban or built
-
up land

High

4

Rangeland

Moderate

3

Agricultural land

Low

2

Forest land

Very Low

1

Wetland

Very Low

1

Water

Very Low

1


Classification and Landslide Factor
Ranking

Factors

Classification
Scheme

Rank

Rating

Rainfall

(mm)

178
-

226

Very

High

5

126
-

178

High

4

78
-

126

Low

3

40
-

78

Moderate

2

1


40

Low


1


Cartographic Model
-

Landslide

Ranking


Weighting


Landslide Factor Weighting: Scenario A

Instability Factors

Scenario A

%

Tectonic Features


1

0.14

Lithological

Formation


1

0.14

Slope Angle


1

0.14

Land Use


1

0.14

Drainage Network


1

0.14

Road Network


1

0.14

Rainfall


1

0.14

Total

7

1


Landslide Factor Weighting: Scenario B

Instability Factors

Scenario B

%

Tectonic Features


2

0.18

Lithological Formation


2

0.18

Slope Angle


2

0.18

Land Use


2

0.18

Drainage Network


1

0.09

Road Network


1

0.09

Rainfall


1

0.09

Total

11

1


Landslide Factor Weighting: Scenario C

Instability Factors

Scenario C

%

Tectonic Features


1

0.09

Lithological Formation


3

0.27

Slope Angle


3

0.27

Land Use


1

0.09

Drainage Network


1

0.09

Road Network


1

0.09

Rainfall


1

0.09

Total

11

1


Landslide Factor Weighting: Scenario D

Instability Factors

Scenario D

%

Tectonic Features


1

0.08

Lithological Formation


3

0.23

Slope Angle


3

0.23

Land Use


3

0.23

Drainage Network


1

0.08

Road Network


1

0.08

Rainfall


1

0.08

Total

13

1


Landslide Factor Weighting: Scenario E

Instability Factors

Scenario E

%

Tectonic Features


2

0.20

Lithological

Formation


2

0.20

Slope Angle


2

0.20

Land Use


1

0.10

Drainage Network


1

0.10

Road Network


1

0.10

Rainfall


1

0.10

Total

10

1


Factor Modelling
-

Flooding

Flood Factors


Rainfall

(mm)



Slope (%)




Land Use



Drainage density




Road

(% each watershed)




Elevation (m)


Flood Factor
Ranking

Factors

Classification
Scheme

Rank

Rating

Rainfall

(mm)

1

-

40

Low


1

40

-

78

Moderate

2

78

-

126

Low

3

126
-

178

High

4

178
-

226

Very

High

5

Elevation (m)

477.0


931.4

Very low

1

286.4


477.0

Low

2

147.1


286.4

Moderate

3


55.5


147.1

High

4

0


55.5

Very High

5

Flood Factor
Ranking

Factors

Classification

Scheme

Rank

Rating

Slope (%)

569.1


2748.7

Very low

1

257.7


569.1

Low

2

85.9


257.7

Moderate

3

21.5


85.9

High

4

0
-

21.5

Very High

5

Drainage density (% each
watershed)

0


0.004674

Very low

1

0.004674


0.006769

Low

2

0.006769


0.0083

Moderate

3

0.0083


0.009508

High

4

0.009508


0.020628

Very High

5

Factors

Classification

Scheme

Rank

Rating

Road

(% each watershed)

0.000194


0.004626

Very low

1

0.004626


0.009335

Low

2

0.009335


0.018198

Moderate

3

0.018198


0.039249

High

4

0.039249


0.071101

Very High

5

Land Use (related to water
absorption and drainage
capacities)

Wetland, Forest< Water

Very Low

1

Rangeland (Non
-
wetland)

Low

2

Agricultural land

Moderate

3

Barren land

High

4

Urban or built
-
up land

Very High

5

Flood Factor
Ranking







Cartographic Model
-

Flood

Ranking

Weighting


Flood Factor Weighting:

Scenario A


Flood Factors

Scenario A


%

Rainfall

(mm)


1

0.17

Slope (%)


1

0.17

Land Use


1

0.17

Drainage density


1

0.17

Road

(% each watershed)


1

0.17

Elevation (m)


1

0.17

Total

6

1


Flood Factor Weighting:
Scenario B

Flood Factors

Scenario B


%

Rainfall

(mm)


2

0.22

Slope (%)


2

0.22

Land Use


2

0.22

Drainage density


1

0.11

Road

(%
)

1

0.11

Elevation (m)


1

0.11

Total

9

1


Flood Factors

Scenario C


%

Rainfall

(mm)


3

0.33

Slope (%)


2

0.22

Land Use


2

0.22

Drainage density


0.5

0.06

Road

(%)

0.5

0.06

Elevation (m)


1

0.11

Total

9

1

Flood Factor Weighting:

Scenario C


Flood Factors

Scenario D

%

Rainfall

(mm)


2

0.22

Slope (%)


3

0.33

Land Use


1

0.11

Drainage density


1

0.11

Road

(%
)

1

0.11

Elevation (m)


1

0.11

Total

9

1

Flood Factor Weighting:

Scenario D


Flood Factors

Scenario E

%

Rainfall

(mm)


2

0.22

Slope (%)


2

0.22

Land Use


3

0.33

Drainage density


0.5

0.06

Road

(%
)

0.5

0.06

Elevation (m)


1

0.11

Total

9

1.00

Flood Factor Weighting:

Scenario E


Users / Uses of Susceptibility Maps


The

occurrence

map

can

be

used

to

identify

areas

where

historical

landslide

or

flood

activities

and

areas

susceptible

to

future

landslide

or

flood
.




This

will

highlight

potential

regions

of

physical

instability

and

inundation
.




As

such

,

the

landslide

and

flood

susceptibility

map

will

prove

to

be

a

practical

tool

in

hazard

mitigation

planning,

urban

planning,

natural

resource

management

and

disaster

response

management
.

Suggested Users

Suggested users of this information include but are not limited to them :



Landuse Planners


Property Developers


Geologists and Geographers


Disaster Management Officers


Local Government Agencies/ Regional Co
-
operations


Landslide technical specialists


Environmental planners


Researchers


General Public


Suggested Uses


Uses of landslide and flood susceptibility maps:



Landuse Planning

-

Provides planners with a practical and cost
-
effective
way to zone areas susceptible to landsliding.



Development Control

-

Can be used as a tool to help identify land areas
best suited for development (to determine landuse capability) by examining
the potential risk of landsliding



Building Regulation



Negotiating Insurance Premiums


Thank You