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Sink-based solutions can ease Chattogram's waterlogging
Sustainable solutions is needed for Chattogram's waterlogging problem.
Sink-based solutions can ease Chattogram's waterlogging
Between 1989 and 2011, approximately 15 percent of the exposed land in the Sholakbahar ward of the city was converted into various types of built-up areas, increasing the risk of waterlogging. FILE PHOTO: PALASH KHAN
Waterlogging in our port city in recent years has caused enormous suffering and economic loss. The government of Bangladesh has recently initiated efforts to find sustainable solutions to this problem. This hydro-climatic disaster occurs when the amount of source water exceeds what the sinks can accommodate. A better understanding of the sources and sinks of water will foster sustainable solutions to this issue.
Waterlogging primarily occurs during the monsoon season, characterised by heavy rainfall. A practical solution entails—(i) identifying the sinks and (ii) enhancing their capacity to ensure that the volume of water from the source does not surpass it. Furthermore, we must tackle the factors that diminish the capacity of sinks, such as landfilling, the removal of hills, and eutrophication, among others.
Inland water bodies
The most easily accessible water sink is the inland water bodies, which include ponds, lakes, canals, and drainage networks. To get a rapid solution to waterlogging, we must increase the water-retention capacity of these inland water bodies. Dredging is a proven method to enhance the volume of water that reservoirs can hold. Additionally, dredging boosts interactions between lake water and groundwater. However, it is vital to manage the dredged materials properly, as mismanagement can cause them to return to the water bodies shortly thereafter.
During heavy rainfall on certain days in the rainy season, a significant volume of water rapidly accumulates on the surface. This extra water necessitates enhanced drainage systems to keep the city free from flooding. Expanding and deepening the canals could increase their capacity to handle excess water. Furthermore, we could construct new lakes and drainage systems within the city, particularly in the areas most affected; this approach could significantly enhance the water retention capacity.
Alongside enhancing the capacity of the sinks, it is equally crucial to mitigate factors that restrict the volume of sinks—(i) landfilling in any form must cease immediately; (ii) hill-cutting should be halted as it generates a large volume of clastic sediment, much of it ends up at the bottom of inland water bodies; (iii) strict solid waste management must be enforced to prevent any forms of solid waste, such as non-degradable plastics and household materials, from entering the drainage system as solid waste can restrict flow velocity and reduce the water retention capacity of reservoirs; and (iv) chemical and bio-waste from domestic and industrial sources should be segregated and disposed of separately since inland water bodies gradually lose volume due to harmful algal blooms and eutrophication, exacerbated by increased nutrient levels from such waste.
The groundwater sink
Groundwater is a crucial destination for rainwater through the process of infiltration. Unfortunately, this aspect is often overlooked when planning to eliminate waterlogging. The reduction of open land restricts the infiltration process. Consequently, a substantial volume of water overflows that should ideally transfer into the groundwater; an increase in surface water heightens the likelihood of waterlogging. A research paper published by the Department of Geography and Environmental Studies at the University of Chittagong finds that between 1989 and 2011, approximately 15 percent of the exposed land in the Sholakbahar ward of the city was converted into various types of built-up areas. The situation is presumably similar in other wards of the city corporation. Reducing such a significant amount of open space presents a serious risk of waterlogging.
Increasing the amount of open space is a potential measure to ensure accelerated infiltration. Additionally, we could construct tiny artificial ponds throughout the city, designed with coarser rocks at the bottom, as fine-grained particles limit infiltration. The ponds need not be large; they could be situated along the streets in a manner that also contributes to the city's beautification. Furthermore, we can plan to establish recharge wells and soak pits to enhance infiltration into the groundwater.
Impermeable streets also impede groundwater recharge. Permeable city roads can be constructed to facilitate the percolation of more water from the lane into the ground.
By implementing the aforementioned sink-based solutions, the city's waterlogging problems can be eased. In addition to tackling waterlogging, these measures will enhance functional hydrology and foster a clean aquatic environment that aligns with biodiversity.
Mohib Billah is doctoral researcher in the Department of Geography and Geology at the University of Turku in Finland.
Between 1989 and 2011, approximately 15 percent of the exposed land in the Sholakbahar ward of the city was converted into various types of built-up areas, increasing the risk of waterlogging. FILE PHOTO: PALASH KHAN
Waterlogging in our port city in recent years has caused enormous suffering and economic loss. The government of Bangladesh has recently initiated efforts to find sustainable solutions to this problem. This hydro-climatic disaster occurs when the amount of source water exceeds what the sinks can accommodate. A better understanding of the sources and sinks of water will foster sustainable solutions to this issue.
Waterlogging primarily occurs during the monsoon season, characterised by heavy rainfall. A practical solution entails—(i) identifying the sinks and (ii) enhancing their capacity to ensure that the volume of water from the source does not surpass it. Furthermore, we must tackle the factors that diminish the capacity of sinks, such as landfilling, the removal of hills, and eutrophication, among others.
Inland water bodies
The most easily accessible water sink is the inland water bodies, which include ponds, lakes, canals, and drainage networks. To get a rapid solution to waterlogging, we must increase the water-retention capacity of these inland water bodies. Dredging is a proven method to enhance the volume of water that reservoirs can hold. Additionally, dredging boosts interactions between lake water and groundwater. However, it is vital to manage the dredged materials properly, as mismanagement can cause them to return to the water bodies shortly thereafter.
During heavy rainfall on certain days in the rainy season, a significant volume of water rapidly accumulates on the surface. This extra water necessitates enhanced drainage systems to keep the city free from flooding. Expanding and deepening the canals could increase their capacity to handle excess water. Furthermore, we could construct new lakes and drainage systems within the city, particularly in the areas most affected; this approach could significantly enhance the water retention capacity.
Alongside enhancing the capacity of the sinks, it is equally crucial to mitigate factors that restrict the volume of sinks—(i) landfilling in any form must cease immediately; (ii) hill-cutting should be halted as it generates a large volume of clastic sediment, much of it ends up at the bottom of inland water bodies; (iii) strict solid waste management must be enforced to prevent any forms of solid waste, such as non-degradable plastics and household materials, from entering the drainage system as solid waste can restrict flow velocity and reduce the water retention capacity of reservoirs; and (iv) chemical and bio-waste from domestic and industrial sources should be segregated and disposed of separately since inland water bodies gradually lose volume due to harmful algal blooms and eutrophication, exacerbated by increased nutrient levels from such waste.
The groundwater sink
Groundwater is a crucial destination for rainwater through the process of infiltration. Unfortunately, this aspect is often overlooked when planning to eliminate waterlogging. The reduction of open land restricts the infiltration process. Consequently, a substantial volume of water overflows that should ideally transfer into the groundwater; an increase in surface water heightens the likelihood of waterlogging. A research paper published by the Department of Geography and Environmental Studies at the University of Chittagong finds that between 1989 and 2011, approximately 15 percent of the exposed land in the Sholakbahar ward of the city was converted into various types of built-up areas. The situation is presumably similar in other wards of the city corporation. Reducing such a significant amount of open space presents a serious risk of waterlogging.
Increasing the amount of open space is a potential measure to ensure accelerated infiltration. Additionally, we could construct tiny artificial ponds throughout the city, designed with coarser rocks at the bottom, as fine-grained particles limit infiltration. The ponds need not be large; they could be situated along the streets in a manner that also contributes to the city's beautification. Furthermore, we can plan to establish recharge wells and soak pits to enhance infiltration into the groundwater.
Impermeable streets also impede groundwater recharge. Permeable city roads can be constructed to facilitate the percolation of more water from the lane into the ground.
By implementing the aforementioned sink-based solutions, the city's waterlogging problems can be eased. In addition to tackling waterlogging, these measures will enhance functional hydrology and foster a clean aquatic environment that aligns with biodiversity.
Mohib Billah is doctoral researcher in the Department of Geography and Geology at the University of Turku in Finland.
