NOVEMBER 28, 2016

COASTAL EROSION RISK ANALYSIS

Liton Chandra Mazumder Michael G. Tadesse Mohamed H.M. Elamen

BHOLA DISTRICT, BANGLADESH

Outline

1. Introduction

2. Study Area

3. Objective

4. Methodology

5. Results & analysis

6. Conclusions

7. Recommendation

8. References

Introduction●With half of the world’s population living near the coast, an

immense threat is posed by coastal hazards to life and health, livelihood, and the economy.

●Coastal Erosion: wearing away of material from the coastal profile due to imbalance in the supply and export of material from a certain section.

●Slow, silent disaster (Makenro, 2000)

●Adversely affects ecosystem, navigation, agriculture development, and drainage system

●1 million people displaced and 9000 hectares of land are inundated annually in Bangladesh

Study area● Area & Population

○ 3403.48 sq.km

○ 1.8 million

● Economy○ Fishing (60%),

○ agriculture(30%)

○ other (10%)

● Natural Charact.○ 2 -3 meters M.S.L

○ Annual rainfall is 2360 mm (Banglapedia)

Bhola District, Bangladesh

Bhola District

● largest island in the coastline● Emerged in the Meghna estuary

800 years ago● Situated at the mouth of Meghna

River ○ Exposed to cyclones and

storms● 90 km long and 20 km wide ● 6 Upazilas (Sub-Districts) chosen

for the study● Major sediment conduits through

the Meghna estuary raise the land whereas simultaneous strong tidal waves accounts for land erosion.

● Squeezed to 3400 km2 (2004) from 6400 km2 (1960)

Economic &

societal distribut

ion

Motivation

Dynamic Delta

Consequential

cascading

impactsFamilies lose their agricultur

al land

Potential Factors of Erosion

○ Large River Discharge through the GBM river system

○ Strong tidal action (Long wave action)-

○ Storm surges (Devastating action of major cyclones)

○ Accelerated Sea level rise(SLR)

○ Longshore current

○ Anthropogenic activities

1. Large River Discharge through the GBM river system ●(GBM) is drained into the Bay of

Bengal via the Meghna Estuary

●Discharge is 15 times during monsoon period compared to dry season

●20,000 m3/s dry season Vs 100,000 m3/s monsoon season

●Max 160,000m3/s in wet season.

2. Tidal Range at different locationsLocation Name of the channel Season MaxWL(mP

WD)Min(mP

WD)Max Tidal

Range(m)

Daulotkhan

RB of West Shahabazpur Channel

Dry 2.4 -1.02 3.4

Tazumuddin

RB of West Shahabazpur Channel

DryMonsoo

n

1.683.49

-1-0.41

2.683.89

Char fession

Channel between Charfession and

Monpura

DryMonsoo

n

1.32.8

-0.9-0.43

2.143.2

3. Cyclones in Bangladesh• Cyclones hit the coastal regions of Bangladesh almost every year,

in early summer (April‐May) or late rainy season (October‐November).

• On average, a severe cyclone strikes Bangladesh every three years (GoB, 2009).

• Between 1877 and 1995 Bangladesh was hit by 154 cyclones (including 43 severe cyclonic storms, 43 cyclonic storms, 68 tropical depressions)

• Recently since 1995, five severe cyclones hit coast of Bangladesh coast in May 1997, September 1997, May 1998, November 2007 and May 2009.

OBJECTIVE Identify and rank hotspot areas in

order to define priorities and support

disaster reduction plans by calculating coastal indexes for

hazards and the associated exposure.

METHODOLOGY

Problem identification

Data Collection

FFFFFF

FFFFF

f

ExposureGGGGGGGGGf

HazardVVVVVVVVVv

Coastline Digitizati

on

Defining Buffer

Zone

Population DataPopulation indicator

map

Busi.settings indicator

map

Landuse indicator

map

Transport indicator

map

Business setting

digitizing

Supervised Land use

classification

Road Asset dataHazard

MapExpos

ure Map

Risk Map

Adaptation strategies

Risk analysis

Data collection

Landsat Satellite image (1978 - 2015)

Supervised classification of land use

Population density of upazilas [Sub-District]

Transportation (Road Asset)

Business settingsEX

POSU

RE

HA

ZAR

D

Imagery processing

Landsat (L1-5, L 4-5, L7, L8)

QGIS 2.18 & ArcMAP 10.2

Google Earth Pro 7.1.7.2606

Comparison of LANDSAT images from 1978 to 2015

Coastline Change [1978-2015]1989 1999 2008 20151978

Cross Sections

19 sections were selected to assess the erosion rate along the

coast

Defining Buffer Zone Max Erosion rate = 132 m/Year

Projected for 60 years ~ 8Km

iPop iLU

iBus iTrn

Population Indicator

UpazilaPopulation

Density (P/Km2)

Bhola Sadar 1040

Burhanuddin 730

Charfassion 309

Daulatkhan 480

Lalmohan 640

Tazumuddin 640

Landuse Indicator

Identifying Land Use types

Classifying areas

Google Earth Pro ™ (Pro7.1.7.2606)

FAO Data used as a framework

Big Cities Residential areas

Cropland

Coast line

Business Settings Indicator

Identifying the number of business setting close to the coastline from Google map

Classifying the business depending on priorities of the total number settings

Transport Asset

Indicator

RESULTS & DISCUSSIONS

Hazard Map

Population Indicator

North upazilas

● High population density (1040 P/km2)

● High iPop→ high iExp

South upazilas

Low population density (230 P/Km2)

Low iPop→ low iExp

Land Use IndicatorMain classes :

Crop areas, residential areas, big cities and coastline & forest

South upazilas

• Higher exposure to erosion

• More area is planted with crops

• Big cities located close to coast

North upazilas

• Lower exposure to erosion

• More area is used for residential purposes

• Big cities are located away from coastline

Business IndicatorMain classes :

Big markets, small markets and ports

South upazilas • Businesses are less exposed to

erosion • Decreased markets density

decreased population density

North upazilas• Busniess highly exposed to

erosion • Increased markets density

decreased population density • Increased ports due to increased

business activities resulted in higher exposure rate

Transport Indicator

Main classes : Unpaved Roads, Paved Roads

North upazilas Low percentage of the road asset Low iTrn → low iExp

South upazilasHigh percentage of the road assetHigh iTrn → high iExp

Exposure Indicator Map

Risk Map

North upazilas

- Upper parts

High iPop, iBus→ high iExp

High iexp +Med iHaz→ high CI

- Lower parts

Med iPop, iBus→ Med iExp

High iHaz + Med iexp →Med CI

South upazilas

Low iPop, iBus→Low iExp

Low iHaz +Low iHaz→Low CI

ADAPTATION POLICIES FOR RISK REDUCTION

RESILIENCE APPROACH Focused in the Upper Parts of northern upizals where the risk mainly derived from increased exposure

●Promote green infrastructure solutions : ○ Floating ports-Business settings.

○ Waterways transportation -transportation.

●Identify hotspot areas ●urban planning to address and avoid areas prone to erosion ●Increase public awareness and educate stakeholders.●Work toward more resilient building materials design codes

HAZARD MITIGATION APPROACH- Relevant to Lower Parts of the northern upizzals where hazard is the main source of risk:

• Heightening and strengthening embankment.• Putting sandbags and concrete block on the slope of the

embankment polder.• Proper management practices ;improved monitoring to

potential breaching parts of the coast• Increase number of cyclone shelters. • Enhance early warning and cyclone tracking system.• Promote ecosystem services role in reducing hazard ;

implement Healthy coastals.

CONCLUSION●A preliminary risk analysis → identify hotspot areas in order to

prioritize disaster reduction plans

●6 upazilas were chosen for the study

●Shoreline retreat (hazard) was computed using geospatial techniques and a buffer zone was demarcated in order to calculate the corresponding exposure

●Coastal Risk index was computed to analyse the risk of coastal erosion

●The Norther part of the island is susceptible to high erosion rate with a maximum erosion rate of 130 m/year

RECOMMENDATION●Coastal managers should give high priority to the the northern part

of the island and deploy the necessary resources.

●Further, vulnerability need to be assessed and strategic planning should be carried out to increase resilience reduce impact of climate change (Ashraful Islam, 2015 ).

●Using advanced geospatial techniques Digital Shoreline Analysis System (DSAS) for accurate shoreline change determination.

●Integrated coastal zone management plays a vital role to mitigate the problem and define suitable adaptation strategies.

REFERENCES

1. Hugh Brammer (2014). Bangladesh’s dynamic coastal regions and sea-level rise

2. Md. Ashraful Islam (2015). Assessment of Coastal Vulnerability Due to Sea Level Change at Bhola Island Bangladesh: Using Geospatial Techniques

3. Bangladesh Bureau of Statistics. http://www.bbs.gov.bd/

4. Magnus Krantz(B178 1999),COASTAL EROSION ON THE ISLAND OF BHOLA, BANGLADESH,

5. Md. Shamsuddoha,Rezaul Karim Chowdhury;CLIMATE CHANGE IMPACT AND DISASTER VULNERABILITIES IN THE COASTAL AREAS OF BANGLADESH

6. Rubayat Alam1, Md. Saiful Islam2, Md. Raqubul Hasib3, Md. Zahirul Haque Khan4;Characteristics of Hydrodynamic Processes in the Meghna Estuary due to Dynamic Whirl Action

7. Mizanur Rahman;Bhola Island, Bangladesh,Risks of erosion and disasters on livelihood

8. The 5th International Coordination Group (ICG) Meeting GEOSS Asian Water Cycle Initiative (AWCI) Tokyo, Japan, 15-18, December 2009:Country Report: Bangladesh

9. Susmita Dasgupta et al; Vulnerability of Bangladesh to Cyclones in a Changing Climate,Potential Damages and Adaptation Cost

10. http://www.conscience-eu.net/what_is_coastal_erosion_and_when_is_it_a_problem/index.htm

In Memory of the 1970 Bhola Cyclone Casualties

Dhirobala Mazumder (1930 - 1970)

The cyclone has left more than 500,000 people dead including my four family members and 35 extended family members

ধন্যবাদ   አመሰግናለሁ شكرا    Gracias