Development of a GIS-based Landslide and Flood Risk Model for the Caribbean

ByJacob Opadeyi PhD, Gabrielle Thongs MSc, Leah Fouchong BSc, Roxann Smith BSc, Desiree

Joseph Bsc, Shelly Bradshaw BSc Department of Geomatics Engineering and Land Management

The University of the West IndiesSt. Augustine

Trinidad

Background

• The location of the Trinidad in the extreme south of the Caribbean means the country experiences a tropical marine climate.

• Floods and landslides are annual events associated with the rainy season in Trinidad and Tobago.

• Flooding and landslides are the most common and significant localized hazard.

To the end of William Road, El Socorro South, yesterday (May 27th 2010). Around 6.30 am the Caroni River, which runs to the back of El Socorro South burst its bank due to heavy rainfall. As a result

hundreds of acres of crops were submerged in water.

Trinidad Guardian 28 May 2010  

Two people are dead and one family is hoping that five of its members who are in critical condition live, after a landslide struck the village of Delaford on Tobago's west end.

Caribbean Net News  Tuesday, November 16, 2004

Geraldo Greene, a 76-year old pensioner suffered a cruel death on Friday when a landslide destroyed part of his Santa Cruz home killing him in the process. Trinidad Express - Aug 6, 2001

Background• Trinidad and Tobago faces a number of natural

disaster issues

• Vulnerability assessment and risk mapping are the important first steps for any initiative for disaster reduction.

• A risk assessment is not only to find out where risk related problems are located, but also to quantitatively or qualitatively determine the significance of risks (Smith 2001, Greiving et al 2006)

Landslide and Flood Risk MappingObjective

To evaluate and rank the risk level to landslide of the resident population and the physical assets (buildings) of Trinidad.

Input data• Landslide susceptibility maps• Population spatial distribution• Building spatial distribution

Conceptual Design

Areal Population Density

Landslide Susceptibility

Population Risk to Landslide

Risk = Susceptibility + vulnerability (Population, Buildings)

Areal Buildings Density

Buildings Risk to Landslide

Buildings & Population Risk to Landslide

Inputs

Results

Landslide Susceptibility

Instability Factors

• Tectonic Features • Lithological Formation• Slope Angle • Road Network • Drainage Network • Land Use • Rainfall

Cartographic Model - Landslide

Ranking Weighting

Landslide Factor RankingInstability Factors

Classification Susceptibility Level

Rank

Road Network Proximity (m)

0-100m Very High 5

101-200m High 4

201-300m High 3

301-400m Moderate 3

401-500m Low 2

501-600m Low 2

>600m Very Low 1

Landslide Factor Weighting: Scenario E

Instability FactorsScenario 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 0.10Total 10 1

Landslide Susceptibility MapSummation of land areas in each susceptibility class

Classes COUNT Area by cell Area (ha) % of total

Very Low 6159,360 615936,000

61,594 12.93

Low 15534,674 1553467,400

155,347 32.62

Moderate 14014,869 1401486,900

140,149 29.42

High 8397,885 839788,500

83,979 17.63

Very High 3522,375 352237,500

35,224 7.40

Total 4762916,300

476,292 100.00

Population Density Classification Scheme

Population Density by ED per hectares Vulnerability level0 - 19 Very Low19 - 76 Low76 - 191 Moderate191 - 1,032 High1,032 - 4,874 Very High

Building Density Classification Scheme

Building Density By ED per hectares Vulnerability level0 - 8 Very Low8.0 - 20 Low20 - 51 Moderate51 - 135 High135 - 441 Very High

Vulnerability

Population Vulnerability Class

Building Vulnerability Class

Very Low Low Moderate High Very High

1 2 3 4 5

Very low 1 2 3 4 5 6

Low 2 3 4 5 6 7

Moderate 3 4 5 6 7 8

High 4 5 6 7 8 9

Very High 5 6 7 8 9 10Risk Level Risk Value

Very low <3

Low 3-5

Moderate 6

High 7

Very High > 7

Single-Risk (Population) MapSingle-Risk (Buildings) MapMulti-Risk (Buildings and population) Map

Results: Landslide Risk Maps

Landslide Population Risk Assessment

Single Risk Classification Scheme

Vulnerability Class

Susceptibility Class

Very Low Low Moderate High Very High

1 2 3 4 5

Very low 1 2 3 4 5 6

Low 2 3 4 5 6 7

Moderate 3 4 5 6 7 8

High 4 5 6 7 8 9

Very High 5 6 7 8 9 10Risk Level Risk Value

Very low < 3

Low 3-5

Moderate 6

High 7

Very High > 7

Landslide Population Risk (Sum of Land Area under each risk level)

Risk Level Number of cells Area (m2) Area (HA) % of Trinidad

urban land mass

Very Low 32,352 3,235,200 323.52 0.61%

Low 523,056 52,305,600 5,230.56 9.84%

Moderate 1,188,482 118,848,200 11,884.82 22.36%

High 1,485,898 148,589,800 14,858.98 27.96%

Very High 2,084,492 208,449,200 20,844.92 39.22%

Landslide Building Risk Assessment

Landslide Building Risk Assessment(Sum of Built-up Area under each risk level)

Risk Level Number of cells Area (m2) Area (HA) % of Trinidad urban

land mass

Very Low 648,679 64,867,900 6,486 12.2%

Low 1,271,283 127,128,300 12,712 23.9%

Moderate 1,513,640 151,364,000 15,136 28.5%

High 1,249,585 124,958,500 12,495 23.5%

Very High 631,093 63,109,300 6,310 11.9%

Landslide Multi-Risk Assessment: Building and Population

Multi-Risk Classification Scheme

Vulnerability Class

Susceptibility Class

Very Low

Low Moderate High Very High

1 2 3 4 5

Very low 1 3 4 5 6 7 1

Low 2 5 6 7 8 9 2

Moderate 3 7 8 9 10 11 3

High 4 9 10 11 12 13 4

Very High 5 11 12 13 14 15 5Multi-Risk Level Risk Value

Very low < 6

Low 6-7

Moderate 8-9

High 10-11

Very High > 12

Landslide Multi (Building & Population) Risk Assessment(Sum of Land Area under each risk level)

Risk Level Number of cells Area (m2) Area (HA) % of Trinidad

urban land mass

Very Low 505,088 50,508,800 5,050.88 9.50%

Low 919,685 91,968,500 9,196.85 17.31%

Moderate 1,197,265 119,726,500 11,972.65 22.53%

High 1,201,305 120,130,500 12,013.05 22.61%

Very High 1,490,937 149,093,700 14,909.37 28.06%

Flood Risk MappingObjective

To evaluate and rank the risk level to flooding of the resident population and the physical assets (buildings) of Trinidad

Input data• Flood susceptibility Map• Population spatial distribution• Building spatial distribution

Conceptual Design

Areal Population Density

Flood Susceptibility

Population Risk to Flooding

Risk = Hazard Susceptibility + Vulnerability (Population, Buildings)

Areal Buildings Density

Buildings Risk to Flooding

Buildings & Population Risk to Flooding

Inputs

Results

Factor Modelling - Flooding

Flood Factors• Rainfall (mm) • Slope (%) • Land Use • Drainage density • Road (% each watershed) • Elevation (m)

Cartographic Model - FloodRanking Weighting

Flood Susceptibility MapSummation of land areas in each susceptibility class

Classes COUNT Area by cell Area (ha) % of total

Very Low 2,327,910 232,791,000

23,279 4.86

Low 9,959,195 995,919,500

99,592 20.79

Moderate 16,847,280

1,684,728,000

168,473 35.16

High 13,471,559

1,347,155,900

134,716 28.12

Very High 5,304,962 530,496,200

53,050 11.07

Total

4,791,090,600

479,109 100.00

Population Vulnerability Classification Scheme

Population Density By ED per hectares Vulnerability level0 - 19 Very Low19 - 76 Low76 - 191 Moderate191 - 1,032 High1,032 - 4,874 Very High

Building Vulnerability Classification Scheme

Building Density By ED per hectares Vulnerability level0 - 8 Very Low8.0 - 20 Low20 - 51 Moderate51 - 135 High135 - 441 Very High

Single-Risk (Population) MapSingle-Risk (Buildings) MapMulti-Risk (Buildings and population) Map

Results: flood risk maps

Flood Population Risk Assessment

Single Risk Classification Scheme

Population Vulnerability Class

Susceptibility Class

Very Low Low Moderate High Very High

1 2 3 4 5

Very low 1 2 3 4 5 6

Low 2 3 4 5 6 7

Moderate 3 4 5 6 7 8

High 4 5 6 7 8 9

Very High 5 6 7 8 9 10Risk Level Risk Class

Very low < 4

Low 4-5

Moderate 6

High 7

Very High > 7

Flood Population Risk (Sum of Land Area under each risk level)

Risk Level Number of cells Area (m2) Area (HA) % of Trinidad urban

land mass

Very Low 1,194,834

119,483,400

11,948 22.48%

Low 1,687,858

168,785,800

16,878 31.76%

Moderate 1,644,578

164,457,800

16,445 30.95%

High 696,494

69,649,400

6,965 13.11%

Very High 125,510

12,551,000

1,255 2.36%

Flood Building Risk Assessment

Flood Building Risk Assessment(Sum of Land Area under each risk level)

Risk Level Number of cells Area (m2) Area (HA) % of Trinidad

urban land mass

Very Low

1,405,680

140,568,000

14,057 26.45%

Low

1,716,196

171,619,600

17,162 32.29%

Moderate

1,496,094

149,609,400

14,961 28.15%

High

625,967

62,596,700

6,260 11.78%

Very High

105,337

10,533,700

1,053 1.98%

Flood Multi-Risk Assessment: Building and Population

Multi-Risk Classification Scheme

Vulnerability Class

Susceptibility Class

Very Low

Low Moderate High Very High

1 2 3 4 5

Very low 1 3 4 5 6 7 1

Low 2 5 6 7 8 9 2

Moderate 3 7 8 9 10 11 3

High 4 9 10 11 12 13 4

Very High 5 11 12 13 14 15 5Multi-Risk Level Risk Value

Very low < 6

Low 6-7

Moderate 8-9

High 10-11

Very High > 12

Flood Multi (Building & Population) Risk Assessment(Sum of Land Area under each risk level)

Risk Level Number of cells Area (m2) Area (HA) % of Trinidad

urban land mass

Very Low

925,747

92,574,700

9,257 17.42%

Low

1,467,641

146,764,100

14,676 27.62%

Moderate

1,334,220

133,422,000

13,342 25.11%

High

1,402,912

140,291,200

14,029 26.40%

Very High

218,754

21,875,400

2,188 4.12%

Uses• Development control and planning • Disaster mitigation planning • Disaster management • Policy formulation • Law reforms • Site analysis • Review of insurance premium

Users• Physical Planning Offices • Non-Governmental Organizations • Environmental Agencies • Works Departments • Utility Companies • Insurance Agencies • National Disaster Offices • Security and Protective Services • Lending Agencies • Meteorology and Hydrology Departments • Educational Institutions • Land Developers • General Public • Foreign Investors

Questions &Comments