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Plan to set rainwater treatment plants with Tk 2 crore |
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September 19, 2000
Dhaka (UNB) – Local experts at a seminar yesterday rejected any chance of land subsidence in the capital in the near future for pumping out underground water and claimed “the capital is not going to sink.” But, they warned of significant land settlement for large drawdown due to installation of additional tube wells to meet the future water demand. They feared that many pumping wells would go inoperative with the present rate of drawing water. They also reported contamination of water with lead and cadmium in some parts of the city, linking the reason directly with drawdown. Dhaka Water and Sewerage Supply Authority (DWASSA) organised the seminar on “Updating the Existing Groundwater and Land Subsistence Model Project,” at WASA Bhaban in the afternoon. WASA managing director Engr Khondakar Azharul Huq moderated the seminar, where a study report was presented. A group of experts from Bangladesh University of Engineering and Technology (BUET) conducted the study to modify the existing groundwater and land subsidence model of Dhaka WASA, developed in 1990. “We must move away from the present trend of withdrawal of groundwater...we’ve to plan very carefully,” Engr Huq told the seminar. He said Dhaka WASA is developing a conjunctive approach to utilise groundwater, rainwater and surface water. As part of the programme, Dhaka WASA is implementing the Chandnighat water treatment plant to purify river water. Besides, the WASA is running a pilot project at the rooftop of WASA Bhaban to make rainwater usable. After the success of the project, Dhaka WASA is also planning its second rainwater plant at Gonobhaban, said the WASA managing director. He said the organisation has also a plan to set up rainwater treatment plants on rooftops at 100 government buildings in the city at a cost of Tk 2 crore. Rainwater will be cheapest to purify. Moreover, such plant has some advantages, including reduction of pressure on the groundwater during rainy season and recharge of groundwater with rainwater in excess of plant capacity. The city roads will not be inundated if we can set up plants on rooftops of 50 per cent government buildings, Engr Huq said. About water contamination with lead and cadmium, he said: “We are already concerned about it.” WASA-Land Subsidence, 2-Last (Dhaka) As per the study, deepest level water table was found in Motijheel, Tejgaon and Khilgaon areas at the monitoring wells established recently under the study. The deepest level was found during June 2000 at 40 meter below the measuring level, which was at 22 meter below the ground level in 1990. The annual abstraction of WASA has increased from 177 million cubic metre (MCM) in 1990 to 346 MCM in 1999. The number of private wells has increased significantly in Narayanganj. The number of private wells was 130 in 1990 and increased to 289 in 1999. The study predicted that in 2010 the water level in central part of Dhaka (Motijheel, Tejgaon and Khilgaon) would go at a level of 36 metre, if withdrawal continues at the present rate. With the withdrawal rate increased by the present trend, the drawdown in 2010 will reach 56 metre and it will increase to 65 metre if 450 tube wells remain in operation from current year to 2010. If the situation prevails, many of the existing WASA tube wells would have to be abandoned in phases, said the study. The survey (topographic survey) indicated that the maximum subsidence of 2.73 cm in Dhaka city has occurred near the New Airport during the period between 1990 and 1999. “This can be considered negligible,” it said. The study recommended Dhaka WASA to establish a groundwater or water management cell to coordinate the water resources management. The WASA should actively consider extending the present groundwater and subsidence model to incorporate the modeling of contaminant transport in groundwater. So, to make the existing model as a complete planning tool for WASA, contaminant transport modules should be incorporated with the present modules. Some additional monitoring wells should be installed to record contamination level with time at both lower and upper aquifers and aquitards. The report said WASA water has deteriorated in quality and suggested expansion and strengthening of quality monitoring programme for hazardous pollutants to include more tube wells and to be conducted at monthly interval for the safety of the people. The existing model incorporating the contaminant transport module should be used for planning tube well installation whenever required in the future, the study recommended. |