Md. Rezuanul Islam, GIS Assistant, Asian Disaster Preparedness Center (ADPC), Dhaka â 1206, Bangladesh. E-mail: fahiemislam@gmail. com. Contact ...
Waterlogging Vulnerability Assessment of Coastal Urban Community: A Case Study of Chittagong City Corporation Area, Bangladesh Md. Rezuanul Islam, GIS Assistant, Asian Disaster Preparedness Center (ADPC), Dhaka – 1206, Bangladesh. E-mail: fahiemislam@gmail. com. Contact number: (+88)01917286701 Debasish Roy Raja, Assistant Professor, Department of Urban and Regional Planning, Chittagong University of Engineering and Technology (CUET), Chittagong - 4349, Bangladesh. Vulnerability analysis
Abstract In coastal urban areas Waterlogging has been a global hotspot and potential vulnerability to urban habitant lifelines and safety due to climate change and hasten urban development. The recurrent waterlogging in coastal urban areas of Chittagong City Corporation (CCC) results high magnitude of losses indicating continual vulnerability of the region during monsoon period. The present research has established a prototype for rainstorm and tidal water induced waterlogging vulnerability assessment through the combination of GIS based Analytical Hierarchy Process (AHP) model and Community Vulnerability Assessment Tool (CVAT). Extensive field data has been used to prepare the attribute map layers like tidal water effect, frequency of waterlogging, water stagnation hour and drainage condition for waterlogging affected communities. ASTER GDEM and rainfall data has used to determine the topographical characteristics and the frequency of waterlogging in affected communities respectively. The different attribute data layers are multiplied with weight value derived from AHP model to deduce the waterlogging vulnerability index map for CCC area. From the research 13.5 sq.km out of 168 sq.km are found directly vulnerable to waterlogging hazard. The research also reveals that 52 sq.km (31%) areas are indirectly vulnerable to waterlogging. The overall Figure: Chittagong City Corporation area vulnerability of CCC community is high in respect of different aspects such as social, physical, critical facilities, economic and environmental. The findings of the research Methodology can be used to prioritize risk mitigation investments, measures to strengthen the emergency preparedness and response mechanisms for reducing the losses and damages due to future waterlogging events in CCC area.
Physical vulnerability
Pitch road Brick road Mud road
Karnaphuly river
(A)
(B) Figure: Physical vulnerability to waterlogging hazard (A) Residential area (B) Road
Social vulnerability
Critical facilities vulnerability
(B)
(A)
Key words: AHP, CVAT, Vulnerability, Waterlogging Introduction ŸChittagong is the second largest urban area as well as coastal area of Bangladesh
surrounded by hill tracts. Majority of the people along coastal areas living between 0 to 5 meter elevation from sea level (Hoque et al. 1996). ŸThe geomorphology of coastal Chittagong is self responsible for natural disasters like Waterlogging, Landslide, Flood, Cyclone and Storm surge, Flash flood, Drought, Tornado, Riverbank erosion, Salinity intrusion and Earthquake (Shamsuddoha and Chowdhury, 2007). Ÿ
(C)
(D)
Figure: Attribute maps (A) Drainage condition map (B) Topography map (C)Frequency of waterlogging map (D) Tidal water effect map
Figure: Flow diagram of Methodology
• Due to unplanned urbanization, improper drainage planning and management, Results and Discussion excessive encroachment of natural water bodies, heavy rainfall and tidal water effect Among 41 wards, 44 waterlogging affected communities are results waterlogging problem in CCC area. identified in 22 wards. • Last five years, 1/3 of the City of Chittagong went under water during the rainy season (Ashraf & Chowdhury, 2009).
Table: Status of influencing factors to waterlogging hazard in CCC area Attribute Factors
Overall Status
Drainage
13 wards are found drainage with bad condition
Tidal water effect
10 communities are identified as affected severely
Topography Maximum water logging affected community ranges from 3 to 8 meter high from mean sea level. Frequency 5 communities are found as affected for Twenty to Twenty four times of by water logging hazard. waterlogging
Ÿ40,000 residents living in around 350 plots along 29 roads of the posh CDA Residential
Areas are now forced to shift their houses elsewhere as abrupt inundation keep them hostage during waterlogging phenomena (CDA 2014)
Depth of inundation
ŸChittagong city is not perfectly protected from tidal water effect of Bay of Bengal due
to improper management and lack of sluice gates on the mouth of different canals connecting with Karnaphuly River, results tidal water entrance to the port city through 22 points of different canal
Water stagnant duration
• Recent horrible Water logging event: 22 June, 2014. - Reasons: Torrential rainfall (675 millimeter rain in 72 hours) and Tidal water. - Duration: 2 days (The News Today, 23 June, 2014). - Affected population: Approximately 2 million people Objectives 1. To prepare waterlogging vulnerability index map for Chittagong City Corporation (CCC) area.
Figure: Waterlogging vulnerability index map for CCC area Table: Allocation of waterlogging affected communities within defined vulnerability classes Vulnerable Vulnerability Vulnerability % of area classes index values Area (sq.km)
Vulnerable ward no.
Low
< 22.01
2.5
1.5
1, 13, 20, 23, 26, 29, 30, 40
Moderate
22.01 – 26.0
4
2.4
3, 7, 8, 19, 24
High
26.01 – 30.0
3
1.8
4, 16, 34
Very high
30.01 – 35.0
4
2.4
5, 6, 17, 27, 33, 35
12 numbers of new wards has been found as indirectly vulnerable and among them ward no 28, 31 and 32 are completely indirectly vulnerable.
Table: Attribute scores by AHP
2. To analyze community vulnerability to water logging and landslide hazard in CCC area according to different aspect of physical, social, economical, environmental and critical facilities.
Precipitation
0.2406
Topography
0.1320
Tidal water effect
0.0749
Source: Field survey, 2014
Figure: Waterlogging inventory map
Figure: Overlay operation by AHP method
Environmental vulnerability Secondary hazard site Dustbin Electric pole Electric tower Electric transformer Light post Telephone pole Traffic pole Water reservoir
Number of vulnerable site 7 1856 25 204 43 359 2 2
Approximately 52 sq.km. of CCC area is Conclusion indirectly vulnerable This study has assessed the vulnerability of waterlogging hazard for CCC area due to water logging which depicts that Chittagong city is greatly vulnerable to waterlogging hazard. hazard which is almost In CCC, about 39% of city's people, one sixth of city's residential structures, 47% of CCC roads, 18% of educational institutes and more than 3000 31% of total area. structures used for economic activities are vulnerable. One of the main
Badurtola (Ward no-06), Katalganj, Probortak moore (ward no-16) and Brick field road (ward no-34) remain water logged averagely for more than 4 hours during rainy season. Whereas waterlogging phenomena is quite common in Hazipara, wazdia, Aluminum factory road, Sugandha residential area, Solokbahar, 2 no. gate, South Bakalia, East Madarbari and Firingee Bazar area has gone under water for maximum 2 hours. The recent horrible waterlogging occurred at West Sholoshahar in 2012, eastern part of its inundated with water for 24 hours and the water level was 3.5 feet in that area.
0.5167
Economic vulnerability
Figure: Critical facilities vulnerability to waterlogging hazard
Figure: Economic infrastructure vulnerability to waterlogging hazard in CCC area
Waterlogging affected community among Panchlaish, West Sholoshahar, Solokbahar, South Agrabad and Patharghata ward has gone for more than 3.5 feet under water during waterlogging phenomena. The last most devastating waterlogging phenomena happened in Patharghata during July 28-31 (673.61 mm) in 2009 when Brick field road went 5 feet under water.
Drainage condition
Figure: Social vulnerability to waterlogging hazard in CCC area
Figure: Indirect vulnerable area to waterlogging hazard
objectives of this study is to prepare vulnerability index for waterlogging hazard which will help to reduce the risk of people. As CCC belongs to coastal area and north-south hill range crosses the city area, so the waterlogging phenomena are quite very severe than any other location of Bangladesh. The presence of Bay of Bengal, Karnaphuly River and improper drainage system together makes the waterlogging situation very common to the city area. In these circumstances, it would be rational to identify vulnerable locations due to waterlogging hazard into city area which can provide supportive actions for preparing disaster management plan. In this study Community Vulnerability Assessment Tool (CVAT) and GIS has been applied in this small area of Chittagong division, it can be also applied to any type of hazard in any location of the country, both micro and macro levels. Finally on the basis of the research findings, it can be concluded that if the government and other concerned authorities take necessary steps, vulnerability of waterlogging hazard can be reduced to an extent tolerable to the city people.
Submitted to UNISDR Science and Technology Conference on the Implementation of the Sendai Framework for Disaster Risk Reduction 2015-2030
