Hydrological processes of adsorption,sedimentation, and infiltration into the lake bed during the 2004 urban flood in Dhaka city,Bangladesh |
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| Authors: | Kenji Okubo M Shah Alam Khan M Qumrul Hassan |
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| Institution: | (1) Graduate School of Environmental Science, Okayama University, Okayama 700-8530, Japan;(2) Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, Dhaka, 1000, Bangladesh;(3) Department of Geology, University of Dhaka, Dhaka, 1000, Bangladesh |
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| Abstract: | The urban flood of Dhaka city in September 2004 is a result of heavy rainfall (341 mm a day or more than 600 mm in 5 days).
In addition to the local rainfall, elevated water levels in the surrounding rivers may have affected the flood duration by
bank filtration. Two lakes, Banani and Gulshan, in the mid of the city are the part of general storm water retention system
in Dhaka. Flood water runs through the lakes acting as channels to the pumping station downstream. A tank model is used in
this study to describe the total drainage process with the hydraulic geometry and resistance laws to derive cross-sections
and friction factors of the quasi-uniform flows. Assuming the dissolved matters of the flood water was of similar composition
as in the lake sediments, the process was a combination of adsorption and sedimentation. Lake sediment samples collected in
March 2004 show an anomaly of chromium which may reflect the previous 1998 flood, and there may be a diffusive leakage from
the source area to the adjacent zones. Further evidence of infiltration process is seen in records of diurnal thermal stratification
of Lake Banani. It responds to only heavy rainfalls over 100 mm/day, and the fact means that infiltration to the groundwater
is rather intermittent. |
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