Development of Open Space Management System to Response Scenario Earthquake in Dhaka Metropolitan Area

Abstract

The urbanized areas of Bangladesh are subjected to potential earthquake hazards and risks due to the proximity of seismically active zones. Dhaka Metropolitan Area, the capital of Bangladesh, is ill-planned and highly urbanized with a large population. The inhabitants of the city contribute thirty-six percent of the national GDP. These factors make the city highly vulnerable to earthquakes. The seismic hazard assessment carried out by the Comprehensive Disaster Management Program (CDMP) showed significant risks, yet preparedness measures for the city are lacking. Open spaces are essential in earthquakes as they can provide various options, from immediate evacuation to long-term sheltering of the resulting homeless population. Cases worldwide have benefitted from utilizing open spaces, and even the contingency plans suggest its use. Nonetheless, no comprehensive research or data is available regarding the open spaces. This study addressed that gap in the immediate response to urban mega-disaster. The present study aimed to develop an open space management system for responding to a scenario earthquake in Dhaka. The first step was to assess the suitability of existing open spaces in the Dhaka Metropolitan Area to serve as emergency shelters using the modified Comprehensive Open Space Suitability Index (COSI). For that, the available open space footprints were mapped using satellite imagery. Then, these open spaces were ranked according to their area, connectivity, accessibility, hazard exposure, and nearness to facilities. Among the one thousand one hundred and ninety-seven identified open spaces, two hundred and seventeen were found to be suitable. At the same time, hundred and fifty-one were moderately suitable, and the rest were deemed less suitable (not to be interpreted as unusable).

Out of the two hundred and seventeen suitable sites, fourteen sites had to be left out of consideration since they are within the Key Point Installation premises and include National Parliament, Airport, Prime Minister’s Office, various country’s High Commissions/Embassies, and High Court. After that, generalized liquefaction analysis based on geomorphological classes revealed that thirty-seven sites had to be excluded as they exhibited high to very high liquefaction potential. It means only one hundred and sixty-six open spaces were selected as safe sites for long-term shelter establishment. Given that liquefaction may render potential sites unusable due to earthquakes, much importance was emphasized on its effect in the study area. Furthermore, eight sites across the city were selected as a case study for detailed liquefaction potential investigations. Probabilistic seismic hazard assessment and site response analysis were conducted, and all eight sites showed less than 0.15g Peak Ground Acceleration (PGA) value for a ten percent probability of exceedance in fifty years. The results were used to calculate liquefaction potential through deterministic, probabilistic, and artificial neural network approaches. All results stated that the eight sites were safe for post-earthquake shelter placement. The deterministic approach was basically used for safety-based analysis. In contrast, the probabilistic approach is the likelihood of liquefaction, meaning it is probability-based. Still, the artificial neural network approach is more robust than the three approaches and gives realistic results by establishing precise nonlinear relationships. All eight sites revealed a very low (less than five) liquefaction potential index value in an earthquake of 7.5 magnitude scenario with PGA 0.15g. This was followed by establishing standard requirements of the shelters that would be placed in the open spaces, including living space per person (2.3 m2 per person, considering population density), appropriate shelter materials (waterproof, lightweight and strong), essential water, sanitation and hygiene services (accounting for gender sensitivity), health and nutrition Out of the two hundred and seventeen suitable sites, fourteen sites had to be left out of consideration since they are within the Key Point Installation premises and include National Parliament, Airport, Prime Minister’s Office, various country’s High Commissions/Embassies, and High Court. After that, generalized liquefaction analysis based on geomorphological classes revealed that thirty-seven sites had to be excluded as they exhibited high to very high liquefaction potential. It means only one hundred and sixty-six open spaces were selected as safe sites for long-term shelter establishment. Given that liquefaction may render potential sites unusable due to earthquakes, much importance was emphasized on its effect in the study area. Furthermore, eight sites across the city were selected as a case study for detailed liquefaction potential investigations. Probabilistic seismic hazard assessment and site response analysis were conducted, and all eight sites showed less than 0.15g Peak Ground Acceleration (PGA) value for a ten percent probability of exceedance in fifty years. The results were used to calculate liquefaction potential through deterministic, probabilistic, and artificial neural network approaches. All results stated that the eight sites were safe for post-earthquake shelter placement. The deterministic approach was basically used for safety-based analysis. In contrast, the probabilistic approach is the likelihood of liquefaction, meaning it is probability-based. Still, the artificial neural network approach is more robust than the three approaches and gives realistic results by establishing precise nonlinear relationships. All eight sites revealed a very low (less than five) liquefaction potential index value in an earthquake of 7.5 magnitude scenario with PGA 0.15g. This was followed by establishing standard requirements of the shelters that would be placed in the open spaces, including living space per person (2.3 m2 per person, considering population density), appropriate shelter materials (waterproof, lightweight and strong), essential water, sanitation and hygiene services (accounting for gender sensitivity), health and nutrition items, emergency infrastructures and service facilities, security and cultural considerations, and operation and maintenance of the shelters. The parameters were standardized based on literature review and expert opinions, thus ensuring an ideal model appropriated in the context of the Dhaka Metropolitan Area. Finally, a field demonstration was conducted on the Bangladesh University of Professionals Playground to validate the established model shelter standards. This study gives the main guidelines for identifying and establishing a network of open spaces according to suitability, ensuring the sites are safe and what standards the shelters must maintain to be effective in the post-earthquake scenario. Implementing that will be a significant step towards building an earthquake-resilient Dhaka Metropolitan Area from the viewpoints of response and recovery.