Wasa wary of groundwater depletion, want provision of harvesting rainwater in building code, plans to recharge natural water reservoir below the surface
Dhaka Wasa is considering a plan to recharge the underground aquifers with rain water in eight areas across the capital this year to top up the rapidly depleting groundwater table.
As the city’s water table is falling by 2.5 to 3.5 metres per year due to excessive extraction of groundwater by deep tube wells, the government agency is also mulling
over making water recharging facilities mandatory in the proposed national building code, said Wasa sources.
The Ministry of Housing and Public Works has prepared a draft of the building code with this provision. The building construction guideline of Rajdhani Unnayan
Kartripakkha (Rajuk) also has the same requirement.
Both the building code and construction guideline are now awaiting approval from the ministry.
Dhaka Water Supply and Sewerage Authority (Wasa) has made the move after delivering two successful water recharging pilot projects in the city’s Segunbagicha and
Lalmatia last year.
It now aims to implement a third project to build eight recharge pits and injection wells in Uttara, Mirpur, Banani, Gulshan, Khilgaon, Motijheel, Mohammadpur and
Gandaria during this rainy season.
Institute of Water Modelling (IWM), a government trust, will do the job for Dhaka Wasa. They will operate the pits and wells for a year before handing over the
operation to Wasa.
The project includes developing zone-wise prototype design of artificial recharge system and preparing aquifer map and groundwater zoning map of Dhaka city.
With a total of 10 recharging pits, Wasa expects to pump 50 lakh litre of water into the underground aquifers annually.
The authorities, though, need 1642.5 crore litres of water a year to recharge the underground aquifers in the capital.
Experts said building just a few structures for the purpose of recharge in a city of around 1.2 million people is quite inadequate.
“To make the water table of Dhaka city stable, we need to pump 45 crore litres of water into the aquifers daily. This is very much possible,” said Mizanur Rahman,
senior groundwater specialist at IWM.
Artificial recharge by harvesting rainwater from concrete rooftops of 60 percent buildings in the capital may replenish 25 crore litres of water per day, he mentioned
adding, the deficit can be covered by reducing the extraction of groundwater.
“We have checked the quality and quantity of the city’s rainwater under the first pilot project delivered last year with the help of Bangladesh University of
Engineering and Technology and found the water recharging suitable,” said Mizanur.
Contacted, Wasa Managing Director Taqsem A Khan said they will go for a massive recharging programme using the most cost effective way possible.
Furthermore, Wasa will halve its dependency on groundwater by the next 10 years by introducing three new water treatment plants in Khilkhet, Pagla and Sayedabad, he
added.
These units will produce around 117 crore litres of water per day by treating water of rivers.
Although four rivers flow around the capital, the city has been using groundwater for a long time.
According to the statistics of Bangladesh Water Development Board, groundwater level in Mirpur dropped 53.75 metres between 1991 and 2008, while the decline was 18.59
metres in Mohammadpur, 37.4 metres in Sabujbagh, 8.22 metres in Sutrapur, and 14.14 metres in Dhaka Cantonment during the same period.
Dhaka Wasa’s daily production now stands around 210 crore litres against the requirement of 230 crore litres. It produces around 88 percent water from 613 deep tube
wells, while the rest from four water treatment plants.
Besides, there are 1,500 legal and 2,000 illegal private deep tube wells in the city.
The Rajuk has prepared “Imarat Nirman Bidhimala-2012”, the new guideline, making rainwater harvesting compulsory for private and public building owners, said Sheikh
Abdul Mannan, member (planning) of Rajuk.
The guideline stipulates any building with a minimum rooftop area of 300 square metres must have provision for harvesting rain water.
-With The Daily Star input
