Aug 15, 2010

Water Resources Condition in Dhaka

Dhaka Water Supply and Sewerage Authority (DWASA) is entrusted with supply of piped water to Dhaka Metropolitan City and its adjacent area (Map). At present 75% city area is under DWASA water supply coverage, out of which 87% is from groundwater sources, the remaining 13% of the water is supplied from the surface water treatment plants. The population of Dhaka is presently around 12 million and the growth trend indicates that by the year 2025 it would be about 24 million and this will increase water demand area manifold.

In order to address the situation DWASA engaged Institute of Water Modelling (IWM) to conduct a study from November 2004 for two years period. This study, in essence, was formulated by DWASA aiming at developing a comprehensive water abstraction strategy for Dhaka city for the next 25 years. Major components of this study were:
  1. Assessment of available surface water and groundwater resources including defining of aquifer layers in Dhaka City areas. 
  2. Development of a comprehensive water abstraction strategy, a demand management plan and a monitoring system including a pre-feasibility study. 
  3. Groundwater resource assessment of Singair Upazilla of Manikganj district including establishment of a groundwater monitoring system.

The above noted study results reveal that continuous abstraction of huge water volume and in response inadequate and less groundwater recharge in the upper aquifer in most part of the city area is resulting in groundwater mining situation. It has been found that the groundwater table is declining at a rate of 2-3m per year on average (Figure 1). The present rate of depletion is alarming and may cause devastating environmental degradation. Due to increase in demand, it is envisaged that more wells would be installed by DWASA and other organisations including private users. This would further decline the piezometric level in both Upper and Lower Dupitila aquifer.
Forecasts of Water Demand by Population (Source: IWM, 2006)

In addition to declining groundwater table the specific drawdown during continuous pumping by Deep Tube Wells (DTW) installed earlier in the Upper Dupitila aquifer is increasing and as a result number of under-performing & failed DTW is increasing day by day. Study results also reveal that if similar groundwater depleting trend prevail and wells discharge declining from design capacity, in total 166 and 223 production wells will be under threat of defunct up to the year 2010 and 2013 respectively due to non- availability of sufficient water column in the UWC for pumping.

It may mention here that using the population of 2005, a baseline study carried out under DWASA-IWM Resource Assessment project (2006) forecasts the demand for water up to 2030 for 25 years. The results are shown in Table and in Figure 2. Baseline results show that with the current population of 8.31 million in Dhaka WASA area, the total demand is 1606 MLD and it will rise up to 4073 MLD by the year 2030, an approximate rise by 2.5 times.

It is reported that DWASA supply to city dwellers in Zone-4(old) is not sufficient; particularly in the Mirpur area it is too low. In this area Upper Dupitila aquifer unit-1 is under threat of becoming partial dry aquifer, hence productivity will become much less from this aquifer unit. The UWC length of the installed well is not sufficient to get required pumping level due to prevailing groundwater mining situation. Moreover, till 2013 there will be little or no scope of water supply from surface water sources in this area.