landslide tragedy of bangladesh

The First World Landslide Forum, 18-21 November 2008, United Nations University (UNU), Tokyo, Japan

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Landslide Tragedy of Bangladesh

Golam Mahabub Sarwar Executive Director, Committed to Earth Care (CEC), Bangladesh, email: [email protected]

Abstract: Landslide is a regular geologic hazard in Bangladesh, especially in Chittagong, the South-eastern Part of the country. Landslides in Bangladesh and its associated causes were studied using multidisciplinary approach taking two recent landslides as reference. Landslide caused death to more than 300 peoples in Bangladesh since 2000, with a loss of hundred of houses and millions of dollars of properties. One single event, the landslide of 11 June 2007 caused death to 135 people, affecting 1.5 million people of the region. Most of the landslides happened after heavy rainfall. Heavy monsoon rainfall intensified by strong storm from the Bay of Bengal (BOB) caused an abnormal precipitation in the area caused the referred landslide. Combined effect of rainfall and hill cutting induced slope instability triggered landslide in Chittagong. Combined effect of hill cutting and climatic change induced erratic behaviour of the nature caused 11 June Tragedy. Detailed Area Planning, landslide vulnerability zoning, landslide database development, and a geophysical analysis of the area are recommended a complete understanding of the landslides of Chittagong. Influential peoples of the societies are involved with hill cutting in Bangladesh, violating existing rules and regulations. Legal instruments should be in place and the enforcement of existing rules should be ensured to avoid further 11 June Tragedy.

Key Words: Landslide, Chittagong, impacts, hill cutting, slope instability, Bangladesh

1. Introduction

Landslide is becoming a concern of great priority because of its devastating nature worldwide (Evans et al. 2007; Havenith et al. 2007; Kyoji, Wang & Fukuoka 2004; Paudel et al. 2003). Landslide is an inveterate problem for south eastern part of Bangladesh and Chittagong city is particularly highly vulnerable to this hazard, with an increasing trend of frequency and damage. More than 300 people were dead in Bangladesh by landslide hazards since 2000. A total of 135 fatalities were recorded in one single event of 11 June 2008, with a repetition on 20 August 2008, adding 11 deaths in record. Slope instability caused by indiscriminate hill cutting activities and heavy rainfall are triggering factors of landslides of Chittagong. This paper focuses the hazards of landslide in Chittagong with a special referencing of two recent devastating landslides, and some potential recommendations are placed.

Chittagong city is the most important business centre of the country having a population of five million is situated at the right bank of the Karnafulli river with a geographic

coverage of 22°14Ń-22°24´30´Ń latitude and 91°46É-91°53É Longitude. About half of the area of the city is plain land and the rest half is characterized by the presence of hillock and small hills. Surface run-off drains out to the Karnafulli River by a chain of small and medium canal that ultimately flows to the Bay of Bengal.

2. Flashback

a). 11 June 2007: At the very early morning of 11 June 2007, the city of Chittagong experienced a deadly landslide with huge number of casualties. The most affected areas are Motijharna of Lalkhan Bazaar, Power Colony, Kushumbagh Residential area, Taragate, Devpahar, Shaheed Minar area of Chittagong area, and Lebu Bagan of Chittagong Cantonment area. A total of 5,072 families were homeless with a death toll of 135 and 213 wounded. Extremely Heavy rainfall counting as long as 267 mm in 24 hours was observed on the day, causing water logging in the area, submerging ground floors of 500 buildings of city’s commercial area Agrabad. Landslide and flush flood affected 1.5 million people of Chittagong

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region. Rice flour, sugar, pulse and other food grains stored in warehouses of Majheerghat, Sagorika road, Chaktai, and Patharghata were degraded because of water logging situation.

b). 18 August 2008: The landslide of 18 August 2008 took place at the very early in the morning killing 11 people of the city vanishing two whole families of Hossain Colony of Matijharna area of Lalkhan Bazaar. A total of 10 people were trapped to death by rubble of collapsed house, including six members of a same family, while one more was death in hospital. The devastating event completely bulldozed 13 cottages in a sudden moment. The night was full of shower of rain having a record of 142 mm in 24 hours till 12.00 noon of the 18th August, according to local weather department record (Hayat, 2008). Areas of Bakulia, Bahoddarhat, and Chandgaon were water logged because of heavy rainfall. Hossain Colony was built on an abundant property of Chittagong Water Supply and Sewerage Authority (WASA), state owned and the only water supply company of the city.

Another landslide was observed at Bhaditala village under Sadar sub-district of Cox’s Bazaar, a neighbouring district of Chittagong. It was also a rain induced landslide that happened at around 4.00 am leading 3 deaths. The average rainfall of the city was 133mm in 24 hours of time (Hayat, 2008).

Rescue operation was participated by army, police, fire fighter, NGO activists and other volunteers. Rescuing the affected people was under challenge because of bad weather situation, especially heavy rainfall and flooding event with an additional drawback of inadequate rescue equipments. Rescue operation was observed very slow because of lack of technical knowledge, poor coordination, and absence of landslide contingency plan in place. Professional rescue coordination was not in place, even though the concerned authority experienced similar disaster event on 21 November 1997 when an earth quaque of Richter scale only 6.1 caused a death toll of 6 people (BBC, 1997) when ground floor of one four storied building was trapped under soil and it took three days for the rescue team to take out the trapped people.

3. Causes of Landslide in Chittagong

The steepness of a hill is the main factor for the movement of the materials that flow down towards the foot of the hill. Steep slope push down debris or mud converting gravitational energy into kinetic energy. A natural hill is a stable surface of the earth system having a balance of its components. Every natural hill is maintaining its stability by natural condition of the system that sometimes disturbed by improper interactions of human being and landslides of Chittagong are examples of human induced landslides where hill slopes are being steeped day by day by hill cutting activities and other associated factors those could be summarized as, but not limited to:

Slope instability by land degradation: Soils are extracted haphazardly from the hills of Chittagong region for the activities of housing, urbanization, industrialization, road construction, brick kiln construction or other commercial purposes. Practice of cutting hills is booming up with growing demand of home building. Quddusi (2007) mentioned that more than 100 hills of Chittagong city were demolished in last 30 years of times. Horizontal extension of Chittagong city, which is presently observed at a rate of 92 hectares per year by hill demolition (Biswas, 2007). Basement of a hill is the area where hill cutting is initiated by soil grabber decreasing base area of the hill leading to a steep slope and instable condition. The susceptibility of a hill is moderate and high at a slope of 200-300 and 400-600 respectively (Nagarajan et al. 2000), whereas hills of Chittagong are cut at 700 or greater slope (Islam, 2008). Hills are first deforested for soil extraction exposing the land surface of the hill increasing its vulnerability to erosion. Soils of open hill surface absorb rain water quickly that dissolve soil nutrient loosing its compaction and adding heavy weight to the basement of the hill. Slope instability turning by decreased base area, and loose muddy soil because of rainwater absorption can not hold the extra weight added by rain water, resulting downward soil movement or landslide.

A group of organized people including prominent political leaders of the city, leading real estate businessmen, truck owners, and brick-


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field owners are generally blamed for the senseless hill cutting activities in the region who are indirectly backed by Chittagong Development Authority (CDA), Chittagong City Corporation (CCC), and Department of Environment (DoE) by their silent role in controlling hill grabbing. More than a dozen of points of Chittagong including posh area of Khulshi, Nasirabad, Panchlaish, and Zakirhossain road, Shugandha residential area and other areas of Shantinagar, Oxygen, Polytechnic, Roufabad, Fatehabad, Shershah colony, Sholoshahar, Hamzerbag, Foy’s lake, Pahartoli, Kattoli, Motijharna, Devpahar, Rubigate, and Baizid Bostami (Biswas, 2007).

Heavy rainfall: A heavy rainfall during a shorter period of time can lead to a large scale landslide in a hill area. A study by Yalcin (2007) concluded that an intense rainfall of 70mm per hour or greater will create landslide favourable condition. Rainfall in Chittagong is second highest in the country with an annual average of approximately 3000mm per year, having maximum recorded rainfall in June (Figure 1a). The month of June and July shows most landslide frequency in Chittagong (Figure 1b) confirming strong relationship of heavy rainfall and landslides in the country.

Figure 1a: Rainfall pattern of Chittagong in

2004

Total rainfall of Chittagong in 24 hours

before the event was 267 mm and this amount of heavy rain in such shorter period of time

triggered landslide in unstable hills of the area where hills are formed by sandstones, siltstones and shales, which are rich in pyrites and lime. Excess rainwater dissolves these compounds breaking the strength of hill basement.

Figure 1b: Average landslide frequency in

Chittagong by month.

Deforestation, Seismic activity, and abnormal tidal flow in the city might have contributed to landslide in Chittagong, in addition to hill cutting and heavy rainfall. Deforested areas of hills are easily exposed and top soils are eroded by surface run-off or by wind erosion. Forest covered areas are less vulnerable to landslide than deforested area and debris stored areas are more in deforested area than a forest covered area. Vegetation protect earth surface from exposure and roots of a tree stabilize the strength of soil compaction acting as cementing material and reducing soil erosion. On the other hand, Seismic activities destabilize the soil structure of the region triggering landslide. Huge amount of strain energy is released by earthquake forwarding shear stress to slope destabilization system. Despite the fact that Chittagong is a city of small hill, its one third areas are covered by land of low elevation that experience abnormal tidal flow during spring tide of Monsoon season. Tidal water level was observed flowing at a higher level of one and a half to two meter higher than the season’s average tidal height. Surface run-off could not find its way out but saturated the soils of hill base loosing its compaction.

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4. Discussion

Landslide in Chittagong is influenced by heavy rainfall. A detailed scientific study is needed to understand the threshold of rainfall for landslide potentiality. It is not completely understood the exact role of rainfall for causing landslide in Chittagong. This component should be studied thoroughly for a better understanding of landslides in the region. Rainfall data of a significant historical period is an important component for the probability assessment of landslide (Ko, 2004). Information technology and database management in Bangladesh is still it its infant stage. Most of the data available from Bangladesh Meteorological Department (BMD) is error prone, inaccurate, and incomplete. In addition, unnecessary bureaucracies are placed to access the existing data that demand an input of high level of effort to access. All environmental data of Bangladesh, including meteorological sources, should be easy access to research activities for an updated understanding of the system that will facilitate all concerned including government itself to understand the disaster and to prepare for it in a better, efficient and professional way.

At the same time, Detailed Area planning (DAP) of the city and a better management of government owned land are needed to minimize landslides and its hazards in Chittagong. Landslide vulnerability area need to be identified and highly vulnerable area should be declared as ‘Red Zone’ for housing or any other settlement activities. In addition to marking red zone, government land should be taken proper care by its respected owner organizations. Security fences should be built round the hill slope of the property of respective organization to prevent potential illegal settlement as because poor people will always try to find a cheaper housing option despite of risk of danger. Relocation of present inhabitants of dangerous hill slope is another issue to be considered. A high level working body should be formed to find out potential relocation site with financial support from emergency disaster fund or any other potential funding sources. After relocating people from the hill slope, afforestation should be done with plant species of medium height

having long root to strengthen the soil stability of the area.

A landslide database is essential to have a better understanding of causes, impacts and trends of landslide in Bangladesh. It is will helpful to government and other organizations those are interested in working on the issue in work plan formulation and decision making process. A landslide database should be developed by government or by any other organization with due governmental support. In addition to the database, a landslide vulnerability mapping should be done using modern technic like Geographica Information System (GIS) and Remote Sensing (RS) technology that will be used as a strong tool for a better action plan. Furthermore, a geophysical analysis of the area is needed for a better understanding of geology and geomorphology of Chittagong region. Navigating access to the potential resources of international knowledge and expertise could be a good initiative for the understanding of the complex system.

The water drainage system of the city is very poor. Flash flood driven water stagnation is a common feature of Chittagong city. There are 22 big canals in Chittagong to drain out the city’s rainwater which have lost their water carrying capacity because of hill cutting induced siltation (Ashraf, 2007) and also of poor management. Drainage system of the city should be improved dramatically to drain out city’s rainwater. Canal grabber should be removed and the flow of canals should be ensured for the improvement of water logging situation. In addition, landslide risk mitigation plan should be developed with efficient enforcement of existing legal instruments.

Rescue operations in recent landslides had an experience of poor coordination and inadequate rescue tools. Landslide disaster contingency plan at both government and community level should be formulated with definite coordination body and trained manpower equipped with necessary tools. Chittagong City Corporation should have plan in place to evacuate its residents in case of emergency situation.


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5. Conclusion

Hill cutting and heavy rainfall are prime factors for landslides in Chittagong that causes death to hundreds people with a great property loss. This catastrophe could be checked by controlling the grabbing of government owned land and by understanding the rainfall pattern and its true relationship with landslide in the region. Detailed landuse planning of the city, a landslide database, landslide mapping and geophysical analysis of the city is essential to minimize landslides and its impacts in the region. In addition, a landslide contingency plan should be in place that would direct proper coordination of the needs of crisis period. Furthermore, incorporating international resources with total plan and actions will enhance the capacity of concerned organizations in dealing the hazard. 6. References Ashraf, A 2007, Personal communication with city

planner and engineer Ali Ashraf, Chairman, Institute of Engineers, Chittagong, Bangladesh.

BBC 1997, Six dead in Bangladeshi earthquake, 22 November 2007, http://news.bbc.co.uk/1/hi/world/south_asia/33820.stm

Biswas, S 2007, What caused landslide deaths in Chittagong? Weekly Holiday, 22 June 2007, Dhaka, Bangladesh.

Evans, S G, Guthrie, R H, Roberts, N J, Bishop, N F 2007, The disastrous 17 February 2006 rockslide-debris avalanche on Leyte Island, Philippines: a catastrophic landslide in tropical mountain terrain, Natural Hazards and Earth System Sciences 7, pp89-101

Havenith, H B, Torgoev, I, Meleshko, A, Alioshin, Y, Torgoev, A, Daneels, G 2006, Landslides in the Mailuu-Suu Valley, Krygyzstan – Hazards and Impacts, Landslides 3, pp137-147

Hayat, T 2008, Chittagong Landslide Kills 11, The Daily NewAge, 19 August 2008, Dhaka Bangladesh

Islam, M S 2008, Challenges of Dev: Hill Cutting and Landslide, Speech at Roundtable Discussion arranged by the Daily Star, 30 August 2008, Chittagong, Bangladesh

Ko, C K, Flentje, P, Chowdhury, R 2004, Interpretation of probability of landsliding triggered by rainfall, Landslides 1:263–275

Kyoji, S, Wang, G, Fukuoka, H 2004, Assessment of Landslide Risk during Earthquake/ Rainfall on Urban Areas, Annuals of Disaster Prevention Research Institute, Kyoto University, No. 47C, Kyoto, Japan.

Nagarajan, R, Roy, A, Kumar, R V, Mukherjee, A, Khire, M V 2000, Landslide hazard susceptibility mapping based on terrain and climatic factors for tropical monsoon regions, Bull Eng Geol Env 58, pp275–287

Paudel, P P, Omura, H, Kubota, T, Morita, K 2003, Landslide damage and disaster management system in Nepal, Disaster Prevention and Management 12(5), pp413-419

Yalcin, A 2007, Environmental Impacts of Landslides: A Case Study from East Black Sea Region, Turkey, Environmental Engineering Science 24(6), pp.821-833.

Suggested citation

Sarwar G M, 2008, Landslide Tragedy of Bangladesh, The First World Landslide Forum, 18-21 November 2008, United Nations University (UNU), Tokyo, Japan.

http://news.bbc.co.uk/1/hi/world/south_asia/33820.stm�

http://news.bbc.co.uk/1/hi/world/south_asia/33820.stm�

landslide tragedy of bangladesh

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