Gulam Rabbani :
The demand for water is constantly increasing in Dhaka city on account of increased population, industrialization and rapid expansion of the city. Dhaka Water Supply and Sewerage Authority (WASA) and others are relying mainly on underground water to meet the demand. As a result underground water level in the city is falling drastically which is posing serious environmental threats.
Experts say if the groundwater level declination continues at the present rate, this will create pressure on water storage and may invite ecological and environmental hazards in Dhaka City and its surroundings.
Failure to increase the use of surface water sources will increase the risk of natural disasters, including earthquakes in the city, they also warned.
According to the Bangladesh Water Development Board (BWDB) database, the water table of Dhaka city has plunged by 75 meters in the past five decades and more than 60 meters in last three decades. The average groundwater is now at a depth of over 80 meters in many parts of the city.
The average rate of annual decline in different parts of the city is 0.17 to 0.6 m from 1970 to 1980, 0.15 to 0.69 m from 1980 to 1990, 0.56 to 2.26 m from 1990 to 2000 and 1.24 to 3.0 m since 2000, according to the database.
If water extraction continues like the current ratio, the depth of underground water may go down to 120 meters by 2050, said study of the BWDB.
Apart from Dhaka WASA, thousands of industries and households are extracting underground water through deep tube wells to make up their demand. Most of the tube wells set up by industry owners and household owners are illegal, and there is no authority to see and monitor them.
Although the Dhaka WASA claims that about 65 percent of the water currently supplied by WASA comes from underground sources, the real picture is different. WASA documents say that about 75 percents of the water are still being extracted from the ground.
A decade ago, about 80 percent of the water produced by Dhaka WASA was from underground sources and 20 percent was surface water. In 2010, Managing Director of Dhaka WASA Taqsem A Khan announced a plan to increase surface water production to at least 70 percent. The organization had set a deadline of 2021 to achieve this goal, but they have failed.
Dhaka WASA had more than 650 deep tube wells in 2013. Since then new tube wells have been installed every year. Besides, the number of privately owned deep tube wells has also increased. At present, WASA lifts water through 923 deep tube wells installed in different parts of the city.
Dhaka WASA prepared “water supply master plan for Dhaka city’ where of the organization said, ‘Such unusual obstractions may endanger the aquifer environment and also create a threat to sustainability of the city. The level of the water table is reported to be sharply depleting, resulting in declining yield from existing tube wells. Due to mining, the groundwater level is falling by about 2-3 meters per year. The groundwater is estimated to be 80 meters below the surface compared 10m in 1970 in the upper aquifer.”
Abu Naser Khan, Chairman of Poribesh Bachao Andolon (Poba), an environmentalist organization, said, “Groundwater levels are not easily replenished. As a result, these are falling down gradually. About 80% of the water used in our country, especially in Dhaka city, are ground water. Because of this arbitrary use of underground water, we will not get extractable water in the near future, or we will have to extract it at a high price. This will increase the cost of living.”
Poba Chairman also said, “Apart from this, our multi-storey buildings those we are randomly establishing in the city may face caving if the ground water vacuum increases. And small earthquakes can cause big disasters in the city. Nearby canals, beels and rivers may become dehydrated due to this which is also threatening biodiversity. Industrial production may be disrupted.”
Dr Anwar Zahid, Director of the Groundwater Hydrology department of the BWDB, said, “Rain water harvesting during rainy-season and use for household purposes can reduce the pressure on groundwater system. Installation of area wise surface water treatment plants, reuse of treated storm and sewage water mainly for washing, gardening, toilet flushing, artificial recharge by injecting treated river water and rain water and digging of recharge basins could improve the groundwater table condition.”
Proper implementation of existing laws, regulations and motivation is required to reduce system loss and misuse of supplied groundwater as well as to safeguard environment and ecology, added the official.
