Mighty river systems of bangladesh and their impact on severe floods in bangl...Jahangir Alam
Mighty river systems of Bangladesh and their impact on severe floods in Banglades:
River Systems
Mighty River Systems of Bangladesh
Impact of River Systems in Flood
Flood in Bangladesh
Bangladesh is a country of rivers. The environment and livelihood of 160 million people is largely dependent on rivers and its resources. There are around 230 rivers which occupy about 7 percent of the total land area of Bangladesh.
The Ganges-Brahmaputra-Meghna (GBM) river basin is a transboundary river basin with a total area of just over 1.7 million km2, distributed between India (64 percent), China (18 percent), Nepal (9 percent), Bangladesh (7 percent) and Bhutan (3 percent).
The River Systems of
Bangladesh:
Major 3 river systems are:
The Brahmaputra-Jamuna
The Ganges-Padma and
The Meghna [surma-kusiara]
Total River number = 230
River comes from India = 54
River comes from Myanmar = 03
Mighty river systems of bangladesh and their impact on severe floods in bangl...Jahangir Alam
Mighty river systems of Bangladesh and their impact on severe floods in Banglades:
River Systems
Mighty River Systems of Bangladesh
Impact of River Systems in Flood
Flood in Bangladesh
Bangladesh is a country of rivers. The environment and livelihood of 160 million people is largely dependent on rivers and its resources. There are around 230 rivers which occupy about 7 percent of the total land area of Bangladesh.
The Ganges-Brahmaputra-Meghna (GBM) river basin is a transboundary river basin with a total area of just over 1.7 million km2, distributed between India (64 percent), China (18 percent), Nepal (9 percent), Bangladesh (7 percent) and Bhutan (3 percent).
The River Systems of
Bangladesh:
Major 3 river systems are:
The Brahmaputra-Jamuna
The Ganges-Padma and
The Meghna [surma-kusiara]
Total River number = 230
River comes from India = 54
River comes from Myanmar = 03
Landforms of bangladesh and their relation to natural hazardsJahangir Alam
Landforms of Bangladesh and their Relation to natural hazards:
Bangladesh is situated between 23 34’ and 26 38’ North latitude and 88 01’ and 92 41’East longitude.
The topography is flat with elevation not exceeding 10 meters above mean sea level.
Floodplain and piedmont plains occupy almost 80 percent of the land area.
It is a low-lying, riverine country located in South Asia with a largely marshy jungle coastline of 580 km (360 mi) on the northern littoral of the Bay of Bengal.
Bangladesh has a tropical monsoon climate characterized by heavy seasonal rainfall, high temperatures, and high humidity.
To know about the land forms of Bangladesh.
To know about the hazards of Bangladesh.
To find out the relationship between landforms and Hazards.
Topography is a configuration of a land surface including it’s relief and contours, the distribution of mountains and valleys , the patterns of rivers and other natural features that produce the landscape .
There are three distinctive natural features in Bangladesh.
A broad alluvial plain subject to frequent flooding.
A slightly elevated relatively older plain
A small hill region drained by fant flowing rivers.
Now a days climate is rapidly changing. Its' effect on Bangladesh is described in this document. Mainly focused on the sea level rise of Bangladesh. Hope many will get idea about this.
Thanks to all.
Fluvial Morphology handbook for students.
Contents are: definition, scope, importance of Fluvial Morphology, sediment load, channel pattern and process, role sediment to build delta, Reynolds number, Froude Number, channel pattern of Tista and Jamuna River, causes and consequences of flood, benefit of flood, flood and floodplain, hydraulic geometry, water resource management (in Bangladesh), hydrograph, origin and development of river, tributary and distributary and many more.
Presentation made by Prof. Dr. Khin Ni Ni Thein, GWP Steering Committee Member at the occasion the launch of the GWP Towards 2020 Strategy. World Water Day 2014 in Tokyo, Japan.
Landforms of bangladesh and their relation to natural hazardsJahangir Alam
Landforms of Bangladesh and their Relation to natural hazards:
Bangladesh is situated between 23 34’ and 26 38’ North latitude and 88 01’ and 92 41’East longitude.
The topography is flat with elevation not exceeding 10 meters above mean sea level.
Floodplain and piedmont plains occupy almost 80 percent of the land area.
It is a low-lying, riverine country located in South Asia with a largely marshy jungle coastline of 580 km (360 mi) on the northern littoral of the Bay of Bengal.
Bangladesh has a tropical monsoon climate characterized by heavy seasonal rainfall, high temperatures, and high humidity.
To know about the land forms of Bangladesh.
To know about the hazards of Bangladesh.
To find out the relationship between landforms and Hazards.
Topography is a configuration of a land surface including it’s relief and contours, the distribution of mountains and valleys , the patterns of rivers and other natural features that produce the landscape .
There are three distinctive natural features in Bangladesh.
A broad alluvial plain subject to frequent flooding.
A slightly elevated relatively older plain
A small hill region drained by fant flowing rivers.
Now a days climate is rapidly changing. Its' effect on Bangladesh is described in this document. Mainly focused on the sea level rise of Bangladesh. Hope many will get idea about this.
Thanks to all.
Fluvial Morphology handbook for students.
Contents are: definition, scope, importance of Fluvial Morphology, sediment load, channel pattern and process, role sediment to build delta, Reynolds number, Froude Number, channel pattern of Tista and Jamuna River, causes and consequences of flood, benefit of flood, flood and floodplain, hydraulic geometry, water resource management (in Bangladesh), hydrograph, origin and development of river, tributary and distributary and many more.
Presentation made by Prof. Dr. Khin Ni Ni Thein, GWP Steering Committee Member at the occasion the launch of the GWP Towards 2020 Strategy. World Water Day 2014 in Tokyo, Japan.
The population of Bangladesh is projected to be double the current 2010 level by 2050. Demand for water will rise with the increasing demand for rice. Winter months, i.e., November to March, are very dry in Bangladesh due to low rainfall whereas about 95% of annual rainfall occurs during April to October.
Presented by Jaap de Heer
Revitalizing the Ganges Coastal Zone Conference
21-23 October 2014, Dhaka, Bangladesh
http://waterandfood.org/ganges-conference/
An optical fiber (or optical fibre) is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair.Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications
VULNERABILITY ASSESSMENT AND DAMAGE MITIGATION FOR RCC BUILDINGS DUE TO NON S...Johana Sharmin
This presentation was prepared to portray vulnerability assessment and damage mitigation for RCC buildings due to Non-Seismic Hazards in Bangladesh for the internal meeting of DDC office in Dhaka, Bangladesh. This is entirely based on the PWD-JICA manual for CNCRP project. In this presentation, we emphasized wind load and flood water calculation, their impact on our regular RCC building, and mitigation measures. The excel files are not included for the confidentiality purpose. This presentation helped our colleagues who were not interested in reading the manuals. I felt joyful and curious while I worked in this presentation with my colleague.
In this Assignment I discuss about Optical fiber, Evolution of optical fiber: from the beginning to present and beyond, Types of optical fibers used in commercial applications, Losses in optical fiber link, Submarine cable system worldwide, SONET, Fiber optic network backbone in Bangladesh, Applications of optical fiber in 4G technologies and beyond
Indian Climatic Conditions and their impact on building designSaransh Gupta
This presentation describes the different weathers of India, factors affecting climate, Indian climatic zones and the building design criteria with respect to these climatic zones of India.
This presentation will cover:
General information about Bangladesh
Seasons of Bangladesh
River of Bangladesh
Amount monthly precipitation over the year
Average humidity over the year
Water quality standards
Hazards Bangladesh faces
Flood and drought event in Bangladesh
Water pollution in Bangladesh
Government’s law and policy
This presentation is about the types of climate in India.
Presentations are made by students of K.R. Mangalam University from SOAD department 2nd year.
Subject: Climatology
This ppt is for educational purposes.
The six climates are normally designated as Hot and Dry, Warm and Humid, Moderate, Cold and Sunny, Cold and Cloudy and Composite. The criteria of allocating any location in India to one of the first five climate zones are that the defined conditions prevail for more than six months.
India is home to an extraordinary variety of climatic regions, ranging from tropical in the south to temperate in the Himalayan north, where elevated regions receive sustained winter snowfall. The nation's climate is strongly influenced by the Himalayas and the Thar Desert.Though the Tropic of Cancer—the boundary between the tropics and subtropics—passes through the middle of India, the bulk of the country can be regarded as climatically tropical.
It is a presentation about the
Koppen's climate classification system. It provides an overview of Koppen system.It is an informative and engaging overview of the Koppen climate classification system, providing a useful resource for anyone interested in understanding how climate is classified and how it impacts different regions around the world.
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This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
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The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
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Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
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An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
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The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
Macroeconomics- Movie Location
This will be used as part of your Personal Professional Portfolio once graded.
Objective:
Prepare a presentation or a paper using research, basic comparative analysis, data organization and application of economic information. You will make an informed assessment of an economic climate outside of the United States to accomplish an entertainment industry objective.
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Synthetic fiber production is a fascinating and complex field that blends chemistry, engineering, and environmental science. By understanding these aspects, students can gain a comprehensive view of synthetic fiber production, its impact on society and the environment, and the potential for future innovations. Synthetic fibers play a crucial role in modern society, impacting various aspects of daily life, industry, and the environment. ynthetic fibers are integral to modern life, offering a range of benefits from cost-effectiveness and versatility to innovative applications and performance characteristics. While they pose environmental challenges, ongoing research and development aim to create more sustainable and eco-friendly alternatives. Understanding the importance of synthetic fibers helps in appreciating their role in the economy, industry, and daily life, while also emphasizing the need for sustainable practices and innovation.
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A Strategic Approach: GenAI in EducationPeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
3. 3
Aim
In this section we will try to make Bangladesh
familiar on several basic issues from its physical &
environmental settings.
Objectives
To understand the geographical location/settings in Bangladesh
To focus the climate of Bangladesh
To highlight the river systems of Bangladesh
To illustrate the floods in Bangladesh
4. 4
Bangladesh: Geographical Settings
Bangladesh, on the northern coast of the Bay of Bengal,
is surrounded by India, with a small common border
with Myanmar in the southeast.
The country is low-lying riverine land traversed by the
many branches and tributaries of the Ganges and
Brahmaputra rivers.
Tropical monsoons and frequent floods and cyclones
inflict heavy damage in the delta region.
5. 5
Bangladesh: Geographical Settings
Geographical Location:
Bangladesh is right on the Tropic of Cancer. More
Precisely it is between 200
35' and 260
75' North of the
Equator.
The 900
East longitude bisects the country, whose
West-East spread is from 880
3' to 900
15' East.
6. 6
Bangladesh-Geographical Settings
Geography
Area: 147, 570 sq. km. (55,813 sq. mi.); about the
size of Iowa.
Cities: Capital--Dhaka (pop. 10 million). Other
cities--Chittagong (2.8 million), Khulna (1.8
million), Rajshahi (1 million).
Terrain: Mainly flat alluvial plain, with hills in the
northeast and southeast.
Climate: Semitropical, monsoonal.
10. 10
Bangladesh-Geographical Settings
Most parts of Bangladesh are within 10 meters
(33 ft) above the sea level, and it is believed that
about 10% of the land would be flooded if the sea
level were to rise by One (1) metre (3 ft).[29]
Because of this low elevation, much of this region is
exceptionally vulnerable to seasonal flooding due
to monsoons.
The highest point in Bangladesh is in Mowdok
range at 1,052 metres (3,451 ft) in the Southeast of
the country.
11. 11
Bangladesh: Physical Environment
•Major natural assets of Bangladesh are its access to the
open Ocean, the tropical climate, the abundance of good
soils, and the seasonal abundance of rainfall and river
flow.
•It is often said that Bangladesh is poor in natural
resources, but this is not true.
•By natural resources some refer only mineral and gas
resources, which are apparently scarce in the alluvial
basin, but even that superficial view has began to change
with further exploration.
12. 12
Bangladesh: Physical Environment
As tropical climate is another asset, which enables crops to
be grown throughout the year, unlike countries in high
latitudes.
In Bangladesh, temperatures are seldom below 7 degree
Centigrade, considered critical tropical plant growth.
Sunshine is abundant, even during the rainy season (“the
Monsoons”), enables high-yielding crops to be grown.
13. 13
Climate of Bangladesh
Sub-divisions of Climate
Climatic change
Climatic zones
Impact of climate
Climate of Bangladesh
The Ganges Padma River System
The Brahamaputra & jamuna River System
The Surma-Meghna River System
Impact of river systems
River Systems of
Bangladesh
Flood
Types of flood
Factors of flood
Impact of flood
Historical overview
Flood mitigation Practice in Bangladesh
Possible flood mitigation strategies
Floods in Bangladesh
17. 17
Climate of Bangladesh:
In Bangladesh we see tropical climate. But has
a great impact of monsoon climate. For this
reason three seasons are observed in
Bangladesh. These are ;
Summer, Winter, and Rainy season.
Climate the average condition of the atmosphere near
the earth surface over a long period of time, taking into
account temperature, precipitation, humidity, wind,
cloud, barometric pressure etc.
Climate:
18. 18
Summer Season
Time: From March to May.
Temperature: Highest temperature is about
34ºc and lowest is 21ºc.
Wind Flow: In summer moist and dry
monsoon wind is flow from south west and
other cold and dry monsoon wind is flow from
north west.
Rainfall: For these two winds Nor’wester is
happen in Summer. Average rainfall is 51cm..
19. 19
Winter Season
Time: From November to February.
Temperature: Highest and lowest
Temperature: About 29ºand 11ºc.
Wind flow: Cold Northeast monsoon wind is
blow in this season.
It’s lowest humidity is 36%
Rainfall: It is about 5 to 15cm.
20. 20
Rainy Season
Time: From June to October.
Temperature: Average Temperature is 27ºc.
Wind blow: Southwest monsoon wind is blow.
Rainfall: Average highest and lowest rainfall is
340cm and 119cm
21. 21
Characteristics of climate in Bangladesh :
Main characteristic of climate in Bangladesh is warm moist
Summer and cold temperate Winter.
When season changes then the speed of wind is also change.
June-July is the warmest and December-January is coldest
month.
.
23. 23
Sub-divisions of Climate :Sub-divisions of Climate :
We all ready know that Climate is a average condition of
some elements such as follows ~
Atmospheric pressure & winds
Temperature
Humidity
Clouds
Rainfall
24. 24
Atmospheric pressure & winds :Atmospheric pressure & winds :
These are characterized by seasonal reversals between
Summer & Winter in Bangladesh.
In winter, a centre of high pressure lies over the North-
Western part of India.
In summer a centre of low pressure develops over the
East-Central part of India.
Temperature :Temperature :
January is the coldest month, average temperature
is about 17°C in the north-western part & north-eastern
parts to 20°C-21°C.
April is the hottest month, average temperature is about
27°C in the northeast to 30°C in the extreme west central
parts.
25. 25
It has an important role upon climate. The condition of
humidity in Bangladesh given bellow ⇒⇒
Humid
condition
Period Area %
Least humidity March & April Western part +57%
January to March Eastern part +59%
Relative humidity June to September Everywhere 80%
Average relative
humidity
Whole year Everywhere 70.5% -
78.1%
Humidity :Humidity :
26. 26
Clouds:Clouds:
In Bangladesh, the cloud cover has two opposing seasonal
patterns, coinciding with the winter monsoon & the summer
monsoon.
Cloud`s
covertness
Period Area %
Winter
monsoon
Almost
everywhere
About 10%
Pre-monsoon Almost
everywhere
30-40%
Summer
monsoon
north-western 75%
Southern &
Eastern
90%
Cloud covertness in Bangladesh given bellowCloud covertness in Bangladesh given bellow ~
29. 29
Figure :-Figure :-
Humid conditionHumid condition
of Bangladesh.of Bangladesh.
Figure :-Figure :-
Cloud covertness.Cloud covertness.
0
10
20
30
40
50
60
70
80
90
Western part Eastern part Everywhere Everywhere
(March & April) (January to March) (June to September) (Whole year)
Least humidity Relative humidity Average relative
humidity
Humidity (%)
0
10
20
30
40
50
60
70
80
90
100
Almost
everywhere
Almost
everywhere
North-western Southern &
Eastern
Winter monsoon Pre-monsoon Summer monsoon
Cloud covertness (%)
30. 30
Climatic stations :Climatic stations :
Bangladesh Meteorological Department is responsible
for observation, recording & archiving of climatic data
of various stations in the Country. Like – Cox's Bazar,
Bhola, Jessore, Dhaka, Dinajpur,etc.
Weather report :Weather report :
Bangladesh Meteorological Department prepares the
weather reports of the country, which broadcast by
Mass-communication.
32. 32
Climatic change :Climatic change :
Besides Deforestation has an important role upon climatic
change. Higher rate of population growth is responsible
for Deforestation.
Any climatic change in Bangladesh will, of course, be a part
of Worldwide climatic changes.
The temperature has been increasing since the beginning of the
20th century. It is called GLOBAL WARMING and due to the
burning of fossil fuel.
33. 33
Climatic Zones:Climatic Zones:
Bangladesh is located in the tropical MONSOON region.
On the basis of entire climatic condition Bangladesh can
be divided into seven distinct climatic zones, as follows -
Name Area Temp(°C) Rainfall
South-eastern Costal belt &
chittagong
13°C-32°C +2540 mm
North-eastern East & south sylhet 10°C-32°C 3000 mm
Upper northern Northern part 10°C-32°C +2000 mm
North-western Kushtia,Bogra,Rangp
ur
10°C-32°C 1750 mm
Western Greater Rajshahi 7°C-35°C 1500 mm
South-eastern Jessore,Rajbari,etc. 12°C-32°C +1500 mm
South-central Most of the central
part
15°C-31°C +1900 mm
35. 35
Climatic sub-region are
Shown in the map ~
A- South-eastern zone
B- North-eastern zone
C- Upper northern zone
D- North-western zone
E- Western zone
F- South-eastern zone
G- South-central zone
36. 36
Impact of Climate
Impact on Agriculture
Impact on Industries
Impact on Forest resources
Impact on fisheries
Impact on trade and commerce
Impact on transportation
37. 37
Above figures show us Cyclone & Flood affected area of Bangladesh,Above figures show us Cyclone & Flood affected area of Bangladesh,
which is the extreme view of weather as well as climate.which is the extreme view of weather as well as climate.
39. 39
Bangladesh is a land of river. River is an important
feature of physiographic . The pride of Bangladesh is
its rivers with one of the largest networks in the world
with a total number of about 700 rivers including
tributaries, which have a total length of about 24,140
km.
RIVERRIVER: A volume of water which flows in a channel: A volume of water which flows in a channel
from high ground to low ground and ultimately to afrom high ground to low ground and ultimately to a
lake or the sea.lake or the sea.
41. 41
RIVER SYSTEM OF BANGLADESH
The river system of Bangladesh is divided in three types:The river system of Bangladesh is divided in three types:
1. GANGES PADMA RIVER SYSTEM
2. BRAHMAPUTRA & JAMUNA RIVER SYSTEMN
3 The SURMA-MEGHNA RIVER SYSTEMN
44. 44
GANGES/PADMA RIVER
SYSTEM:
This river being originated
Himalayas and are mainly snow-
fed.
The mighty river Ganges enters
Bangladesh through its north
western side and changes its
name to Padma.
The Kumar, Mathabhanga,
Bhairab,Garai, Madhumati,
Arialkhan are the chief branches of
the Padma & the Mahananda is
the main tributary .
The Punarbhaba,pagla,kolik,Tangan
are the tributaries of Padma
46. 46
The Padma Ganges & its
distribution system.
RIVER MILES KM
Total length of 700 river . 13770 22155
Padma
a. West region
b. At pabna
c. At Nawabgang
d. At taltala confluence
554 892
43 70
57 92
21 33
199 320
The Padma Ganges 190 305
Mathabhanga 80 128
Ichamati 56 90
Bhaira 99 590
Kumar 275 443
kubadak 174 280
Chidra 117 188
Garai, Madhumati 195 314
48. 48
BRAHMAPUTRA & JAMUNA
RIVER SYSTEM :
The Jamuna-Brahmaputra is 292 kilometers
long and extends from northern Bangladesh to
its confluence with the Padma. Originating as
the Yarlung Zangbo Jiang in China's Xizang
Autonomous Region (Tibet) and flowing
through India's state of Arunachal Pradesh,
where it becomes known as the Brahmaputra
("Son of Brahma"), it receives waters from five
major tributaries that total some 740 kilometers
in length. At the point where the Brahmaputra
meets the Tista River in Bangladesh, it
becomes known as the Jamuna. The Jamuna is
notorious for its shifting subchannels and for
the formation of fertile silt islands (chars). No
permanent settlements can exist along its
banks.
50. 50
The Jamuna &
Brahmaputra River
system
RIVER MILES KM
Total length of 700 rivers 13770 22155
Teesta 174 280
Old Brahmatutra 217 350
Dhaleswari 139 224
Buriganga 17 27
51. 51
THE SURMA-MEGHNA
RIVER SYSTEM:
The third network is the Surma-Meghna
system, which courses from the
northeastern border with India to
Chandpur, where it joins the Padma.
The Surma-Meghna, at 669 kilometers
by itself the longest formed by the
union of six lesser rivers river in
Bangladesh, is. Below the city of
Kalipur it is known as the Meghna.
When the Padma and Meghna join
together, they form the fourth river
system--the Padma-Meghna--which
flows 145 kilometers to the Bay of
Bengal.
52. 52
The Meghna& Surma
distribution system.
RIVER
MIL
ES
KM
Total length of 700 rivers 13770 2215
5
Surma-Meghna (Border to
chadpur)
375 574
Meghna from Chandpur to
Bay of Bengal
99 160
Surma 217 350
kushiyara 68 110
53. 53
NAME OF THE RIVER MILES AREA COVER
Surma Meghna 416 sylhet(180),comilla(146),barisal(90)
Karatoya,atrai,hursagar 371 Dinajpur(161)rajshahi(160)pabna(50)
Donai,karatoya 280 Rangpur(120)bogra(98)pabna(62)
Ganges,padma 233 Rajshahi(90)pabna(60)dhaka(60)
Garai,Modhumati,Baleswar 231 Kushtia(36)faridpur(70),khulna(104)
Old Brahmaputra 172 Mymenshingh(172)
Brahmaputra & Jumuna 172 Rangpur (75)Pabna(75)
Bangshi 148 Mymenshingh (123 Dhaka(25)
Ghagat 247 Rangpur(247)
Dhanu,Boulai 146 Sylhet (68) Mymenshingh(78)
Nobaganga 144 Kushtia (16) Jessore (128)
Kushiyara 142 Sylhet (142)
Bhogal-kangsa 140 Mymenshingh(140)
RIVER & ITS COVER AREA
54. 54
Impact of River Systems
Impact on Economy
Impact on Agriculture
Impact on Flood
Impact on Environment
56. 56
Flood
At the present time 130 million people of Bangladesh are facing a
series of environmental problems.
Flooding is one water- related environmental problem that is directly
related to human activities.
The magnitude and intensity of flooding are very much dependent
on land-use practices in the watershed of each rivers or streams.
Finding solutions to the flooding problem is imperative.
57. 57
Flood relatively high flow of water that overtops the natural or
artificial banks in any of the reaches of a stream.
Unusual or above normal surface-water flow that inundates
otherwise high ground is called a flood.
Riverine floods occur when the amount of water flowing in a
drainage basin or watershed (the area that collects and directs the
surface water into the streams that drain it) exceeds the carrying
capacity of rivers which drain the area.
DEFINITION OF FLOOD
58. 58
TYPES OF FLOOD
Monsoon flood-caused by major rivers usually in the
monsoon (during June-September).
Flash flood-caused by overflowing of hilly rivers of eastern
and northern Bangladesh (in April-May and September-
November).
Tidal flood-caused by storm surges.
Local flood.-Rain floods caused by drainage congestion and
heavy rains.
62. 62
Long-term Causes
Topographical Characteristics
Subsidence and Compaction of Sediments
Riverbed Aggradations
Deforestation in the Upstream Region
Damming of Rivers
Soil Erosion due to Tilling
Excessive Development/Unplanned development
Seismic (Earthquake) and Neotectonic Activities
Greenhouse Effect/snow malting in Himalayans
Local Relative Sea Level Rise
63. 63
•About 50% of the country is
within 6-7 m of MSL.
Figure 1: Topography of Bangladesh
Source:
National Plan for Disaster Management
2007-2015
Ministry of Food and Disaster Management
April 2007
84. 84
Summarized Table of floods in Bangladesh from 1904 to 2004
# of
Event
s
Killed Injured Homeless Affected Total
Affected
DamageU
S (000's)
Flood 62 49,680 102,020 60,853,724 278,043,273 338,999,017 9,165,100
ave. per
event
801 1,646 981,512 4,484,569 5,467,726 147,824
Created on: Aug-1-2004. - Data version: v07.04
Source: "EM-DAT: The OFDA/CRED International Disaster Database,
www.em-dat.net - Université catholique de Louvain - Brussels - Belgium"
Source:http://www.sdnbd.org/sdi/issues/floods_drainage/2004/data/index.htm
Historical effect due to flood
85. 85
Top 10 Natural Disasters in Bangladesh
Disaster Date Killed
Famine 1943 1,900,000
Epidemic 1918 393,000
Wind Storm 12-Nov-1970 300,000
Wind Storm 30-Apr-1991 138,866
Wind Storm Oct-1942 61,000
Wind Storm 11-May-1965 36,000
Flood Jul-1974 28,700
Wind Storm Jun-1965 12,047
Wind Storm 28-May-1963 11,500
Wind Storm 9-May-1961 11,000
(sorted by numbers of people killed )
Source:http://www.sdnbd.org/sdi/issues/floods_drainage/2004/data/index.htm
86. 86
Disaster Date Affected
Flood 22-Jul-1987 73,000,000
Flood Aug-1988 73,000,000
Flood Jul-1974 38,000,000
Flood May-1984 30,000,000
Drought 5-Jul-1983 20,000,000
Flood Jul-1968 15,889,616
Wind Storm 11-May-1965 15,600,000
Wind Storm 30-Apr-1991 15,438,849
Flood 8-Jul-1998 15,000,050
Flood 15-Jun-1995 12,656,006
Top 10 Natural Disasters in Bangladesh
(affected sorted by numbers of
people )
Source:http://www.sdnbd.org/sdi/issues/floods_drainage/2004/data/index.htm
88. 88
Flood Mitigation Practices in
Bangladesh
Structural Mitigation
Flood Action plan
Non structural Mitigation
Flood warning System
Others
89. 89
Flood Action PlanFlood Action Plan (FAPFAP) :
FAP is an initiative to study the causes & nature ofFAP is an initiative to study the causes & nature of
floodflood
in Bangladesh & to prepare guidelines for controllingin Bangladesh & to prepare guidelines for controlling
It.It.
It included 29 different components of which 11 wereIt included 29 different components of which 11 were
regional.regional.
It has 11 guiding principles.It has 11 guiding principles.
90. 90
Flood Forecasting
Flood warning has been in a state
of continuous development since
1972.
Source:
National Plan for Disaster
Management
2007-2015
Ministry of Food and Disaster
Management
April 2007
92. 92
Structural Solutions
Structural solutions call for the engineering of
structures such as embankments along rivers,
dams, drains, reservoirs, and other structures
designed to control the natural flow of rivers.
Dredging and Re-excavation of
Rivers
Dams
Others
94. 94
Conclusions
The climate, river systems and the flood, all are
closely related. The Climate of Bangladesh is
closely related with the monsoon which is also
closely related with the flood and river systems.
The climate of Bangladesh is changing. The
result is observed in the flood by the river
system.
The life of Bangladeshi people are closely
related with the climate, rivers and floods.
Editor's Notes
Season climatic type, at any place, associated with a particular time of the year. The change of season is mainly due to the change in attitude of the earth's axis in relation to the position of the sun at a particular place. In temperate latitudes four seasons are recognised: spring, summer, autumn (fall), and winter. Tropical regions have two seasons - the wet and the dry. monsoon areas around the Indian Ocean have mainly three seasons: cold, hot, and rainy.
Bangladesh is called the land of six seasons (Sadartu). It has a temperate climate because of its physical location. Though the climate of Bangladesh is mainly sub-tropical monsoon, ie warm and humid; Bangla calendar year is traditionally divided into six seasons: Grisma (summer), Barsa (rainy), Sarat (autumn), Hemanta (late autumn), Shhit (winter) and Basanta (spring). Each season comprises two months, but some seasons flow into other seasons, while others are short. Actually, Bangladesh has three distinct seasons: the pre-monsoon hot season from March through May, rainy monsoon season which lasts from June through October, and a cool dry winter season from November through February. However, March may also be considered as the spring season, and the period from mid-October through mid-November may be called the autumn.
The pre-monsoon hot season is characterised by high temperature and occurrence of thunderstorms. April is the hottest month in the country when mean temperature range from 27°C in the east and south to 31°C in the west-central part of the country. After April, increasing cloud-cover dampens temperature. Wind direction is variable in this season, especially during its early part. rainfall accounts for 10 to 25 percent of the annual total, which is caused by thunderstorms.
Southerly or south-westerly winds, very high humidity, and heavy rainfall and long consecutive days of rainfall characterise the rainy season, which coincides with summer monsoon. Rainfall of this season accounts for 70 to 85 percent of the annual total. This is caused by the tropical depression that enter the country from the bay of bengal.
Low temperatures, cool air blowing from the west or northwest, clear sky, and meagre rainfall characterise the cool dry season. Average temperature in January varies from 17°C in the northwest and northeastern parts of the country to 20°C-21°C in the coastal areas. Minimum temperature in the extreme northwest in late December and early January reaches 3°C to 4°C.
Summer (grisma) Comprises Baishakh and Jyaistha (mid-April to mid-June), the two Bangla calendar months, when days are hot and dry. But the influence of summer is usually felt from mid-March. The heat of the sun dries up the waterbodies including the rivers, canals and the wetlands. The summer days are longer than the nights. At this time the southerly or southwesterly monsoons flow over the country. When dry and cool streams of air flowing from the west and northwest come in contact with rain laden clouds, storms occur, which, at times, take a violent form. These storms are popularly known as kalbaishakhi (nor'wester) or destructive Baishakh storm.
The Bengali year begins with summer, with the Pahela Baishakh (first day of Baishakh) being the Bangla New Year. Hindus observe many seasonal festivals during this period, including jamaisasthi (the sixth day of the bright fortnight in Jyaistha when a son-in-law is blessed by his parents-in-law). Summer is a season of fruits, with mango [Am], blackberry [Jam], starapple [jamrul], jackfruit [Kathal], pineapple [Anaras], guava [Peyara], litchis, deuya (Artocarpus lacucha), watermelon, chalta (Dillenia indica), latkan (Baccaurea remiflora), palmyra [tal], and hog-plum (amda) available in plenty. This is also the time when Roses, Bakul, Beli, Tagar and Jaba flowers blossom.
Winter (shit) The fifth season and the colder part of the year, in contrast to Summer, the hotter. According to the Bangla calendar it spreads over the months of Paus and Magh (mid-December to mid-February). But practically, November through February is the winter season in Bangladesh. Average temperatures in January vary from about 11°C in the northwestern and northeastern parts of the country to 20°C to 21°C in the coastal areas. Northern Bangladesh is cooler than southern Bangladesh, with occasional cold spells that claim lives. During this season, a centre of high pressure lies over the northwestern part of India (Himalayan zone). A stream of cold air flows eastward from this high pressure and enters Bangladesh through its northwest corner. During this season, winds inside Bangladesh generally have a northerly component (ie, flowing from north or northwest).
The winter season is very dry, which accounts for less than 4 percent of the total annual rainfall. Average rainfall during the season varies from less than 2 cm in the west and south to slightly over 4 cm in the northeast. Rainfall in this season is caused by the wind coming from the Mediterranean region that enters the country from the northwestern part of India along the Ganges basin. Rainfall amount is slightly enhanced in the northeastern Bangladesh by the orographic effect of the Meghalaya Plateau. These rainy spells bring the temperature down. The nights are longer than the days and mornings are often foggy. This is the time when deciduous trees shed their leaves.
Winter is the best and most enjoyable season of Bangladesh. A larger variety of vegetables are available in the markets. So is fish, particularly large koi, magur, shing. Special flowers of the season are Ganda and Suryamukhi. Boroi (jujube) and oranges are among the fruits of this season. Date juice is extracted during this time, to be used as juice or made into gud (molasses). This is the season for pitha or rice cakes such as bhapa pitha, chitai pitha, patisapta and puli pitha.
The rainy season (barsa) Traditionally spreads over Asadh and Shraban (mid-June to mid-August). However, the rainy season may start from the end of Baishakh and last up to the beginning of Kartik (mid-May to late-October). During the rainy season, the southwest monsoon winds bring plenty of rainfall (70 to 85 percent of the annual total) and occasionally lasting for days without end without any respite. Most of the floodplains of the country remain inundated during this period. Depending upon the local elevation, the depth and duration of barsha varies in different parts of Bangladesh. For instance, in low lying parts like haors, beels, jheels of Sylhet, Netrokona, Kishoreganj, Gopalganj and Pabna districts inundation lasts for the longest period (more than six months). In other places, like the central parts of Bangladesh, it lasts for about 3 to 4 months. In the rural areas, boat navigation becomes a common mode of transport during this season.
Plants, half-dead with the summer heat, receive a new lease of life under cool rains and Bangladesh becomes green. Farmers are busy for harvesting jute, in the flood free areas and/or shallowly flooded (0 to 30 cm depth) areas for preparing paddy seedbeds. Barsha is also important for the fishing community of Bangladesh. hilsa fish is available in plenty during this season. The inundated floodplains become a large habitat for a wide variety of aquatic flora and fauna. At this time plenty of edible herbs grow everywhere, as does the national flower lotus. This is the season for keya, kadam, kamini, jui, gandharaj and other fragrant flowers, as well as fruits like guava, pineapple, and pomelo.
Main characteristic of climate in Bangladesh is warm moist
Summer and cold temperate Winter.
When season changes then the speed of wind is also change.
June-July is the warmest and December-January is coldest
month.
Atmospheric pressure and winds These are characterised by seasonal reversals between summer and winter in Bangladesh. During the winter season, a centre of high pressure lies over the northwestern part of India. A stream of cold air flows eastward from this high pressure and enters the country through its northeast corner by changing its course clockwise, almost right-angle. This wind is the part of the winter monsoon circulation of the South Asian subcontinent. During this season, wind inside the country generally have a northerly component (flowing from north or northwest).
On the other hand, during the summer season, a centre of low pressure develops over the west-central part of India because of intense surface heat. As a result, a stream of warm and moist air from the Bay of Bengal flows toward the above-mentioned low pressure through Bangladesh (similar flow prevails from the Arabian Sea toward India). This wind is the part of the summer monsoon circulation of the sub-continent. So, the prevailing wind direction in Bangladesh during the summer season has generally a southerly component (flowing from the south, southwest or southeast). However, wind directions during the transition seasons (in spring and autumn) are variable. Generally, winds are stronger in summer (8-16 km/hr) than in winter (3-6 km/hr). The mean pressure is 1,020 millibars in January and 1,005 millibars during March through September.
Humidity March and April are the least humid months over most of the western part of the country. The lowest average relative humidity (57%) has been recorded in Dinajpur in the month of March. The least humid months in the eastern areas are January to March. Here the lowest monthly average of 58.5% has been recorded at Brahmanbaria in March. The relative humidity is everywhere over 80% during June through September. The average relative humidity for the whole year ranges from 78.1% at Cox's Bazar to 70.5% at Pabna.
Clouds In Bangladesh, the cloud cover has two opposing seasonal patterns, coinciding with the winter monsoon and the summer monsoon. As a result of the flow of cold-dry winds from the northwestern part of India during the winter season, the cloud cover is at a minimum. On an average, the cloud cover in this season is about 10% almost all over the country. With the progression of the season, the cloud cover increases, reaching 50-60% by the end of the pre-monsoon hot season. During the summer monsoon season, which is also the rainy season, the cloud cover is very widespread. In the months of July and August, which is the middle of the rainy season, the cloud cover varies from 75 to 90% all over the country. However, it is more extensive in the southern and eastern parts (90%) than in the northwestern part (75%). After the withdrawal of the summer monsoon, the cloud cover decreases rapidly, dropping to 25% in the northern and western parts, and 40-50% in the southern and eastern parts
Rainfall The single most dominant element of the climate of Bangladesh is the rainfall. Because of the country's location in the tropical monsoon region, the amount of rainfall is very high. However, there is a distinct seasonal pattern in the annual cycle of rainfall, which is much more pronounced than the annual cycle of temperature. The winter season is very dry, and accounts for only 2%-4% of the total annual rainfall. Rainfall during this season varies from less than 2 cm in the west and south to slightly over 4 cm in the northeast. The amount is slightly enhanced in the northeastern part due to the additional uplifting of moist air provided by the Meghalaya Plateau. As the winter season progresses into the pre-monsoon hot season, rainfall increases due to intense surface heat and the influx of moisture from the Bay of Bengal. Rainfall during this season accounts for 10%-25% of the total annual rainfall which is caused by the thunderstorms or nor'wester (locally called Kalbaishakhi [Kalbaishakhi]).
The amount of rainfall in this season varies from about 20 cm in the west central part to slightly over 80 cm in the northeast. The additional uplifting (by the Meghalaya Plateau) of the moist air causes higher amount of rainfall in the northeast. Rainfall during the rainy season is caused by the tropical depressions that enter the country from the Bay of Bengal. These account for 70% of the annual total in the eastern part, 80% in the southwest, and slightly over 85% in the northwestern part of Bangladesh. The amount of rainfall in this season varies from 100 cm in the west central part to over 200 cm in the south and northeast. Average rainy days during the season vary from 60 in the west-central part to 95 days in the southeastern and over 100 days in the northeastern part. Geographic distribution of annual rainfall shows a variation from 150 cm in the west-central part of the country to more than 400 cm in the northeastern and southeastern parts. The maximum amount of rainfall has been recorded in the northern part of Sylhet district and in the southeastern part of the country (Cox's Bazar and Bandarban districts).
Climatic stations Bangladesh Meteorological Department is responsible for observation, recording and archiving of climatic data for various stations in the country. Climatic stations are scattered around the country - to record the diverse geographic conditions of the country. The major climatic stations from which long-term climatic data are available are - Barisal, Bhola, Bogra, Chittagong, Comilla, Cox's Bazar, Dhaka, Dinajpur, Faridpur, Feni, Hatiya, Ishwardi, Jessore, Khepupara, Khulna, Kutubdia, Madaripur, Maijdi Court, Mymensingh, Patuakhali, Rajshahi, Rangamati, Rangpur, Saidpur, Sandwip, Sitakunda, Sreemangal, Sylhet and Teknaf.
Weather report Bangladesh Meteorological Department prepares the weather reports of the country. The department is responsible for observation, recording, operation and maintenance of weather stations and weather instruments, and for reporting of daily/weekly weather information to the public. Every day, all weather stations around the country transmit their recorded data electronically to the Headquarters of the meteorological department in Dhaka. The details of data are analysed, interpreted and mapped here. The result of the analysis, combined with the observation of upper air, satellite imagery and radar imagery (collected in Dhaka) are used for weather forecasting. Observation and interpretation of satellite and radar imageries are important for prediction of severe weather and cyclones. Weather bulletins and forecasting by the Bangladesh Meteorological Department for 6-hour, 12-hour and 24-hour periods are broadcast on radio and television. During an impending cyclone, observation and forecasting are made and warnings issued almost continuously through radio and television. In addition to radio and television, daily newspapers publish weather reports regularly on the basis of information supplied by the meteorological department.
Climatic change Any climatic change in Bangladesh will, of course, be a part of worldwide climatic changes. It is generally claimed that the temperature of the earth has been increasing since the beginning of the 20th century. This phenomenon, called global warming, is attributed to the increase in atmospheric carbon dioxide (CO2) due to the burning of fossil fuel. However, not all scientists subscribe to the global warming hypothesis.
It has been estimated by some scientists that the concentration of CO2 in the atmosphere during the pre-industrial period was 285-290 ppmV (parts per million by volume). Observed concentration of CO2 in the atmosphere at the Muana Loa Observatory in Hawaii shows an increasing trend, from 315 ppmV in 1958 to 352 ppmV in 1988. If this trend continues, then it will reach 450 ppmV by the year 2050. Temperature of the earth has increased by 0.3-1°C since the beginning of the 20th century as a consequence of increased CO2 in the atmosphere. Computer simulation of global temperature change shows that if the CO2 concentration of the atmosphere becomes doubled from its present-day value, then global temperature would increase 1.3°-4°C. In low and tropical latitudes the change would be very small (only 0.05°-0.25°C). On the other hand, temperature increase would be much higher in the middle and high latitude regions (5°-9°C). Moreover, there will be differential temperature increase in summer and winter - temperature increase in the winter season will be higher than that in the summer.
According to some analysts, the effects of increased temperature will have both destructive and beneficial consequences - destructive to some areas and beneficial to other areas. Global warming will cause the polar ice caps and Himalayan ice caps to melt at a slow pace. As a consequence, it is estimated that the sea level will rise 2-3 metres by the year 2050. In that case, all low coastal plains and delta areas around the world will be submerged - thereby reducing the area of fertile agricultural lands and food production, and increasing food shortage, hunger, poverty and human misery on a global scale. If this prediction comes true, then a significant area of the southern half of Bangladesh will be submerged by the Bay of Bengal. However, there is another side to the argument. Actually climatic changes on a global scale do not occur overnight; in fact, they occur only over a time scale of thousands of years.
River and Drainage System the rivers of Bangladesh are very extensive and distinguish both the physiography of the country and the life of the people. Bangladesh is called a land of rivers as it has about 700 rivers including tributaries. The rivers are not, however, evenly distributed. For instance, they increase in numbers and size from the northwest of the northern region to the southeast of the southern region. The total length of all rivers, streams, creeks and channels is about 24,140 km. In terms of catchment size, river length and volume of discharge, some of these rivers are amongst the largest on the earth. Usually the rivers flow south and serve as the main source of water for irrigation and as the principal arteries of commercial transportation. The rivers also provide sweetwater fish, an important source of protein. A large segment of population is thus engaged in the fishing sector. On the other hand, widespread riverbank erosion and regular flooding of the major rivers cause enormous hardship and destruction of resources hindering development. But it is also true to say that the river system brings a huge volume of new silt to replenish the natural fertility of the agricultural land. Moreover, the enormous volume of sediments that the rivers carry to the bay of bengal each year (approximately 2.4 billion tons) builds new land along the sea front, keeping hope alive for future extension of Settlement. Finally, during the monsoon, rivers also drain excess discharge to the Bay. Thus this great river system is the country's principal resource as well as its greatest hazard. The system can be divided into four major networks: (1) brahmaputra-jamuna river system, (2) ganges-padma river system, (3) surma-meghna river system, and (4) chittagong region river system
The first three river systems together cover a drainage basin of about 1.72 million sq km, although only 7% of this vast basin lie within Bangladesh. The combined annual discharge passing through the system into the Bay of Bengal reaches up to 1,174 billion cu m. Most of the rivers are characterised by fine sandy bottoms, flat slopes, substantial meandering, banks susceptible to erosion, and channel shifting.
The Ganges-Padma system is part of the greater Ganges system. The Ganges has a total length of about 2,600 km and a catchment area of approximately 907,000 sq km. Within Bangladesh, Ganges is divided into two sections - first, the Ganges, 258 km long, starting from the western border with India to its confluence with Jamuna at Goalandaghat, some 72 km west of Dhaka. The second is the Padma, 126 km long, running from Goalandaghat confluence to Chandpur where it joins the Meghna. The Padma-Ganges is the central part of the deltaic river system with hundreds of rivers. The total drainage area of Ganges is about 990,400 sq km of which only 38,880 sq km lie in Bangladesh.
The recorded highest flow of Ganges was 76,000 cumec in 1981, and the maximum velocity ranging from 4-5 m/sec with depth varying from 20m to 21m. The average discharge of the river is about 35,000 cumec with an approximate annual silt load of 492 tons/sq km. The average gradient for the reach between Allahabad to Benaras is 1:10,500, from Farakka (India) to Rampur-Boalia in Rajshahi (Bangladesh) is 1:18,700, from Rampur-Boalia through Hardinge Bridge to Goalandaghat is 1:28,000. The slope flattens to 1:37,700 for a distance of 125 km from Goalandaghat to Chandpur. Within Bangladesh, the mahananda tributary meets the Ganges at Godagari in Rajshahi and the distributary Baral takes off at Charghat on the left-bank. The important distributaries taking off on the right-bank are the Mathabhanga, gorai-madhumati, Kumar, and arial khan.
Brahmaputra-Jamuna system the Brahmaputra-Jamuna river is about 280 km long and extends from northern Bangladesh to its confluence with the ganges. Before entering Bangladesh, the brahmaputra has a length of 2,850 km and a catchment area of about 583,000 sq km. The river originates in Tibet as the Yarlung Zangbo Jiang and passes through Arunachal Pradesh of India as Brahmaputra (son of Brahma). Along this route, the river receives water from five major tributaries, of which Dihang and Luhit are prominent. At the point where Brahmaputra meets the tista in Bangladesh, it is called the jamuna. The Brahmaputra-Jamuna throughout its broad valley section in Assam and in Bangladesh is famous for its braided nature, shifting sub channels, and for the formation of chars (island/sandbars) within the channel.
The recorded highest peak flow of Brahmaputra-Jamuna is 98,000 cumec in 1988; the maximum velocity ranges from 3-4 m/sec with a depth of 21-22m. The average discharge of the river is about 20,000 cumec with average annual silt load of 1,370 tons/sq km. The average slope of the Jamuna is about 1:11,400; however, the local gradient differs quite considerably from the average picture.
Within Bangladesh, the Brahmaputra-Jamuna receives four major right-bank tributaries - the dudkumar, dharla, Tista and hurasagar. The first three are flashy, rising in steep catchment on the southern side of the Himalayan system between Darjeeling and Bhutan. The Tista is one of the most important rivers of the northern region. Before 1787 it was the principal water source for the karatoya, atrai and Jamuneshwari. A devastating flood of 1787 brought in a vast amount of sand wave through the Tista and choked the mouth of the Atrai; as a result the Tista burst into the course of the ghaghat river. The Tista has kept this course ever since. The present channel within Bangladesh is about 280 km long, and varies between 280 to 550 m in width. It joins the Brahmaputra just south of Chilmari upazila. The Dharla and Dudhkumar flow parallel to Tista. The Dharla is a fast flowing river in the monsoon but with the fall of water level it becomes braided. The Dudhkumar is a small river and flows southeast to join the Brahmaputra. The combined discharge of the Atrai and Karatoya passes through the Hurasagar to the Jamuna.
The old brahmaputra and the dhaleshwari are the important left bank distributaries of the Jamuna. Prior to the 1787 Assam flood, the Brahmaputra was the main channel; since then the river has shifted its course southward along the Jhenai and Konai rivers to form the broad, braided Jamuna channel. The old course, named the Old Brahmaputra is now essentially a high-flow spill channel, active only during the monsoon. Taking off at Bahadurabad, the Old Brahmaputra flows southeast, passes by Jamalpur and Mymensingh towns and joins the Meghna at Bhairab Bazar. Its average gradient is 4.76 cm/km. Along its southeasterly journey, Dhaleshwari bifurcates at least twice. Two of its important branches are the Kaliganga and buriganga. The Dhaleshwari eventually meets the Shitalakshya at Narayanganj.
The Surma-Meghna system the Meghna is the longest (669 km) river in Bangladesh. It drains one of the heaviest rainfall areas (eg, about 1,000 cm at Cherapunji in Meghalaya) of the world. The river originates in the hills of Shillong and Meghalaya of India. The main source is the barak river, which has a considerable catchment area in the ridge and valley terrain of the Naga-Manipur hills bordering Myanmar. The Barak-Meghna has a length of 950 km of which 340 km lie within Bangladesh. On reaching the border with Bangladesh at Amalshid in Sylhet district, the Barak bifurcates to form the steep and highly flashy rivers surma and kushiyara. The Surma, flowing on the north of the Sylhet basin, receives tributaries from the Khasia and Jaintia hills of Shillong. Some of the important tributaries of these two rivers are Luba, Kulia, shari-goyain, Chalti-nadi, Chengar-khal, piyain, Bogapani, Jadhukata, Someshwari and kangsa. The Surma meets the Meghna at Kuliarchar upazila of Kishoreganj district. The Kushiyara receives left bank tributaries from the tripura hills, the principal one being the manu. Unlike the Surma, the tributaries of the Kushiyara are less violent, although prone to producing flash floods, due in part to the lesser elevations and rainfall of Tripura hills.
Between the Surma and Kushiyara, there lies a complex basin area comprised of depressions or haors, meandering flood channels, and abandoned river courses. This area remains deeply flooded in the wet season. The two rivers rejoin at Markuli and flow via Bhairab as the Meghna to join Padma at Chandpur. The major tributaries of any size outside the Sylhet basin are the Gumti and khowai rivers, which rise in Tripura. Other hilly streams from Meghalaya and Assam join the Meghna. The total drainage area of the Meghna up to Bhairab Bazar is about 802,000 sq km, of which 36,200 sq km lie in Bangladesh. The peak flow of the Meghna is 19,800 cu m/sec, and the maximum velocity range from 1-2 m/sec with depth varying from 33m to 44m. The average discharge of the river is about 6,500 cu m/sec. It has a steep slope while flowing in the Indian hilly part. At flood stages, the slope of the Meghna downstream at Bhairab Bazar is only 1:88,000. In terms of drainage pattern, the Meghna exhibits a meandering channel, and at some places it reflects an anastomosing pattern.
The Chittagong Region system the rivers of Chittagong and chittagong hill tracts are not connected to the other river systems of the country. The main river of this region is karnafuli. It flows through the region of Chittagong and the Chittagong Hills. It cuts across the hills and runs rapidly downhill to the west and southwest and finally to the Bay of Bengal. chittagong port is located on the bank of Karnafuli. The river has been dammed upstream at Kaptai to create a water reservoir for hydroelectric power generation. Other important rivers of the region are the feni, Muhuri, sangu, matamuhuri, Bakkhali, and naf.
The four mighty river systems flowing through Bangladesh drain an area of some 1.5 million sq km. During the wet season the rivers of Bangladesh flow to their maximum level, at about 140,000 cumec, and during the dry period, the flow diminishes to 7,000 cumsec. All the estuaries on the Bay of Bengal are known for their many estuarine islands.
Floods are more or loss a recurring phenomenon in Bangladesh and often have been within tolerable limits. But occasionally they become devastating. Each year in Bangladesh about 26,000 sq km, 18% of the country is flooded. During severe floods, the affected area may exceed 55% of the total area of the country. In an average year, 844,000 million cubic meter of water flows into the country during the humid period (May to October) through the main rivers Ganges, the Brahmaputra - Jamuna and the Meghna. This volume is 95% of the total annual inflow. By comparison only about 187,000 million cubic meter of stream flow is generated by Rainfall inside the country during the same period. . The floods of 1954, 1955, 1974, 1987, 1988, 1998 and 2004 all caused enormous damages to properties and considerable loss of life. The consecutive floods of 1987, 1988 1998 and 2004 caused heavy damage. The magnitude and duration of flood was quite normal during the monsoon of 2006.
The land to the west of Brahmaputra is generally higher than that in the eastern part of the country. Several large depressions have been formed during the process of delta building, particularly in greater Mymensingh and Sylhet districts. The country consists of the flood plains of the Ganges, the Brahmaputra and the Meghna rivers and their numerous tributaries and distributaries. The Ganges and the Brahmaputra join together in Bangladesh near Goalundo and is known as the Padma River. The river Meghna joining the Padma near Chandpur flows to the Bay of Bengal as the Meghna River.
Basic Features of Floods in Bangladesh
The following aspects summarize the basic features of floods in Bangladesh.
Bangladesh has to drain out runoff of an area which is 12 times larger
than its size. Only 7.5 per cent of the combined catchment areas of the
Ganges, Brahmaputra and Meghna rivers (i.e., 0.12 Mkm2 out of 1.55
Mkm2) are within Bangladesh. The remaining 92 per cent are distributed
over Nepal, India, China and Bhutan.
Annually, 1,360,000 million m3 of discharge originate outside
Bangladesh. About 85 per cent of this discharge is generated between
June-October.
The amount of water which passes over the country can create a pool
having a depth of about 9 meters.
Besides water the rivers also carry high loads of silt from the steep and
denuded upstreams — an estimated 1.2 to 2.4 billion tonnes of
sediments are carried annually to the Bay of Bengal. The combined
annual sediment load of the Ganges and Brahmaputra is estimated to
be 1185 million tons. Their respective share is 38 per cent and 62 per
cent.
About 1/3 of Bangladesh or 49,000 sq. km. area are influenced by tides
in the Bay of Bengal.
Monsoon flood.
Monsoon flood is an annual event forced mainly by intensive river inflow through Ganges, Brahmaputra and Meghna Rivers and rainfall over Bangladesh as causes the water level in the rivers to rise and fall slowly during the monsoon season.
Flash flood.
Flash flood occurs only in the northeastern Bangladesh in the period pre- to post-monsoon forced by intense rainfall in the Meghalaya Hills and in parts of eastern Bangladesh in the post-monsoon.
The rivers Punarbhaba, Karatoa, Dhala and Teesta to the north Someswari, Kangsa, Jadukata, Sarigoyin, Surma and Kushiyara, Manu, Khowi, Gumti, Muhuti, Halda, Sangu, Mathamuhuri along with many other smaller hill streams to the east of the country, are vulnerable to flash flood.
Tidal flood.
The coastal areas of Bangladesh are subjected to this kind of flooding. Inundation occurs due to storm-tidal surges associated with cyclonic storms and spring tides. (Bhuiya, 2000)
Local flood.
Known by their rapid rise and short duration occurring in response to intensive-localized rainfall. Rapid rise in river stage and associated with high flow velocity cause intensive damage to crops and properties.
Monsoon downpour
Monsoon downpour- An increased amount of precipitation can Cause flooding. An above normal monsoon downpour in the Ganges- Brahmaputra-Meghna drainage system is thought to be the primary Cause of the flood.
Synchronization of Flood Peaks
The synchronization of flood peaks for the major three rivers took place within a two week time period, causing a sudden increase in water level in virtually all areas of the country (GOB and UNDP, 1989; Brammer, 1990). While the synchronization of flood peaks can explain the cause of the 1988 flood, it fails to explain the reason for an overall increased propensity for low frequency floods in recent years such as occurred in 1974, 1984, 1987, and 1991. The answer might lie in other long-term processes that reduce the water carrying capacity of the drainage system and decrease land elevation with respect to the base level of the rivers in Bangladesh.
Long term cause
Topographical Characteristics
Inadequate Sediment Accumulation
Limited data show that the average sediment accumulation rates in the coastal areas of Bangladesh is 5-6 mm/year for the last few hundred years, which is not enough to keep pace with the rising sea level at 7mm/year. As a result, land elevations must have been decreasing over time in Bangladesh, resulting in more flooding inundation.
Subsidence and Compaction of Sediments
Sediments on a delta plain are rich in decomposed organic matters, and are subject to compaction due to dewatering and sediment weights. Most deltas subside due to the weight sediments, and due to overdraft of groundwater to meet the demand of increased population. Subsidence and compaction reduce land elevations with respect to sea level. No direct measurements of subsidence or compaction are known for Bangladesh. However, the groundwater table in Dhaka City has had a considerable lowering by as much as 9 to 12 meters over the last 3 decades. Experience in other countries indicate that at least 9 meters of permanent lowering of groundwater table causes 30 cm of land subsidence. Therefore, it is likely that land elevations in many parts of Dhaka City have been lowered by up to 30 cm, contributing to increased flood depth.
Riverbed Aggradation
Riverbed aggradation is most pronounced for the Ganges and its distributaries. From the border with India to the point where the Ganges meets the Brahmaputra River, the riverbed has aggraded as much as 5-7 meters in recent years. The average width of the Ganges has decreased from 1.27 km in 1973 to 1.01 km in 1985. Riverbed aggradation is so pronounced in Bangladesh that changes in riverbed level can be observed during one's lifetime. For example, the Old Brahmaputra River was navigable for steamers only about 30 years ago, and is presently an abandoned channel. This situation is true for many other distributaries of the Ganges and Meghna Rivers, such as the Madhumati, Bhairab, Chitra, Gorai, Ghorautra Rivers, etc. Riverbed aggradation reduces the water carrying capacity of rivers, causing floods due to bank overflow. This recent increase in riverbed levels has undoubtedly contributed to the increased flooding propensity in Bangladesh.
Deforestation in the Upstream Region
A rapid increase in population in the Indian Subcontinent over the course of the 20th century has resulted in an acceleration of deforestation in the hills of Nepal to meet the increasing demands for food and fuel wood. Deforestation of steep slopes is assumed to lead to accelerated soil erosion and landslides during monsoon precipitation, which in turn is believed to contribute to devastating floods in the downstream regions, such as in Bangladesh. Deforestation within Bangladesh also contributes to the soil erosion. The amount of forest cover in Bangladesh was reduced from 15.6% in 1973 to 14.6% in 1985-86, and eventually to13.4% in 1987. A minimum of 25% forest cover is suggested for a healthy ecosystem. The amount of forest cover in Bangladesh at the present time believed to be less than 10%.
Damming of Rivers
(F) Damming of Rivers: Damming of a river reduces the velocity of water flow downstream from the dam. As a result of reduced velocity, the sediments carried by the river start to settle down faster on the riverbed, causing riverbed aggradation and in turn reducing the water carrying capacity of the river (Shalash, 1982). The Farakka Barrage on the Ganges has already caused tremendous damage to the agriculture, navigation, environment, and hydrodynamic equilibrium in Bangladesh (Shahjahan, 1983; Siddiqui, 1983; Broadus et al., 1986; Khalequzzaman, 1989).
Soil Erosion due to Tilling
Ploughing makes the land surface more susceptible to soil erosion. Surface run-off can easily wash away the topsoil from cultivated lands. This surface erosion reduces land elevation, which in turn increases flooding intensity in an area. According to the Report of the Task Forces (RTF) on Bangladesh Development Strategies for the 1990s, soil erosion is a serious problem in many parts of Bangladesh. Hilly areas in Sylhet, Chittagong, and Chittagong Hill Tract districts are more susceptible to soil erosion. About 55% of Chittagong Hill Tract area is highly susceptible to soil erosion. Heavy monsoon showers remove the surface soil through runoff. Eroded sediments are deposited on the riverbeds, reducing the water carrying capacity and increasing flooding propensity in a watershed. Soil erosion also reduces land elevations and increases elevations of riverbeds, contributing to increased flood depths. The land elevations in other parts of Bangladesh must have reduced over time due to soil erosion. Aside from this, the tilling on the mountain slopes of the Himalayas is thought to be responsible for massive soil erosion in Nepal , which eventually causes rapid riverbed aggradation in Bangladesh. Moreover, construction sites in cities can contribute to soil erosion if silt fences or sediment retention ponds are not employed properly. In Bangladesh, no such measures are in practice at construction sites.
Excessive Development/Unplanned development
Rapid population growth creates extra pressure on the land of already overcrowded Bangladesh. Agricultural lands give way to housing developments and roads. This rapid development and urbanization has almost undoubtedly must have aggravated the flooding problem in Bangladesh. Urban population has increased from 1.81 million (4.33% of total population) in 1951 to 25.2 million in 1990. The current urban population is more than 30 million (25% of total population), and is projected to exceed 58 million (36% of total population), by the year 2010. Unplanned urbanization can adversely impact flooding situation in a watershed. Prior to urbanization there exists a greater lag time between intense rainfall and peak stream flow. After urbanization the lag time is shortened, peak flow is greatly increased, and the total run-off is compressed into a shorter time interval, creating favorable conditions for intense flooding. For example, in a city that is totally served by storm drains, and where 60% of the land surface is covered by roads and buildings (like Dhaka City), floods are almost six times more numerous than before urbanization.
Following urbanization, it is necessary to adjust drainage capacity in the watershed to take into account the “basin development factor (BDF)” in order to accommodate the extra runoff that results due to urbanization. The amount of adjustment in the carrying capacity of natural streams following urbanization depends on the degree of BDF. For an increase the amount of impervious surface by 10% in a watershed, a 23% increase in the drainage capacity by dredging or deepening of streams is required. Dhaka City is located in the watersheds of Buriganga and Sitalakha Rivers. A significant increase in the amount of impervious surface in these watersheds has taken place due to expansion of the Dhaka Metropolitan area over the last few decades. However, no attempts have been taken to increase the carrying capacity of these rivers to accommodate for the BDF. On the contrary, many of the rivers including Buriganga are being filled up people. The illegal encroachment onto the rivers is contributing to the reduction in water carrying capacity during floods. Moreover, the internal drainage system consisting of tributaries to Buriganga and Sitalakha Rivers has been diminished due to unplanned land use practices. For instance, it is apparent from topographic maps that Dhanmondi Lake and Baridhara Lake are remnants of tributaries to Bugiganga-Sitalakha Rivers. Also, filling up of Dholaikhali channel has reduced the runoff capacity from Dhaka City. The lack of an efficient storm sewer system in Dhaka City also contributes to the reduction of water carrying capacity, causing water logging throughout the monsoon season. According to reports published in national newspapers, Dhaka City has experienced serious water logging problems during the wet months of July to October in 1999, and during July to September in 2000
Gabtoli turag
Seismic (Earthquake) and Neotectonic Activities
I) Seismic (Earthquake) and Neotectonic Activities: Bangladesh lies on the Indian lithospheric plate, which is pushing against the Asian plate, causing growth of the Himalayas and occasional earthquakes in the region. Earthquakes cause movement of the land, and this can change the topography of the region and alter river courses. A sudden change in a river course can cause substantial flooding. For example, the Old Brahmaputra changed its course to its present location following an earthquake in the mid eighteenth century (Er-Rashid, 1978). The northern regions of Bangladesh are earthquake-prone (Morgan and McIntyre, 1958). Neotectonic activities (recent movements in the Earth's crust) are affecting river courses in the area. The Madhupur tract and the Barind tract are undergoing such neotectonic activities (Morgan and McIntyre,
1958). Most of the recent floods have been approximately simultaneous with earthquake activities. For example, the 1950 earthquake in Assam caused "swallowing" of the Brahmaputra, by causing to breach its banks and flood in the region (The Times of India, 1988). The floods of 1988 and 1991 also are coincident with earthquake activities in northern parts of Bangladesh (The Times of
India, 1988; The New York Times, 1991). Recently, a powerful earthquake occurred on October 20 of 1991 in northern India, which was preceded by a flood in Bangladesh and was followed by another flood in the Ganges valley in India (The Philadelphia Inquirer,
1991).
Floods can be both a cause of or an effect of an earthquake. Flood water places an extra hydrostatic pressure on unstable and mobile crustal blocks. If this extra pressure reaches the
threshold strain limit along a fault zone or plate boundary within the Earth's crust, it can cause an earthquake to occur due to a sudden release of the strain energy accumulated over time.
Similarly, an earthquake can change the surface drainage pattern and consequently the course of a river, causing sudden flooding in an area. Even though the cause and effect relationship between
floods and earthquakes is not very clear, historic records suggest a relationship between these two phenomena.
Greenhouse Effect/snow malting in Himalayans
(J) Greenhouse Effect: The world is about to enter a period of rapid warming. Should the greenhouse effect become a reality, the low lying coastal areas will be affected by a rising sea level of even greater magnitude (Milliman et al. 1989; Gable and Aubery, 1990). Bangladesh will be severely impacted by such an increase in
sea level (Broadus et al., 1986; Khalequzzaman, 1989; Ali and Huq, 1989; Brammer 1989; Hossain 1989). Besides many other adverse environmental, economic, and climatic consequences (Huq and Ali, in press), the base level of all rivers will change following any change in the sea level. The effect on flooding of a higher base level resulting from a rising sea level has already been discussed earlier in this section. The greenhouse effect will also increase the amount of rainfall and storminess, which will further aggravate the flood problem.
Local Relative Sea Level Rise
The ultimate destination of all rivers is the ocean. The land elevations are measured with respect to the sea level in an area. Therefore, any change in the sea level causes land elevations to change as well. At the present time the sea level is rising globally. If the sea-level rises in an area at rates faster than the rates of land aggradation due to sedimentation, then land elevations decreases over time. Any decrease in land elevations can cause increased inundation by rivers overflowing at bankfull stage. The rate of local relative sea-level rise is 7 mm/year in the coastal areas of Bangladesh. According to a study, the local relative sea level at Chittagong Port has increased by as much as 25 cm between 1944 and 1964. The relative sea level in the Bay of Bengal is predicted to rise 83 to 153 cm by the year 2050. An increase in the sea level raises the base level of rivers, which in turn reduces the gradients of river flow. As a consequence, the amount of river discharge decreases, creating a backwater effect further inland. The backwater effect caused by sea-level rise can result in more flooding of lands from "piled up" river water inland. This certainly seems to be one of the contributing factors for the increased flooding intensity in Bangladesh.
Source:Md.Osman Harun or Rashid,Roll-020300,(2003-04)Mapping of the Flood Affected Area of Bangladesh,1955-2004,Unpublished Report,Geography & Environment,Jahangirnagar University,Savar,Dhaka
In recent years, the Government of Bangladesh (GoB) has been placing increased emphasis on reduction of the human, economic and environmental costs of disasters, through enhancing the national capacity for disaster mitigation.
The programs on disaster management in Bangladesh focus equally on structural and non-structural practices intended for disaster mitigation:
Non-Structural Mitigation: Non-structural mitigation practices pursued by the GoB focus on (1)
preparedness and possibilities for action to reduce risks and losses, and (2) better coordination
mechanisms between all actors involved (GoB, NGO and community people at the grass-roots level)
during all phases of disaster. Such practical measures under the recently completed project: "Support for
Disaster Management" involve the following.
i) Legislation, Policy and Planning
The Disaster Management Legislation (Act) and the Clear and Comprehensive National Policy on
Disaster Management and National Disaster Management Plan have already been drafted and are
now under consideration of the GoB.
ii) Training and Public Awareness
The Disaster Management Bureau (DMB) has conducted 447 training courses, workshops and
seminars attended by government and semi-government officials of different levels, as well as
various stakeholders. In addition, the DMB has developed Disaster Management training modules
and has supported the arrangement of disaster management training workshops.
iii) Institutional Arrangements
The GoB has taken a number of significant steps for building up institutional arrangements from
national to union levels for effective and systematic disaster management.
1. Naming of the Ministry of Relief and Rehabilitation as the Ministry of Disaster Management &
Relief (MDMR)
2. Establishment of Disaster Management Bureau (DMB) in 1993
3. Establishment of Council and Committees at the national, district, upazilla and union levels
4. Establishment of Emergency Operations Centre (EOC)
iv) Warning Systems
In Bangladesh there are two warning systems: flood warning and cyclone warning
FLOOD ACTION PLAN
After the 1988 floods, a debate on how to address the flooding problem began to develop through various
preliminary studies. These proposed interventions ranging from an almost purely structural “once-for-all”
massive engineering solution, to a mainly non-structural “living with the floods” approach. The debate was
subsequently short-circuited by a set of eleven principles prepared to guide future studies; directives from
senior levels of Government to proceed despite the unresolved issues; and also, in part, international
commercial interests that favored structural interventions.
The compromise five-year plan that emerged from this debate was called the Flood Action Plan (FAP).
FAP consisted of regional planning studies, project preparation studies, and pilot projects. FAP was
strongly opposed by local and international NGOs, organized around a coalition of
environmental NGOs that initially raised awareness through public meetings outside Bangladesh. The
opposition to FAP challenged a number of basic assumptions related to structural flood control, among
these, that flood control was desirable; that the major rivers could be embanked sustainably despite large
sediment loads and alluvial soils; that structural measures were affordable; and that planners could work in
isolation from the people for whom the interventions were intended.
The FAP process gradually produced a consensus on several issues, among them support for a softer
“controlled flooding” concept in place of the more hard-edged idea of “flood control;” the need for greatly
enhanced people's participation; and an emphasis on improving drainage through dredging planned at the
river system level. In the end, the FAP did not recommend large-scale works; rather, it initiated guidelines
on people’s participation and environmental assessment.
It is clear now that FAP resulted in a new planning approach. It is now widely accepted that planning must
be participatory and that consultation at all levels is essential to correctly identify development needs and
interventions. Furthermore, greater emphasis on participation has led to the recognition that as people’s
lives are not compartmentalized by sectors, so too must planning be multi-objective and multi-sectoral.
Other outcomes of FAP included much greater emphasis in the planning process on environmental and
institutional aspects, flood mitigation as an integral part of flood management, acceptance that flood control
should be addressed in a regional context, and that cooperation among riparian countries is essential.
Many of these new concepts are enshrined in the first National Water Policy, established in 1999 and in the
National Water Management Plan that will be completed 2001. The challenge will be to put these lofty
principles into practice in the field. Progress is likely to be slow, given public sector capacity limitations.
Structural Solutions
Flood management strategies adopted in the country have continuously evolved over the last 50
years, in three distinct phases of their development, and with mixed experiences. Initially, the
emphasis was on structural measures through the implementation of some large-scale flood
control, drainage and irrigation (FCDI) projects. However, it was soon recognized that their
implementation involved large investments, as well as longer duration for their completion. It was
then opted for the construction of small and medium scale FCD projects so as to provide early
benefits. Thereafter, it was realized that water resources development should not be focused only
on agriculture but take also into account other sectors related to water resources utilization and
development. Environmental protection also came to the fore.
As a result, since the 1960’s about 628 large, medium and small-scale FCDI projects have been
implemented; they comprise levees and embankments, drainage channel improvements, drainage
structures, dams and barrages, pumping systems, etc. They have provided flood protection to
about 5.37 million ha of land, which is about 35% of the total area.
Structural solutions call for the engineering of structures such as embankments along rivers, dams, drains, reservoirs, and other structures designed to control the natural flow of rivers.
Structural solutions treat the problem section of a river basin in isolation (Rashid and Paul, 1987); and generally do not take into account the possible geologic consequences (Khalequzzaman, in press). Structural solutions are in practice on a limited scale in Bangladesh as part of a flood control project (Rashid and Paul, 1987).
A megascale structural solution to the flood problem in Bangladesh is now under way. The United Nations Development Program and the Government of Bangladesh have outlined a plan for
flood control in Bangladesh (GOB and UNDP, 1989; Boyce, 1990; McDonalds, 1991). This plan, referred to in this paper as the flood control megaproject, will be sponsored by the World Bank. The flood control megaproject calls for the construction of hundreds of kilometers of tall embankments along the great rivers of the
Bangladesh delta, enormous drains, and "compartments" on the flood plains. Huge areas of the countryside will be divided into embanked "compartments" in which controlled flooding will be managed by intakes from rivers and offtake through the drains (Figure 1). Although the efforts of the World Bank are appreciated, the wisdom of such a scheme as a possible solution to the flood problem is debatable on the basis of adverse consequences that would follow the implementation of this megaproject.
Natural processes can not be prevented by confronting them. However, a comprehensive knowledge of these processes can help us to better plan land use and mitigate their effects by helping us find ways to adjust to the processes while safeguarding the environment. The primary mechanism for any delta growth is deposition of river-borne sediments. The planned embankments will prevent sedimentation on Bangladesh's delta plain, causing riverbed
aggradation and subsequent submergence of the areas behind those
embankments by the rising sea. Other problems that would follow the
implementation of such a megaproject include flash floods, possible
shifts in river courses, loss of a huge land area to the project,
loss of land fertility, and possible relocation of people. Building
such embankments will also create a chronic necessity to maintain
them for generations--not a easy task for Bangladesh.
The structure of the embankments under the proposed
megaproject in Bangladesh is similar to those built along the lower
Mississippi River in the United States of America. Despite
enormous expenditures for annual maintenance and very close
monitoring of the project by the Army Corps of Engineers, the
embankment project has proven to be a complete failure. The
embankments were nearly wiped out during the floods of 1973 and
1984 (McPhee, 1989).
Implementation of the flood control megaproject proposed by
the World Bank will not solve the flood problem, but rather will
create a series of geologic and environmental problems. Bangladesh
has been formed by sediment from the rivers that drain it. The
country will eventually be wiped out by the rising sea should the
major rivers be prevented from depositing their sediment load on
the delta.
Non-structural measures such as flood forecasting and warning were later incorporated, as it was
felt that structural measures alone could not mitigate flood problems. The Flood Forecasting and
Warning System (FFWS), established in the 1970s, was modernized in 1996 and then again as of
2000. It now covers all the flood-prone areas of the country with 85 flood-monitoring stations, and
provides real-time flood information and early warning with lead-times of 24 and 48 hours. The
FFWS is currently assisting Government, disaster managers and the communities living in the
flood prone areas in matters of flood preparedness, preparation of emergency mitigation plans,
agricultural planning and rehabilitation, etc
In addition, more emphasis is now put on other non-structural means for flood mitigation, in
particular by adopting a policy of involving communities in flood management, the stopping of
encroachments on the flood plains through legislation controlling the developments in the flood
plains and wetlands. In addition, a new concept is being introduced of controlled flooding as per
desire of the stakeholders, instead of protecting some areas to make them completely flood-free. A
pilot project was established in which flooding is allowed in each unit as decided by the
stakeholders through consultation among themselves.The basic requirement for formulating a solution to the flood
problem is an understanding of underlying geologic processes that
cause floods. Flooding in Bangladesh is but a part of the overall
hydrodynamic process active in the entire region. Only solutions
that are in harmony with the natural processes can prevail.
Confrontation with the natural processes will lead to
disequilibrium within the hydrodynamic system in the region and to
more problems. Therefore, any structural solution will merely be
a very short-term solution. In the long run, any type of a
"troubleshooter" solution (such as building embankments along the
riverbanks where floods have occurred) will almost definitely
aggravate the situation.
The geologic solution is more farsighted in nature--it is to
permit the delta to grow both vertically and horizontally at a rate
that would keep pace with the relative sea level rise in the
region (Khalequzzaman 1991). A detailed study of the geologic
processes, namely hydrodynamics of the rivers and channels,
dynamics of sedimentation, amount and rate of sediment
accumulation, rate of erosion and subsidence, and rate of local sea
level rise, is necessary in order for the success of any
development plans or preventive measures to mitigate the flooding
problem. Only a better understanding of all geologic processes can
help us to solve the problem of flooding while safeguarding the
environment (Stoddart and John, 1984).
Geologic solutions to the flood problem can be viewed in the
context of the two most important parameters: land elevation and
water carrying capacity of the basin. Increases in land elevation
and water carrying capacity of the rivers will reduce flooding
propensity in Bangladesh. The following paragraphs discuss
possible ways of helping to increase land elevation and capacity of
the river basin. Structural elements such as dams, sluice gates,
along with dredging and dispersion of sediments will have to be
applied in order to achieve the desired goal of increasing land
elevation and capacity of the drainage basin. This will in turn
help mitigate the flood problem in Bangladesh.
(A) Dredging and Re-excavation of Rivers: Continuous dredging of
the rivers and channels and dispersion of the dredged sediments on
the delta plain will not only increase elevation of the land, but
will also increase the capacity of the rivers. These factors will
in turn reduce the severity of annual flooding. Adequate sediment
supply, accumulation and dispersion are primary requirements for
accelerated growth of the Ganges-Brahmaputra delta at a rate that
is sufficient to keep pace with the rising sea level.
The rivers in Bangladesh carry ample sediment for dredging and
dispersion on the flood plains in spite of the fact that the
average sediment load of the Ganges-Brahmaputra river system has
declined from 2.4 billion tons/year (67% delivered by the Ganges)
to 1.6 billion tons/year (Milliman and Meade 1983; Meade, 1983)
since the diversion of the Ganges through the Farakka-Barrage
damming project. Calculation of the sediment budget in Bangladesh,
based on limited data on the rate of sedimentation, shows that only
10-15% of the sediment load carried by the rivers are deposited on
the flood plains and delta plains (Figure 2). The major portion of
the sediment bypasses the continental shelf to feed the world's
largest submarine fan (Bengal Fan), which extends more than 3,000
km south into the Bay of Bengal (Curray and Moore, 1974; Emmel and
Curray 1984).
Calculations of sediment budget and accumulation show that
only 30% of the present suspended sediment influx of 1.6 billion
tons/year in the coastal areas is capable of aggrading an area of
30,000 sq. km, the area of all coastal districts of Bangladesh, at
a rate which exceeds the projected sea level rise of 1 cm/year (the
rate predicted by the Environmental Protection Agency of the USA
for the next century). The same amount of sediment dispersed over
a 150,000 sq. km area (greater than the size of Bangladesh) is
capable of aggrading at a vertical rate of 0.3 cm/year, which would
be enough to keep pace with the present rate of local relative sea
level rise (Figure 3). Moreover, there has been a recent increase
in the amount of total suspended and bedload discharge of the
Brahmaputra River due to massive deforestation of the Tibetan and
Nepalese slopes. Soil loss in the Himalayas averages about 60
cm/1000 years. The recent increase in sediment discharge has
caused the river bed level to rise about 5-7 m, thus decreasing
bankfull stage and increasing its flooding propensity (Alexander
1989a). If dredged and dispersed properly, this extra source of
sediment can help the delta to grow.
A volumetric calculation of sediment shows that a 1 m increase
in depth of a 1 km stretch of a river with a width of 100 m will
generate 100,000 m3 of available sediment from the dredging process.
This amount of sediment, if dispersed uniformly on the flood plains
over a 1 km2 area on both sides of the river, will increase the
elevation of the flood plains by 5 cm; and will also increase the
discharge capacity of the river by 100, 000 m3. An increase in
flood plain elevation of 5 cm may not seem very significant; but in
an area where the elevation gradient is only 10 cm/km, like the
coastal areas of Bangladesh an increase in relative sea level of 5
cm is capable of shifting the shorelines in a landward direction by
0.5 km (Figure 4). The pre rate of local relative sea level rise
exceeds the rate of sediment accumulation by 0.2 cm/year. At this
rate, it will take 25 years for the sea level to rise 5 cm. Thus,
occasional dredging of all rivers and channels in the low-lying
areas affected by floods, and dispersion of the dredged sediment on
the flood plains will not only increase discharge capacity of the
rivers but will also help flood plain accretion to keep pace with
the rising sea.
(B) Preventing Land Degradation: Suspended sediments adhere to the
stems of plants. Farmers can be advised to leave a few inches of
stem remaining from their rice crops during harvesting before the
rainy season. They should also be given more information about the
problem of soil erosion. Ploughing makes the soil more susceptible
to erosion from surface runoff. Wise tilling practices such as
putting tall earthen boundaries between large farm lands and
contour tilling can prevent sediments from draining out to the
channels by run-off.
(C) Flood Preparedness: An understanding of how individuals have
adapted to and are affected by floods may suggest new and less
costly ways of reducing flood damages (Paul 1984). Indigenous
solutions such as the building of suitable housing, shelters and
infrastructures also deserves serious consideration (Islam 1980;
Rashid and Paul 1987, Alexander 1989b).
(D) Interbasinal Cooperation: Only 7% of the river basin area
falls within Bangladesh (Figure 5). Without regional cooperation
between the co-riparian nations any major interbasin development
activity is almost impossible. In order for any interbasinal flood
control project to be successful, it will have to be designed to
serve the common interests of the people of the countries
concerned. For example, construction of reservoirs in the upstrem
regions of the Brahmaputra to hold excess water during rainy
seasons can reduce flood propensity in Bangladesh. The trapped
water can be used to produce electricity during the summer months,
to meet some of the irrigation demands for Bangladesh and energy
demands of Nepal and India. Siltation is a major problem for any hydroelectric reservoir. The accumulated material in the proposed reservoir can be removed through pumping into the downstream flow of the Brahmaputra. This
excess material can serve as an additional source of sediment for delta growth in Bangladesh, if the material is properly dredged outand dispersed onto the flood plains.
![1
Bangladesh: Geographical &
Environmental Settings-
Location, Climate,
River systems, and
Floods in Bangladesh
Course Title: Bangladesh: Socio-Economic
Perspective [Course No. BAN-201]
Course Teacher : Dr. M. Mizanur Rahman](https://image.slidesharecdn.com/l-02-bangladesh-geographicalenvironmentalsettings-150807172322-lva1-app6891/85/L-02-bangladesh-geographical-environmental-settings-1-320.jpg)
