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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