Groundwater depletion

Photo: A.M.Ahad / Driknews

About 65% of the surface of Metro Dhaka was water bodies (Ponds, small lakes, steams etc.) about 20 years ago. The soil profile of Dhaka and its surrounding areas is clay with silt with some silt-loam composition. Water percolates very slowly through these soils from the water bodies to recharge the ground water table. During the rainy season the water bodies around Dhaka were filled up and a significant quantity of surface water would also runoff into the streams and rivers. Water from the filled up water bodies used to slowly percolate over time and recharge the groundwater, thus elevating the water table to a constant level every year until lately with introduction of massive land filling projects to build houses for an ever growing Dhaka population. A significant portion of those water bodies was filled and so most of the rainwater escapes Dhaka through surface runoff, creating artificial flooding in many areas. Because of land filling surface water does not percolate and recharge the groundwater table. It is estimated that we are losing 1-2 inches of water table every year. With more and more land filling and concretisation of Metro Dhaka, this rate of groundwater depletion would be worse.
Our surface water has already been poisoned and would not be fit for human consumption. We don't have the sophisticated water purification system to get rid of some of the nasty chemicals in our surface water. We have to devise a way of recharging our groundwater from natural precipitation during the rainy season. If we don't plan now, we will face a major disaster down the years.
One possible suggestion to accelerate groundwater recharging would be to dig thousands of 20x20 feet deep pits all around metro Dhaka and fill them with sands. During the rainy season water would percolate faster through these sand pits and recharge our precious groundwater.