Assessment of Urban Flood Modelling in Karachi (A Case Study of DHA Karachi Floods 2020)

Abstract

Flood has become an immense phenomenon because of the diversity in the Pakistan ecosystem. Karachi is the financial capital, as well as a gateway for carrying out trade with the international community using the oldest portin the country. Karachi is a strategic city in Pakistan that was once known asa fishing village. The coastal area has almost all the important critical facilities, housing schemes as well as infrastructure present near it. In past, the city was not known for any risk posed by any disaster but inthe past few years, an increase in industrialization and urbanization had been seen in the city, and with a population of about 20 million inhabitants, the city become vulnerable to different hazards because of which various social, economic, and environmental stresses and problems had emerged. Karachi land use, land cover as well as drainage networks have been changed because of Industrialization and urbanization. After rainfall urban flooding has become a continuously occurring phenomenon almost every year as most of the drains and tributaries have been blocked. Flooding in Karachi because of late summer season monsoon rainfall has resulted in an overflow of the rainwater resulting in urban flooding. In Karachi, city flood is a common issue that is constantly causing socio-economic problems as well as a significant loss to humans, their livelihood, their property as well as critical facilities. In Karachi, there are two natural drainage networks containing two river systems namely Malir and Lyari rivers. Lyari passes through the city centerand a major portion of the stormwater is drained by it while Malir is in the eastern part of Karachi city. Poor urban planning and management had severely affected both rivers and linked tributaries. This study discusses that changes in LULC and poorly maintained drainage networks are the factors thatcaused urban flooding in Karachi as well as DHA. This research aims to identify the factor that led to the urban flooding in DHA as well as develop a flood hazard-vulnerability map of Karachi city to identify the flood-prone areas of the city. This study also focuses on the impact of rainfall on the DHA Karachi and what damages are caused to it. GIS has been used for carrying out mapping of Karachi city land use, land cover, drainage patterns as well as DHA surface drainage networks. In this study thematic analysis for DHA and flood vulnerability analysis for Karachihave been done. Methodology greatly includes questionnaires, expert knowledge, and judgment. Thematic analysis was used to identify the factors responsible for causing vulnerabilities and damages in DHA.The Delphimethod is used for flood indicators. GIS has been used for carrying out mapping of Karachi city land use, land cover, drainage patterns, DHA sewerage drainage as well as for carrying out flood hazard-vulnerability assessment. DEM, GIS, SRTM has been used to mark the boundaries of Karachi, DHA, and drainage networks on the digitized map. The data collected from the questionnaires showed that poor drainage network was the main cause of urban flooding in DHA and phase 6 was mostly damaged as a lot of land encroachment has been done in this phase. Streets were mostly damaged as stagnant water caused crackers in them thus causing power outrage and difficulty in evacuation. The flood hazard-vulnerability map generated shows the areas located in Korangi as well as in districtswest, central and east had high to very high flood vulnerability. These are the flood-prone areas that are greatly impacted by urban flooding. These maps could be utilized for improving the natural drainage networks as well as flood mitigation and preparedness measures. This study may provide a guideline to disaster planning, management, and development authorities as well as a baseline for the researchers to carry out their research. Recommendations have been given by analyzing the status of the city to protect and reduce the continuous impacts of flooding in the years to come.

Keywords: Urban flood, Karachi, DHA, Drainage networks, Land use, Land cover, Hazard-vulnerability assessment, GIS.