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Spatial and Temporal Analysis of Groundwater Level Fluctuation in Dhaka City, Bangladesh

Akther, H.
Department of Geography and Environment, University of Dhaka, Dhaka 1000, Bangladesh.

Ahmed, M. S.
Department of Geography and Environment, University of Dhaka, Dhaka 1000, Bangladesh.

Rasheed, K. B. S.
Department of Geography and Environment, University of Dhaka, Dhaka 1000, Bangladesh.

Abstract/ Executive Summary:

This study was conducted to determine the present status of groundwater level in Dhaka city. During 2005, about 1.6 Mm³ day^-1 of groundwater was withdrawn by Dhaka Water Supply and Sewerage Authority (DWASA) against the city’s total demand of 2.1 Mm³ day^-1. Compared to the exploitation of groundwater, the recharge to aquifer is very negligible as the geological settings and urbanization has retarded both the vertical and horizontal recharges. Consequently, groundwater table is continuously declining at an average rate of 2 m year^-1 since, 1986. Continuous groundwater mining has caused the dry season water table to move downward from -54 to -45 m depth from the sea level. The severe decline of groundwater level was observed in the central part of the city, compare to the river periphery, creating a cone of depression. If this falling trend of the groundwater level continues that might create an increased pressure on water storage and may invite land subsidence or other environmental hazards. So, the aquifer requires sustainable management to protect future water quality and to ensure that the resource can continue to meet the quantitative demands being placed upon it.

Keywords: Groundwater Level, Fluctuation, Dhaka City, Bangladesh

Location: Dhaka City

Start Date: 00-01-2003

End Date: 00-12-2005

Program Area: Crop-Soil-Water Management

Commodity: Groundwater

Objectives:

This study described the status and trends of groundwater level fluctuation in Dhaka City from 1986 to 2005

Methodology:

Study Area The study was conducted from January 2003 to December 2005 in Dhaka City which is a Metropolis as well as the capital city of Bangladesh, lies between latitude 23°40´ N to 23°54´ N and longitudes from 90°20´ E to 90°30´ E and covers an area of about 470 km² having the altitude of 6.5 to 9 m above mean sea leve. Geologically, it is an integral part in the southern tip of the Madhupur Tract, an uplifted block in the Bengal basin, with many depressions of recent origin in it. It is bounded by the Tongi khal in the North, the Buriganga river in the South and Southeast, the Balu River in the East and the Turag River in the West. The area is characterized by a tropical monsoon climate with an average annual precipitation of 2500 mm (from 1986 to 2005). The rainfall was unevenly distributed throughout the year, maximum during July and August. The annual mean temperature is 26°C with long-term average maximum and minimum monthly temperatures at Dhaka ranges from 25.5 and 11.7°C in January to 35.1 and 23.4°C in April. The evaporation over the area is fairly high. Dhaka is zoned for water supply purposes into six districts with newer zones having the higher numbers. Data Collection and Analysis The groundwater data from January 1986 to December 2005 was procured from the groundwater circle II (GWC II) a wing of Bangladesh Water Development Board (BWDB). GWC II in Dhaka City has been maintaining and keeping records of groundwater observation wells since 1963. The records are published annually in the BWDB water supply papers. The dug/piezometric surface wells give weekly records whereas the auto recording wells give daily records. The data from dug well in fact reflect the water table but not the piezometric surface. At present there are eleven observation wells nine piezometric and two auto- recording wells in the Dhaka city. Groundwater abstraction, supply and demand data were collected from DWASA. Other relevant data were procured from varies government and semi-government organizations. Bangladesh water development board supplied weekly groundwater level data for corresponding measuring point of different observation wells. This data was converted into monthly average groundwater level of each observation wells and monthly data of each year from 1986 to 2005 of each observation well were calculated. Groundwater table with respect to PWD (Public Works Department) sea level was calculated as deducting the groundwater level below measuring point from the elevation of measuring point in m (PWD). The negative value indicates water level below sea level.

Source of Information: Asian Journal of Earth Sciences, 2: 49-57.

Article Link (Online Journal): DOI: 10.3923/ajes.2009.49.57 URL: https://scialert.net/abstract/?doi=ajes.2009.49.57

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The existence of the thick and productive Dupi Tila aquifer beneath Dhaka has been of immeasurable benefit to a city with limited financial resources. Groundwater drawn locally from this aquifer continues to be the prime source to meet demands for domestic, industrial and commercial water supplies provided either by the public utility or by private well owners. As a resource supplying of Mega city the aquifer requires sustainable management not only to protect future water quality but also to ensure that the resource can continue to meet the quantitative demands being placed upon it. Accordingly, some immediate measures, such as surface water treatment plants need to be set up by DWASA to reduce dependence on ground water. As an alternate measure a well field or surface water reservoir may be constructed in the adjoining areas to augment groundwater. If possible, some artificial recharge like injector wells may be set up to supplement the natural infiltration. Some permanent bench mark observatory station like surface settlement plates and compression indicator at different depths may be set up immediately by DWASA to monitor any evidence of land subsidence.

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