Chittagong is Bangladesh’s second largest and busiest maritime port city. It is situated on the bank of the river Karnaphuly in the south-east part of the country (Saha, 2020). In order to remove excess water volume, drainage is a necessary component of many environments, including urban, rural, forest and agricultural (Parkinson, 2003). According to CDA Existing Plan-1995, there are twelve drainage areas in Chattogram city that discharges the water from the city to the river, Karnaphuly. There are also three types of drainage system that exists in the Chattogram city as, primary drainage system or Primary Khals, secondary drainage system and Tertiary Drainage system (CDA, 1995). The drainage congestion is the most susceptible aspect of Chattogram’ s drainage system. Every year during the rainy season, the roadways and low-lying regions in Chattogram City are submerged, causing water logging and urban flood which make life difficult for the residents. Urban flooding and water logging thus emerged as one of the port city's main issues. Water logging occurs frequently in the city's low-lying sections after normal rainfall. The inhabitants of Chittagong's low-lying neighborhoods suffer as a result (Kamal, 2003). Urban drainage includes the extraction of unanticipated water from urban environments, such as storm water, sewerage, and gray and household wastewater (McInerney & Magar, 2014) On the other hand, road drainage, which is intended to divert water into ditches beside roadways, accounts for the majority of drainage systems in urban regions. These drainage systems are prone to erosion, which can lead to issues with sedimentation in adjacent bodies of water (Pidwirny, 2006). Water Pollution is one of the most significant phenomena to concern about in present world. According to a recent study, the intensity of the city's rainfall has also grown. For example, 1.5 hours of intense rainy weather can produce 4 million cubic meters of runoff, which the city's poor drainage system is sadly not equipped to handle (Hoque, Nandi, & Palit, 2012). Drainage congestion is a matter to concern about as water pollution is much more related to this. Drainage congestion causes the overflow of water which later gets connected with the other water bodies by the urban flood (Kamal, 2003). Bangladesh, one of the most populous countries in the third world, is suffering from severe water pollution and scarcity, just like the rest of the world. Even though 97% of people have access to water, there is always doubt about the quality of the water (WHO, Sustainable Development & Healthy Environment, 2018). A drinking water's microbiological and several crucial physiochemical tests, like pH, BOD, COD, Color, temperature, TDS, and metal concentration, can determine the water's quality. Because of the implications for public health, the detection of bacterial contamination and its physicochemical characteristics has garnered significant attention globally (WHO, Guidelines for drinking water quality, 1993). Over 28 billion disease episodes occur each year in poor nations due to ten primary water-borne diseases; in these countries, diarrheal diseases are the leading cause of death, particularly in newborns, and they are also highly endemic (Classen, Schmidt, Rabie, Roberts, & Cairncross, 2007). One of Bangladesh's main cities in development is Chittagong. Beyond the fact that Chittagong City Corporation provides them with a portion of purified water, the majority of people use groundwater as their primary source for residential requirements. Merely 1% of the land can be used for transportation, garbage disposal, agricultural, drinking, and industrial consumption (Ahmed, et al., 2013; Rahman, 2002). This research aims to determine the drainage congestion as the causal factor of urban flood and urban flood is the cause of water pollution. This research also aims to assess the impacts of water pollution on the urban neighborhood of the port city, Chattogram.

The port city of Bangladesh is well known for its thriving ecosystem, dynamic culture and creative economy. But its water bodies are seriously threatened by the industrialization and urbanization that is happening too quickly. At present there are some challenges that need to be identified to mitigate the problem like drainage water logging, sewage problem, solid waste, industrial discharge, climate change effect, heavy rainfall etc. the problem must be mitigated soon. To mitigate the problem there need some conservation initiative. They are: legal protection of the water bodies, stop plastic throwing in the drains, industrial regulations, water bodies culture, proper education to the residents of the city, community engagement and collaborative approaches are mostly needed. To consume the impacts of water pollution industrial effluent control, public awareness, regulation and enforcement of environmental law, collaborative approach, community participation, investment in more research is crying need for the port city Chattogram, Bangladesh. To effectively solve Chattogram city’s water pollution, implementing the mentioned things would involve coordinated efforts from a variety of stakeholders, including government agencies, non-government agencies, business and the general public.

Water pollution is the most vital issue in the aspect of Chattogram city. Drainage congestion is one of the causes of water pollution as the drainage congestion make the overflow of water. The overflow of water makes urban flood which carries number pollutants from the drainage water to the other water bodies lies in the study area. The water samples of the drainage water highlights that the water are much more polluted than it should be. Drainage water must be polluted, but if there was normal flow of water, the pollutants would be less in amount. Congested drains create more pollutants as it helps the pollutants to get together. It also helps to grow the mosquito germs which make the vector borne diseases in the study area. Statistical analysis also found the significant correlation between drainage congestion and water pollution. However, water pollution came up with some impacts on the study area. It creates diseases in human body. It also impacts on the urban natural and social environment and urban neighborhood of the study area. It’s time people should understand the fact and to be aware about the water pollution.