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Using the stagnant water

S.K Lala
THE day is July 28, Dhaka city stands half paralysed because of stagnancy of water due to the exceptionally heavy rainfall the night before. With global climate change such a situation is likely to recur, but our drainage system does not have the capacity to cope with it. To design and develop an effective drainage system will not only be a time consuming exercise but will also, apart from being very costly, be almost impossible as unplanned construction is widespread and could be a orohibitine factor.
Such being the scenario on one side, on the other we must not forget the continuous depletion of our groundwater reserves. I do not have the facts and figures but surely the water and sewerage authority is fully aware of the rate of drop in underground water level every year. The continuous extraction of underground water is surely causing changes to the subsoil strata, which may become a cause of catastrophe sometimes in future unless the same is continuously studied and monitored by experts in the field and protective measures are thought of right now.
What I oresent here can be a likelv
solution to both of the above problems. It is a simple one, and can be adopted almost immediately without making any major changes in the city structure
as it exists now. What I propose is putting the surface runoff back into the ground through tubewells, which will not extract water but function as an
injector.
The city may be divided into recharge zones. In each of these zones the lowest spot can be identified and earmarked, and a filtration bed can be constructed on that. The surface runoff will come down to these filtration beds, in each of which there will be a tubewell that will function as a "soakwell."
The depth of the tubewells and the position of the strainers (these strainers shall have wider slots than conventional ones to allow quicker ingress of waler into the ground) at predetermined layers of sand in the underground strata must definitely be higher than the layers from which Wasa is now pumping out water for our daily use. Mother earth will surely take care of the rest. This is an idea that may be explored further by experts in the field.
Further, it has been observed that in areas where large water bodies exist, such as Gulshan and Dhanmondi.
drainage has not been a serious problem as surface runoff water flowed into the same. But these lakes are now full and hardly can contain any more water. If there is heavy rain within a short time, these areas will also become water logged. Recharge tubewells can also provide a solution to this problem.
In each of these lakes, a couple of recharge tubewells can be installed, with strainers above the highest level of water in the lake to allow in-flow into the well. Strainers will also be fitted at the bottom of these tubewell at predetermined sand strata. No filtration bed will be necessary, lakes will not overflow, and ground water will get recharged. Some sculptures can be placed on top of these tubewells and there can be some paintings on the body of the lube that gets exposed when water level falls, which will be an added aesthetic attraction.
S K. Lala is a Civil Enaineer