hydrologic characteristics of flood...
TRANSCRIPT
HYDROLOGICAL ASPECTS OF FLOOD 2007
FINAL REPORT
R 03/ 2008
May 2008
A.K.M. SAIFUL ISLAM ANISUL HAQUE
SUJIT KUMAR BALA
INSTITUTE OF WATER AND FLOOD MANAGEMENT
BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY Dhaka-1000, Bangladesh
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Table of Contents Table of Contents............................................................................................................................ ii
List of Tables .................................................................................................................................. v
List of Figures ................................................................................................................................ vi
List of Photographs ...................................................................................................................... viii
List of Abbreviations ..................................................................................................................... ix
Acknowledgement .......................................................................................................................... x
Executive Summary ....................................................................................................................... xi
Chapter 1: Introduction ................................................................................................................... 1
1.1 Background........................................................................................................................... 1
1.2 Objective ............................................................................................................................... 2
1.3 Data and Methodology.......................................................................................................... 2
Chapter 2: Source and causes of Flood 2007.................................................................................. 4
2.1 Chronology of Flood 2007.................................................................................................... 4
2.2 Causes of Flood..................................................................................................................... 5
Chapter 3: Hydrologic characteristics of Flood 2007 ..................................................................... 9
3.1 Introduction........................................................................................................................... 9
3.2 Comparison of Floods in Major Rivers ................................................................................ 9
3.2.2 Brahmaputra at Bahdurabad station............................................................................. 12
3.2.3 Ganges at Hardinge Bridge station .............................................................................. 12
3.2.4 Meghna River at Bhairab Bazar Staion ....................................................................... 13
3.3 Conclusions......................................................................................................................... 16
3.3.1 Flood Magnitude / Peak ............................................................................................... 16
3.3.2 Flood Entrance ............................................................................................................. 16
3.3.3 Flood Duration............................................................................................................. 16
Chapter 4: Inundation maps using satellite images....................................................................... 18
4.1 Introduction......................................................................................................................... 18
4.2 Study Area .......................................................................................................................... 20
4.3 Data and Satellite Images.................................................................................................... 22
4.3.1 MODIS/TERRA Satellite images ................................................................................ 22
4.3.2 Flood inundation map based on RADARSAT images ................................................ 22
4.3.3 Water level data in major rivers of Bangladesh........................................................... 22
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4.4 Methods............................................................................................................................... 23
4.4.1 Detecting water related surface using MODIS data .................................................... 23
4.4.2 Modified algorithm of flood inundation maps............................................................. 24
4.5 Validation of proposed techniques...................................................................................... 29
4.6 Results and discussions....................................................................................................... 30
4.6.1 Spatial extents of floods in Bangladesh ....................................................................... 30
4.6.2 Temporal characteristics of floods............................................................................... 35
4.7 Conclusions......................................................................................................................... 37
Chapter 5: Floods around Dhaka city ........................................................................................... 38
5.1 Hydrologic condition of Dhaka city ................................................................................... 38
5.2 Hydrologic Characteristics of Major Floods in Dhaka City ............................................... 40
5.2.1 Buriganga River at Dhaka (Mill barrack) Station........................................................ 40
5.2.2 Balu River at Demra Station ........................................................................................ 40
5.2.3 Turag River at Mirpur Station...................................................................................... 43
5.2.4 Tongi Khal at Tongi Station ........................................................................................ 43
5.3 Conclusions......................................................................................................................... 45
5.3.1 Flood Peak ................................................................................................................... 45
5.3.2 Flood Duration............................................................................................................. 45
5.3.3 Flood Entrance ............................................................................................................. 45
Chapter 6: Performance of flood control works around Dhaka city............................................. 46
6.1 Comparison of the performance of Flood control structures .............................................. 46
6.2 Performance of Goranchat Bari and Kallayanpur pump station......................................... 49
6.3 Performance of Rampura and Dholai Khal pump station................................................... 49
6.4 Unprotected East part of the Dhaka city ............................................................................. 50
6.5 Filed visit to flood control structures of Dhaka City on August 16, 2007.......................... 52
6.5.1 Dholai Khal Pump House ............................................................................................ 52
6.5.2 Rampura temporary pump station................................................................................ 52
6.5.3 Segunbagicha temporary pump station........................................................................ 52
6.5.4 Kallayanpur pump station ............................................................................................ 53
6.5.5 Goranchatbari Pump station......................................................................................... 53
6.5.6 Temporary Pumps along the Buriganga River............................................................. 53
6.5.7 Hatir Jheel Lake and Begun Bari Khal ........................................................................ 54
6.5.8 Begun Bari Khal .......................................................................................................... 54
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Chapter 7: Conclusions and recommendations............................................................................. 57
7.1 Conclusions......................................................................................................................... 57
7.2 Recommendation ................................................................................................................ 60
References..................................................................................................................................... 62
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List of Tables
Table No. Title Page No.
Table 3.1: Comparison of characteristics of Flood 2007, 2004, 1998 and 1988 in major rivers.
............................................................................................................................... 11
Table 4.1: MODIS derived indices used to detect spatial and temporal distribution of flood...
............................................................................................................................... 24
Table 5.1: Comparison of characteristics of Flood 2007, 2004, 1998 and 1988 in the
surrounding rivers of Dhaka city. ......................................................................................... 42
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List of Figures Figure No. Title Page No.
Figure 2.1: Date of crossing danger level in various upstream gauge stations adjacent the boarder
of the country. ......................................................................................................................... 5
Figure 2.2: Ganges-Brahmaputra-Meghna (GBM) Basin and River networks enter into
Bangladesh.............................................................................................................................. 7
Figure 2.3: TRMM 3B42 3-hourly rainfall over the globe............................................................. 7
Figure 2.4: Monthly rainfall over Ganges Basin during July using TRMM 3-hourly data. ........... 8
Figure 2.5: Monthly rainfall over Brahmaputra Basin during July using TRMM 3-hourly data. .. 8
Figure 2.6: Monthly rainfall over Meghna Basin during July using TRMM 3-hourly data........... 8
Figure 3.1: Water Level Hydrographs of major rivers for four major flooding years: (a) 1988, (b)
1998, (c) 2004 and (d) 2007.................................................................................................. 10
Figure 3.2: Water level hydrograph of (a) the Brahmaputra at Bahadurabad, (b) the Ganges at
Hardinge Birdge and (c) the Meghna river at Bhairab Bazaar stations of floods in 2007,
2004, 1998 and 1988............................................................................................................. 14
Figure 4.1: Figure Location map of the study area....................................................................... 21
Figure 4.1: ..................................................................................................................................... 22
Figure 4.2: Water level hydrographs of major rivers in Bangladesh for (a) year 2007 and (b) year
2004. Flood starts earlier in 2004 than in 2007. ................................................................... 26
Figure 4.3: Flood chart for developing Flood inundation map using MODIS data...................... 27
Figure 4.4: MODIS derived indices: (a) EVI, (b) LSWI and (c) DVEL for the Seven Land use /
Land cover areas shown in Figure 4.1 .................................................................................. 28
Figure 4.5: Spatial comparison of (a) MODIS derived inundation map of 29 July 2007, (b)
MODIS 8-day false colour composite map (RGB=Band 6,Band2,Band1) of 29 July 2007,
(c) Long term water bodies in 2007 using MODIS data, (d) Inundation map using
RADARSAT image on August 03........................................................................................ 31
Figure 4.6: Overlay of MODIS derived inundation map on DOY 209 with the nearest available
RADARSAT derived inundation map on DOY 215. Inundation area derived from MODIS
includes Flood pixels and pixels of Long term water bodies................................................ 32
Figure 4.7: Correlation of inundation area determining from MODIS with that of RADARSAT.
Correlation coefficient R2 is found very high of about 0.96................................................. 32
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Figure 4.8: Temporal Changes of Flood and Mixture pixels for four types of paddy fields (Single
cropped irrigate rice, Single cropped rain fed rice, Double cropped irrigated rice, and Triple
cropped irrigated rice), Forest and Settlement areas............................................................. 33
Figure 4.9: Spatial distribution of flood inundated area during July and August months of 2007
and 2004. Flood pixels are in blue colour, Mixture pixels are in green colour, Long term
water bodies are in white colours and other areas are in white colour. ................................ 34
Figure 4.10: Flood inundation map of Bangladesh using MODIS images for (a) Year 2004 and
(b) Year 2007. Flood pixels are in blue colour, Mixture pixels are in green colour, Long
term water bodies are in white colours and other areas are in white colour. ........................ 35
Figure 4.11: Spatial distribution of (a) start date, (b) end date and (c) duration of flood for 2004
and 2007................................................................................................................................ 36
Figure 5.1: Greater Dhaka city area and surrounding river systems............................................. 39
Figure 5.2: Water Level Hydrographs of surrounding rivers for four major flooding years: (a)
1988, (b) 1998, (c) 2004 and (d) 2007.................................................................................. 41
Figure 5.3: Water level hydrograph of (a) the Buriganga at Dhaka, (b) the Balu at Demar, (c) the
Turag river at Mirpur and (d) the Tongi Khal at Tongi stations of floods in 2007, 2004,
1998 and 1988....................................................................................................................... 44
Figure 6.1: Map of flood control works of Dhaka city during Flood 2007. ................................. 47
Figure 6.2: Difference of riverside and protected side water level during floods in (a) 1998, (b)
2004 and (c) 2007 of the surrounding major flood control works........................................ 48
Figure 6.3: Preformence of Goranchat Bari and Kallyanpur pump station during floods in (a)
1998, (b) 2004 and (c) 2007................................................................................................. 51
Figure 6.4: Performance of Rampura and Dholai Khal pump station during floods in (a) 1998, (b)
2004 and (c) 2007 ................................................................................................................ 51
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List of Photographs
Photograph No. Title Page No.
Photo 6.1: Inlet of Dholai Khal pump house [Floating mat of waste carries by Dholai khal. Solid
waste management of the city needs to be improve ] ........................................................... 55
Photo 6.2: Rampura temporary pump station [Negligible impact on drainage congestion.
Permanent pumps needs to be installed.].............................................................................. 55
Photo 6.3: Data collection from Kallayanpur pump station [Digital data recording system can
help researchers and other users to get information quickly] ............................................... 55
Photo 6.4: Retention pond of Goranchat Bari [Only pumping stations where water is not much
polluted and air is fresh.] ...................................................................................................... 55
Photo 6.5: Dredging in Turag river to fill wetlands of Dhaka west. [Serious thread to retention
ponds of Goranchat Bari pumping stations] ......................................................................... 55
Photo 6.6: Temporary pumps to drain water logged near Kellar More [Drainage congestion
inside embankment. Some says that this polluted water is major cause of water born
diseases ] .............................................................................................................................. 55
Photo 6.7: Temporary pumps near Hazaribag [Untreated waste water causes serious pollution of
Buriganga river. Water treatment system should be used.] .................................................. 56
Photo 6.8: Retention ponds of Kallayanpur pump station [Encroachments gradually increases and
reduces retention pond area. Authority should act immediately. ] ....................................... 56
Photo 6.9: Buriganga River near Kellar mor [Water hyacinth grows due to polluted water comes
from the pumping of untreated drainage water inside embankment] ................................... 56
Photo 6.10: Inside WL of Segun bagicha temporary pump station [Similar story of Rampura
pump station. Permanent system should be installed.] ......................................................... 56
Photo 6.11: Illegal encroachments tried to grasp Hatir Jheel Lake, one of the major retention area
of the heart of the city. .......................................................................................................... 56
Photo 6.12: Polluted water is discharge in the Begun Bari Khal. The water becomes polluted
while it was carried by a Panthopath Box culvert................................................................. 56
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List of Abbreviations
BIWTA Bangladesh Inland Water Transport Authority BUET Bangladesh University of Engineering and Technology BWDB Bangladesh Water Development Board BMD Bangladesh Meteorological Department DL Danger Level DWASA Dhaka Water and Sewerage Authority FCD Flood Control and Drainage FCDI Flood Control, Drainage and Irrigation FFWC Flood Forecasting and Warning Center GBM Ganges-Brahmaputra-Meghna IFCDR Institute of Flood Control and Drainage Research (now IWFM) ILWIS Integrated Land and Water Information System IWFM Institute of Water and Flood Management MODIS Moderate Resolution Imaging Spectroradiometer PWD Public Works Department RHWL River High Water Level TRMM Tropical Rainfall Measuring Mission
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Acknowledgement
The authors wish to express their sincere thanks to the Committee for Coordination and
Development of the Institute of Water and Flood Management (IWFM) of Bangladesh
University of Engineering and Technology (BUET) for taking initiatives to conduct this present
study. We also pay our sincere gratitude to Prof. Rezaur Rahman, the then Director of the
institute for his continuous support in completing the research study successfully.
We also like to express our sincere gratitude to the Employees of BWDB and Dhaka WASA for
helping the BUET study team to provide necessary in situ data during the flood. We like to give
special thanks to Mr. Shariful Islam, Executive Engineer of Goranchat Bari Pump Station of
BWDB for this cooperation and support during our field visit. We are very thankful to
employees of Rampura regulator and Segunbagicha regulator of Dhaka WASA for providing
valuable information about flood control structures around the Dhaka city.
We offer our special thanks to Mr. Ahmedul Hasan of CEGIS for providing Inundation maps
produced by the RADASAT satellite. We also thank Mr. Motaleb Hossain Sarkar of CEGIS for
his valuable suggestion regarding flood inundation maps. This study has been funded by
Bangladesh University of Engineering and Technology (BUET).
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Executive Summary
In the middle of 2007, Bangladesh was hit by a severe flood, a natural disaster which takes
people’s life, kills livestock, destroys infrastructures and communication system, damages crops,
and fish ponds. Despite many adverse impacts, flood is an acceptable phenomenon for
Bangladesh because of its immense benefits on agriculture and food production, fisheries and
livestocks.
Normal flooding brings many benefits such as increase of soil fertility, recharge of aquifer,
improvement of ecosystem, and increase of fish production, etc. It is an established fact that after
each major flood, the agricultural sector of the country gets boom up and the food production
increases dramatically.
Flood 2007 is the 5th major flood for the period of last twenty years, when more than 35% of the
country area was inundated. The people of the country suffered greatly and the production of
Aman crop was seriously damaged during the 2007 flood. Like other major floods in the past,
Flood 2007 also has its own significance and characteristics, which need to be studied to adopt
better flood management strategies. Institute of Water and Flood Management (IWFM) usually
carries studies on water and flood management of Bangladesh. In no exceptions, a study team
was formed by the institute right after the Flood 2007 to study the hydrologic aspects of it. The
findings of the investigation have been presented in this report.
This study has given focus on the hydrologic characteristics of floods by analyzing hydrologic
data of three major rivers: the Ganges, the Brahmaputra and the Meghna (GBM). The main
source of monsoon river flood in Bangladesh is rainfall in the GBM basin which is carried by the
tributaries and distributaries of these three major rivers. The first crossing of danger level inside
Bangladesh was observed on 19th July 2007 at Durgapur station of the Someswari river and at
Sunamganj station of the Surma river. On next day, flood water crosses danger level at
Kanaighat station of the same Surma river. However, crossing of danger level at Amalshid
station in the Kushiyara river of Meghna basin was much later on 28th July 2007. Flood in
Brahmaputra basin was observed on the last week of July. On 26th July 2007, flood water crossed
danger level at Dalia of the Teesta river. On the next day, water level of the Dharala river at
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Kurigram station was above the danger level. The Brahmaputra river at Noonkhawa and at
Chilmari stations overtopped danger levels on 28th July 2007. During 2007 Flood, the water level
of the Ganges river did not cross the danger level. The far most gauge station inside the country
on the Ganges is located at Pankha, where the water level was always below the danger level. No
peak synchronization of flood like 1998 and 2004 was occurred in the country during 2007 flood,
as the Ganges experienced no crossing of danger level of water over the flood period.
The magnitude of water level above the danger level in the Brahmaputra river during Flood 2007
was higher than that of during Flood 2004, similar to Flood 1998 and much lower in Flood 1998.
In the Ganges river, there was no flood during 2007 and 2004 floods. On the other hand, the
most severe flood was observed in the Ganges basin of Bangladesh during 1998 and 1988 floods.
The magnitude of water level above danger level in the Meghna river during 2007 was almost
half of that was during 2004 flood. The most severe flood in terms of magnitude occurred in this
basin during 2004 and 1988 floods. The magnitude of the peak flood during 1998 flood in this
basin was also much higher than that of 2007 flood. The duration of water level above the danger
level in the Brahmaputra river in 2007 flood was longer than that of 2004 and 1988 floods but
much shorter than 1998 flood (about one third). In 1998 and 1988, flooding was occurred in the
Ganges basin and the most prolonged flooding was observed during 1998 flood. Duration of
floods in the Meghna river basin of Bangladesh in 2007 flood is similar to that of 2004 flood. It
is to be mentioned that long lasting flood was observed in this basin during 1988 flood and was
twice the duration of flood during 2007 flood. During 1998 flood, the duration of flood in the
Meghna river basin of Bangladesh was shorter than that of 1988 flood but was much longer than
that during the 2007 and 2004 floods.
It is a fact that the main source of river floods in Bangladesh is the huge rainfall in upper
catchment of the GBM basin. So, rainfall data from TRMM satellite was analyzed to reveal
characteristics and amount of rainfall over the GBM basin during 2007 flood. Mean monthly
rainfall plot of TRMM satellite data shows that for both the Meghna and Brahmaputra basins,
rainfall was higher in July 2007 than that of last two years. This excess rainfall was accumulated
and carried by the Brahmaputra and the Meghna rivers to Bangladesh and caused flooding.
For detecting spatio-temporal extent of inundation of floods during 2007 and 2004 floods, time-
series MODIS surface reflectance data were used for the study. Flood inundation maps were
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developed from vegetation and land water surface indices derived from surface reflectance. The
inundation map developed from MODIS data has been compared with a consequent
RADARSAT image. The estimates show a strong correlation with the inundated area derived
from RADARSAT products [R2: 0.96]. The products derived from MODIS 500m imagery show
the ability to study flood dynamics and perform similar to RADARSAT based flood assessments.
As MODIS products have a great advantage in the high-frequent observation, it may be
concluded that this developed method is a useful one to clarify the entire extent of the temporal
floods in Bangladesh.
A special emphasis has been given to reveal hydrologic characteristics of floods in and around
the Dhaka city. Dhaka is not only the nation’s capital but also will become a mega city by 2010.
Dhaka city always draws special attention during flood period due to its strategic importance.
Date of crossing of danger level at the rising stage of flood was first week of August during 2007
flood. The danger level was first crossed at Tongi Khal on 1st August 2007. On next day, the
danger level was crossed on Balu rive at Demra and after two days the danger level was crossed
at Mirpur of the Turag river. After one week of crossing danger level of the Tongi Khal, water
level of the Buriganga river crossed its danger level. In 1998 and 1988, floods observed first in
the Turag river, later in the Tongi Khal and finally in the Buriganga river. But, Flood 2004 was
observed first in the Turag river, then in the Buriganga river and finally in the Tongi Khal.
Magnitude of the peak flood above danger level of all the rivers around the Dhaka city in 2007
was below the level of flood in 2004, 1998 and 1988. The heights of flood peak were found for
1988 for all the rivers around Dhaka. In 1998 and 2004, magnitude of the highest flood level was
similar and lower than that of in 1988. Duration of floods in the Buriganga river was only a
single day in 2007. Flood duration of other adjacent rivers was more than twenty days in 2007.
The longest flood was found in 1998 and it was almost 3 times longer than floods in 2007.
Durations of water level above danger level in 1998 and in 2004 were similar to the duration of
flood 2007.
The performance of three permanent pump stations at Dholai Khal, Goranchat Bari and
Kallayanpur was found satisfactory. The water levels of protected side were far below than that
of river side. On the other hand, the difference of the water level between country and protected
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side at Rampura regulator, where temporary pumps were installed, was close to zero during all
the major floods. Performance of the temporary pumps was insignificant and had very little
effect on the drainage congestion in flood season. It was found during field visits that urban
encroachments are gradually increasing and the retention pond areas of the Kallaynpur and
Goranchat Bari pump stations are reducing. This phenomenon is supposed to enhance the water
logging from a small amount of intense precipitation.
The eastern part of Dhaka city has suffered from flooding during all the major floods. This part
of the city should be protected by road cum embankment. But, before the construction of such
an embankment, the drainage system of the Dhaka East should be well planned. The city
dwellers have bad experience of water logging and drainage congestion in the western part due
to the embankment. Lessons should be learned from the drainage situation of western part of
the city. During floods in 2007, the number of patients of Diarrhoea and other water borne
diseases was all time high. The main source of illness is drinking water supplied by Dhaka
Water Supply and Sewerage Authority (WASA). Entrance of waste water in the water supply
pipe through leakage and faulty joints are reported as one of the main causes of these diseases.
Except a few, the most of the industries discharged untreated waste water in the river. This
untreated water is recognized as the main source of water pollution during flood.
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1.1
Chapter 1: Introduction
Background
Flood is natural and recurring phenomenon for Bangladesh due to its unique geographic location.
The country is located at a floodplain delta of three major river basins: the Ganges, the
Brahmaputra and the Meghna (GBM). Every year, one fourth to one third of the country is
inundated during monsoon season by overflowing rivers. These normal flooding brings many
benefits such as increase of soil fertility, recharge of aquifer, improve of ecosystem, and increase
of fish production, etc. This regular and natural flood is acceptable for the nation because of its
immense benefits on agriculture and food production, fisheries and livelihood. However, the
degree of this inundation sometimes become severe and causes damage to infrastructures, crops,
communication system, and human being. Flood in 2007 was one such sever flood in recent
years in terms of magnitude and duration.
Four types of flood are encountered in Bangladesh: Flash Floods, River Floods, Tidal Floods and
Storm Surge (K. M. N. Islam, 2006). Flash floods are observed in northern and north-east hilly
region of Bangladesh in the pre-monsoon months of April and May. Flash floods are known for
its sudden high discharges and velocities, and abrupt rise and recession. The steeper slopes cause
rapid high velocities of runoff in response to the rainfall in the hills. The most common forms of
floods in the country are known as river floods caused from huge rainfall during monsoon season
from June to September. Rainfalls in the GBM basin during monsoon season are carried by the
tributaries and distributaries of the respective major rivers system. Finally, huge amount of water
carried by these three major rivers often overflows banks of the country and stays long time
during the monsoon season. Another type is tidal flood which is observed in the south west and
south central parts of the country. Tidal rivers and estuaries experience this type of flood due to
astronomical tide from the Bay of Bengal. Sometimes this type of flood in the estuary can
prolong the duration of the river flood by slowing down of the flood recession. Apart from the
above three types of normal flood, coastal area is occasionally hit by storm surge flood when a
heavy cyclone passes over the land. Storm surge often causes huge fatalities and deaths of
livestock due to its magnitude and the fastest travel time.
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1.2
1.3
In 2007, Bangladesh has been suffered from heavy monsoon river floods during the month of
July and August. Flood water came mostly through the two major rivers of the Brahmaputra and
the Meghna. Flood 2007 is the 5th major flood of last twenty years where more than 35% of the
country area is inundated. People suffered greatly and the production of Aman crop was
seriously damaged during this flood. Unlike other major floods in the past, Flood 2007 also has
its own significance and characteristics which need to be studied to adopt better flood
management strategies.
Institute of Water and Flood Management (IWFM) usually carries studies on water management
and floods of Bangladesh. Islam et al. (2002) have conducted a study on the Hydrologic
characteristics of floods in 1998. Chowdhury et al. (1998) have studied the impact of 1998 flood
on Dhaka city and performance of flood control works. Rahman et al. (2005) have investigated
the hydrologic aspects of Flood-2004 in major rivers of Bangladesh and special emphasis has
given on the floods of Dhaka city. In no exceptions, a study team has been formed by the
institute right after the Flood 2007 to study the hydrologic aspects of it. The findings of that
investigation have been presented in this report.
Objective
The main objectives of this study are as follows:
to investigate hydrologic characteristics of flood in 2007,
to compare Flood 2007 with the major floods in recent history,
to investigate the causes of flood 2007,
to develop flood inundation map using satellite images, and
to evaluate the performance of flood control works around Dhaka city.
Data and Methodology
This study has been carried out based on secondary data and field visits. Water level data has
been collected from Bangladesh Water Development Board (BWDB). Daily rainfall data were
provided from various meteorological stations of Bangladesh Meteorological Department
3
(BMD). Several field visits were conducted in and around Dhaka city during the September and
October 2007. The main objectives of this field visits was to investigate the flood situation and
the performance of the flood control works around the city. During the field visits, the study
team interviewed local people and officials of the responsible authorities. Data analysis was
conducted based on the performance of flood control works.
Satellite images are taken from MODIS TERRA 8-day reflectance (Surface Reflectance 8-Day
L3 Global 500m) during the 2004 and 2007. A total of MODIS 92 images were used to
determine flood inundation area. Rule based classification techniques were used to derive
inundation maps from MODIS images. One RADARSAT ScanSAR Wide Beam image of 3rd
August 2007 was used to compare inundation area derived from MODIS image.
3-hourly rainfall data with 0.25×0.25 degree resolution measured by Tropical Rainfall Measuring
Mission (TRMM) satellite with the 3B42 (Version 6) processing algorithm has been used to
quantify the precipitation over Ganges-Brahmaputra-Meghna (GBM) basin. Mean monthly
rainfall has been calculated for Monsoon season starting from satellite launch of 1998 to 2007.
4
2.1
Chapter 2: Source and causes of Flood 2007
Chronology of Flood 2007
Flood 2007 was observed, at first, in the rivers of the Meghna basin, later in the rivers of the
Brahmaputra basin. The date of crossing danger level is shown in the Figure 2.1 along the names
of the various gauge stations. The first crossing of danger level inside Bangladesh was observed
on 19 July 2007 at Durgapur station of the Someswari river and at Sunamganj station of the
Surma river. On the next day, flood water crossed danger level at Kanaighat station of the same
Surma river. However, crossing of danger level at Amalshid station in the Kushiyara river of the
Meghna basin was much later on 28 July 2007.
Flood in the Brahmaputra basin was observed on the last week of July. On 26 July 2007,
floodwater crossed danger level at Dalia of the Teesta river. On the next day, water level of
Dharala river at Kurigram station showed above the danger level. The Brahmaputra river at
Noonkhawa and at Chilmari stations was overtopped above their danger level on 28 July 2007.
During 2007 Flood, the water level of the Ganges river was not crossed above the danger level.
The far most gauge station inside the country on the Ganges is located at Pankha where water
level was always below the danger level. Since there was no sever flood in the Ganges river, so
unlike floods in 1998 and 2004, there occurred no peak synchronization in 2007 flood.
Figure 2.1: Date of crossing danger level in various upstream gauge stations adjacent the boarder of the country.
2.2 Causes of Flood
Figure 2.2 shows the GBM basin and its major river networks. Three major rivers - the Ganges,
the Brahmaputra and the Meghna carry huge amount of water during monsoon season and cause
monsoon flood of the country. Most of the rainfall occurs in the GBM basin during the monsoon
season, namely June to August. This heavy rainfall creates overland flows and runoff which
eventually flow into the above three major rivers. If rainfall amount of any year is much higher
than that of a normal year, river overflows its bank and cause flood. When these rivers enter into
Bangladesh, they carry huge amount of water and cause flooding in Bangladesh. It takes nearly a
month for rainwater in the GBM basin to reach Bangladesh carried by these major rivers.
5
6
To investigate the source of the floods 2007, the total monthly rainfall occurred in the GBM
basin during the monsoon season has been estimated and analyzed. Monthly rainfall over GBM
basin has been calculated using 3-hourly TRMM satellite data. Figure 2.3 shows an example plot
of 3-hourly rainfall over the globe using TRMM images of 0.25×0.25 degree resolution. Monthly
rainfall has been estimated by adding all the 3-hourly data over the monthly period. Finally,
using ILWIS Geoinformatics software, the total monthly rainfall for each of the GBM basins has
been calculated. Figure 2.4 shows TRMM derived total monthly rainfall of July over the Ganges
basin for 1998-2007. In the Ganges basin, rainfall in 2007 was not much higher than that of other
years. This represents the fact that during 2007, there was no significant flood occurred in the
Ganges river basin. Figure 2.5 shows TRMM derive accumulated rainfall during July of each
year from 1998 to 2007 for the Brahmaputra basin. Rainfall in July of 2007 was much higher
than the average rainfall in the Brahmaputra basin. Due to this heavy rainfall in this basin during
July, the water level of the Brahmaputra river crossed danger level and flooding occurred at end
of July.
Similar scenario of the rainfall in the Brahmaputra basin can be found for the Meghna basin for
2007. Figure 2.6 shows rainfall occurred in the Meghna basin in July for 1998-2007 using
TRMM 3-hourly data. In this basin, rainfall is higher in July than last two years and causes
flooding in the downstream of this basin. Such heavy rainfall increase the amount of water in the
river and danger level of the Meghna river was crossed in the middle of July of 2007.
The amount of rainfall during 2007 in the Meghna basin was less than that of 2004. Therefore, in
this basin, duration and magnitude of flood in 2007 should be smaller than that of flood in 2004.
In the following sections, the magnitude and duration of the recent floods will be compared
where we will see the appropriateness of this conclusion. The amount of rainfall in the
Brahmaputra basin in 2007 was slightly less than that in 2004. But the magnitude of peak flood
in 2007 was slightly higher han that of flood in 2004. It can be inferred that the amount of
rainfall in the Brahmaputra basin is not the only factor that afects flood peak and duration.
Figure 2.2: Ganges-Brahmaputra-Meghna (GBM) Basin and River networks enter into
Bangladesh
Figure 2.3: TRMM 3B42 3-hourly rainfall over the globe
7
0
20000
40000
60000
80000
100000
120000
140000
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Year
Mon
thly
Rai
nfal
l (m
m)
Figure 2.4: Monthly rainfall over Ganges Basin during July using TRMM 3-hourly data.
0
10000
20000
30000
40000
50000
60000
70000
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Year
Mon
thly
Rai
nfal
l (m
m)
Figure 2.5: Monthly rainfall over Brahmaputra Basin during July using TRMM 3-hourly data.
0
2000
4000
6000
8000
10000
12000
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Year
Mon
thly
Rai
nfal
l (m
m)
Figure 2.6: Monthly rainfall over Meghna Basin during July using TRMM 3-hourly data.
8
9
3.1
3.2
Chapter 3: Hydrologic characteristics of Flood 2007
Introduction
The main sources of river floods in Bangladesh are the bank overflow from the major rivers and
their tributaries or distributaries. Three major river systems of Bangladesh - the Brahmaputra, the
Ganges and the Meghna carries huge amount of water from the precipitation over large area of
the GBM basin. About 80% of the annual rainfall of Bangladesh occurs during monsoon season
between June to September. The major cause of the monsoon flood relies of the intensity,
duration and magnitude of the rainfall in the GBM basin. The study of the hydrological behavior
of the three above mentioned major rivers would pave to the understanding of the hydrologic
characteristics of flood 2007. Monsoon flood in major rivers for 2007 has been compared with
major floods in recent past. The elements of the comparison are mainly focused on the
magnitude, flood peak, duration of flood.
Comparison of Floods in Major Rivers
A comparison of floods in major rivers in 2007 with other major floods of recent past in 2004,
1998 and 1988 was conducted. Water level data from one gauge station in each major river is
used for this comparison. Bahadurabad in the Brahmaputra river, Hardinge Bridge in the Ganges
river and Bhariab Bazar in the Meghna river were the three well known gauge stations where
records of historic flood are available and used in this study. Figure 3.1 shows water level
hydrographs of three major rives for floods in 2007, 2004, 1998 and 1988. It can be found for
these hydrographs that floods in major river systems have distinct characteristics and patterns.
Comparison was made in terms of danger level, the date of crossing of danger level of falling
curve, the date of crossing of danger level of recession curve, the height of peak flood level
above local datum (PWD) and the duration of flood above danger level. A summary of this flood
statistics are presented in Table 3.1. In the following sub sections, the characteristics of floods in
each major rivers of Bangladesh will be discussed in detail.
(a) Flood 1988
-
4
8
12
16
20
24
1-M
ay
16-M
ay
31-M
ay
15-J
un
30-J
un
15-J
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30-J
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14-A
ug
29-A
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13-S
ep
28-S
ep
Wat
er le
vel (
m, P
WD
)
Ganges(at Hardinge Bridge)
RHWL
RHWL
RHWL
DL
DL
DL
Brahmaputra(at Bahadurabad)
Meghna(at Bhairab Bazar)
(b) Flood 1998
-
4
8
12
16
20
24
1-M
ay
16-M
ay
31-M
ay
15-J
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30-J
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ep
28-S
ep
Wat
er le
vel (
m, P
WD
)
Ganges(at Hardinge Bridge)
RHWL
RHWL
RHWL
DL
DL
DL
Brahmaputra(at Bahadurabad)
Meghna(at Bhairab Bazar)
(c) Flood 2004
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4
8
12
16
20
24
1-M
ay
16-M
ay
31-M
ay
15-J
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30-J
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14-A
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ep
28-S
ep
Wat
er le
vel (
m, P
WD
)
Ganges(at Hardinge Bridge)
RHWL
RHWL
RHWL
DL
DL
DL
Brahmaputra(at Bahadurabad)
Meghna(at Bhairab Bazar)
(d) Flood 2007
-
4
8
12
16
20
241-
May
16-M
ay
31-M
ay
15-J
un
30-J
un
15-J
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30-J
ul
14-A
ug
29-A
ug
13-S
ep
28-S
ep
Wat
er le
vel (
m, P
WD
)
Ganges(at Hardinge Bridge)
RHWL
RHWL
RHWL
DL
DL
DL
Brahmaputra(at Bahadurabad)
Meghna(at Bhairab Bazar)
Figure 3.1: Water Level Hydrographs of major rivers for four major flooding years: (a) 1988, (b) 1998, (c) 2004 and (d) 2007
10
11
Table 3.1: Comparison of characteristics of Flood 2007, 2004, 1998 and 1988 in major rivers.
Parameters River Gauge Stn. 2007 2004 1998 1988
Brahmaputra Bahadurabad 19.5 19.5 19.5 19.5
Ganges Hardinge Bridge
14.25 14.25 14.25 14.25
Danger Level in meters above PWD datum
Meghna Bhairab Bazar 6.25 6.25 6.25 6.25
Brahmaputra Bahadurabad 27.07.07 & 08.09.07
11.07.04 07.07.98 09.07.88 & 24.08.88
Ganges Hardinge Bridge
- - 20.08.98 16.08.88
Date of crossing Danger Level at rising stage
Meghna Bhairab Bazar 30.07.07 & 12.09.07
11.07.04 20.07.98 06.07.88 & 14.08.88
Brahmaputra Bahadurabad 06.08.07& 17.09.07
26.07.04 12.09.98 12.07.88 & 04.09.88
Ganges Hardinge Bridge
- - 15.09.98 07.09.88
Date of crossing Danger Level at falling stage
Meghna Bhairab Bazar 21.08.07 & 25.09.07
18.08.04 25.09.98 05.08.88 & 27.09.88
Brahmaputra Bahadurabad 0.88 0.68 0.87 1.12
Ganges Hardinge Bridge
- - 0.94 0.62
Height of peak flood level in meter above Danger Level
Meghna Bhairab Bazar 0.69 1.53 1.08 1.41
Brahmaputra Bahadurabad 21 15 67 16
Ganges Hardinge Bridge
0 0 26 23
Duration of flood in days above Danger Level
Meghna Bhairab Bazar 37 38 67 75
12
3.2.2 Brahmaputra at Bahdurabad station
The magnitudes of water level of peak flows at Bahdurabad in the Brahmaputra in 2007, 2004,
1998, 1988 were found 0.88m, 0.68m, 0.87m and 1.12m PWD above danger level respectively
(Table 3.1). In this river basin, magnitude of Flood 2007 was much smaller than the other two
major floods in 1998 and 1988. In terms of magnitude of peak flow, Flood 2007 in this basin is
higher than Flood 2004. Water level hydrographs of the Brahmaputra river at Bahdurabad was
plotted for floods in 2007, 2004, 1998 and 1988 and are shown in Figure 3.2 (a).
The date of crossing danger level in the Brahmaputra river at Bahdurabad during 2007, 2004,
1998 and 1988 was on 27th, 11th, 7thand 9th of July respectively. It has been found that Flood
2007 was delayed than the past three major floods. The recession also took place quickly and the
duration of flood was not long as compared to the floods in 1998. The durations of flood at
Bahdurabad in the Brahmaputra during 2007, 2004, 1998 and 1988 were found 21, 15, 67 and 75
days respectively. The duration of flood in the Brahmaputra river basin in Bangladesh in 2007
was higher than floods in 2004 and 1988 but much lower than floods in 1998.
3.2.3 Ganges at Hardinge Bridge station
At Hardinge bridge of the Ganges river, the magnitudes of water level during floods in 2007, and
2004 was always below the danger level. During 1998 and 1988, magnitudes of the peak flow
were found 0.94m and 0.62m PWD above danger level respectively. In terms of magnitude,
severe flooding occurred in the Ganges river basin of Bangladesh during 1998. Water level
hydrographs of the Ganges river at Hardinge Bridge was plotted for floods in 2007, 2004, 1998
and 1988 and are shown in Figure 3.2 (a). The dates of crossing of danger level in the Ganges
river for flood 1998 and 1988 were on 20th and 16th of August respectively. The durations of
flood at Hardinge Bridge in the Ganges in 1998 and 1988 were found 26 and 23 days
respectively.
13
3.2.4 Meghna River at Bhairab Bazar Staion
The magnitudes of peak flows at Bhairab Bazar in the Meghna in 2007, 2004, 1998, 1988 were
found 0.69m, 1.53m, 1.08m and 1.41m PWD above danger level respectively (Table 3.1).
Magnitude of Flood 2007 was much lower than the other three major floods of recent past. Water
level hydrographs of the Meghna river at Bhairab Bazar was plotted for floods in 2007, 2004,
1998 and 1988 and are shown in Figure 3.2 (c). The start of crossing danger level in the Meghna
river for flood 2007 was on the 30th July which was delayed than other 3 major floods. The
recession also takes place quickly and the duration of flood was not long as compared to the
floods in 1998 and 1999. The durations of flood at Bhairab bazaar in the Meghna in 2007, 2004,
1998 and 1988 were found 37, 38, 67 and 75 days respectively. It can be inferred that in terms of
magnitude and duration, Flood 2007 in the Meghna river were less significant than those of other
three floods of recent past.
(a) Brahmaputra at Bahdurabad
17
18
19
20
21
30-J
un
10-J
ul
20-J
ul
30-J
ul
9-A
ug
19-A
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8-Se
p
18-S
ep
28-S
ep
Wat
er L
evel
(m,P
WD)
1988199820042007DLRHWL
RHWL
DL
(b) Ganges at Hardinge Bridge
8
9
10
11
12
13
14
15
16
30-J
un
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ul
30-J
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p
18-S
ep
28-S
ep
Wat
er L
evel
(m,P
WD
)
1988199820042007DLRHWL
RHWL
DL
(c) Meghna at Bhairab Bazar
4
5
6
7
8
30-J
un
10-J
ul
20-J
ul
30-J
ul
9-A
ug
19-A
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29-A
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8-Se
p
18-S
ep
28-S
ep
Wat
er L
evel
(m,P
WD
)
1988199820042007DLRHWL
RHWL
DL
Figure 3.2: Water level hydrograph of (a) the Brahmaputra at Bahadurabad, (b) the
Ganges at Hardinge Birdge and (c) the Meghna river at Bhairab Bazaar stations of floods
14
15
in 2007, 2004, 1998 and 1988.
16
3.3 Conclusions
Conclusion on the investigations on hydrological characteristics of floods in major rivers can be
focused on the following points:
3.3.1 Flood Magnitude / Peak
The magnitude of water level above danger level in the Brahmaputra river during Flood 2007
was higher than Flood 2004, similar to Flood 1998 and much lower than Flood 1998. In the
Ganges river, there was no flood occurred in Bangladesh during 2007 and 2004. On the other
hand, the most severe flood was observed in the Ganges basin of Bangladesh during 1998 and
1988. The magnitude of water level above danger level in the Meghna river during 2007 was
almost half of it during 2004. The most severe flood in terms of magnitude occurred in this basin
during 2004 and 1988. Also, during 1998 the magnitude of the peak flood in this basin was much
higher than that of 2007.
3.3.2 Flood Entrance
Date of crossing of danger level at Bhadurabad in the Brahmaputra river was at the end of July
2007. On the other hand, the first flood wave in the Brahmaputra river was observed in early
weeks of 2004, 1998 and 1988. There was no flooding in the Ganges river basin of Bangladesh
during 2007 and 2004. The entrance of flood wave in the Ganges basin was observed in the
middle of August in 1998 and 1988. In the Meghna basin, the first flood wave entered into
Bangladesh in the last week of July in 2007. In 2004 and 1988, flood was observed in the
Meghna river basin of Bangladesh much earlier (at the beginning of July) than in 2007, while in
1998, the first flood wave was observed in the middle of July.
3.3.3 Flood Duration
The duration of water level above danger level in the Brahmaputra river in 2007 was higher than
that of 2004 and 1988 but much lower than 1998 (about one third). Therefore, in terms of
duration, Flood 2007 in the Brahmaputra river basin was moderate than recent known floods.
17
There was no flood observed in the Ganges river basin of Bangladesh in 2007 and 2004. In 1998
and 1988 flooding was occurred in the Ganges basin and most prolonged flooding was observed
in 1998. Duration of floods in the Meghna river basin of Bangladesh in 2007 is similar to that of
2004. Although the long lasting flood was observed in this basin in 1988 and it was twice the
duration of flood in 2007. In 1998, the duration of flood in the Meghna river basin of Bangladesh
was less than 1988 but has much higher than in 2007 and 2004.
18
4.1
Chapter 4: Inundation maps using satellite images
Introduction
Flood is very common phenomenon in Bangladesh due to its geographic location. Natural river
floods occurred almost every year during monsoon season between June to September. Every
year one fourth to one third of the country is inundated during monsoon season by overflowing
rivers. Flood disrupts people’s live, damage infrastructures and road networks in urban areas. In
rural areas it damages crops, causes death to livestock and people become isolated due to the
unavailability of communication mode. On the other hand flood has many positive impacts to the
environment. Flood supplies nutrients to the soil, recharges ground water, enhances diversity of
aquatic species, and naturally washes out solid wastes. It is very common that crop production in
the country gets almost doubled right after any major flood. Therefore, understanding the current
status of flood inundation in time and space is important in evaluating the relationships between
variations in the water regime, local agricultural activity, and ecosystem behavior from a global
viewpoint.
Remote sensing images can be effective and efficient tools to determine flood inundation areas.
In the past, many studies have been conducted using remote sensing data to detect spatial and
temporal changes of flood inundation areas, delineate wetlands and study its changes, flood
damage assessments in urban areas, dynamics and behaviors of floods. Those studies mainly
detect surface water resources using a range of sensors and satellites. To select suitable sensor
which is both cost effective and efficient to develop flood inundation is a major challenge. One
of the major problems of optical sensors is its inability to penetrate clouds. On the other hands, in
the monsoon period when flooding occurs, the sky is covered most of the days by cloud. In this
context, Synthetic Aperture Radar (SAR) has been considered as the most effective sensor in
detecting flood inundated area. In the past, images from various satellites such as RADARSAT,
JERS-1, ERS-1/2, and ENVISAT have previously been used to detect inundated areas in
numerous of possible ways (Henry, Chastanet, Fellah, & Desons, 2003; Heremans et al., 2005;
Hirose, Maruyama, Quy, Tsukada, & Shiokawa, 2001; Ishitsuka, Saito, Murakami, Ogawa, &
Okamoto, 2003; Laugier, Fellah, Tholey, Meyer, & De Fraipont, 1997; Liew et al., 1998;
Nguyen & Bui, 2001; Wang, 2002, 2004).
19
Although RADARSAT and other synthetic aperture radars are a capable of monitoring land
surface, it is not feasible to use them for monitoring a huge areas for a long time due to its high
data acquisition cost. Keeping in mind the cost of production, inundation maps were developed
using data from various low resolutions optical sensors. Data from NOAA/AVHRR of 1.1km,
SPOT of 1km (Harris & Mason, 1989; Liu, Huang, Li, & Wan, 2002; Xiao et al., 2002a), SSM/I
of 13km, and MOS/SMR of 23km spatial resolution (Jin, 1999; Tanaka, Sugimura, & Tanaka,
2000; Tanaka, Sugimura, Tanaka, & Tamai, 2003) has been considered as alternative means of
mapping water surface. Most of these data are freely available from internet for daily basis which
makes it possible to detect changes of inundation areas for a large area.
The spatial resolution of SSM/I and MOS/SMR is very high as compare to NOAA/AVHRR and
SPOT data. This makes NOAA/AVHRR and SPOT an effective tool to detect inundation and
temporal changes in the extent of flooded areas. Various techniques such as discrimination of
low cloud coverage by Bryant and Rainey (2002), discrimination between water and land
surfaces using band rations by Sheng and Gong (2001) are also developed to reduce and detect
the effect of cloud cover. Deriving indices such as Normalized Difference Water Index (NDWI)
by Xiao et al. (2002b) is also efficient in detecting the inundation and transplantation of rice.
On the other hand, right after its launching in December 1999, MODIS satellite with its
moderate-resolution optical sensor of 250–500 m becomes useful tools for scientific studies and
research. Many studies were conducted to determine surface water content such as estimating the
extent of paddy fields by Xiao et al. (2006; 2005), detecting inundation areas through vegetation
cover conversion by Zhan et al. (2002) etc. The Dartmouth Flood Observatory (2006) monitors
flood disasters all over the world using MODIS data. Up to 2007, the observatory published an
annual inundation map of Bangladesh via the Internet (Anderson, Brakenridge, & Caquard,
2005).
Sakamoto et al. (2007) was developed a methodology to detect the spatio-temporal flood
distribution in the Cambodia and Vietnam using MODIS data. The main advantages of this
methodology are: (1) time series data is available during flood period, (2) data is available for the
globe, (3) data can be downloaded free of cost through internet and (4) the accuracy of flood
inundation map lies within the acceptable range [R2 lies between 0.77 and 0.97]. Application of
20
4.2
their methodology for flood inundation mapping of Bangladesh is also a difficult task due to
dissimilarity of the hydro-geological conditions among Cambodia, Vietnam and Bangladesh.
Some modifications are essential to adopt their methodology that is proposed in this study. Using
this modified methodology, spatio-temporal changes in the extent of flood inundation of
Bangladesh are studied. Temporal changes in the extent of the inundated region in the
Bangladesh are assessed at a resolution of 500m for recent major floods in 2004 and 2007.
Study Area
Bangladesh is taken as study area which is located between Latitude 20–27 °N and Longitude
88–93 °E (Figure 4.1). The country is located a floodplain delta of three major river basins: the
Ganges, the Brahmaputra and the Meghna (GBM). About 80% of the annual rainfall of
Bangladesh occurred during monsoon season between June to September. The major cause of the
monsoon flood relies of the intensity, duration and magnitude of the rainfall in the GBM basin.
Every year one fourth to one third of the country is inundated during monsoon season by
overflowing rivers. However, the degree of this inundation sometimes become severe and cause
damage to infrastructures, crops, communication system, and human being. Floods in 2007 and
20004 were one such sever floods in recent years in terms of magnitude and duration.
The spectral signature has been changed for different land use types and therefore, study of those
signatures is very important to classify the inundated areas from satellite image. A total of nine
categories of land use /land type have been selected to analyze inundation areas (Figure 4.1).
These are 1) single-crop rainfed rice in the Haor area of north-eastern region , 2) single-crop
irrigate rice in the south-west region, 3) double-cropped irrigated rice in north region, 4) triple-
cropped irrigated rice in the Brand area of north-west region, 5) forest area in the Sundarbans, 6)
settlement area of Dhaka city , 7) Kaptai lake, 8) Bay of Bengal ocean, and 9) the Padma river.
In the following sub section, the temporal variations of various indices based on spectral
reflections sensed by satellite on those nine land use categories will be discussed.
Figure 4.1: Figure Location map of the study area
21
22
4.3
Data and Satellite Images
4.3.1 MODIS/TERRA Satellite images
This study uses MODIS satellite images acquired by TERRA instrument which can be freely
downloaded through the Earth Observing System Data Gateway (EOS, 2006). The present study
involves an analysis of 8-day composite data of MODIS during 2007 and 2004. The label of this
product is “MODIS/TERRA SURFACE REFLECTANCE 8-DAY L3 GLOBAL 500 M SIN
GRID V005”. The spatial resolution of this product is approximately 500 m, and atmospheric
correction has already been carried out (Vermote & Vermeulen, 1999). This 8-days average data
is delivered as a composite product called MOD09 which took the best surface spectral-
reflectance within this period with the least effect of aerosols and other atmospheric ingredients.
4.3.2 Flood inundation map based on RADARSAT images
Inundation map produced by Center for Environmental Geographic Information Services
(CEGIS) are used as a reference to evaluate the estimates derived from MODIS data. This map
area produced based on Digital Elevation Model (DEM) data, hydrological data, and
RADARSAT images acquired on 3rd August (DOY 215) using the ScanSAR Narrow B Mode .
Bearing in mind that C-band microwaves can penetrate cloud cover and easily discriminate open
water on the basis of backscatter coefficient data at a high resolution (50 m), it is assumed that
inundation map based on the RADARSAT images reveal the details of the flood distribution at a
satisfactory spatial resolution, even under cloud coverage. The inundated areas in this map were
aggregated within each grid at 500 m resolution to enable comparisons with results derived from
the MODIS data.
4.3.3 Water level data in major rivers of Bangladesh
Three major rivers of the country - the Brahmaputra, the Ganges and the Meghna carry huge
amount of water from the precipitation over their basins. Figure 4.2 shows a time series of daily
averaged water level hydrographs of major rivers in Bangladesh for 2007 and 2004. Water level
data from one gauge station in each major river is used for this comparison. Hydrographs are
23
4.4
plotted at Bahadurabad sations of the Brahmaputra river, Hardinge Bridge station of the Ganges
river and Bhariab Bazar station of the Meghna river. These stations are very well known gauge
stations, where records of historic floods are available and used in this study. Magnitude of peak
floods in Brahmaputra river was found 0.88m and 0.68m above danger level during floods in
2007 and 2004 respectively. Flood 2007 was more severe in Brahmaputra river basin than Flood
2004. The highest water level in Meghna river was found 0.69m and 1.53m above danger level
during floods in 2007 and 2004 respectively. In terms of magnitude, the floodwater level in
2007 was well below in comparison to that of 2004 in the Meghna river basin.
Duration of days above danger level in the Brahmaputra river was found 21day and 15days for
Flood 2007 and Flood 2004 respectively. Flood 2007 was longer than Flood 2004. In terms of
both duration and magnitude Flood 2007 exceeds Flood 2004 in the Meghna river basin. In the
Meghna river, duration of floods above danger level was 37days and 38days during floods in
2007 and 2004. Flood 2007 stays similar days to floods in 2004 in the Meghna river basin.
Methods
4.4.1 Detecting water related surface using MODIS data
In the past, Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water
Index (NDWI) were used to identify water related surface (Rogers & Kearney, 2004). The main
reason of using NDWI is that short-wave infrared (SWIR) is highly sensitive to moisture content
in the soil and the vegetation canopy. A number of studies have been conducted in use of the
spectroscopic characterization of SWIR to detect water content (Gao, 1996; Jackson et al., 2004;
McFeeters, 1996; Rogers & Kearney, 2004; Tong et al., 2004). Xiao et al. (2002b) showed that
NDWI in paddy fields exceeds NDVI derived from SPOT data for the same period of flooding
and rice-planting in eastern Jiangsu Province, China. In recent years, Xiao et al. (2006; 2005)
used anomalies between the Land Surface Water Index (LSWI) and Vegetation Indexes (NDVI
or EVI) in an algorithm to estimate the distribution of paddy fields in South China and South and
Southeast Asia. In table 4.1, detail description of the indices derived from MODI S data along
with the band number and solar spectrum has been presented.
Methodology used in the present study is originally developed by Sakamoto et al. (2007) to
detect the spatio-temporal flood distribution in the Cambodia and Vietnam from the smoothed
indexes of these differences. Sakamoto et al. (2006; 2005) derived a methodology to classify
cropping systems (e.g., double-cropping system in the rainy/dry season, triple-cropping system)
and noted regions where the number of crops per year was increased from two to three over the
interval 2002 to 2003. With some modification, the same approach is applied to the EVI and
LSWI time-series to develop flood inundation maps. Moreover, analysis has been carried out to
determine spatial extents and temporal changes of flood inundation within Bangladesh during
floods in 2007 and 2004.
Table 4.1: MODIS derived indices used to detect spatial and temporal distribution of flood.
Indices Equation
Normalized Difference Vegetation Index (NDVI) REDNIR
REDNIRNDVIρρρρ
+−
=
Normalized Difference Water Index (NDWI) SWIRRED
SWIRREDNDWIρρρρ
+−
=
Enhanced Vegetation Index (EVI)
15.765.2
+×−×+−
×=BLUEREDNIR
REDNIREVIρρρ
ρρ
Land Surface Water Index (LSWI)
SWIRNIR
SWIRNIRLSWIρρρρ
+−
=
Where, NIRρ is the reflectance of near infrared (841–875 nm, MODIS Band 2), REDρ is the
reflectance of red (621–670 nm, MODIS Band 1), BLUEρ is the reflectance of blue (459–479 nm,
MODIS Band 3) and NIRρ is reflectance of short-wave infrared (1628–1652 nm, MODIS Band 6)
of the solar spectrum.
4.4.2 Modified algorithm of flood inundation maps
The algorithm used by the Sakamoto et al. (2007) was modified in this study. A flow-chart of the
method used in this study has been shown in Figure 4.3. The previous algorithms are examined
and some components are excluded from it. In previous algorithm, wavelet based filter is used to
smooth data by removing noise component and interpolate of missing information. This
algorithm creates artificial data and therefore, that algorithm of filtering was not used in this 24
25
study. The first step is to detect cloud cover pixel from the image. If blue reflectance (Band 3 of
MODIS) is equal to or greater than 0.2 (Thenkabail, Schull, & Turral, 2005; Xiao et al., 2006), it
is considered as cloudy pixel. Using this formula data over cloudy pixel was removed from the
image. Next step is to estimate EVI, LSWI and their difference DVEL for each of the land class
cover types. In this study, discrimination of Water-related pixel and Non-Flood pixel was
conducted in accordance with the pioneering method developed by Xiao et al. (2006; 2005).
EVI, LSWI and DVEL are exclusively used to discriminate Flood, Mixed, Non-Flood and
Water-related pixels. Changes of EVI, LSI and DVEL for different land use types during 2007
are shown in Figure 4.4. If EVI is greater than 0.3, it can be classified as Non-Flood related
pixel. The EVI curve of “Forest (the Sundarbans)” land use type exhibits a value more than 0.3
during the year except flood season. EVI of permanent water bodies such as “River” and “Sea”
land use type are less than 0.05 or even negative value throughout the year. DVEL of “River”
and “Sea” land use type have a DVEL value less than 0.05. It can be infrared that water related
pixel should have DVEL less than 0.05. But for “Lake” land use type, DVEL value is not always
less than 0.05. To overcome this problem, another criterion is set to identify water related pixel.
In such cases, if EVI is less than or equal to 0.05 and LSWI is less than or equal to 0, the pixel
will be identified as Water-related pixel.
After identifying Water-related pixel it is essential to classify whether it is Flood pixel or Long
term water bodies or a Mixed type pixel. Due to moderate resolution (500m) sensor of
MODIS/TERRA, a pixel can be composed of various mixture types of land surfaces. It is
difficult to identify vegetation mixed with water and vegetation completely flooded by water. It
is found from Figure 4.4 that EVI of “Sea”, “Lake” or “River” is below 0.1 and this criterion can
be used for further classification of Water-related pixel. If Water-related pixel has EVI less than
0.1, it will be considered as Flood pixel. If EVI is greater than 0.1 but less than 0.3, Water-
related pixel will be identified as Mixed pixel. Finally, the areas which are inundated through out
the year should be separated from Flood and Mixed pixels. There have been many water bodies
in Bangladesh such as Beels and Haors where water can be found more than 6 months.
Therefore, Water-related pixel which has inundation period more than 120 days will be classified
as Long term water bodies.
Using this proposed methodology, changes of spatial extent with time are analyzed and flood
inundation maps are developed for 2004 and 2007.
Figure 4.2: Water level hydrographs of major rivers in Bangladesh for (a) year 2007 and (b) year
2004. Flood starts earlier in 2004 than in 2007.
26
Figure 4.3: Flood chart for developing Flood inundation map using MODIS data
27
Figure 4.4: MODIS derived indices: (a) EVI, (b) LSWI and (c) DVEL for the Seven Land use /
Land cover areas shown in Figure 4.1
.
28
29
4.5
Validation of proposed techniques
The proposed technique used to identify the water surface from MODIS time series data and
validated it with standard product. Figure 4.5(a) shows the distribution of inundated regions on
the 28th July 2007 (DOY 209) determined using the MODIS. In this image, Flooded, Mixed,
Long term water bodies are represented by Blue, Green and white colour. False-colour image of
MOD09 8-day composite data and daily MOD09 data for the same date are shown in Figure
4.5(b). Presence of cloud in the False colour composite image can be visualized as white
coloured pixel. Long term water bodies derived from MODIS data are also shown in the same
Figure 4.5(c). Distribution of inundation area on the 3rd August of 2007 (DOY 215) using
RADARSAT is shown in Figure 4.5(d). Inundation of RADARSAT images were developed by
used ruled based method. A threshold value more than 0.6 was considered as inundation area for
RADARSAT image. Inundated region is clearly identified in detail without any cloud-cover
effects using RADARSAT images. The influence of cloud cover is considerably reduced in
MOD09 8-day composite data as shown in Figure 4.5(b). Although, MOD 09 production is not
cloud free and need correction for cloud removal.
A comparison of MODIS derived inundation map on 28th July (DOY 209) with the subsequent
available RADARSAT derived inundation map on 3rd August (DOY 215) is shown in Figure 4.6
using image crossing. Most of the area in both images shows quite a good match between images
from these two types of satellite and sensors. In south west part, MODIS shows more inundation
areas than RADARSAT. On the other hand, in the north-east region RADARSAT presents more
area as inundated than MODIS image. Figure 4.7 shows scattered plot of the crossing of both the
inundation maps. Value of R2 was found 0.96 between the inundation map derived from MODIS
and RADARSAT. A very good agreement between these two products shows the high
capabilities of estimating inundating area using MODIS with this algorithm.
Although inundation areas in both images shown high correlation, it is difficult to detect
inundated regions under high-vegetation coverage using moderate resolution optical sensors such
as MODIS. Therefore, it would be difficult to accurately identify the inundated area of flooded
forests or marsh in the MODIS products. Figure 4.8 shows temporal changes of flood and
mixture pixels for four types of paddy fields (single cropped irrigate rice, single cropped rain fed
30
4.6
rice, double cropped irrigated rice, and triple cropped irrigated rice), forest and settlement areas.
During flood season (May to September), more mixed pixels were found in the triple and double
cropped irrigate areas than other land use types. Mixed pixels may lead to errors of
underestimation of Flood areas in MODIS products than that of RADARSAT products. Hence,
north east region where mostly double and triple irrigated rice grows shows less Flood pixels
than other regions. It is possible to enhance the estimation accuracy using DEM data or higher-
resolution data (Brivio, Colombo, Maggi, & Tomasoni, 2002; Wang, Colby, & Mulcahy, 2002)
which need to be investigated in future. Although there is a fundamental overestimation problem
resulting from mixed pixel effects, it can be assumed that temporal MODIS products provide
useful criteria for determining flood inundation.
Results and discussions
4.6.1 Spatial extents of floods in Bangladesh
The spatial extents of flood inundation were changed with the progress of flood and can be
visualized through displaying successive maps. Changes of the extent of the flood inundation in
Bangladesh during floods in 2007 and 2004 were studied. Due to limitation of space, 3 images of
each major flood were used for analysis. Figure 4.9 shows the estimated flood area for the 20th
July [DOY 201] to 5th August [DOY 217] during floods in 2007 and 2004 respectively. In 2004,
flood started following a rapid increase in water level from 20th July (Figure 4.2) and reached its
largest extent during 28th July [DOY 209]. Flood 2007 started two weeks later than floods in
2004, therefore the increase of the extent of water level from 28th July [DOY 209] and reaches its
largest extend on 5th August [DOY 217]. Upon visualization, it is clear that the spatio-temporal
distribution of the inundated area varies from year to year. The scale of the inundation varies
with the amount of water carried by the rivers.
It is also possible to detect maximum extent of the flooded area by overlaying a series of images
during the flood (Sheng & Gong, 2001). This inundation map can be useful to create flood
vulnerability maps and flood risk zones. Figure 4.10 shows maximum area of food inundation
during floods in 2004 and 2007 respectively. Blue, green, and white colours represent areas of
Flood, Mixture, and Long-term water bodies, respectively. It is also evident from this map that
the extent of flooding varies from year to year. The areas which are common for both major
floods should be classified as the most vulnerable areas.
Figure 4.5: Spatial comparison of (a) MODIS derived inundation map of 29 July 2007, (b) MODIS 8-day false colour composite map (RGB=Band 6,Band2,Band1) of 29 July 2007, (c) Long term water bodies in 2007 using MODIS data, (d) Inundation map using RADARSAT
image on August 03
31
Figure 4.6: Overlay of MODIS derived inundation map on DOY 209 with the nearest available
RADARSAT derived inundation map on DOY 215. Inundation area derived from MODIS includes Flood pixels and pixels of Long term water bodies.
Figure 4.7: Correlation of inundation area determining from MODIS with that of RADARSAT.
Correlation coefficient R2 is found very high of about 0.96.
32
Figure 4.8: Temporal Changes of Flood and Mixture pixels for four types of paddy fields (Single
cropped irrigate rice, Single cropped rain fed rice, Double cropped irrigated rice, and Triple cropped irrigated rice), Forest and Settlement areas
33
Figure 4.9: Spatial distribution of flood inundated area during July and August months of 2007 and 2004. Flood pixels are in blue colour, Mixture pixels are in green colour, Long term water
bodies are in white colours and other areas are in white colour.
34
Figure 4.10: Flood inundation map of Bangladesh using MODIS images for (a) Year 2004 and (b) Year 2007. Flood pixels are in blue colour, Mixture pixels are in green colour, Long term
water bodies are in white colours and other areas are in white colour.
4.6.2 Temporal characteristics of floods
The start date, end data and duration of flood varies for each flood. Time series MODIS data can
be effectively used to determine these dates and produce spatially distributed maps of these
dates. Figure 4.11 shows estimates of the start dates, end dates, and duration of inundation
during floods in 2007 and 2004. As these dates are based on images of 8-days average value, it
is not possible to represent exact start and end dates rather it represent start and end weeks of
flood.
The start dates for floods in 2004 are earlier floods in 2007. Date of crossing danger level at
Bahdurabad of the Brahmaputra river was found 27th of July and 11th of July during floods in
2007 and 2004 respectively (Figure 4.2). This similar pattern has been found in the spatial
distribution of flood inundation maps of 2007 and 2004 (Figure 4.11). The duration of floods at
the Bahadurabad in the Brahmaputra river was found 21 days and 15 days during floods in 2007
and 2004 respectively. The pixel information of the flood duration maps (Figure 4.11) shows
more red colour for floods in 2004 than floods in 2007.
35
Figure 4.11: Spatial distribution of (a) start date, (b) end date and (c) duration of flood for 2004
and 2007
36
37
4.7
At Bhiarab bazaar station in the Meghna river, date of crossing danger level was 30th of July and
11th of July during floods in 2007 and 2004 respectively (Figure 4.2). When focusing on the
Flood pixels in Figure 4.11, the timing of the appearance of Flood pixels in 2004 and 2007 is
obviously shows the similar characteristics. Duration of floods above danger level at the Bhairab
bazaar station in the Meghna river was 37 days and 38 days during floods in 2007 and 2004
respectively (Figure 4.2). In the flood duration map, similar features were found for this river
basin. The colour of inundation pixels is more reddish for floods in 2004 than that of 2007.
Conclusions
This study modifies a methodology which was developed by Sakamoto et al. in order to detect
spatial extents and temporal changes of flood inundation of Bangladesh during monsoon season.
Using this modified methodology, MODIS satellite images were used develop flood inundation
maps for floods in 2007 and 2004. This low resolution (500m) MODIS based maps area
compared with subsequent flood inundation maps based on high resolution (50m) RADARSAT
satellite images. MODIS estimates show strong correlation with the inundation areas derived
from RADARSAT with R2 values of 0.96. Considering this fact, the flood maps derived from
MODIS images shows ability to flood characteristics and behavior. Such inundation maps will
be useful for integrating water resources management and the maintenance of ecosystems of
wetlands of Bangladesh.
38
5.1
Chapter 5: Floods around Dhaka city
Hydrologic condition of Dhaka city
Dhaka city is surrounded by four major river systems as shown in Figure 5.1. The south of
Dhaka city is surrounded by the Buriganga river. The western part of Dhaka is bounded by the
Truag river which is connected by a small Tongi Khal on the north. The eastern part of Dhaka is
bounded by the Balu river which is also hydrologically connected with Tongi Khal. In terms of
flood protection works, Dhaka city can be divided into two parts: Dhaka west and Dhaka east.
The area of Dhaka west is 243 km2 and is surrounded by embankment and embankment cum
road, where as the area of Dhaka east is 119 km2 and consists of unprotected lowlands within the
floodplain of the Balu river (JICA, 1987). The most of the areas of Greater Dhaka city are urban
areas including residential areas, large commercial complex, offices, schools, hospitals and small
garments & other industries. The population of Greater Dhaka city was 4.47 million in 1990,
which is projected to increase to 8.59 million in 2010 (JICA, 1991). Dhaka is not only the
nation’s capital but also has potential to become a mega city by 2010. Condition of Dhaka city
during flood period always draws special attention due to its strategic importance.
Hence, a special emphasis was given to reveal the hydrologic characteristics of the Dhaka.
Analysis has been carried out on the flood situation of Dhaka city during the flood in 2007.
Hydrologic aspects of Flood 2007 of the surrounding rivers of Dhaka city are also compared
with the major floods in recent past.
Figure 5.1: Greater Dhaka city area and surrounding river systems
39
40
5.2 Hydrologic Characteristics of Major Floods in Dhaka City
Water level data of one major station in each of the four surrounding rivers of Dhaka city has
been analyzed. Data from Dhaka station in the Buriganga river, Mirpur station in the Turag river,
Tongi station in the Tongi Khal and Demra station in the Balu river were used to compare flood
situation. Figure 5.2 shows water level hydrographs of surrounding rivers for four major flooding
years, namely 1988, 1998, 2004 and 2007. In the next subsections, details condition of the rivers
during the above four mentions major flood periods will be discussed.
5.2.1 Buriganga River at Dhaka (Mill barrack) Station
The magnitudes of peak flows at Dhaka (Mill barrack) station in the Buriganga river in 2007,
2004, 1998, 1988 were found 0.02m, 0.7m, 1.23m and 1.58m PWD above danger level
respectively (Table 5.1). During Flood 2007, water level in the Buriganga river crossed danger
level. The magnitude of peak flood was much higher in 2004, 1998 and 1988. The highest water
level was found in 1988. Water level hydrographs of the Buriganga river at Dhaka station was
plotted for floods in 2007, 2004, 1998 and 1988 and shown in Figure 5.3(a). The start of crossing
danger level in the Buriganga river was found on 7th August, 20th July, 26th July and 29th August
for floods in 2007, 2004, 1998 and 1988 respectively. Flood wave came later in 2007 than floods
in 2004 & 1998 and earlier than flood in 1988. Durations of flood in the Buriganga river at
Dhaka station in 2007, 2004, 1998 and 1988 were found 1, 17, 56 and 22 days respectively.
Floods 2007 was of the shortest duration, while Flood 1998 was of the longest in the Buriganga
river. It can be concluded that in terms of magnitude and duration, Flood 2007 in the Buriganga
river was less significant than those of other three floods of recent past.
5.2.2 Balu River at Demra Station
The height of peak flood level at Demra station at Balu river in 2007 was 0.5m above danger
level. During the other major floods – 2004, 1998 and 1988, the danger level in the Balu river
was not defined. Water level hydrographs of Demra river at Balu was plotted for floods in 2007,
2004, 1998 and 1988 and are shown in Figure 5.3(b). The date of crossing danger level in
Buriganga river was found on 7th August for flood in 2007. Duration of flood in Balu river at
Demra station in 2007 was 20 days.
(a) Flood 1988
4
5
6
7
8
9
12-J
ul
22-J
ul
1-Au
g
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ep
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Wat
er le
vel (
m, P
WD
)
Buriganga river at DhakaBalu river at DemraTurag river at MirpurTongi khal at TongiDhaka DL=6.0Mirpur DL=5.94Demra DL=5.75Tongi DL=6.08
(b) Flood 1998
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Buriganga river at DhakaBalu river at DemraTurag river at MirpurTongi khal at TongiDhaka DL=6.0mMirpur DL=5.94mDemra DL=5.75mTongi DL=6.08m
(c) Flood 2004
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Wat
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m, P
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)
Buriganga river at DhakaBalu river at DemraTurag river at MirpurTongi khal at TongiDhaka DL=6.0mMirpur DL=5.94mDemra DL=5.75mTongi DL=6.08m
(d) Flood 2007
4
5
6
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10-J
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vel (
m, P
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)
Buriganga river at DhakaBalu river at DemraTurag river at MirpurTongi khal at TongiDhaka DL=6.0mMirpur DL=5.94mDemra DL=5.75mTongi DL=6.08m
Figure 5.2: Water Level Hydrographs of surrounding rivers for four major flooding years: (a) 1988, (b) 1998, (c) 2004 and (d) 2007
41
42
Table 5.1: Comparison of characteristics of Flood 2007, 2004, 1998 and 1988 in the surrounding rivers of Dhaka city.
2007 2004 1998 1988 Parameters River Gauge Stn.
Buriganga Dhaka 6 6 6 6.1 Turag Mirpur 5.94 5.94 5.94 5.94 Tongi Khal Tongi 6.08 6.08 6.08 6.08
Danger Level in meters above PWD datum Balu Demra 5.75 - - -
Buriganga Dhaka 07.08.07 20.07.04 26.07.98 29.08.88
Turag Mirpur 03.08.07 & 16.09.07
17.07.04 18.07.98 24.08.88
Tongi Khal Tongi 01.08.07 & 18.09.07
21.07.04 22.07.98 28.08.88
Date of crossing Danger Level at rising stage
Balu Demra 02.08.07 & 16.09.07
- - -
Buriganga Dhaka 07.08.07 05.08.04 20.09.98 20.09.88
Turag Mirpur 18.08.07 & 24.09.07
11.08.04 24.09.98 22.09.88
Tongi Khal Tongi 21.08.07 & 25.09.07
11.08.04 24.09.98 21.09.88
Date of crossing Danger Level at falling stage
Balu Demra 16.08.07 & 20.09.07
- - -
Buriganga Dhaka 0.02 0.7 1.23 1.58
Turag Mirpur 0.68 1.35 2.03 2.41
Tongi Khal Tongi 0.78 1.05 1.46 1.75
Height of peak flood level in meter above Danger Level Balu Demra 0.5 - - -
Buriganga Dhaka 1 17 56 22
Turag Mirpur 25 26 69 30
Tongi Khal Tongi 29 22 65 25
Duration of flood in days above Danger Level Balu Demra 20 - - -
43
5.2.3 Turag River at Mirpur Station
The magnitudes of peak floodwater levels at Mirpur station in the Turag river in 2007, 2004,
1998, 1988 were found 0.68m, 1.35m, 2.03m and 2.41m PWD above danger level respectively
(Table 5.1). During Flood 2007, the water level in the Turag river was less than previous three
floods. Unlike the Buriganga river, the highest water level was found in this river in 1988. Water
level hydrographs of the Turar river at Mirpur was plotted for floods 2007, 2004, 1998 and 1988
and are shown in Figure 5.3(c). The dates of crossing of danger level in the Turag river were
found on 3rd August, 17th July, 18th July and 24th August for floods 2007, 2004, 1998 and 1988
respectively. Flood wave came later in 2007 than in floods 2004 and 1998. In general, flood
wave crosses danger level in the Turag river earlier than in the Buriganga river. The durations of
flood in the Turag river at Mirpur station in 2007, 2004, 1998 and 1988 were found 25, 26, 69
and 30 days respectively. Duration of Flood 2007 was similar to Flood 2004 which was almost
one third duration of that of Flood 1988.
5.2.4 Tongi Khal at Tongi Station
At Tongi station in Tongi Khal, the magnitudes of peak floods in 2007, 2004, 1998, 1988 were
found 0.78m, 1.05m, 1.46m and 1.75m above danger level respectively (Table 5.1). Unlike the
Turag and Buriganga river, flood peak was much less in Flood 2007 than other three floods in
recent past. Although the highest water level was found in 1988, there was not much difference
between the peak water level in 1998 and 1988 in this Khal. Water level hydrographs of Tongi
Khal at Togi was plotted for floods 2007, 2004, 1998 and 1988 and are shown in Figure 5.3(d).
Date of crossing of danger level in the Tongi Khal was found on 1st August, 21st July, 22nd July
and 28th August for floods 2007, 2004, 1998 and 1988 respectively. Flood wave came earlier in
2007 than other three major floods. The durations of flood in Tongi Khal at Tongi station in 2007,
2004, 1998 and 1988 were found 29, 22, 65 and 25 days respectively. Flood 2007 was longer
than floods in 2004 and 1988 and shorter than flood in 1998 in terms of duration in the Tongi
Khal. Flood 2007 in the Tongi Khal is prolonged but its severity was much less than previous
floods of recent past.
(a) Buriganga River (at Dhaka)
3
4
5
6
7
8
930
-Jun
10-J
ul
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(m,P
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)
1988199820042007DLRHWL
RHWL
DL
(b) Balu River (at Demra)
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1988199820042007DLRHWL
RHWL
DL
(c) Turag River (at Mirpur)
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(m,P
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)
1988199820042007DLRHWL
RHWL
DL
Tongi Khal (at Tongi)
3
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30-J
un
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(m,P
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)
1988199820042007DLRHWL
RHWL
DL
Figure 5.3: Water level hydrograph of (a) the Buriganga at Dhaka, (b) the Balu at Demar, (c) the Turag river at Mirpur and (d) the Tongi Khal at Tongi stations of floods in 2007, 2004, 1998 and
1988.
44
45
5.3 Conclusions
Hydrological aspects of floods in the surrounding rivers of Dhaka city were discussed in details
in the previous sections. Now, this investigation will be concluded by focusing on some common
characteristics of a flood such as flood peak, flood duration and time of occurrence. In the
following subsections, a summary of numerous critical features of Flood 2007 will be compared
with other three major floods in recent past.
5.3.1 Flood Peak
Magnitude of the peak flood above danger level of all the adjacent rivers of Dhaka city in 2007
was below the level of floods in 2004, 1998 and 1988. The highest flood peak was found in 1988
for all the rivers. In 1998 and 2004, the magnitude of the highest flood level was similar and was
lower than that of in 1988.
5.3.2 Flood Duration
Duration of Floods in the Buriganga was only a single day in 2007. Flood duration of other
adjacent rivers was more than twenty days in 2007. The longest flood was found in 1998 and it
was almost 3 times longer than floods in 2007. Durations of water level above danger level in
1998 and in 2004 were similar to the duration of Flood 2007.
5.3.3 Flood Entrance
The date of crossing of danger level at the rising stage of flood is the first week of August during
flood 2007. Danger level was first crossed in Tongi Khal on 1st August in 2007. Next day, the
danger level of Balu rive was crossed and after two days the danger level of the Turag river was
crossed. After one week of crossing of danger level of the Tongi Khal, the water level of the
Buriganga river crossed the danger level. In 1998 and 1988, floods were observed first in the
Turag river, later in the Tongi Khal and finally in the Buriganga river. But, Flood 2004 was
observed first in the Turag river, then in the Buriganga river and finally in the Tongi Khal.
46
6.1
Chapter 6: Performance of flood control works around Dhaka city
Comparison of the performance of Flood control structures
A number of flood control works were cinstructed to protect the city from the devastation of the
flood. Figure 6.1 shows the location of flood control works around Dhaka city. These flood
control works were prepared and rearranged based on the study of flood mitigation and storm
water drainage plan in the Master Plan for Greater Dhaka Protection Project (JICA, 1987, 1991,
1992). The major structure to protect the western part of the city is earthen embankment along
the surrounding rivers. Eastern part of the city is yet to be protected from monsoon flooding.
Western and eastern part of the city is divided by a highway which also acts as flood protection
wall for western part of the city. Three major permanent pumping stations are situated in the
West Dhaka to drain trapped water inside embankment. Dholai Khal permanent pump station is
located on the canal Dholai Khal which discharges storm water in the Buriganga river. Other
two permanent pump stations are at Kallayanpur and at Goranchatbari. Both of these pump
stations pump storm retained water in the Truag river during flood season. Besides, these pump
stations together with a number of temporary pumps were operating during the flood period. The
capacity of these temporary pumps is much less as compare to the permanent pumps. At least 50
small pumps were operating at the Rampura regulator and 30 small pumps were operating in
Segunbagicha regulator. Along the embankment of the Buriganga between Dholai Khal pump
station and Kallayanpur pump station, temporary pumps were found in more than 27 locations.
In these locations 1 to 4 pumps were installed temporarily during the Flood 2007. The main
purpose of these pumps was to drain out congested water inside the embankment.
Figure 6.2 shows difference of riverside and protected side water level during floods in (a) 1998,
(b) 2004 and (c) 2007 of the surrounding major flood control works. These data were collected
from field visits during and after the major floods in 1998, 2004 and 2007. During last three
major floods, the difference between country side and protected side was found satisfactory for
three permanent pump stations located at Dholai Khal, at Kallayanpur and at Goranchatbari. On
the other hand, the performances of temporary pumps located at Rampura regulator and at
Segunbagicha regulator were not satisfactory. The difference of the water level between country
and protected side at these regulators (where temporary pumps installed) was close to zero. In the
next subsections, details comparison will be drawn on the performance of temporary and
permanent pump stations.
Figure 6.1: Map of flood control works of Dhaka city during Flood 2007.
47
-0.5
0
0.5
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1.5
2
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3
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Jul-2
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Goran chatbariKallayanpurDholai KhalSegun bagichaRampura
(a) Flood 1998
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(b) Flood 2004
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Goran chatbariKallayanpurDholai KhalSegun bagichaRampura
(c) Flood 2007
Figure 6.2: Difference of riverside and protected side water level during floods in (a) 1998, (b)
2004 and (c) 2007 of the surrounding major flood control works.
48
49
6.2
6.3
Performance of Goranchat Bari and Kallayanpur pump station
Figure 6.3 a) to c) shows the water level of river side and protected side of the Turag river at
Goranchat Bari and at Kallayanpur pump stations during floods 1998, 2004, 2007 respectively.
During the flood 1998, Goranchat Bari pump station was not completed and performance of the
station was not possible to ascertain. But during floods in 2004 and 2007, the performance of
Goranchat Bari pump station was very well and pumping was started quite early to avoid any
mishap. It has been found from the plots that pumping should be started when the water level is
4.00 meter above datum. Otherwise, it will be too late to avoid water logging and flooding in the
protected side.
On the other hand, Kallayanpur pump station showed satisfactory performance during all the
three major floods. The difference of water level was always below the flooding level of that
area. It was also found from the plots that it should start pumping when water level is below 4.0
meter above datum.
One factor needs to be considered is rainfall magnitude and duration with in the coverage area of
the pump station. Pumping has been started earlier in 2004 than in 2007 because of a high
intensity rainfall occurred in middle of July. It has been found from the field visit that the
retention pond area of these pump stations are reducing day by day by illegal encroachments.
Although both these permanent pump stations showed satisfactory performance in Flood 2007;
in near future, the performance of the pump stations may be at stake. The Government of
Bangladesh should take necessary actions to define and protect retention pond area from
unauthorized land filling.
Performance of Rampura and Dholai Khal pump station
The performance of Rampura regulator and Dholai Khal pump stations was compared. Figure
6.4 a) to c) shows water levels in both country side and protected side of these flood control
works during floods in 1998, 2004 and 2007 respectively. The permanent pump station in Dholai
Khal shows satisfactory performance during all the three major floods. Water level difference
was very high in this pump station even after a high intensity rainfall.
50
6.4
On the other hand, Rampura regulator on Begunbari Khal has no permanent pump station. A
number of (around 50) temporary pumps with low capacity were operating during Flood 2007.
The difference of water level of country side and protected side was negligible. The area
protected by this regulator suffered from huge water logging during flood season. One solution
of this situation is to install permanent pump station or to close gate earlier and start pumping out
water so that huge water cannot accumulate inside Begunbari Khal.
Unprotected East part of the Dhaka city
Unfortunately, the eastern part of Dhaka city has suffered from flooding in all the major floods.
There has always been a concern about this flood situation of this part of the nation’s capital.
Right after flood in 1998, there has been many concerns and discussions to construct
embankment in the eastern part of the city. Government has been considering to construct
embank or embankment cum bypass road in the east side of the city. But, before construction of
such embankment, the drainage of the Dhaka East should be well planned. City dwellers have
bad experience of water logging and drainage congestion in the western part due to the
embankment. Lessons should be learned from the drainage situation of the western part of the
city. To avoid similar situation in eastern part of the city, details drainage plan such as routes of
canals, retention ponds, location of pump stations and regulators, etc. should be done. Otherwise,
the eastern part will also suffer from water logging even from a small rainfall.
During Flood 2007, a number of people became sick by drinking polluted water. The cases of
diarrhea were gone passed by records of all time high during Flood 2007. According to the local
people, the mean source of this disease was from water supplied by the municipality. Most of the
eastern part of the city was under water during Flood 2007 and the polluted flood water got
chance to enter inside the pipelines of drinking water supply. The water supply lines of the
municipality are not enough sealed to resist intrusion of polluted water. The situation was also
aggravated by discharging untreated water from the industry in to the river system. Except a few
industries of the city, most of them don’t have water treatment plant. During the flood time, these
untreated waste water mixed with flood water increased water borne diseases such as diarrhoea
and skin diseases. Government should take necessary steps, so that every industry should treat
wastewater before discharging into the river or water system. Preservation of ecological
resources and wetlands should be given sufficient consideration.
3
4
5
6
7
8
9
Aug
-01
Aug
-11
Aug
-21
Aug
-31
Sep
-10
Sep
-20
Sep
-30
Oct
-10
Wat
er L
evel
in m
,PW
D
0
50
100
150
200
250
300
350
400
450
500
Rai
nfal
l (m
m)
RainfallGoran chatbari R/SGoran chatbari P/Skallayanpur R/SKallayanpur P/S
(a) Flood 1998
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
Aug
-04
Aug
-14
Aug
-24
Sep
-03
Sep
-13
Sep
-23
Oct
-03
Wat
er L
evel
in m
,PW
D
0
50
100
150
200
250
300
350
400
450
500
Rai
nfal
l (m
m)
RainfallDholai khal R/SDholai khal P/SRampura R/SRampura P/S
(a) Flood 1998
3
4
5
6
7
8
9
Jul-1
2
Jul-1
7
Jul-2
2
Jul-2
7
Aug
-01
Wat
er L
evel
in m
,PW
D
0
50
100
150
200
250
300
350
400
450
500
Rai
nfal
l (m
m)
RainfallGoran chatbari R/SGoran chatbari P/Skallayanpur R/SKallayanpur P/S
(b) Flood 2004
4
4.5
5
5.5
6
6.5
7
7.5
Jul-1
2
Jul-1
4
Jul-1
6
Jul-1
8
Jul-2
0
Jul-2
2
Jul-2
4
Jul-2
6
Jul-2
8
Jul-3
0
Aug
-01
Wat
er L
evel
in m
,PW
D
0
50
100
150
200
250
300
350
400
450
500
Rai
nfal
l (m
m)Rainfall
Dholai khal R/SDholai khal P/SRampura R/SRampura P/S
(b) Flood 2004
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
Jul-2
2
Jul-2
7
Aug
-01
Aug
-06
Aug
-11
Aug
-16
Aug
-21
Wat
er L
evel
in m
,PW
D
0
50
100
150
200
250
300
350
400
450
500
Rai
nfal
l (m
m)
RainfallGoran chatbari R/SGoran chatbari P/Skallayanpur R/SKallayanpur P/S
(c) Flood 2007
3
3.5
4
4.5
5
5.5
6
6.5
7
Jul-2
2
Jul-2
7
Aug
-01
Aug
-06
Aug
-11
Aug
-16
Aug
-21
Wat
er L
evel
in m
,PW
D
0
50
100
150
200
250
300
350
400
450
500
Rai
nfal
l (m
m)Rainfall
Dholai khal R/SDholai khal P/SRampura R/SRampura P/S
(c) Flood 2007
Figure 6.3: Preformence of Goranchat Bari and
Kallyanpur pump station during floods in (a) 1998, (b) 2004 and (c) 2007
Figure 6.4: Performance of Rampura and Dholai Khal pump station during floods in (a) 1998, (b)
2004 and (c) 2007
51
52
6.5 Filed visit to flood control structures of Dhaka City on August 16, 2007
BUET study team has paid several visits to the major flood control structures around the Dhaka
city during Flood 2007. At that time of their visits, study team interviewed local people, pump
operators and responsible employees of both BWDB and Dhaka WASA. Several photographs
were taken to give an idea to the readers about the conditions and the performance of those
structures. In the following subsections, some of the issues will be discussed which were
revealed during the field visits.
6.5.1 Dholai Khal Pump House
During the flood season, the water level of river side is normally higher than that of protected
side. At that time, floating solid waste carried by Dholai khal was accumulated and created mat
near Dholai Khal pump station (Photo 6.1). Solid waste management of the city needs to be
improved and also maintenance of the sewer system should be done more frequently during
flood season.
6.5.2 Rampura temporary pump station
Rampura temporary pump station has negligible impact on the drainage congestion (Photo 6.2).
Pumping capacity of these temporary pumps is much lower than the amount of water stored.
Also, the start time of pumping is always not accurately identified by the authority and most of
the time it is delayed to start pumping. Solution of the problem is to install a permanent pump
house at the end of the Segunbagicha khal which is far upstream of the Rampura regulator.
6.5.3 Segunbagicha temporary pump station
Many temporary pumps were operated on the Segunbagicha regulator during Flood 2007. The
main purpose of these pumps was to keep the level of inside water below flood level.
Unfortunately, these temporary pumps have no significant effect on the water logging. BUET
team has measure inside and outside water level of the Segun bagicha regulator during Flood
2007 (Photo 6.10). Unlike Rampura pump stations, the capacity of these temporary pumps are
not enough to drain out huge amount of retained inside of the Segun Bagicha Khal. One solution
could be installing permanent pumping station upstream of this Khal system.
53
6.5.4 Kallayanpur pump station
Kallayanpur pump station performed very well during the Flood 2007. BUET study team
collected inside and riverside data of the regulator on the pump station during their field visit
(Photo 6.3). Although performance is satisfactory during the Flood 2007, the water logging due
to drainage congestion has been increase in this area. The major cause of this congestion is the
reduction of retention pond area. It was found during field visits that urban encroachments
gradually have increased and reduced retention pond area of the pump station (Photo 6.8).
Retained water was highly polluted and created bad odour. The situation is aggravated day by
day and the concerned authority should act immediately to stop those encroachments inside the
pond area.
6.5.5 Goranchatbari Pump station
The condition of Goranchatbari pump station was found very healthy during flood 2007 (Photo
6.4). It has huge retention area and the pump is operating very efficiently to drain the retained
water into the Turag river. Air was fresh and the aquatic condition was also in good state.
Although the retention area is now sufficient for the drainage water to hold, the situation will be
degraded in near future. Due to the immense pressure of the urbanization, ongoing competition
has been found to fill the wetlands adjacent to the pump station. A number of dredgers were
operating in the Turag river to fill wetlands (Photo 6.5). This land filling will reduce the retention
pond area and will pose serious threat to efficiency and effectiveness Goranchatbari pumping
station.
6.5.6 Temporary Pumps along the Buriganga River
A number of temporary pumps operated during the Flood 2007 on the embankment of Buriganga
river (Photo 6.7). Temporary pumps pumped congested water inside embankment. It has been
found from interviewing local people that this polluted water is major cause of water borne
diseases during flood period.
The Buriganga river suffered from man made interventions along its course. The water condition
becomes degraded day by day. Dumping of industrial wastes along the sides of the river,
polluted its water seriously. Untreated water from Ternaries is one of the major sources of this
industrial pollution. Near Kellar mor, heavy water hyacinth grows due to polluted water from the
54
pumping of untreated drainage water inside embankment (Photo 6.9). Odours and bad smells
from logged water during the flood season are very common along the sides of the embankment
of Buriganga river.
6.5.7 Hatir Jheel Lake and Begun Bari Khal
During Flood 2007, we have found many illegal encroachments to grasp Hatir Jheel Lake, one of
the major retention areas of the heart of the city (Photo 6.11). A number of developing company
filled the lake area to build new hotels and apartments. Also, one of the existing luxury hotels
extended its boundaries inside the lake. This study team found the situation very vulnerable and
the whole lake area might be captured by illegal settlers. Recently, government has taken a
project to improve and restore the Hatil Jheel Lake. Such initiatives could save this lake and its
surrounding environment.
6.5.8 Begun Bari Khal
Begun Bari Khal is one the main natural drainage system of the Dhaka city. Unlike Hatir Jheel
lake, this Khal also suffered by the illegal encroachment from both sides of its embankment. The
retained water from Hatir Jheel Lake is discharged into the Begun Bari Khal. During the flood,
the condition of retained water was found very much polluted. It also identified one of the major
causes of water pollution in the Begun Bari Khal.
Another main source of polluted water is Panthopath Box culvert. This culvert replaced natural
drainage system of the Panthopath and water inside the closed Box culvert is highly polluted. A
number of fatalities were found while cleaning this Box culvert due to the trapped toxic gas
inside the Box culvert. This polluted water carried by the Box culvert is initially drained to the
Hatir Jheel Lake. Finally this polluted water carries all the way to the Begun Bari Khal and it
degrades the ecosystem of the Khal (Photo 6.12).
Photo 6.1: Inlet of Dholai Khal pump house [Floating mat of waste carries by Dholai khal. Solid waste management of the city needs to be improve ]
Photo 6.2: Rampura temporary pump station [Negligible impact on drainage congestion. Permanent pumps needs to be installed.]
Photo 6.3:Data collection from Kallayanpur pump station [Digital data recording system can help researchers and other users to get information quickly]
Photo 6.4:Retention pond of Goranchat Bari [Only pumping stations where water is not much polluted and air is fresh.]
Photo 6.5:Dredging in Turag river to fill wetlands of Dhaka west. [Serious thread to retention ponds of Goranchat Bari pumping stations]
Photo 6.6:Temporary pumps to drain water logged near Kellar More [Drainage congestion inside embankment. Some says that this polluted water is major cause of water born diseases ]
55
Photo 6.7: Temporary pumps near Hazaribag [Untreated waste water causes serious pollution of Buriganga river. Water treatment system should be used.]
Photo 6.8: Retention ponds of Kallayanpur pump station [Encroachments gradually increases and reduces retention pond area. Authority should act immediately. ]
Photo 6.9: Buriganga River near Kellar mor [Water hyacinth grows due to polluted water comes from the pumping of untreated drainage water inside embankment]
Photo 6.10: Inside WL of Segun bagicha temporary pump station [Similar story of Rampura pump station. Permanent system should be installed.]
Photo 6.11:Illegal encroachments tried to grasp Hatir Jheel Lake, one of the major retention area of the heart of the city.
Photo 6.12: Polluted water is discharge in the Begun Bari Khal. The water becomes polluted while it was carried by a Panthopath Box culvert.
56
57
7.1
Chapter 7: Conclusions and recommendations
Conclusions
Flood 2007 has many exceptional characteristics than other floods in recent year. In this study
many of those have been revealed though secondary data and image analysis. This study can be
concluded by the following remarks.
Source of Flood
1. The main source of floods in Bangladesh is rainfall in the upper catchment of the Ganges,
the Brahmaputra and the Megha rivers. Mean monthly rainfall plot of TRMM satellite
data shows that for both the Meghna and the Brahmaputra basin, rainfall is higher in July
2007 than last two years. This excess rainfall was accumulated and carried by the
Brahmaputra and the Meghna rivers and caused flooding in Bangladesh.
Floods in major rivers
2. No flooding has been occurred in the Ganges river during 2007. Water level of the
Ganges river has never exceeded its dangers during floods in 2007 and 2004. The date of
crossing danger level in the Brahmaputra river was found 27th July, 11th July, 7th July and
9th July during floods in 2007, 2004, 1998 and 1988 respectively. Flood 2007 comes later
than previous three floods in recent time in the Brahmaputra river. In the Ganges river,
the dates of crossing danger level were 20th and 16th August during floods in 1998 and
1988 respectively. The dates of crossing of danger level in the Meghna river were 30th
July, 11th July, 20th July and 6th July during floods in 2007, 2004, 1998 and 1988
respectively. Flood came later in the Meghna river than other three previous major
floods in recent past.
3. Magnitude of peak floods in the Brahmaputra river was found 0.88m, 0.68m, 0.87m and
1.12m above danger level during floods in 2007, 2004, 1998 and 1988 respectively.
Flood 2007 was more severe in the Brahmaputra river basin than Flood 2004. In the
58
Ganges river, the heights of peak flood above danger level were 0.94m and 0.62m during
1998 and 1988 respectively. The highest water levels in Meghna river were found 0.69m,
1.53m, 1.08m and 1.41m above danger level during floods in 2007, 2004, 1998 and 1988
respectively. In terms of magnitude, Flood 2007 was well below than Flood 2004 and
other floods in recent past.
4. Durations of floods above danger level in the Brahmaputra river were found 21, 15, 67
and 16 days for floods in 2007, 2004, 1998 and 1988 respectively. Flood 2007 was longer
than floods in 2004 and 1988 though it is shorter than Flood 1998. In terms of both
duration and magnitude Flood 2007 exceeds Flood 2004. Floods above danger level stays
26 and 23 days in the Ganges river during floods in 1998 and 1988 respectively. In the
Meghna river, duration of floods above danger level was 37, 38, 67 and 75 days during
floods in 2007, 2004, 1998 and 1988. Flood 2007 stayed for similar days to floods in
2004 but shorter than floods in 1998 and 1988.
Flood mapping using satellite data
5. Detecting spatio-temporal changes in flood inundation was devised to use in assessing
seasonal and annual changes in inundation cycles from time-series MODIS data. The
estimates show a strong correlation with the inundated area derived from RADARSAT
products [R2: 0.96]. The products derived from MODIS 500m imagery shows the ability
to study flood dynamics and performs similar to RADARSAT based flood assessments.
Considering that MODIS products have a great advantage in the high-frequent
observation, we conclude that this is a useful method to clarify the entire extent of the
temporal floods in Bangladesh.
Floods around Dhaka city
6. The highest water levels above danger level in the Buriganga river were 0.02m, 0.7m,
1.23m and 1.58m during floods in 2007, 2004, 1998 and 1988 respectively. Magnitudes
of peak flood in the Turag river were 0.68m, 1.35m, 2.03m and 2.41m during floods in
2007, 2004, 1998 and 1988 respectively. Water level of flood peaks in the Tongi Khal
were 0.78m, 1.05m, 1.46m and 1.75m during floods in 2007, 2004, 1998 and 1988
59
respectively. The highest water level was 0.5m above danger level during flood in 2007.
Danger level of the Balu river above danger level was not set before 2007 and it was not
possible to estimate it. It was found that in terms of magnitude, Flood 2007 around all the
rivers around Dhaka city were less severe than previous major floods in recent past.
7. Durations of floods above danger level in the Buriganga river were 1, 17, 56, 22 days
during floods in 2007, 2004, 1998 and 1988 respectively. In the Turag river, durations of
floods above danger level were 25, 26, 69, 30 days during floods in 2007, 2004, 1998 and
1988 respectively. Number of days above danger level in the Tongi Khal was 29, 22, 65
and 25 during floods in 2007, 2004, 1998 and 1988 respectively. Based on danger level
on the Balu river, the duration of floods above danger level was more than 20days. In all
the surrounding rivers of Dhaka city, duration of Flood 2007 was more than flood in 2004
but much less than floods in 1998 and 1988.
8. Entrances of floods in the Buriganga river were on 7th August, 20th July, 26th July and
29th August during floods in 2007, 2004, 1998 and 1988 respectively. The dates of
crossing of danger level in the Turag river were 3rd August, 17th July, 18th July and 24th
August during floods in 2007, 2004, 1998 and 1988 respectively. In the Tongi Khal, dates
of crossing of danger level were 1st August, 21st July, 22nd July and 28th August during
floods in 2007,2004, 1998 and 1988 respectively. Based on danger information during
floods in 2007, date of crossing of danger level was 2nd August. Flood 2007 entered all
the surrounding rivers of Dhaka city later than floods in 2004 and 1998. But Flood 1988
around the rivers of Dhaka city was the most delayed flood in recent past.
Performances of flood control works around Dhaka city
9. The performance of three permanent pump stations at Dholai Khal, Goranchat Bari and
Kallayanpur was found satisfactory. The water levels of protected side were far below
than that of river side. On the other hand, the difference of the water level between
country and protected side Rampura regulator where temporary pumps installed was
close to zero during all the major floods. Performance of the temporary pumps is
insignificant and has very little effect on the drainage congestion in flood season.
60
7.2
10. It was found during field visits that urban encroachments gradually have increased and
reduced retention pond area of the Kallaynpur and Goranchat Bari pump stations. This
will enhance water logging from a small amount of intense precipitation.
11. Eastern part of Dhaka city has suffered from flooding in all the major floods. This part of
the city should be protected by road cum embankment. But, before construct such
embankment, the drainage of the Dhaka East should be well planned. City dwellers have
bad experience of water logging and drainage congestion in the western part due to the
embankment. Lessons should be learned from the drainage situation of western part of
the city.
12. During floods in 2007, the number of patients of diarrhoea and other water borne diseases
was all time high. The main source of illness was from drinking water supplied by
municipalities’ authorities. Entrance of waste water in the water supply pipe through
leakage and faulty joints are reported as one of the main causes of these diseases. Except
a few, the most of the industries discharge untreated waste water in the river. This
untreated water is recognized as the main source of water pollution during flood.
Recommendation
This study recommends following aspects to improve the situation during and after the flood.
These recommendations are mostly to improve performance of flood control works in and
around Dhaka city.
1. There should be coordinated approaches among various authorities responsible to flood
control infrastructures and protection services. An authority should be integrated and
monitor during the flood to fight against flood inundation in urban areas and reduce
sufferings of the people.
2. The retention pond areas of both Goranchatbari and Kollaypur pump staions are getting
reduced day by day due to illegal landfills in the wetlands and settlement in retention -
61
pond areas. The concerned authority should act immediately to stop those encroachments
inside the pond area.
3. Permanent pump stations need to be built for both Rampura regulator and Segunbagicha
regulators. Temporary pumps should be replaced by temporary pump stations. The
location of the pump house should be select by suitable studies.
4. Government should take necessary steps so that every industry should treat waste water
before discharging into river or water systems. Preservation of ecological resources and
wetlands should be given sufficient considerations.
5. Lessons should be learned from the drainage situation of the western part of the city. To
avoid similar situation in the eastern part of the city, details drainage plan such as routes
of canals, retention ponds, location of pump stations and regulators etc. should be done.
Otherwise, the eastern part of Dhaka city will also suffer from water logging even from a
small rainfall.
62
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