impact of urbanization on ground water

Research Pro jec t o f Soc ia l Sc ience 2008-09 Ground Water Dep le t i on and Env i r onmenta l C onsequences : A Case S tudy on D haka C i ty

Md. Akter Mahmud of 19

Abstract

The capital city of Bangladesh, Dhaka, has one of the fastest urban growth rates

among the developing countries. As surface water bodies near the city are becoming

increasingly polluted and costly to purify, public water utilities and other water users

are turning to groundwater as potential source of supply. Groundwater grants about

87% of the total water supply of the city. Due to rapid increase in population the

demand of water for the city has raised from 150 mld in 1963 to 2100 mld in 2005.

Thereby, groundwater abstraction in the city has increased more than 700% from 1960

to 1995. But the rate of recharge to the aquifer is decreasing with increase in

pavement area due to rapid urbanization. In this conflicting situation, the groundwater

table in the city area is decreasing significantly putting the aquifer in vulnerable

conditions. The rate of decline of water level is 2-3m per year. Hence, the aquifer is

vulnerable to drying of the wells, contamination of water and possible land subsidence.

This study is aimed to understand the urbanization pattern and its impacts on the

groundwater of the city. Hydrographs from different parts of the city specify the

increasing trend of drop of water level throughout the city and indicate higher

vulnerability of groundwater in the central city area where both the vertical and lateral

recharge is insignificant and the withdrawal rate is higher than the other parts of the

city since the area is densely populated as well as commercial. Therefore, the study

has intended to put forward some measures such as reduction of high dependency on

groundwater, conjunctive use of groundwater and surface water, rainwater harvesting,

preservation of wetlands in and around the city, artificial recharge, reduction of

wastage; that may contribute effectively in the sustainable utilization of groundwater

resource.



Ground Water Depletion and Environmental Consequences: A Case Study on Dhaka City

1.0 Introduction Dhaka has become a mega city with a population of nearly 12.5 million, which is increasing at an annual rate of over 5% (Khondoker, 2006).This growth rate of urban population is also higher than many other mega cities of the world. It is expected that the population of Dhaka will be more than 20 million by the year 2020 (BBS, 2002). Being one of the largest mega cities of the world, Dhaka is facing continuous problems of potable water over the last few decades. Due to increasing population and industrial growth the demand for water is rising rapidly (Bhuiyan et al, 2007). In 2005 Dhaka WASA supplied 1600 million litres per day (mld) against the demand of 2100 million litres per day (mld) from 421 deep tube well. In 2020 the water demand will be 4100 mld (Azam, 2006).At present Dhaka WASA can fulfill less than 70% of the total demand (Haque, 2003). The production capacity of Dhaka WASA is 1860.50 mld where 1528.87 mld is produced from groundwater and 243.47 mld from surface water (DWASA, November 2007). As surface water bodies near the city are becoming increasingly polluted and costly to purify, public water utilities and other water users are turning to groundwater as potential source of supply. Systematic groundwater development started in Dhaka city from 1949 and available records show that groundwater abstraction in the city has increased more than 700% from 1960 to 1995 (Ahmed et al, 1998). As like Dhaka no other mega cities of the world are such dependent on groundwater. It creates a huge pressure on the water table1 of Dhaka. The level of groundwater table of upper aquifer (<170 m depth) is declining about 2-3 meter in every year (DWASA, 2006). As a result in many areas of Dhaka city there is a serious water crisis during the dry season. Due to intensive extraction of groundwater there is a possibility of land subsidence and the ecological balance may also be adversely affected. Moreover, lack of adequate sewerage system, direct industrial disposals and inadequate management of solid waste disposal results groundwater contamination. Therefore this study will attempt to explore on the relation between urbanization and groundwater depletion of Dhaka city, the impacts of urbanization on groundwater and also find out some proposals useful in sustainable groundwater management.

1.1 Objectives of the Study

The major objectives of this research work are as follows.

• To identify the relation between urbanization and groundwater depletion of Dhaka city. • To know the impacts of urbanization on groundwater of Dhaka city. • To find alternative options for the sustainable utilization and conservation of

groundwater that may cope with rapid urbanization.

1.2 Methodology

The entire study is conducted on the basis of secondary data. For this study, necessary data and information were collected from various secondary sources, such as:

•The objective of this research work is to identify the relation between urbanization and groundwater depletion of Dhaka city. Data on Urbanization pattern of Dhaka has been collected from relevant books, Journals and BBS.

•Urbanization, source of water, water supply and demand and groundwater depletion are closely inter-linked to each other. Data on water supply and demand has been collected from the annual and monthly report of DWASA.

1 the surface below which rocks are saturated with water



• Different organizations such as: DWASA, Bangladesh Water Development Board (BWDB), Bangladesh Agricultural Development Corporation (BADC) mainly collects groundwater level data regularly from their monitoring and observation wells. For this study groundwater level data has been collected from Bangladesh Water Development Board (BWDB) and Bangladesh Agricultural Development Corporation (BADC).

• The impacts of urbanization on groundwater of Dhaka have been identified from relevant study conducted by DWASA, BWDB, and IWFM-BUET. Apart from these, relevant essays from various journals, websites and newspaper reports are also studied to identify the impacts of urbanization on groundwater of Dhaka city.

2.0 Study Area Dhaka city possesses a rapid urbanization. The population explosion is higher than spatial expansion. It is very difficult to serve the large population of Dhaka with adequate water supply. Due to large scale abstraction of groundwater, the aquifer of the Dhaka city is more vulnerable than any other areas of the country. That's why, Dhaka city has been selected for the study. To analyze the groundwater level of the city eight locations i.e. Gulsan, Khilgaon, Sutrapur, Lalbagh, Mohammadpur, Mirpur, Dhanmondi and Tejgaon are selected.

Dhaka is situated between latitudes 23°42' and 23°54'N and longitudes 90°20' and 90°28'E. The city is bounded by the rivers Buriganga to the south, Turag to the west, Balu to the east and Tongi Khal to the north. The city has three distinct seasons: winter (November-February), dry with temperature 10° to 20°C; the pre-monsoon season (March-May), some rain and hot with temperature reaching up to 40°C; and the monsoon (June-October), very wet with temperatures around 30°C. Dhaka experiences about 2,000 mm rain annually, of which about 80% falls during the monsoon (Banglapedia, 2006).

2.1 Topography

The topography of the city area is irregular with complicated contour lines. The elevation of the city area ranges from 1.5 to 13 metres. The highest land of the city is located at Mirpur with an elevation of 13 m while the lowest is in the floodplain of the Buriganga River in western part of Mohammadpur and Lalbagh areas. For most of the parts of the city of Dhaka the land level is almost flat and low relief with many depressions here and there. Most areas of Dhaka city remain considerably above the highest levels of flood in ordinary season of inundation. However, the central and northern newly encroached build up areas of the city on the elevated terrace lands of the city is a rolling uneven surface frequently interrupted by numerous depressions and low lands characterised by abandoned channels (Asaduzzaman, et al, 1997). The major part of the city mostly lies between 6 to 8m above the sea level (Ahmed, 1962). In the vicinity of the Dhaka city, the elevation is about 4.5 m (15 feet) above the sea level (Rizvi, 1970). The Central Business District (CBD) and down town areas of Dhaka city is developed on the land with levels of 6 to 8 m (Asaduzzaman, et al, 1997).

2.2 Geology

Dhaka is situated at the southern tip of a Pleistocene terrace, the madhupur tract. Two characteristic geological units cover the city and surroundings, viz Madhupur Clay of the Pleistocene age and alluvial deposits of recent age. The Madhupur Clay is the oldest sediment exposed in and around the city area having characteristic topography and drainage. The major geomorphic units of the city are: the high land or the Dhaka terrace, the low lands or floodplains, depressions and abandoned channels. Low lying swamps and marshes located in and around the city are other major topographic features. The subsurface sedimentary sequence, up to the explored depth of 300m, shows three distinct entities: one is the Madhupur Clay of the Pleistocene age, characterised by reddish plastic clay with silt and very fine sand particles. This Madhupur Clay unconformably overlies the



dupi tila formation of the Plio-Pleistocene age, composed of medium to coarse yellowish brown sand and occasional gravel. The incised channels and depressions within the city are floored by recent alluvial floodplain deposits and are further subdivided into Lowland Alluvium and Highland Alluvium (Banglapedia, 2006).

2.3 Hydrogeology

The Dupi Tila sands aquifer is the main source of water in Dhaka city. Madhupur Clay overlies the aquifer with a thickness of 8 to 45m (averages 10m). The aquifer varies in thickness from 100 to 200m (averages 140m). Groundwater occurs at a depth of 25 to 30m in the central part of the city. In the periphery the groundwater table lies at a depth of 15 to 20m. Under the present conditions the peripheral rivers act as sources of recharge as the Dupi Tila sands are exposed along the riverbeds. Other sources of recharge are vertical percolation of rain and flood water, leakage from water mains and the sewer system and seepage from standing water bodies within the city (Banglapedia, 2006).

2.4 Legal Aspects

In Bangladesh there exist some ordinance, rules, act and policy for the conservation of groundwater either directly or through indirect way i. e. assist in groundwater recharge, provide guidelines for sustainable utilization of groundwater. They are mentioned below.

2.4 1 Ground Water Management Ordinance, 1985

According to the Ground Water Management Ordinance, 1985 (XXXV11 of 1985) the minimum distance between two wells would be:

(i) 2500 feet between two DTWs (ii) 1700 feet between a DTW and a STW (iii) 800 feet between two STWs

On 5 October, 1989, The Ground Water Management Ordinance, 1985 (XXXV11 of 1985) was suspended vide memo no.SRO- 040/89 of The Ministry of Agriculture. As a result tube wells were sunk indiscriminately causing reduced well discharge during irrigation period, especially during peak water demand.

Well discharge not only depends on the static water level but also on well spacing. If wells are sunk within the radius of influence of another, then static and pumping water level of both the tube wells go down more causing reduced yield. In many areas of Bangladesh improper well spacing is also a major cause of less discharge and pump failure especially during peak water demand period of March-April. Inadequate spacing produced deeper pumping levels, increased regional drawdown and decreased well discharge which increases pumping costs and thereby turned the irrigated agriculture uneconomical (Alam, 2006).

2.4.2 National Water Policy, 1999

The National Water Policy, 1999 was formulated for proper utilization and development of surface water and groundwater through skilled and balanced management. To conserve groundwater this policy provides some guidelines i.e. control on groundwater abstraction in areas identified by government, natural wetland conservation in urban areas, encourage tree plantation in areas where the water level goes down, and integrate and encourage public, private research organizations and universities to invent sustainable technology for combined use of rain water, surface water and groundwater.

2.4.3 Wetland Conservation Act, 2000

Open space, parks and wetlands has significance role in groundwater recharge. These areas should be carefully identified and strictly protected from encroachment and pollution. The Wetland Conservation Act, 2000 was introduced for this purpose.

2.4.4 The Environmental Conservation Act and Rules 1997

The 1995 law is an enabling act, which gives the MoEF the power to draw up rules and guidelines for managing the environment and. The law also designates the DoE as the responsible body for enforcing the EIA procedures outlined in the 1997 Rules, along with the



legal procedures to be followed for implementing the EIA process. The rules also designate four classes of possible interventions by degree of expected environmental impact. The Environmental Conservation Rules also contain national environmental standards, including those for water quality standards for different sectors and purposes. Peripheral rivers of Dhaka are polluted from industrial wastes. To ease the pressure on groundwater by increasing the use of surface water, the pollution of these rivers should be prevented. The Environmental Conservation Rules, 1997 might be useful policy instrument to control water pollution from industries. The legal aspects of groundwater conservation are summarized in table 1. Table 1: Groundwater Conservation through Act, Rules, and Policy in Bangladesh Ordinance/Act/Rule/Policy Control/Prevention/Measures Ground Water Management Ordinance, 1985

• Specify well spacing to maintain availability of water.

National Water Policy, 1999 • Regulating and controlling groundwater extraction areas identified by government,

• Natural wetland protection and conservation in urban areas,

• Encourage tree plantation in areas where the water level goes down,

• Integrate and encourage public, private research organizations and universities to invent sustainable technology for combined use of rain water, surface water and groundwater

Wetland Conservation Act, 2000

• Conservation of natural wetlands, parks, open spaces in urban areas to increase the scope of groundwater recharge.

Environmental Conservation Rules,1997

• National environmental quality standards for industrial effluents

• Obtain environment clearance • Requirement of EIA according to categories of

industries

Source: Own illustration.

The demand of water is increasing with rapid urbanization and large scale abstraction of groundwater is continuing as Dhaka is very much dependent on groundwater for it water supply. Intensive abstraction of groundwater may cause well failure, land subsidence, intrusion of contaminants into the subsurface etc.

3.0 Urbanization and Groundwater Depletion

3.1 Urbanization Pattern of Dhaka City

The creation of the independent state of Bangladesh in 1971 bestowed on Dhaka the glory and prestige of the capital of a sovereign country. This led to Dhaka's phenomenal growth. A recent study by World Bank has estimated that about 40% of the total population in Bangladesh will be living in urban area in Bangladesh by 2025 (ADB, 2000). Urban population density in Bangladesh was 2179 persons/sq.km in 1991 and the present density is estimated at approximately 3008 persons/sq.km. Population density of Dhaka mega city was found to be 4795 persons/sq.km in 1991 and the present density is estimated at approximately 8573 persons/sq.km. However, the population density of DCC area is more than three times of the megacity area, as in 1991 it was 15333 persons/sq.km against estimated present density of 18055 persons/sq.km (BBS, 2001). With limited availability of flood-free land, further densification of population along with haphazard encroachment of peripheral land of Dhaka as well as in urban areas of Bangladesh seems inevitable. Dhaka has the lion’s share of urban population. The following table shows the level of urbanization in Dhaka region.



Figure 1: Year Wise Population of Dhaka City

Data Source: Azam, 2006

Year Wise Population of Dhaka

6

7

8

9

10

11

12

13

1991 1993 1995 1997 1999 2001 2003 2005

Year

Popu

latio

n (m

illio

n)

Population(Million)

Table 2: Proportion of Total Population Residing in the Urban Areas of Bangladesh

Years Total population

(‘000)

Annual average

growth rate

Total urban population

(‘000)

Level of urbanization

Annual average

growth rate 1951 4,20,62 0.02 18,19 4.33 1.70 1961 5,08,40 1.91 26,40 5.19 3.79 1974 7,14,79 3.47 62,73 8.78 9.04 1981 8,71,20 2.00 1,35,35 15.54 7.99 1991 11,14,55 2.49 2,24,55 20.15 5.19 2001 12,38,51 1.06 2,86,05 23.10 2.45

Source: BBS, 2001 Table 3: Level of Urbanization of Dhaka Region

Year 1961 1974 1981 1991 2001 Level of

urbanization 14.79 29.56 38.94 54.42 61.48

Source: Jahan, et al, 2007

This table shows that the level of urbanization in has increased in course of time. Much of the urbanization has been concentrated in the Dhaka region, which is 61.48% urbanized, compared to 42.45% in the second most urbanized district, Chittagong. Dhaka is the most important and pivotal urban centre in the country where around 47% of the urban population reside. The level of urbanization of Dhaka district is 91.7% i.e. 7901700 people out of 8618700 populations live in urban area (BBS, 2001).

Figure 1 shows the population has increased from 7.3 million in 1991 to 12.2 million in 2005. It is expected that the population of Dhaka city will be 13.6 million and 24.25 million by the year 2010 and 2025 respectively (Azam, 2006). The primary reason of this fast growing trend of urbanization of Dhaka are largely attributed to the establishment of capital city, locations of various government and non-government offices, industrial and commercial organizations, educational institution etc. (Jahan, et al, 2007).This rapid pace of urbanization creates extreme pressure on basic utility services such as shelter, water, electricity etc.



Data Source: BWDB, 2007

Figure 3: Hydrograph at Khilgaon Figure 2: Hydrograph at Gulshan

Groundwater Level at Gulshan

38.5

43

45.5

51.552.5

58.5

62

35

40

45

50

55

60

65

Year

Gro

undw

ater

Lev

el (m

)

December 2001

December 2002

December 2003

December 2004

December 2006

December 2005

December 2007

Groundwater Level at Khilgaon

49

51.5

52.552

53.5

55.5

59.25

48

50

52

54

56

58

60

Year

Gro

undw

ater

Lev

el (m

)

January 2001

January 2007

January 2006

January 2005

January 2004

June 2003

January 2002

At present, the water demand of Dhaka is 210 crore litres per day and the supply is 170 to 180 crore litres per day. Thus Dhaka is facing shortage of water of 30 to 40 crore litres every day (Daily Prothom Alo, 2008,). Lion’s share of water supply of Dhaka (86.26%) comes from groundwater. Till November 2007 there are 472 deep tube wells which produce 1561.33 mld. The remaining 13.74% surface water comes from different water treatment plants of DWASA (DWASA, November, 2007). As surface water bodies near the city are becoming increasingly polluted and costly to purify, public water utilities and other urban water users are turning to groundwater as potential source of supply. Therefore, the present water supply system of almost entirely depends on groundwater (Hoque, et al, 2004). Groundwater extraction puts heavy pressure on the city’s water table, especially when most of the city’s supply of water depends on what the tube wells extract from the ground (Rahman, 2005). The following table shows the groundwater levels at different locations of Dhaka and the percentage of increase in water level between the year 2001 and 2007.

Table 4: Groundwater level at different locations of Dhaka City (Meter)

Locations

Year

Guls

han

Sabujb

agh

Lalb

agh

Sutr

apur

Moh

amm

adp

ur

Mirpur

Dhan

mon

di

Tej

gao

n

2001 38.5 51.78 39.3 19.5 25.17 45.5 42.5 40.13

2007 62.0 58.75 m

47.5 m 20.5 37.56 68.5 67.0 60.42

% increased

61.04%

13.46%

20.86%

5.13% 49.23%

50.55%

57.65%

50.56%

Source: BWDB and BADC, 2007 Hydrographs of water level monitoring bores have been analyzed to asses the changes in the water level of the Dhaka city. Long term hydrographs from different parts of the city indicate the drop in water level is increasing very rapidly throughout the city. For assessing hydrographs, eight groundwater monitoring station of BWDB and BADC have been selected at different locations i.e. Gulshan, Sabujbagh, Lalbagh, Sutrapur, Mohammadpur, Dhanmondi, Tejgaon and Mirpur.



Groundwater Level at Mohammadpur25.17

28.08

30.1

31.82

32.56

34.56

37.56

25

27

29

31

33

35

37

39

Year

Gro

undw

ater

Lev

el (m

)

December 2001

December 2007

December 2006

December 2005

December 2004

December 2003

December 2002

Figure 8: Hydrograph at Mohammadpur Figure 9: Hydrograph at Dhanmondi

Data Source: BWDB, 2007

Groundwater Level at Dhanmondi

42.5

53.5

55.5

57.25

62.25

65.5

68.5

40

45

50

55

60

65

70

Year

Gro

undw

ater

Lev

el (m

)

December 2001

December 2007

December 2006

December 2005

December 2004

December 2003

December 2002

Source: BWDB, 2007

Figure 5: Hydrograph at Sutrapur Figure 4: Hydrograph at Lalbagh

Groundwater Level at Lalbagh

39.3

41.5

43

44.7644.5

40

40.8

39

40

41

42

43

44

45

46

Year

Gro

undw

ater

Lev

el (m

)

December 2001

December 2006

December 2005

December 2004

December 2003

December 2002

February 2007

Groundwater Level at Sutrapur

19.5

19.25

19.6

19.8

20

21.25

20.5

19

19.5

20

20.5

21

21.5

Year

Gro

undw

ater

Lev

el (m

)

December 2001

December 2004

December 2003

December 2002

December 2006

December 2005

June 2007

Figure 6: Hydrograph at Tajgaon Figure 7: Hydrograph at Mirpur

Groundwater Level at Tejgaon40.13

44.4

49.76

53.26

57.7758.46

60.42

40

45

50

55

60

65

Year

Gro

undw

ater

Lev

el (m

)

July 2001 April 2007April 2006April 2005July 2004July 2003July 2002

Data Source: BADC, 2007

Groundwater Level at Mirpur45.5

47.8

54.36

58.5

63.5

65.5

68.5

45

50

55

60

65

70

Year

Gro

undw

ater

Lev

el (m

)

September 2001

August 2007

August 2006

August 2005

August 2004

August 2003

August 2002



N

Mirpur

MohammadpurKhilgaon

Tejgaon

Dhanmondi

Lalbag

68.5m

37.56m59.25m

40.8m

67m

60.42m

Source: BWDB and BADC 2007 Analysis of the hydrographs can be summarized as follows.

• By analyzing hydrographs, it is found that, the highest depth of groundwater level is 68.5 m in August, 2007 at Mirpur. Total 96 deep tube wells are operated by DWASA in densely populated Mirpur area (40607.59 per sq km). Moreover, no water has been supplied by the surface water treatment plants. For water supply Mirpur is entirely dependent on groundwater. Therefore, the water level decline sharply from 45.5 m in September, 2001 to 68.5 m in August, 2007 at Mirpur. The groundwater level of Dhanmondi is also very high which rises from 42.5 m in December, 2001 to 67 m in December, 2007.

• The declining rate of groundwater level is alarming as well at Tejgaon (62.42 m), Gulsan (62 m), Khilgaon (59.25 m) and Sabujbagh (58.75 m). In these areas the water abstraction rate is higher than the recharge.

• The groundwater level of Mohammadpur, Rayer Bazar, Lalbagh and BUET compound are 37.56 m, 31.25 m, 40.8 and 47.5 respectively. There are few scopes for recharge at Mohammadpur and Rayer Bazar. That is why the water levels are not so high and the declining rate is steady in comparison with other areas.

• Sutrapur represents a different state of groundwater level. This is at the close proximity to the river Buriganga and the recharge is quite significant. Therefore, the change in water level during last seven years is minimum i.e. 19.5 m in December, 2001 and 20.5 m in June, 2007.

• The declining rate of groundwater in Dhaka city is 2-3 m per year. The overall groundwater level in the city is below 50 m.

Map 1: Groundwater level in different monitoring stations of Dhaka city

Legend

Groundwater Monitoring Stations

Not To Scale



3.2 Reason of Groundwater Depletion

Rapid urbanization including construction of roads, buildings, and other engineering structures, flood protection dams and embankments is continuously hindering the natural groundwater recharges from rainfall and perennial water sources existing in and around the city. The survey finds the decline to be more severe mainly to the city centre where concrete coating prevents recharge of the groundwater level from the rainwater (Roy, 2003). Most of the beels and low lying areas surrounding Dhaka city are covered by the thick impervious clay which is not favourable for vertical recharge. Moreover, due to expansion of city, these areas are rapidly urbanized and consequently the local water demand increased. The adjoining contribution to the aquifer system from the rivers is seemed to be very limited indicated by the great differences between the rivers stages and the groundwater level. The river are being silted and reducing the permeability of their beds. Though the rivers eroded the thick sandy clay and some portion of sandy materials, it is evident that the constraints of the sources and their scope to groundwater recharge are very limited in Dhaka city.

3.3 Prediction of Future Water Level

Based on the recharge to the aquifer and water withdrawal for city water supply for different purposes, M. Mozzammel Hoque and Sujit Kumar Bala have predicted the future water level. The results of the prediction are presented in this section to show the groundwater conditions in the year 2020 at different locations of the city.

• In the year 2020 the water level would drop at (-) 58 m from the datum level at Old Dhaka. The yearly rate of decrease in water level is about 1.5 m.

• At the beginning of simulation the water level was at (-) 22m and at the end of the simulation the water level would be at (-) 70 m from the reference level in the recently developed parts of the city. The rate of decrease per year is about 2.5 m, which is alarming.

• At the central part of the city is at (-) 30m the groundwater level will go down at the level of (-) 90 m in the year 2020. In this area both the vertical and lateral recharge is insignificant and the withdrawal rate is higher than the other part of the city since the area is densely populated as well as commercial.

4.0 Impacts of ground water level depletion The vulnerable conditions of the aquifer may result in drying of existing wells, high water production cost, land subsidence, increasing temperature in the micro climate, hampering natural balance, diminishing surface water and intrusion of contaminated water from adjacent rivers. These impacts are described as follows.

4.1 Geological Impact

Rapid urbanization without considering the geological aspects has brought significant changes in the geo-environment of the city area. Water logging, pollution, changes in the hydro-geological system, localized land subsidence and building collapse are the hazards associated with these changes in the geo-environment.

4.2 Land Subsidence

Problems of land subsidence can also follow rapid depletion of aquifers. This can affect both upland and lowland cities. Mexico City (about 2,000 metres above sea level) and Bangkok (at sea level), for example, are both suffering severe groundwater-induced subsidence, resulting in millions of dollars worth of damage.

Land subsidence not only damages individual buildings and roads, but also underground piped services, further increasing water depletion and contamination. Leaks from water mains and sewers, and ruptured oil pipelines and underground tanks can add to shortages and soil and groundwater pollution. Khandakar Fazal Hasan, chief geologist of Bangladesh Agricultural Development Corporation (BADC) said in a website “If water table continues to



fall then a vacuum will be created in the aquifer which could cause a sudden collapse in the surface.” He gave the example of Bangkok city where same thing happened due to over extraction of groundwater (http://www.bangladeshnews.com.bd/2008/03/26/dhaka-sits-on-big-hollow/Dhaka sits on big hollow).

Due to the high withdrawal of water, the sands of the upper most aquifer dewatered first and water table dropped, the clay and silts in the aquifer squeezed and void spaces create in the sandy formation due to lowering of water table and at the same time due to overburden pressure they are sandwitched due to compression.

From the structural point of view Dhaka city is situated in an earthquake prone area. If any major earthquake takes place that may significantly contribute to land subsidence due to variability of ground condition (BWDB, 1991). The maximum subsidence of 17 to 27 mm in Dhaka city occurred near the New Airport and 11 to 63 mm at Mohakhali and Kamlapur area during the period between 1990 and 1999 (BUET, 2000).

4.3 Earthquake

Dhaka city is located within a very high risk zone for high magnitude earthquake that may also facilitate high-scale regional land subsidence and loss of numerous lives and properties once a medium to high magnitude earthquake hits the city. “Declining groundwater level will greatly increase the risks during earthquakes. It could lead to subsidence of the clay soil plate Dhaka is situated on,” said Khandakar Fazal Hasan. (http://www.bangladeshnews.com.bd/2008/03/26/dhaka-sits-on-big-hollow/Dhaka sits on big hollow).

The WASA, in its bid to collect ground water, seems set to install a large number of tube wells with a depth of 1000 feet in the city. The existing 600 feet deep tube wells are not considered adequate to extract water due to a significant lowering of the ground water table. The experts have said in very clear terms that excessive dependence on ground water can invite environmental hazards of various kinds. Experience shows that over-extraction of ground water can cause land subsidence and lead to creation of underground vacuums which make us all the more vulnerable to earthquake. Ground water is not being recharged at the same rate as it is depleted. In effect, the process of digging deeper and deeper will have to be continued endlessly. Clearly, the tube well based water supply has already been stretched to its limits (http://www.sos-arsenic.net/english/groundwater/index.html).

4.4 Change in Aquifer Characteristics

Hydrostratigraphically the aquifer is a confined aquifer as it is capped by a clay silt layer and pre and early development hydrostatics of the aquifer was confined. Due to increasing drop of water level the piezometric surface of the aquifer has fallen more than 50m over the lat three decades in some parts of the city. Due to this drop of water level, the hydrostatics of the aquifer changed to that of unconfined aquifer (Haque, 2004). The following figure illustrates the hydrostatic response of the first aquifer to intensive groundwater abstraction.

4.5 Impact on Environment/ Natural Balance/ Ecological Balance

Dhaka city usually stands on a clay layer named as Modhupur Clay. The thickness of this layer varies from 3-150 ft. in different locations. This layer is quite thick and sloped into the North, South. But due to excessive withdrawal of groundwater, there is a good chance to be dried up this clayish layer. As a result natural/ ecological balance may be adversely affected due to shrinkage of this clayish layer (Haque, 2003). Due to abrupt lowering of water table there is likely to occur environmental effects such as drying of recreation lakes, parks, plants, gardens etc. (BWDB, 1991). If there is no water from the top surface of the soil up to 135-140 ft.; would hamper the natural/ecological balance of the city.

4.6 Scarcity of Water

The water crisis is particularly severe in the urban areas where overpopulation and industrialisation are alarmingly depleting the groundwater. In Dhaka city the depletion rate is three metres every year. More than 80% of Dhaka’s water supply comes from



Figure 10: Large Gap between Production Capacity and Actual Water Production in Mirpur

Production Capacity and Actual Water Production in Zone IV

220

230

240

250

260

270

280

290

300

310

320

Jul-06

Aug-06

Sep-06

Oct-06

Nov-06

Dec-06

Jan-07

Feb-07

Mar-07

Apr-07

Year

Wat

er Q

uant

ity (M

LD)

ProductionCapacity Zone IV

Actual ProductionZone IV

Source: Own Illustration

groundwater alone, and the upper aquifer of Dhaka has already exceeded its withdrawal limit. This means almost half of the deep tube wells supplying water to Dhaka will dry up by 2013. The lower aquifer can only accommodate approximately 50 new tube wells. Effectively, all wells in Dhaka have shown a steady decline in the water table, with some at 65–70 meters below surface level. The lower groundwater tables already are causing well failures. (http://www.adb.org/Documents/Reports/Consultant/TA-4651-BAN/feasibility-study.asp).

Falling water level also causing abandonment of wells as the aquifer is dewatered and running-down of well’s productivity. If the water level goes down to 70 meters due to continuation of the present rate of extraction of groundwater, a large number of WASA pumps will become inoperative. The under groundwater of Dhaka city will dry up by the year 2016 if the present decline in its water level continues due to unabated extraction (Khan, 2007).

It is very difficult to serve the water demand of ever increasing population through tube well based technology. At present, 87% of total water supplied in Dhaka city is produced from groundwater. To ensure the availability of water in the wells, the minimum well spacing should be 2,000 ft. If this spacing is not followed the water production capacity of the wells will be reduced. But in Dhaka, to satisfy the increasing water demand a large number of wells are being installed each year without following the recommended well spacing properly. (DWASA, 2004-2005)

Apart from this, the water level goes down 2-3 m. per year due to intensive groundwater abstraction. As a result, the water extraction capacity of the wells is being reduced (DWASA, 2004-2005). At present, there are more than 100 deep tube wells in Mirpur. But about half of these wells can abstract only one-third of their capacity, as the water level decline sharply at Mirpur (Daily Prothom Alo, March, 2008). The areas where the water crisis is most acute are Pallabi, Mugdhapara, Shewrapara, West Dhanmondi, Rayerbazar, Kamalbagh, Islambagh, Nawabpur, Paikpara, Kalabagan, Naya Paltan, Khilgaon, Moghbazar, Bashabo, Kodomtola, Madartek, Sipahibagh, Meradia, Vuiyapara, Mugda, Manda, Shantibagh, Malibagh, Shiddeshwari, Rampura, Bonosree, Maximum part of Old Dhaka, Poribagh, Crisent Road, Kathalbagan, Hazaribagh, Jigatola, Lalbagh, Azimpur, Noorjahan Road, Salimullah Road Shekhertek, Housing Society and Picci



Culture of Mohammadpur. Badda, Khilkhet, Section-1, 2, 5, 10, 12 of Greater Mirpur, Borobagh, Senpara Porbota, Shewrapara, Kazipara, Kallyanpur, Pirerbagh, Ibrahimpur and Kafrul (Daily Prothom Alo, May, 2008). Table 5: Location of Acute Water Crisis Areas and Their Groundwater Level

Location of Acute Water Crisis Area Groundwater Level at These Locations (2007)

Mirpur 68.5 meter Dhanmondi 67 meter

Tejgaon 60.42 meter Khilgaon 59.25 meter

Basabo, Sabujbagh 58.75 meter Lalbagh 40.8 meter

Mohammadpur 37.56 meter

Source: The Daily Prothom Alo, 2008

Table 5 reveals that, water scarcity is very acute where the groundwater level is much higher than other areas. The groundwater level of Mirpur, Dhanmondi, Tejgaon, Khilgoan, Basabo and Lalbagh are 68.5 m, 67 m, 60.42 m, 59.25 m and 40.8 m respectively and the water crisis in these areas are quite severe. In these consequences, millions of city dwellers are likely to face an acute water crisis in the coming years.

4.7 High Water Production Cost

With rapid urbanization, the water demand of the city is also increasing rapidly. To serve the ever increasing water demand DWASA install a number of new deep tube wells in each year. The falling water level across the extensive part of the city, leading to increased pumping costs through deepening of wells and installation of longer, large diameter pump house and longer screen section (Morris, et al, 2003). In addition, as the water level goes down drastically, the water abstraction capacity of the wells has been reduced. So, more power/electricity, fuel, generator are required to operate these deep tube wells. As a result, DWASA has to expense more on power/electricity supply, fuel, generator etc. Apart from these, Due to lowering of water table re-sinking of many WASA’s tube wells is required at greater depth with more housing length and thereby increased pumping cost (BWDB, 1991). Thus the water cost has been increasing every year.

Table 6: DWASA’s Expenditure on Power, fuel/generator in Different Years (Taka in Lakh)

Year Expenditure on power, fuel/generator

Percentage (%)

2002-2003 6205.38 31.79 2003-2004 7257.94 32.57 2004-2005 11536.40 42.63

Source: DWASA, 2004-2005

The above table shows the expenditure of DWASA on power, fuel/generator in different year. It is observed that, expense on electricity, fuel, generator etc has been increasing over the years. Thus the water production cost of DWASA has also increased.

4.8 Impact on Temperature

The water level of Dhaka city has declined 20 ft in the last seven years. As a result, the temperature of Dhaka city is increasing along with water scarcity (Islam, 2006). The temperature of Dhaka has increased 1.8° C during the last 100 years. The increasing rate of temperature in Motijheel, Tejgaon, Farmgate and Old Dhaka are quite unusual (Daily Prothom Alo, May, 2008).

4.9 Diminishing Surface Water

Problems also result from pumping along streams, where the groundwater is so closely related to water in the stream that pumping from production wells depletes the stream-flow. Problems arise because the pumped water is not readily replaced from the streams or



it is readily replaced but the stream water is either needed downstream or is unsuitable for use (Walton, 1970).

Surface waters are also affected by falling water tables. In various wetlands, for instance, the water table is essentially at or slightly above the ground surface. Dropping water tables result in such wetlands drying up. Further as water tables drop springs and seeps dry up, diminishing stream and river and even to the point of dryness. Thus, excessive groundwater removal leads to the same effects as diversion of surface water of Dhaka city (Shattyajit, 2006).

Water level of the Buriganga, the lifeline of the capital city, has gone down to 6.65 metres this year while the normal level was 7.23 metres in 1998 and 7.68 metres in 1988. Water level of the Turag has dropped to 7.29 metres, Tongi khal 7.01 metres and Balu river 6.98 metres this year. As an increasing number of city people cannot use surface water from rivers, canals, lakes and other water bodies due to the fall in water level and consequent pollution, the pressure on groundwater has increased resulting in the decline of water table. These were revealed at the 'Consultation Workshop on Dhaka City State of Environment Report-2003' jointly organised by the Department of Environment (DoE) and Bangladesh Centre for Advanced Studies. (http://www.sos-arsenic.net/english/groundwater/index.html).

4.10 Contamination of Groundwater

The environmental conditions in most parts of the city are poor, with direct discharges of human and industrial wastes into the river systems possible contamination of groundwater from lack of adequate sewerage system, direct industrial disposals and inadequate management of solid waste disposal. Amongst the occasional groundwater contaminants, hydrocarbons are the deadly contaminants that are assumed to have already occurred in the groundwater of Dhaka city or most likely happen in the near future (DWASA, 2006).

5.0 Recommendations In the future, for the survival of the Dhaka City this lowering trend of ground water must not be go on. Comprehensive efforts should be taken immediately and following suggestions are made for the policy maker to consider and act accordingly;

5.1 De-concentration of Urbanization

Immediately prepare the national physical plan and national urbanization policy to de-concentrate centralized urbanization from Dhaka city. Strategic growth option: It is needed to implement 3 (among 8) options proposed as the long term strategy in the report of ‘Strategic Growth Options – Dhaka 2016 ‘(DMDP 1993. p-51), 3 priority options were: Limiting Dhaka’s growth, Developing new satellite city, Sub-regional dispersal. A national urban strategy would direct or foster urban development in centres other than Dhaka.

• The Task Force on Urbanization (1991) also emphasized on growth and development of medium-sized cities, turning new district towns and other small towns into production centres attractive to rural out-migrants and limiting the growth of large metropolitan cities of Bangladesh. It will reduce the pressure of Dhaka city.

• A well planned public capital investment in the adjacent urban centres may instigate further population agglomeration in those centers and a counter urbanization2 may be started to ease the problems of big cities like Dhaka.

5.2 Reduce Dependency on Groundwater

As soon as possible dependency on the groundwater for the urban use should be reduced. Abstraction of groundwater from the central part of the city should be stopped immediately as in this area both the vertical and lateral recharge is insignificant and the withdrawal rate is higher than the other part of the city since the area is densely populated as well as commercial. For the time being groundwater could be abstracted from the peripheral region

2 A process of population de-concentration. The counter urbanization was first widely appreciated in the USA in the early 1970’s, where population statistics showed metropolitan areas, especially large metropolitan areas, losing population by net migration to non-metropolitan areas.



of the city and for the long run strong suggestion goes for the peri-urban well-fields outside of the city.

5.3 Increase the Use of Surface Water

Surface water treatment plants are much more efficient in supplying water to the metropolitan areas as they are able to handle a larger capacity. Unlike the deep tube wells located within the city, these plants are located near sources of surface water such as nearby rivers. At present, surface water provides 13.74% of total water supply of the Dhaka city from water treatment plants at Sayedabad Phase I, Chandighat, and Narayanganj. For efficient use of surface water following measures are necessary:

• Keeping the peripheral rivers pollution free from industrial, domestic and other wastes. Establishment of new industry at the river bank should be prohibited. The industries that are already established near the river the installed effluent treatment plant should be mandatory to treat their wastes. As the major portion of domestic waste is organic, this may be used in composting fertilizer plants. For inorganic wastes, 3R method i. e. reduction, reuse and recycle; can be introduced. As like peripheral rivers, all lakes, ponds, canals, ditches of the city should also be kept pollution free. The Environmental Conservation Rules 1997 might be useful policy instrument to control water pollution from industries.

• The fertilizer plants upstream release ammonia which is a greater problem in the dry season. Another source of ammonia comes from the sewage lines that are coming from the city and eventually end up 8 dumping the wastes directly into the river. Although the Saidabad plant does have ammonia treatment system, the high levels during the dry season was unaccounted for and is too much for the plant to handle. The SWTP was not designed to handle such a high influx of ammonia or algae coming into the intake pipes. The proposed solution to this problem is that the intake pipe needs to be rerouted to the Meghna River. In many cases, rerouting the intake pipe is the best option as it solves many other problems that are associated with the Saidabad Water Treatment Plant. Shifting the intake point to the Meghna River will also supply the necessary quantity of water needed for usage in the other three phases of the treatment plant. The distance, which the intake needs to be shifted, is about 17 kilometers and would cost around $10 million US. This is almost equal to the budget for SWTP Phase Two and Phase Three (Rahman, 2005).

• The final three phases of the SWTP are still awaiting completion. Not much is required for the second phase of the plant because most of it had been established with the construction of phase one. Facilities such as pumping stations to harvest raw water have already been built for the first phase and are meant to accommodate the second phase as well. A mere eight kilometres of underground pipes need to be installed and added to the already existing 36 pipelines built during phase one of the project for the completion of the plant’s second phase. This will greatly improve the water supply as an additional 22.5 crore or 225 million liters of water will be pumped into the city’s water network from the Saidabad Water Treatment Plant after Phase Two is completed. Nicolas Simard, the process manager at SWTP states, “When all four phases are completed, we will produce 1 million cubic meters of water a day. That’s the same as 1 billion liters of water daily.” Areas such as Old Dhaka, Shantinagar, Motijheel, Elephant Road, Tejgaon, and parts of Dhanmondi and Lalmatia will greatly benefit with the completion of the plant. Once Phase Two or Phase Three of the treatment plant has been built, it should be able to meet the city’s demand for water. So to supply more water, we have to increase the number of treatment plants and develop the distribution network.

5.4 Rainwater Harvesting

Pressures mount on groundwater due to ever increasing population in Dhaka. Harvesting rainwater can be a nice way out in solving this problem. Many countries including Japan use rainwater in chores. Even rainwater is used for drinking too in some countries. Dhaka experiences an average annual rainfall of 1693 mm (BMD, 2005). If this rainwater can be harvested in all the buildings (where possible), it may contribute a lot in the existing water supply.



5.5 Reduction of System Loss

System loss of water is when water is lost or missing from the point of injection to the point of extraction because of the condition of the system it is in. System loss occurs from simple things like leaving the tap on to broken pipes. Other forms of system loss include un-metered usage, evaporation, and illegal connections where water is pilfered or leeched off other users. System loss of water is a common dilemma in many other South Asian countries. For Dhaka this is a huge problem like other large cites in the subcontinent with a system loss of 40 percent. This large percentage is a serious inefficiency for Dhaka’s supply network as much of the water is lost. By fixing most of the degrading or broken pipes and correcting “institutional” leakages and losses - which are illegal connections and incorrect billings - system loss in Dhaka can be lowered (Rahman, 2005). The government did not replace them when developing Dhaka after Bangladesh’s independence in 1947. Instead they have built around them and have simply added to the intricate network of pipelines under the streets of Dhaka. Fixing the broken pipes can be a significant improvement to the water supply of Dhaka. System loss could be reduced to 20 percent by 2010 and 10 percent by 2020 if proper funding is allocated to it.

5.6 Increase the Scope of Recharge

Replenishment of the exhausted Dhaka aquifer is a natural emergency. The recharge of groundwater mainly occurs in two ways; such as:

A. Natural Recharge

B. Artificial Recharge

A .Natural Recharge

Wetlands are characterized as the reservoirs of the surface, rain and ground water. Disappearances of many lakes, canals, and small rivers in and around the city also depreciated groundwater recharge. Reports say that a network of 22 canals that facilitated the natural drainage for the floodwaters and groundwater recharge in this city has disappeared or shrunk over the last four decades. Rapid urbanization including construction of roads, buildings, and other engineering structures, flood protection dams and embankments is continuously hindering the natural groundwater recharges from rainfall and perennial water sources existing in and around the city. Out of 40,167 acres of land under DCC 8668 acres or 21.57% are left as open space. If the current trend in occupation and encroachment continues, only 4% of the land will remain as open space by the year2010 (Haque, 2006). Shrinkage of open spaces reduces the scope of groundwater recharge. For natural recharge, these wetlands, canals and open spaces should be conserved. Strict implementation of Wetland Conservation Act, 2000 might be an effective policy instrument in this regard. Retention ponds can play significant role in natural recharge of groundwater and acts as surface water reservoir as well. In DMDP 1995, the retention ponds of the city have been identified. Such retention ponds should be conserved properly.

B. Artificial Recharge

The underground water table of Dhaka can be recharged easily during the rainy season by artificially infiltrating water through the topsoil layer of ground into the sub-soil reservoirs. This method can also greatly help recharge Dhaka's water tables fast during the rainy season.

Infiltration wells can be dug at a very low cost and these could greatly speed up the water recharging system. It is highly recommended to be very care full and to carry out studies on the probable consequences (especially geochemical) before set up artificial recharge wells or other means.

5.7 Implementation of Laws

The Ground Water Management Ordinance 1985 defines the minimum distance of well spacing. On 5 October, 1989, The Ground Water Management Ordinance, 1985 (XXXV11 of 1985) was suspended vide memo no.SRO- 040/89 of The Ministry of Agriculture. As a result tube wells were sunk indiscriminately. Well discharge not only depends on the static water level but also on well spacing. If wells are sunk within the radius of influence of another, then static and pumping water level of both the tube wells go down more causing



reduced yield. Inadequate spacing produced deeper pumping levels, increased regional drawdown and decreased well discharge which increases pumping costs. To conserve the groundwater of Dhaka city, the Ground Water Management Ordinance 1985 should be enacted immediately.

Open space, parks and wetlands has significance role in groundwater recharge. For natural recharge, these wetlands, canals and open spaces should be carefully identified and strictly protected from encroachment and pollution. Strict implementation of the Wetland Conservation Act, 2000 might conserve these natural recharge areas.

To conserve groundwater National Water Policy 1999 provides some guidelines i.e. control on groundwater abstraction in areas identified by government, natural wetland conservation in urban areas, encourage tree plantation in areas where the water level goes down, and integrate and encourage public, private research organizations and universities to invent sustainable technology for combined use of rain water, surface water and groundwater. Proper implementation of these guidelines will ensure sustainable utilization of groundwater.

5.8 Research Works

Intensive research works should be carried on in the universities and research organizations to find out appropriate devices that may contribute in groundwater recharge, cheap rainwater harvesting technology and categorized usage of water. Absolute pure water is not required for every purposes i.e. toilet flush, car washing. Researcher should focus on whether the same water can be used for different purposes after little treatment. To promote categorized usage of water different water rate may be imposed i.e. different water rate for household usage, commercial or industrial purpose and so on.

Moreover, detailed hydrogeological investigations should be undertaken to find out suitable aquifers underneath the present aquifer system at deeper depth. It is assumed that other potential aquifers may exist in the subsurface beneath the present ‘Dupi Tila’ aquifer, which can be developed for groundwater supplies in this city after careful hydraulic investigations of the aquifer potentials.

6.0 Conclusion

The study was conducted to identify the impact of urbanization on the groundwater of Dhaka city. With rapidly growing population, groundwater abstraction also has increased and thereby water level declines 2-3m per year. Rapid urbanization shrunk the scope of natural recharge. Future city dwellers will be facing massive environmental problems including fresh drinking water if the present situation is not handled carefully and immediately. The future scenario of the groundwater condition of the city can also be simulated and modeled so that we have the understanding for the sustainable use of water from present water supply systems that will facilitate the replenishment of the present groundwater storage of the aquifers mainly in the depressed city central region. Planners and policy makers of the country should keep in mind that the groundwater situation in this city has already reached its alarming state. So any further groundwater development in Dhaka city should call for detailed hydrogeological investigation and detailed exploration. However, the success of different initiatives would be doubtful if the present trend of water demand and groundwater abstraction of the city continued. Large population will generate high water demand which entail more deep tube well installation, more water treatment plants, expanded water distribution network that eventually increase the per capita cost of water. Planners and policy makers should also think about how the massive influx of population to the Dhaka city can be reduced and set up a balanced urbanization throughout the country. In this regard the establishment and proper development of the secondary towns and small towns should be taken into strong consideration. Reference Ahmed, K.M. (et al), 1998, “Effect of Urbanization on Groundwater Regime”,Dhaka City,

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