Geology of Dhaka City
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The rapid growth of population, urbanization, communication and infrastructure development in Bangladesh has sharpened the need of understanding the geological processes that some times cause severe natural and man-made disasters. The... more
The rapid growth of population, urbanization, communication and infrastructure development in Bangladesh has sharpened the need of understanding the geological processes that some times cause severe natural and man-made disasters. The natural landscape of Bangladesh can distinctly be portrayed as active plains of fluvial, deltaic and coastal environments, having few strips of low hills in the east and northeast. The country is prone to annual flood and other climatic hazards. The general elevation of the deltaic and coastal plain land is only 2 to 4m above mean sea level.
There are number of large and small clusters of urban growth throughout the country, among these the capital city of Dhaka, the port cities of Chittagong and Khulna (Mongla Port), Rajshahi, Sylhet, Mymensingh, Bogra and Barisal are important. Most of the urban centers are located on naturally raised land facets. The physical growth of these urban centers is so fast that it has become difficult to maintain a systematic land-use pattern of these clusters. The geological disadvantages or advantages for economic and rational engineering design are overlooked. For this many of the newly grown areas have incurred severe damages due to flood, cyclone and tidal surges, riverbank and coastal erosions, landslides, soil collapse and foundation failures. Due to increased frequency of failures in different projects and structures, the concerned authorities are paying attention to the inherent causes of the failure or taking measures to avoid further disruptions.
After the independence of Bangladesh the development activities started so rapidly that a time lag remained between the planners and developers in interchanging the necessary geo-information and data for rational designing or formulation of the projects. In recent years, the city planners and other national organizations like the city improvement authority, the roads and high ways department and the public works department have extended hand for geological information for proper understanding of geological aspects of their projects. Considering these, the Geological Survey of Bangladesh (GSB) has taken up a National Mapping Programme for preparation of geological maps in the scale of 1: 50,000 and engineering geological maps in the scale of 1: 20,000 of different cities and town of the country. So far the GSB has completed about 35% of country's geological mapping and engineering geological mapping of seven cities and towns, among these the urban geological maps of Dhaka and Chittagong cities are most significant achievements. These maps are yet to be published.
This paper describes the present status, prospects and types of geological or geo-environment data, maps and other information available to planners and developers. The means for optimum utilization of hard achieved geological and geotechnical data for rational utilization in the urban and infrastructure developments are proposed.
There are number of large and small clusters of urban growth throughout the country, among these the capital city of Dhaka, the port cities of Chittagong and Khulna (Mongla Port), Rajshahi, Sylhet, Mymensingh, Bogra and Barisal are important. Most of the urban centers are located on naturally raised land facets. The physical growth of these urban centers is so fast that it has become difficult to maintain a systematic land-use pattern of these clusters. The geological disadvantages or advantages for economic and rational engineering design are overlooked. For this many of the newly grown areas have incurred severe damages due to flood, cyclone and tidal surges, riverbank and coastal erosions, landslides, soil collapse and foundation failures. Due to increased frequency of failures in different projects and structures, the concerned authorities are paying attention to the inherent causes of the failure or taking measures to avoid further disruptions.
After the independence of Bangladesh the development activities started so rapidly that a time lag remained between the planners and developers in interchanging the necessary geo-information and data for rational designing or formulation of the projects. In recent years, the city planners and other national organizations like the city improvement authority, the roads and high ways department and the public works department have extended hand for geological information for proper understanding of geological aspects of their projects. Considering these, the Geological Survey of Bangladesh (GSB) has taken up a National Mapping Programme for preparation of geological maps in the scale of 1: 50,000 and engineering geological maps in the scale of 1: 20,000 of different cities and town of the country. So far the GSB has completed about 35% of country's geological mapping and engineering geological mapping of seven cities and towns, among these the urban geological maps of Dhaka and Chittagong cities are most significant achievements. These maps are yet to be published.
This paper describes the present status, prospects and types of geological or geo-environment data, maps and other information available to planners and developers. The means for optimum utilization of hard achieved geological and geotechnical data for rational utilization in the urban and infrastructure developments are proposed.
Seismic hazard characterization is the foremost module for earthquake risk management in a seismically vulnerable region. The mega city Dhaka in Bangladesh is considered by many researchers as one of the riskiest cities in the world due... more
Seismic hazard characterization is the foremost module for earthquake risk management in a seismically vulnerable region. The mega city Dhaka in Bangladesh is considered by many researchers as one of the riskiest cities in the world due to many non-engineered construction practices and poorly studied tectonic boundary conditions. The city is built on a Plio-Pleistocene terrace, located within the subsiding Bengal basin. The records of historical earthquakes indicate that three large magnitude earthquakes occurred during the last 150 years within and in close proximity to Bangladesh. Magnitudes of these earthquakes ranged from 6.9 to 8.7 occurring between 1885 and 1918. These events caused moderate damage to buildings and other infrastructures in Bangladesh, but the damage in Dhaka city were negligible. It is believed that the 6.9 magnitude Bengal earthquake occurred at about 50 km from the city, although there are multiple controversies about the location of the epicenter. Many consider that the epicenter of this earthquake was 170 km away from Dhaka city and others inferred the epicenter to be somewhere along Madhupur fault, approximately 50 km away. The 1885 Bengal, 1897 Great Indian, and 1918 Srimangal Earthquakes are considered as the seismic sources for site-specific seismic hazard characterization. The peak ground acceleration (PGA), peak ground velocity (PGV), spectral accelerations (SA) of different periods have been calculated at the ground surface based on recently developed ground motion prediction equations and site amplification factors. The amplification factors are predicted from the average shear wave velocity to a depth of 30 m (Vs 30), which are estimated using various geophysical and geotechnical investigations. The study reveals that the city is built on a very firm ground where seismic risks are manageable provided the engineering structures adhere to the norms of seismic regulations and building codes.
Citation
Karim, M. F., Rahman, Z. M., Kamal, M., & Siddiqua, S. (2016, 08). Site-specific earthquake hazard characterization for Dhaka City, Bangladesh. Poster Presentation at 2016 SCEC Annual Meeting.
Citation
Karim, M. F., Rahman, Z. M., Kamal, M., & Siddiqua, S. (2016, 08). Site-specific earthquake hazard characterization for Dhaka City, Bangladesh. Poster Presentation at 2016 SCEC Annual Meeting.