Assessment of Changes in Water Retention Areas in Eastern Dhaka Using RS and GIS
Low-lands, natural depressions and water bodies play important roles in retention of stormwater and floodwater as well as sustenance of natural ecosystem. Historically, the water retention areas in Dhaka have been efficient in storing stormwater while numerous khals gradually drained the water to the surrounding rivers. However, because of increasing population pressure, unplanned development and encroachment, the water retention areas have been diminishing, causing frequent stormwater flooding in the city. Most of the khals have also disappeared in the area. Present urban densification has saturated the western part. While unplanned development is also spreading in the eastern part of Dhaka.
Function of water bodies have enormous impact on land and society and are highlighted water resources management, environmental management, and spatial planning. Proper management of water bodies is essential for a sustainable environment and development. The functions of the water bodies are more diversified in the floodplain areas like Bangladesh. So management of these activities is stands at a critical point as the demand of land is high especially in the urban areas. At present, urbanization rate of Dhaka is tremendously high compared to other areas of Bangladesh. Chowdhury et al. (2001) assess the land use distribution in the northern compartment of eastern Dhaka and observes that the area is undergoing rapid land use change because of urban expansion. Haque (2004) observes that vast extent of open low-laying areas in eastern Dhaka has been undergoing urban development activities, particularly development of housing estates. Based on analysis of aerial photographs (1968) and spot image (2001), Sultana (2005) concludes that the wetlands in both eastern and western parts of Dhaka have reduced. However, these studies do not compare the land use change with the projected land use in the master plan. Thus an assessment of the present land use in eastern Dhaka, with particular attention to water retention areas, will be helpful to determine whether implementation of the master plan for eastern Dhaka would be successful. This study attempt is the first steps of the evaluation process by identify the land use change all over the area.
A master plan (JICA, 1991) was prepared to protect the city from river floods and to improve stormwater drainage, which has been partially implemented for western Dhaka. The plan for the 124 km2 of eastern Dhaka is yet to be implemented. The master plan is based on projected land use of the city and demarcates stormwater retention areas that would be vital for pumped drainage from the planned compartments. This plan has been updated by Halcrow. Annual average rainfall of Dhaka is approximately 2000 mm (Chowdhury, et. al, 1998) which produces a considerable volume of water. Draining out of this huge volume of water by pump or any artificial means is too expensive and unmanageable for the city. So the functions of the wetlands such as lakes, natural depressions and low lying areas are very important for stormwater management of the city. Dhaka WASA has identified these wetlands as only storing areas but also recharge areas for the aquifer below the city since 80% of its total water supply depend on groundwater (Huq, 2002).
The actual land development activities in the eastern part of the city have already deviated significantly from the projected land uses. This may alter rainfall-runoff generation and water retention capacity from their previous estimates on which the plans were based. This deviation calls for an estimate of the present land use, particularly water retention areas so that the stormwater management plan can be revised accordingly.
This study aims at focusing on the land use change of eastern Dhaka over the last 15 years. Since eastern Dhaka is dominated by wetlands, and the wetlands perform important functions for the total environment and ecosystem,the objective of the study is:
° to assess the change in land use, particularly the water retention areas, in eastern Dhaka over a period of the last 15 years;
1.3 Scope and Limitation of the Study
This study focuses on the land use change in eastern Dhaka over a period of 15 years (1889-2004). The study is inducted by analysis satellite data and field observation. Classification process conducted on water bodies, vegetation, urban areas and others areas.
The study is mainly based on satellite images. Therefore classification error may be presented in the processed data. Since field visits were conducted after a relatively long period since the time of image acquisition, field verifications may not have been completely representation.
2.1 Topography and Land Use of Dhaka
JICA (1992) has described the topographic condition of Dhaka. This study mentions that large part of central and southern part of the area is flooded for most of the year. Northern part of eastern Dhaka is higher than other parts of the area.
IWM (2006) has mentioned that every year 60% of the project area are inundated during June to October. Present housing demand highly influences the individual property owners and private land developer’s conversion of land from rural to urban.
Halcrow (2006) has described various aspects of urbanization of eastern Dhaka. In this report, they estimated that 205 Mm3 water have to be pumped after urbanizing the area according to the plan. In this study 80 % rainfall-runoff taken after fully developed the future condition of eastern Dhaka.
Sultana (2005) has observed that the most of the eastern part of Dhaka was wetland or low-lying marshy area in the Balu river floodplain in 1968. This study mentioned that the wetland reduced in aerial extent and retreated towards the river in 2001.
Wahren et al. (2007) has determined the potential water retention causes by land use change and found that changes in land-use (e.g. settlements including road-construction, deforestation, distinct practices in arable and grassland management) contribute to an increased frequency and severity of flood generation.
2.2 Previous Plans
Greater Dhaka East has become important in the present planning perspective for the whole metropolitan area of Dhaka. Three major studies have been performed on the area to study the physical development, flood control and drainage of the area. These are:
I. Feasibility Study on Greater Dhaka Protection Project (Study in Dhaka Metropolitan Area of Bangladesh Flood Action Plan No. 8A) in 1992.
II. Updating/Upgrading the Feasibility Study of Dhaka Integrated Flood Control Embankment cum Eastern Bypass Road Multipurpose Project in 2006.
III. Dhaka Metropolitan Development Plan by RAJUK.
2.2.1 FAP 8A
In FAP 8A three areas have been selected for feasibility study, Dhaka East, DND and Narayanganj West. Flood protection, environmental condition, ecology, population growth, urban development and other related issues have been covered in the study. Relevant information from the study is summarized below.
FAP 8A have conducted for an area of 118.62 km2. This study has divided the total area into four compartments; Northern compartment, Central compartment, Southern compartment-1, and Southern compartment-2 (see Fig. 2.1). These compartments are bounded by embankments and serves specific purpose for the study. Details of the compartments are given in Table 2.1.
Table 2.1: Area of the compartments of Eastern Dhaka in FAP 8A
|Name of Compartment||Area (in ha)||Percent|
Fig. 2.1 Proposed compartments in FAP 8A
220.127.116.11 Land use
FAP 8A has given an indication of land use change based on their base year (1990) land use. It has provided the land use of 2010 based on survey and land use of 1990. In 1990 the dominant land use was Agricultural, which is 75% of the total area. This year the built-up area is 19%. But in 2010 the dominant land use will be built up area according to their projection, which covered 72% of total area and agricultural land use will will reduce to 11% this year. Land use of 1990 and 2010 (projected) are given in Tables 2.2 and 2.3.
Table 2.2: Land use in FAP 8A of Eastern Dhaka (1990)
|Land use Type||Area in ha||Built up area in ha|
Table 2.3: Projected land use in FAP 8A of Eastern Dhaka (2010)
|Land use Type||Area in ha||Built up area|
18.104.22.168 Flood protection and drainage proposal
FAP 8A has divided the Dhaka East area into five drainage zones for flood protection and drainage purposes. Northern and eastern parts of the embankment
Have been designed for 100 year flood frequency and southern part has been designed for 50 year flood frequency. Major Khals for drainage in the area include Boalia Khal, Jamair Khal, Begunbari Khal, etc. Six sluice gates and four pump stations have been proposed for storm water drainage from the area. Special attention is given in the retention pond area of the proposal, which were located at different parts of the area to reduce the internal flood damage.
2.2.2 Halcrow Study
After 2004 flood, this study was conducted to update the previous studies for protection of Eastern Dhaka from flooding damage. This study is carried out to mitigate the flood damage and secondary benefits include the transport benefits. EIA, SIA and water modeling is carried out to update the previous study. Major issues addressed in the study include:
- Flood protection and drainage proposal
Halcrow study covered an area of 124 km2. This study has updated the FAP-8A study and divided the study area into three compartments, Northern compartment, Central compartment, and Southern compartment. Different compartments are divided by sub-embankment (see Fig. 2.3). Details of the compartments are given in Table 2.4.
Table 2.4: Area of the compartment in Halcrow Study
|Name of Compartment||Area (in Km2)||Percent|
22.214.171.124 Flood protection and drainage proposals
In the study the total area is divided into three compartments which was four in the FAP 8A (see Fig. 2.4). In this study, a flood wall has been proposed flood wall at the bottom and top of the embankment. Two water control structures are added in the proposal. Three pump stations have been in the study which was 4 in FAP 8A. In this proposal the retention pond areas are adjacent to the embankment area due to the urban development that took place in other parts of the area.
Dhaka Metropolitan development plan has divided the metropolitan area into 26 Strategic Planning Zone (SPZ). Eastern Dhaka area is constituted of a number of SPZ (see Fig. 2.5) in of Percentage of areas of the Eastern Dhaka in different SPZs is given in Table 2.5
Table 2.5: Strategic Planning Zones (SPZs) locates in Eastern Dhaka
|SPZ No.||SPZ Name||Covered SPZ area||% Area of Eastern Dhaka|
Several time-series land use maps (1989, 1999 and 2004) of eastern Dhaka over a period of the 15 years (1989-2004) have been prepared from satellite images. From these maps changes in land use classes have been detected using RS & GIS techniques. The methodology followed to attain the above-mentioned objective is schematically shown in Fig. 2.1. Operational definitions for the study are given in Appendix A.
Fig 3.1: Flow diagram of methodology
At first the study was conceptualized by studying different books, journals and reports related to the urbanization pattern of Dhaka Metropolitan Development area. From these studies different issues were identified, and the causes and effects of the changes in water retention areas were idealized.
3.3 Literature Review
Available literature related to water resources system and planning of eastern Dhaka were reviewed. The major studies reviewed included FAP 8A, DMDP urban area plan, Updating/Upgrading the feasibility study of Dhaka integrated flood control embankment cum eastern bypass road multipurpose project, etc. Main concerning issues related to the studies have been discussed in Chapter Two.
3.4 Data Collection
The study used satellite data for identifying land use changes over time. Satellite Images were collected in .image format. The raw image format data stores DN (Digital number) value against each pixel value of the image so that various statistical analyses could be performed easily. Pertinent land use data and necessary data related to the study have been collected from various reports and previous studies which have been conducted in the area. Table 3.1 gives the satellite images used for the study.
Table 3.1: Different satellite images have been used in the study
|Landsat Thematic Mapper (TM)/ Landsat 5||7||30 meters||1989||Ganibangla Limited (GBL)|
|Landsat Enhanced Thematic Mapper Plus (ETM+)/Landsat 7||7||30 meters||1999||Ganibangla Limited (GBL)|
|Imaging’s IKONOS Commercial Remote sensing Satellite||4||4 Meter||2004||Ganibangla Limited (GBL)|
3.5 Field Visits
Field visits to the study area were conducted in two steps. First, a Reconnaissance visit was performed for understanding the present situation of the area. Second, after the land use classification, corrections were made based on the visits. Photographs related to the land development activities particularly in the low land were collected during the field visits.
3.6 Image Processing and Analysis
Image processing for the study has been performed in the following steps:
3.6.1 Geometric correction
Geometric correction has been conducted based on GCPs (Ground Control Points). Projection system is Everest datum and Bangladesh Transverse Mercator (BTM). Then the original pixels of the images were re-sampled to match with a common geographicposition of the time series data.
3.6.2 Image subset
After geometric correction, the image of the study area was separated using the subset operation. As the study area is not a rectangle, the subset operation could not be performed based on coordinates (UL X, UL Y, LR X and LR Y; UL=Upper Left, LR=Lower Right). An AOI (Area of Interest) has been used in the image for this application.
3.6.3 Image enhancement
Image enhancement is the process of making an image more interpretable for a particular application (Faust, 1989). Different types of enhancement methods have been proposed in ERDAS IMAGINE. For this study, Contrast Stretching has been used to distinguish different land covers. In contrast stretching, enlarged digital number (input file) according to the certain interval in a different file (output). Contrast stretching relationship and contrast stretching color cell range are shown in Fig. 3.2 and 3.3 respectively.
Fig 3.2: Contrast stretching relationship Fig 3.3: Contrast stretching color cell ranges
For this study, both linear and non-linear contrast stretching were examined and linear contrast stretching was selected for enhancement purpose. A linear contrast stretch is a simple way to improve the visible contrast of an image. So in the land use classification process all types of land are identified easily.
3.6.4 Image classification
Image classification is the main task of the study. Collected satellite images have been classified by the following procedure.
Different types of land uses have been classified in the study. Land uses have been broadly categorized into 5 classes (see Table 3.2) to minimize confusion between classes. This class adequately shows the change over the time period (1989-2004) considered in this study.
Table 3.2: Land use/ land cover categories
|Category No.||Land use /land cover Definition|
|1||Deep Water Body|
For the study, Parametric ISODATA (Iterative Self-Organizing Data Analysis Technique) algorithms have been used for classification. Pixels are analyzed beginning at the upper left corner of the image and going left to right. ISODATA is iterative in that it repeatedly performs an entire classification (generates a thematic raster layer) and recalculates statistics. Self-Organizing refers to the way in which it locates clusters with minimum user input. The ISODATA method uses minimum spectral distance to assign a cluster for each candidate pixel so there is a little possibility of unclassified zone. Fig.3.4 shows the ISO data clustering process. Fig 3.5 shows a flow diagram of the procedure followed from Geometric Correction to Image classification.
Fig 3.5: Data Flow Diagram (DFD) image geometric correction to image classification
3.6.5 Post classification aggregation or recoding
After performing the classification process the data (output .image file) have been recorded according to the classification scheme.
3.6.6 Raster to vector conversion
The classified thematic images have been converted into shape files format to support calculations of different land use areas of time series.
3.7 Land use Map Preparation
Different time series maps have been presented using ArcGIS software. ArcView with compatible extensions have been used.
The study area is one of the prime areas adjacent to the core area of Dhaka city. Different types of activities and developments are taking place in the area in an unplanned manner. Location and the existing conditions are highlighted below.
4.1 Location: Eastern Dhaka is located to the East part of the Dhaka City Corporation areas.
The study area is situated between 90o20’E and 90o30’E longitudes, and 23o54’E and 23o42’E latitudes. The study area is bounded by the Tongi Khal to the north, old Demra road to the south, Balu River to the east, Bishaw, DIT and Dhaka-Mymensing Roads to the west.
4.2 Major Areas
Major areas located in the study area include Foydabad, Rajbari, Moynartek, Mousha, Azompur, Uttar Khan, Dakshinkhan, Anul, Nagoriabari, Mollartek, Kachkura, Dedaria, Askona, Koula, Dumni, Usufganj, Kuril, Northa, Jagannathpur, Napodkhola, Kathalia, Vatara, Nurarchala, Noyanagar, Khilbarirtek, Satarkul, Teckpara, Baidartek, Badda, Merul, Anandanagar, Ansar Camp, Gojaria, Anandanagar, Meradia, Kodomtala, Goran, Basabo, Khilgaon, Dakshingaon, Manda, Mugdapara, Manik Nagar, Dholpur, Gopibag, Ahmadbag, etc.
4.3 Existing Condition
Present land scarcity in the western core city area is influencing the development in the Eastern part area. Low lands and paddy fields are readily converted by the housing estates existing conditions of the area based on literature review and field observations are described below.
4.3.1 Geomorphological condition
On the basis of geomorphological expression and sediment characteristics, the area has been divided into nine geological units having deposits of sand bar/point bar, active natural levee, flood plain, depression, abandoned channel, gully fill, high flood plain, old natural levee and Madhupur clay (RAJUK, 2007).
4.3.2 Physical environment
Physical environment of eastern Dhaka is not in a good condition. Land filling activities have deteriorated the environmental condition of the area. Natural depressions and wetlands have been filled by solid wastes to reduce the filling cost in many parts of the study area. Not only natural depression areas and water bodies but also the rivers are facing encroachment problem in the area. Even before 15 years, this area had a number of depression area and water bodies Figs 4.2 and 4.3 are indicate the wetland filling situation in different parts of the study area.
4.3.3 Urban development
Unplanned urban development is sprawls in the area. Most of area is developed with narrow roads constructed without any plan and standard. So the inhabitants of the area are facing a lot of transport-related troubles in their daily life. Development authorities have not taken any initiative to upgrade the living conditions of the area. Figure 4.4 shows a typical urban area development.
4.3.4 Water bodies
A good number of water bodies and depressions still exist in the area. But the development of settlement and private housing is diminishing them very quickly. Water bodies near the settlements are polluted if not filled up already. Figure 4.5 shows the condition of a typical water body in the area.
IMAGE CLASSIFICATION AND MAP PREPARATION
Image classification is a process of arranging the pixels into a defined number of individual classes. Before performing the classification some preliminary information is essential to know about the image. Band information of the image and the spectral reflectance pattern of different land uses are the most important among the different preliminary information.
5.1 Band Information
Three different satellite images have been used to identify the land use over a period of 15 years. Landsat TM, Landsat ETM+ and IKONOS images have been used in the study. Information about the different images are given below.
5.1.1 Landsat TM image
The Landsat Thematic Mapper (TM) is a sensor carried on board Landsats 4 and 5 and has acquired images of the Earth nearly continuously from July 1982 to the present, with a 16-day repeat cycle. Landsat Thematic Mapper (TM) or Landsat 5 collect images in seven different bands. Three basic colors, near infrared, mid infrared and thermal band are included among the bands. Details of the band information are given in Table 5.1.
Table 5.1: Band information of Landsat TM image
|Band Number||Name of the band||Wavelength (micrometers)||Resolution (meters)|
|Band 4||Near Infrared||0.76-0.90||30|
|Band 5||Mid Infrared||1.55-1.75||30|
|Band 6||Thermal Band||10.40-12.50||120|
|Band 7||Mid Infrared||2.08-2.35||30|
Table 5.1 shows the band number, band name, wavelength and resolution of Landsat TM image. The first three bands are blue, green and red. After that near infrared, mid infrared, thermal band and again mid infrared band are included in the image. This image has 30 meters resolution. Only the thermal band acquires images in 120 meters resolution.
5.1.2 Landsat ETM+ image
The Landsat Enhanced Thematic Mapper Plus (ETM+) is a sensor carried on board the Landsat 7 satellite and has acquired images of the Earth nearly continuously since July 1999, with a 16-day repeat cycle. Landsat Enhanced Thematic Mapper Plus (ETM+) or Landsat 7 collects images in seven different bands like Landsat Thematic Mapper. Landsat series maintain a chronology of band. So the difference between TM and ETM+ is very little.
Table 5.2: Band information of Landsat ETM+ image
|Band Number||Name of the band||Wavelength (micrometers)||Resolution (meters)|
|Band 1||Blue||0.45 – 0.515||30|
|Band 2||Green||0.525 – 0.605||30|
|Band 3||Red||0.63 – 0.69||30|
|Band 4||Near Infrared||0.75 – 0.90||30|
|Band 5||Mid Infrared||1.55 – 1.75||30|
|Band 6||Thermal Band||10.40 – 12.5||60|
|Band 7||Mid Infrared||2.09 – 2.35||30|
Table 5.2 shows the band number, band name, wavelength and resolution of Landsat ETM+ image. Sequence of the bands of the images is the Landsat TM but the wavelength is more fractional than the Landsat TM. Major distinctive features in ETM+ are that the thermal band has 60 meters resolution which is 120 meters in TM.
5.1.3 IKONOS image
The launching on September 24, 1999 of Space Imaging’s IKONOS commercial remote sensing satellite, including the deployment of its digital camera system designed and built by ITT, marks the beginning of the long-awaited era of one-meter resolution Earth imaging. The first images, beginning with a stunning high-resolution view of Washington DC, became available in early October 1999. Imaging’s IKONOS commercial remote sensing satellite collects image in four different bands.
Table 5.3: Band information of IKONOS image
|Band Number||Name of the band||Wavelength (micrometers)||Resolution (meters)|
|Band 1||Blue||0.45 – 0.53||4|
|Band 2||Green||0.52 – 0.61||4|
|Band 3||Red||0.64 – 0.72||4|
|Band 4||Near Infrared||0.77 – 0.88||4|
Table 5.3 describes the different band information of IKONOS images. IKONOS images contain only four bands. The first three are blue, green and red, and the last one is near infrared. In all the bands the pixel size is four meters.
5.2 Spectral Reflectance Analysis
Reflectance of different bands of the image is essential in the classification process. Five types of land use, deep water body, depression storage, open space/landfill, urban area and vegetation, give different types of reflectance in different bands. Reflectance patterns of Lnadsat TM, Landsat ETM+ and IKONOS are described below.
5.2.1 Reflectance of Landsat TM
Fig 5.1: Reflectance of different land use in Landsat TM image
Figure 5.1 shows the reflectance pattern of different land uses in different bands of Landsat Thematic Mapper image. Reflectance pattern of deep water body and depression storage is nearly similar but the difference is visible in the bands 1, 2 and 3. Reflectance of the depression is higher in these three bands compared to the deep water body. It indicates that the deep water body absorbed more than the depression storage. Reflectance pattern of the urban area and open space/landfill is similar in pattern but the open space/landfill gives higher value in all the bands compared to the urban area. Since the land filling activity use sand, the reflectance is higher. Vegetation gives more reflectance in bands 4 and 5.
5.2.2 Reflectance of Landsat ETM+
Fig 5.2: Reflectance of different land use in Landsat ETM+ image
Figure 5.2 shows the reflectance pattern of different land uses in different bands of Landsat Enhanced Thematic Mapper image. Low reflectance value in bands 1, 2 and 3 (Blue, Green and Red) is given by deep water body and vegetation. After these are the depression storage and the urban area, and the highest value is given by open space and landfill. Open area landfill also gives the highest value in other bands of the image. In band 6 reflectance of all land uses is the higher compared to the other bands of the image. In band 7 all reflectance is relatively low.
5.2.3 Reflectance of IKONOS
Fig 5.3: Reflectance of different land use in IKONOS image
Figure 5.3 illustrates the reflectance pattern of different land uses in different bands of IKONOS images. The deep water body shows the lowest reflectance in all bands. It indicates that the deep water bodies absorb the most of the wavelength. After that, vegetation gives low reflectance in bands 1, 2 and 3 (Blue, Green and Red) but it gives the highest reflectance in band 4 (Near Infrared). Like the previous two cases the pattern of the urban area and open space/ landfill is similar. But the reflectance of the open space/ landfill is higher in all bands than the urban area.
5.3 Surface profile comparison of water body and landfill area in IKONOS image
Special attention is given to the water bodies in the study. So surface profile of water bodies and landfill is observed in different bands of IKONOS image.
Fig 5.4: Surface profile comparison of water body and landfill area in IKONOS image
Figure 5.4 compares the reflectance of water body and landfill areas. Band 1 (blue) does not give any significant difference. Band 2 (Green) gives small amount of difference between the two land uses. Band 3 (Red) has a significant difference between two land uses. Finally, band 4 (Near Infrared) gives a strong difference between the two land uses. So, we can draw a conclusion that for identifing the water body and landfill area near infrared would be ore useful than the basic bands of IKONOS imagess
5.4 Classified Land Use of Different Years
Classified land use maps for the study period are shown in Figs 5.5 to 5.7.
Fig 5.5: Classified land use map of 1989 of eastern Dhaka
Fig 5.6: Classified land use map of 1999 of eastern Dhaka
Fig 5.7: Classified land use map of 2004 of eastern Dhaka
Table 5.4: Classified land use of eastern Dhaka of year 1989
|Land use||%||Area in km2|
|Deep Water Body||14.24||17.660|
Table 5.4 shows the land use in year 1989 of eastern Dhaka. In this year the most dominant land use was depression storage. Urban areas are the next dominant land use. After that vegetation, open space/landfill and deep water body are the major land use types.
Table 5.5: Classified land use of eastern Dhaka of year 1999
|Land use||%||Area in km2|
|Deep Water Body||9.66||11.978|
Table5.5 shows the land use in 1999 of eastern Dhaka. In this year the urban area became the dominant land use. After that the depression storage and vegetation are the major land use types. Deep water body and the open space/landfill are the least dominant land use types.
Table 5.6: Classified land use of eastern Dhaka of year 2004
|Land use||%||Area in km2|
|Deep Water Body||7.98||9.895|
Table 5.6 shows the land use in 2004 of eastern Dhaka. In this year the major land use is also urban area like the previous year (1999). After that depression storage and vegetation are major land use types. Finally, the deep water body and the open space/landfill are the major land use types for the year.
5.5 Observed Land Use Changes
According to the classification we can observe some land use change in eastern Dhaka over the period of 15 years (1989-2004).
- Deep water body has decreased over the period. Also depression storage, open space/landfill and vegetation have reduced during this period.
- Urbanization is growing in a haphazard manner in the study area. According to the field survey it is found that the urban growth does not maintain any planning standard in the area.
- In reality this depression storages are agricultural lands in the dry season. Since the images are monsoon image these areas are shown perform as a depression storages.
- Rural settlement of the area may be classified as vegetation because naturally some vegetation are located in and around the rural settlement which dominated the reflectance. Another reason is the building materials. If the settlement uses any materials that are of indigenous types (straw, leave and like other), reflectance of vegetation could be obtained.
- Depth of water may vary in the deep water bodies depending on the time of the monsoon period, gives varying reflectance which may sometime show it to be a depression. But the sum of the water bodies is not influenced by such effect.
5.6 Present Land Use and Proposed Retention Pond Areas
Halcrow (2006)have proposed retention pond updating of the flood action plan No.8A (FAP 8A) (see Fig. 8.5). This study already considers previous urbanization and changed the location of the retention ponds proposed by FAP 8A. But different places of the retention pond areas have become urbanized in the absence of regulatory control in the area. If similar urbanization continues to take place in the area, most of the water bodies will disappear in future.
Fig 5.8: Halcrow proposed retention pond in classified map of 2004
View With Charts And Images
The following conclusion can be drawn from the study.
1. Deep water body has decreased by 6.26% over a period of 15 years (1989-2004). Depression storage has reduced by 9.58% and vegetation has reduced by 9.25% during this period. The open space/landfill area has also reduced by 11.33%. The urban area has increased by 35.89% within the 15 years.
2. Due to lack of regulatory control in the area, different types of development activities are takes place. In most cases the land developers are developing different projects in the low-lying areas.
3. Two different plans have been prepared for flood protection and drainage of the area, “Flood Action Plan No. 8A in 1992” and “Updating/Upgrading the Feasibility Study of Dhaka Integrated Flood Control Embankment cum Eastern Bypass Road Multipurpose Project in 2006”. But no provisions have been made to enforce the proposals of these plans. If the current development activities continue, the water bodies of Eastern Dhaka will disappear in near future.