Groundwater level is plunging in Dhaka. Experts call for making rainwater harvesting mandatory
Call it the fallout of rapid urbanisation or plain negligence of the authorities, groundwater in Dhaka is sinking at an alarming rate. According to a study by the Institute of Water Modelling in Dhaka in 2009, groundwater in the city is going down three metres every year. It has sunk by 50 metres in the past four decades and is at over 60 metres below the ground.
Officials at the Dhaka Water Supply and Sewerage Authority said the city faces a demand-supply gap of 500 million litres a day. This means one-third of the city’s population does not get adequate water supply every day. Last summer the government had to deploy troops to manage water distribution in Dhaka.
A group of architects, engineers and urban planners of the city recently held a seminar with participation of government officials. The government must include rainwater harvesting in building bylaws to save Dhaka, the seminar organised by the Institute of Engineers, Bangladesh, and international nonprofit WaterAid concluded.
The present building bylaws of Dhaka, which came into force in 2008, are not enough to ensure natural recharge of groundwater. They suggest 40-50 per cent of building premises should remain unpaved and half the unpaved area should be under green cover to allow natural recharge of aquifers—groundwater meets over 80 per cent of the city’s water supply.
This is not possible, said Mustapha Khalid Palash, an architect who was the main speaker at the seminar. Almost 65 per cent of the city is paved. The remaining area does not ensure natural recharge of aquifers because top soil at most places is clayey. The authorities must take up rainwater harvesting on war footing to ease water crisis in the fast-growing, densely populated city, Palash added.
The situation was not so bad until three decades ago when Bangladesh had just attained independence. With sudden influx of people the capital city began to expand. Low-lying marshland was filled with earth and swallowed by the city. Development took place around the region’s longest water channels, Banani and Gulshan. As the population increased—it has grown 13 times since 1963—developers and the government targeted the channels.
The city authorities converted parts of the Banani-Gulshan wetland into roads and sold the rest to developers and industrialists. Over the years they expanded their territories by filling up the channels. By the time the Wetland Protection Act came into force in 2000, residential buildings, industrial units and numerous slums and squatters had constricted the channels and fragmented them into lakes, said Iqbal Habib, architect and activist of Bangladesh Poribesh Andolon, a green group. The law did not abate encroachment.
In 2006, BELA (Bangladesh Environmental Lawyers Association) filed a petition in the Dhaka High Court to save Gulshan Lake. The court asked the city authorities to prohibit filling the lake. But encroachment continued. In 2009 BELA again approached the court and demanded demarcation of waterbodies. “Despite the court order the authorities have not demarcated the spread of the lakes,” said Syeda Rizwana Hasan, activist and member of BELA.
Demarcation of the lakes would help remove encroachments and revive them, Habib said. The lakes are not only groundwater recharge points, they act as sponge in case of flooding, he added. Removing years of encroachments is not an easy task. Palash said mandating rainwater harvesting would at least help arrest groundwater level, for now.