Spatial Assessment of Water Quality in Peripheral Rivers of Dhaka City for Optimal Relocation of Water Intake Point

Abstract

In order to meet the ever increasing demand of drinking water, Dhaka Water Supply Authority (DWASA) of Bangladesh has installed a number of deep tube wells that tap the upper aquifers. However, in most parts of the city, the current groundwater abstraction exceeds the recharge rate, causing the groundwater to be mined systematically and be depleted of its reserve. Thus, there is an urgent need to alleviate the demand on the upper aquifers and explore more sustainable sources to augment the present water supply. This implies a conjunctive use of groundwater and surface water in order to maintain the balance between anthropogenic demand and water’s natural availability. However, the surface water along these peripheral rivers is known to be highly polluted due to municipal and industrial untreated wastewaters that are discharged. This study analyzes the present water quality scenario along the surrounding rivers of Dhaka City pertaining to a 2-day field survey during the dry season of 2005. It uses a Geographic Information System (GIS) as a tool to arrive at a solution for relocation of the current intake point for surface water withdrawal. Derivation of water quality profiles (as a function of distance) along the downstream and upstream reaches of the current intake location indicated that a new location 12 km upstream of the present intake point could potentially be ideal for withdrawing surface water during the monsoon season. Such a proposed location was considered optimal due to the anticipated moderate construction costs of the transmission system that would be necessary to draw water to the current treatment plant. The study lays the foundations for the Dhaka City planners and designers to make a qualitative resource assessment of surface water. Such an assessment can eventually evolve to a long-term monitoring system of water supply sources for any city using GIS tools.