Restoration of the Waterlogging Problem in the Greater Metropolitan Areas of Bangladesh

Abstract:

Prolonged waterlogging during the summer monsoon in various parts of Dhaka, Chittagong, and other metropolises in Bangladesh has become a long-standing problem. Long-term waterlogging in urban areas has led to extreme traffic jams, as well as stagnation in family and business activities, which has an adverse impact on daily life and the economy. So far, no effective research has been done to solve this problem in Bangladesh. Large-scale groundwater abstraction in Dhaka has led lowering of the groundwater table (> 70 m), while a lack of green space has greatly hindered aquifer recharge. The drawdown has led to land subsidence on the order of 11-12 mm/yr exacerbating the waterlogging.

The main objective of this study is to investigate the infiltration of water into the Dupi Tila aquifer beneath the 6-7 m thick Modhupur clay to address the problem of waterlogging and simultaneously reduce the depletion of the groundwater table. As an effective solution to this problem, the construction of wells down to the aquifer top will enable the rapid infiltration of water into the depleted aquifer. The wells will be connected to trenches to expedite the water flow into the wells. Trenches and wells will be filled with coarse aggregates to act as a natural filter. Flow from the bottom of the wells through the sandy aquifer to the lowered water table will further filter the recharge water. As part of the work, a stratigraphic model has been created based on existing subsurface lithological data of Dhaka city. Scale model experiments have verified the rapid discharge of trapped water @ 1L per 30 sec and decreased to 17 minutes to drain 10L water as the aquifer approaches to saturation. We will validate our model experiment in the waterlogged area of the Dhaka University campus.

Restoration from the waterlogging problem will help to improve socio-economic and environmental conditions. The life span of urban infrastructures will be increased and traffic congestion during the rainy season will be mitigated. Waterlogging mitigation will also help to protect society from environmental diseases, such as dengue, that are endemic in the summer. Furthermore, it will reduce the depletion of the groundwater table and mitigate the subsurface aquifer damage. This technique is suitable for implementing in many waterlogging megacities with reasonable costs.