Flood and Floodplain Management of Bangladesh

8/12/2019 Flood and Floodplain Management of Bangladesh

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An Assignment on

Flood and Floodplain Management of BangladeshSubmitted to

Mohammed Jamal UddinAssociate Professor

Submitted byMd. Bodrud-doza (563)Tareque Ahmed Bhuiyan (1479)

Syed Rakibur Rahman (553)

Fahad Ahmed (559)

Sarmin Akhtar Shimu (542)

Department of Environmental SciencesJahangirnagar University, Dhaka-1342


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Table of ContentTopics Page no

Definition of flood 01

Types of flood in bangladesh 02

Factors of flood in bangladesh 02

Causes of flood in bangladesh 03-06

Bangladesh land classification due to flood condition 07

Floodplain 07-08

Floodplain areas 08-14

Floodplain management 15-21

References 21

Name of Figures Page no

Map of Flood prone areas and River system of Bangladesh. 01

Causes of Flood of Bangladesh 04

Bangladesh land classification due to flood 07

Map of the Floodplain areas of Bangladesh 09

Maps of major floodplain areas of bangladesh 12-13

Map of floodplain areas and rivers of bangladesh 14


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FloodandFloodplainManageme

ntofBangladesh

Flood is a consequence of migration of the boundary between land and water bodies,

reflecting the normal interaction of the atmosphere, hydrosphere and lithosphere.

Two major factors are responsible for flood generation and impart specific features to

it. The first is the physical process, which generates the change of position between

the lithosphere, atmosphere and hydrosphere. Secondly, the flooded area, depth ofinundation, and its duration, depend on the geographic situation in the region where

the flood takes place. Due to the great variety in operation of the natural processes

and the endless variation in the condition of the geographic arena where they act,

many different kinds and scales of floods can be distinguished. Growing human

influence is becoming evident from the increasing frequency of floods of

anthropogenic origin.

DEFINITION OF FLOODA flood is an overflow of water that submerges land. The European Union (EU)

Floods Directive defines a flood as a covering by water of land not normally covered

by water. Flood relatively high flow of water that overtops the natural or artificial

banks in any of the reaches of a stream. When banks are overtopped, water spreads

over the floodplain and generally causes problems for inhabitants, crops and

vegetation.

In Bangladesh, the definition of flood appears differently. During the rainy season

when the water flow exceeds the holding capacity of rivers, canals, beels, haors, low-

lying areas it inundates the whole area causing damage to crops, homesteads, roads

and other properties. In the Bangladesh context there is a relation between

inundation and cropping.

Fig-1: Map of Flood prone areas and River system of Bangladesh


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TYPES OF FLOOD IN BANGLADESHFloods in Bangladesh can be divided into three categories:

(1) Monsoon flood - seasonal, increases slowly and decreases slowly, inundates vastareas and causes huge losses to life and property.

(2) Flash flood - water increases and decreases suddenly, generally happens in thevalleys of the hilly areas

(3) Tidal flood - short duration, height is generally 3m to 6m, blocks inland flooddrainage.

In Bangladesh the following types of floods are also normally encountered:

Local floods due to high localized rainfall of long duration in the monsoon season

often generate water volumes in excess of the local drainage capacity, causing

localized floods due to drainage congestion.Floods due to storm surges in the coastal areas of Bangladesh, which are generated

by tropical cyclone, cause extensive damage to life and property. These cyclones

are predominant during the post-monsoon (October and November) and pre-

monsoon (April to June) period.

FACTORS OF FLOOD IN BANGLADESHThe factors for causing floods in Bangladesh are:

(1) General Low topography of the country with major rivers draining throughBangladesh including a congested river network system,

(2) Rainfall in the upstream country or in the mainland,

(3) snow-melt in the Himalayas and glacial displacement (natural),

(4) River siltation/lateral river contraction/landslides,

(5) Synchronization of major river peaks and influences of one river on the other,

(6) Human intervention of the environment,

(7) Tidal and wind effects on slowing down the river outflow (backwater effect),

(8) Construction of barrages and protective works along the banks of the river - some

are very close to both the banks - in the upper reaches thus making the passage of

water flow downstream increasingly narrower and resulting in greater acceleration of

water flow downstream presently than before.


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(9) Deforestation in the upper reaches of the rivers is not only leading acceleration of

water flow downstream but also lead deposition of loads in the river beds, resulting

in reduced channel flow and consequent overland runoff water and

(10) Tectonic anomalies (earthquake) those change in river flow/morphology.

CAUSES OF FLOOD IN BANGLADESHThere are many physical and human causes that allowed the floods to be worse; such

as:

The Physical Causes of the Floods Most of the country consists of a huge flood plain and delta. Snowmelt from the Himalayas takes place in late spring & summer.

70% of the total area is less than 1 meter above sea level. 10% of the land area is made up of Lakes and Rivers. Bangladesh experiences heavy monsoon rains, especially over the highlands. Tropical storms bring heavy rains and coastal flooding. The main cause was the above average & long period of heavy rain which

caused all 3 rivers to have their peak flow at the same time.

In the spring, melting snow from the Himalayas further increases the flood risksas torrents of melt water enter the rivers at their source.

The Human Causes of the Floods Deforestation in Nepal and the Himalayas increases run off and add to

deposition and flooding downstream.

Urbanization of the flood plain has increased magnitude & frequency of floods.


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Global warming is blamed for sea level rise, increased snow melt & increasedrainfall in the region.

The building of dams in India has increased the problem of sedimentation inBangladesh.

Poorly maintained embankments (levees) leak & collapse in times of highdischarge. Increasing population pressure in Bangladesh itself has resulted in the sinking of

many new wells resulting in the lowering of the water table and the

subsequent subsidence of land making it even more prone to flooding.

Fig-2: Causes of Flood of Bangladesh

Short-term Causes of FloodMonsoon downpour:An increased amount of precipitation can cause floodingSynchronization of Flood Peaks:The synchronization of flood peaks for the majorthree rivers took place within a two week time period, causing a sudden increase in

water level in virtually all areas of the country


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Long-term causes of Flood1. Sea level rise2. Compaction and subsidence of

sediments

3. River bed aggradations4. Accumulation of inadequate

sediment

5. Deforestation in the upstreamregion

6. Rivers damming7. Soil erosion due to tilling8. Excessive development9. Seismic (Earthquake) and

Neotectonic activities

10.Climate Change

(1) Sea level rise: The Ocean is the final destination of all the rivers. With respect tosea level in an area the land elevation is measured. Therefore, any change in sea level

causes land elevation to change.

(2) Compaction and subsidence of sediments: On a delta plain, sediments are rich indecomposed organic matter, and are subject to compaction due to dewatering and

the weight of the overburden. Most deltas subside due to the weight of the thick

sediment layer. Subsidence along with compaction reduces land elevation with respect

to the rising sea level.

(3) River bed aggradations:The large-grained sediments are deposited near the sourcearea on the river beds due to relatively higher settling velocity, forming sand bars. If

sedimentation continues on the riverbeds the river gradient decreases rapidly because

of low gradients and high sediment loads, the riverbeds of most of the rivers inBangladesh aggrades very quickly.

(4) Accumulation of inadequate sediment: Data showed that the average sedimentaccumulation rate for the last few hundred years in the coastal areas of Bangladesh is

5-6 mm/year, which is not enough to keep pace with the rising sea level. As the result,

net land elevations must have been decreasing over time, resulting in more flood

inundations.

(5) Deforestation in the upstream region: An extreme amount of deforestationincreased in the hills of Nepal due to rapid increase in population in the IndianSubcontinent over the course of the present century to meet the increasing demand

for food and fuel wood. Deforestation of steep slopes is assumed to lead to

accelerated soil erosion and landslides during monsoon precipitations. This in turn is

the result of devastating floods in the downstream regions in Bangladesh.

(6) Rivers damming:River damming reduces the velocity of water flow downstreamfrom the dam. As a result of reduced velocity, the sediments carried by the river start

to settle down faster on the riverbed, causing riverbed aggradations and in turn

reducing the water carrying capacity of the river. The Baraka Barrage (river barrier

between Bangladesh and India) on the Ganges has already caused tremendous


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damage to the agriculture, navigation, environment, and hydrodynamic equilibrium

in Bangladesh.

(7) Soil erosion due to tilling: The land surface becomes more susceptible to soilerosion because of ploughing. The surface run-off can easily wash away the topsoil

from cultivated land. This surface erosion reduces land elevation, which in turn

increases flood intensity in an area. The land elevations in Bangladesh must have been

reduced over time due cultivation.

(8) Excessive development: In overcrowded Bangladesh the enormous amount ofincreasing population produced an extra pressure on the land and as a result,

agricultural lands are given way for roads and to real state for housing developments.

This continuous growth in populations and urbanizations creates flooding problems in

Bangladesh.

(9) Seismic (Earthquake) and Neotectonic activities: A vibration in the earth or themovement of land produced by earthquake is known as seismic. This can change the

structure of the region and castrate river courses. Bangladesh lies on the Indian

lithosphere plate, which is pushing against the Asian plate, causing growth of the

Himalayas and occasional earthquakes in the region. A sudden change in a river

course can cause substantial flooding. The northern regions of Bangladesh are

earthquake-prone. Geotectonic activities (recent movements in the Earth's crust) are

affecting river courses in the area. Most of the recent floods have been approximately

simultaneous with earthquake activities. The floods of 1988 and 1991 also arecoincident with earthquake activities in northern parts of Bangladesh. A powerful

earthquake occurred recently on 20th October 1991 in northern India, which was

preceded by a flood in Bangladesh and was followed by another flood in the Ganges

valley in India. Floods can be either 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. Historic records show the relationship between

floods and earthquake even though the cause and effect relationship between them is

not very clear.

(10) Climate Change: Scientists assumed that the flood increased as the world getswarmer, which is absolutely true as the world is about to enter a period of rapid

warming. Rising sea level of even greater magnitude will cause flood on the low land

and slow the speed at which rivers can remove water from the land. Bangladesh will

be severely impacted by such an increase in sea level. Besides many other adverse

environmental,


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BANGLADESH LAND CLASSIFICATION DUE TO FLOOD CONDITIONIn order to understand the flooding and flood management, it is better having look

into the land types. Seasonal flooding regime has been characterized by means of

inundation land types. Usually, it is classified into 5 categories and detailed description

of land type with the area coverage is given in table:

Land type Description Nature offlooding Area in ha AreaHigh Land Land above normal

inundation

Intermittent

of flooded

4199952 29

Med. High Land Land normally inundated

up to 90 cm deep

Seasonal 5039724 35

Med. Low Land Land normally inundated

up to 90-180 cm deep

Seasonal 1771102 12

Low Land Land normally inundatedup to 180-300 cm deep

Seasonal 1101560 08

Very Low Land Land normally inundated

deeper than 300 cm

Seasonal or

perennial

193243 01

Normally, 20-25% of the country is inundated during every monsoon from June to

September. In case extreme flood events 40-70% area can be inundated, this was

amply proved during the extreme flood events of 1954-55, 1974, 1987-88 and 1998.

Fig-3: Bangladesh land classification due to flood

FLOODPLAINThe relatively broad and smooth valley floor that is constructed by an active river &

periodically covered with floodwater from the river during intervals of out bank flow

is termed as floodplains. Five main types of floodplain landscape are-

i. Active floodplains

ii. Piedmont plains

iii. Meander floodplains

iv. Tidal floodplains

v. Estuarine floodplains


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(1) Active floodplains:It comprise the youngest alluvial land within and alongside themain rivers which is subjected to alternate deposition of new sediments and erosion

by shifting channels within the major river coarse.

(2) Piedmont plains:Piedmont plains comprise gently sloping land at the foot of hillswhere rivers or streams have deposited colluvial & alluvial sediments derived from the

hills.

(3) Meander floodplains: Floodplains have been formed by big rivers laying downdeposits within & alongside their channels during floods.

(4)Tidal floodplain: Tidal floodplains have a distinctive, almost- level landscapecrossed by uncountable, inter- connecting tidal rivers & creeks. In tidal areas, flood

levels are lower than on meander floodplains.

(5) Estuarine floodplains: Estuarine floodplains differ from meander floodplain inbeing almost level, lacking meander scars & abandoned channels & having almost

uniformly silty deposits. They differ from tidal floodplains in lacking a close network

of tidal creeks & in having predominantly silty deposit.

FLOODPLAIN AREAS1. Old Himalayan Piedmont Plain2. Tista Floodplain3. Old Brahmaputra Floodplain4. Jamuna (Young Brahmaputra)

Floodplain

5. Haor Basin6. Surma-Kushiyara Floodplain7. Meghna Floodplain

(a) Middle Meghna Floodplain,

(b) Lower Meghna Floodplain,

(c) Old Meghna EstuarineFloodplain,

(d) Young Meghna Estuarine

Floodplain

8. Ganges River Floodplain9. Ganges Tidal Floodplain;10.Sundarbans11. Lower Atrai Basin12.Arial Beel13.Gopalganj-Khulna Peat Basin14.Chittagong Coastal Plain15.Northern and Eastern Piedmont

Plain


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Fig: Map of the Floodplain areas of Bangladesh


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Floodplain areas:Floodplains of Bangladesh have been divided into 18 sub-units.1. Old Himalayan Piedmont Plain:It comprises gently sloping land at the foot of hillsformed with fluvial and alluvial sediments derived from the hills deposited by rivers

or streams. A portion of the Old Himalayan Piedmont Plain stretches into Bangladesh

at the northwestern corner of the country. This occupies most of the Dinajpur region.

2. Tista Floodplain: It is a big sub-region stretches between the Old HimalayanPiedmont Plain in the west and the right bank of the N-S flowing Brahmaputra in the

east. Most of the land is shallowly flooded during monsoons.

3. Old Brahmaputra Floodplain:The Old Brahmaputra floodplain extending from thesouthwestern corner of the Garo Hills along the eastern rim of the Madhupur Tract

down to the Meghna exhibits a gentle morphology composed of broad ridges and

depressions. The latter are usually flooded to a depth of more than one meter,whereas the ridges are subject to shallow flooding only in the monsoon season.

4. Jamuna (Young Brahmaputra) Floodplain: A dual name is used for the mightyBrahmaputra, because the Jamuna channel is comparatively new and this course must

be clearly distinguished from that of the older Brahmaputra.

5. Haor Basin: It is a large, gentle depressional feature, is bounded by the OldBrahmaputra floodplain in the west, the Meghalaya Plateau's foothills in the north,

Sylhet High Plain in the east and Old Meghna Estuarine floodplain on the south. It is

regularly flooded during the monsoon.

6. Surma-Kushiyara Floodplain:Surma-Kushiyara Floodplain comprises the floodplainof rivers draining from the eastern border towards the Sylhet Basin (Haor Basin).

Some small hill and piedmont areas near Sylhet are included within the boundaries.

This area is subject to flash floods in the pre-monsoon, monsoon and post-monsoon

seasons, so the extent and depth of flooding can vary greatly within a few days.

7. Meghna Floodplain:Meghna floodplain is divided into four sub-regions:a) Middle Meghna floodplain,

b) Lower Meghna floodplain,

c) Old Meghna estuarine floodplain, and

d) Young Meghna Estuarine floodplain

(a) Middle Meghna Floodplain:The main channel of the Meghna upstream from itsjunction with the Dhaleshwari and Ganges as far as Bhairab Bazar is known as the

middle Meghna. Seasonal flooding from the Meghna is mainly deep. Basin sites are

submerged early and drain late.


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(b) Lower Meghna Floodplain: Southward from the junction of the Meghna andGanges, the sediments on the left bank of the lower Meghna comprise mixed alluvium

from the Ganges, Jamuna and Meghna. These deposits are predominantly silty. This

floodplain area has a slightly irregular ridge and basin relief, but also has large mounds

used for settlement and cultivation. Seasonal flooding was formerly moderately deep,fluctuating in depth twice daily with the tides in the south, but flooding is mainly

shallow and by rainwater within the area protected and drained by the Chandpur

irrigation project.

(c) Old Meghna Estuarine Floodplain: The landscape in this extensive unit is quitedifferent from that on river and tidal floodplains. Virtually everywhere, this flooding

is by rainwater ponded on the land when external rivers flow at high levels; the

exceptions are the narrow floodplains alongside small rivers (such as the Gomuti)

which cross the unit from adjoining hill and piedmont areas.

(d) Young Meghna Estuarine Floodplain: This sub-unit occupies almost the level landwithin and adjoining the Meghna estuary. It includes both island and mainland areas.

Flooding by salt water occurs mainly on the lamed margins and during exceptional

high tides during the monsoon, also when storm surges associated with tropical

cyclones occur.

8. Ganges River Floodplain: It is comprises the active floodplain of the Ganges andthe adjoining meander floodplain. The latter mainly comprises a smooth landscape of

ridges, basins and old channels. Seasonal flooding is mainly shallow in the west andnorth, with the highest ridge crests remaining above normal flood levels, but flood

depths increase towards the east and the south. Flooding is mainly by accumulated

rainwater and the raised groundwater table, except on the active Ganges floodplain

and close to distributary channels which cross the meander floodplain.

9. Ganges Tidal Floodplain: The boundary between this unit and the Gangesfloodplain is traditional. The tidal landscape has a low ridge and a basin relief crossed

by innumerable tidal rivers and creeks. There is mainly shallow flooding at high tides,

either throughout the year, or only in the monsoon, except in the extensive areas

where Embankments prevent tidal flooding. Within embankments, there is seasonal

flooding with accumulated rainwater.

10. The Sundarbans or the immature delta:South and southwest of the Ganges tidalfloodplain, there is a broad belt of land, barely above sea level with an elevation of

only 0.91m. This very low land of some 4,827 sq km area contains the Sundarbans

forest and the reclaimed estates (cultivated land) - classified as the Sundarbans unit.

There are two possible causes for the existence of such a large very low estuarine area

- insufficient deposition by the Ganges distributaries or subsidence. On the other hand,

it is possible that subsidence has played a major part in depressing this area.


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11. Lower Atrai Basin: A small physiographic unit occupies a low-lying area wheremixed sediments from the Atrai and Ganges and from the Barind Tract overlie the

down-warped southern edge of the Barind Tract. Deep flooding can still occur within

polders as well as outside when there is heavy rainfall locally and when flash floods

flow down the Atrai or off the adjoining Barind Tract, causing natural or manmadebreaches of embankments.

12. Arial Beel:It is a large depression of about 723 sq km lying between the Gangesand the Dhaleshwari south of Dhaka. The deep seasonal flooding is predominantly by

accumulated rainwater, which is unable to drain into rivers when they are running at

high levels. Much of this unit remains wet in the dry season.

13. Gopalganj-Khulna Peat Basin:Gopalganj-Khulna peat basin occupies a number oflow-lying areas between the Ganges River Floodplain and the Ganges tidal floodplain.

The major two beels of the area are Baghia Beel and Chanda Beel. The basins aredeeply flooded by clear rainwater during the monsoon.

14. Chittagong Coastal Plain:The plain along the coast extends from the Feni River tothe mouth of the Matamuhuri delta, a distance of 121 km. The whole of the mainland

area is subjected to flash floods. Flooding is mainly shallow and fluctuates in depth

with the tide (except where this is prevented by river or coastal embankments). The

average daily rise in the tide is about two meters. Some soils on tidal and estuarine

floodplains become saline in the dry season.

15. Northern and Eastern Piedmont Plains: Generally sloping piedmont plains borderthe northern and eastern hills; (similar piedmont plains adjoining the hills in

Chittagong region have been included in the Chittagong coastal plain). The whole

area is subject to flash floods during the rainy season. On the higher parts, flooding is

mainly intermittent and shallow; but it is moderately deep or deep in the basin.

MAPS OF MAJOR FLOODPLAIN AREAS OF BANGLADESH


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MAPS OF MAJOR FLOODPLAIN AREAS OF BANGLADESH


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MAP OF FLOODPLAIN AREAS AND RIVERS OF BANGLADESH


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FLOODPLAIN MANAGEMENTAreas that are vulnerable to flooding are called floodplains or flood hazard lands.

These are lands adjoining a river, lake or other watercourse, which has been, or may

be, covered by floodwaters.

Floodplains are managed to reduce damage and loss. Floodplain management has

three components:

Prevention land use planning and regulation of development, increasing publicawareness of potential risks;

Protection structural/protective works such as dams and dykes, purchasing ofhazardous land to convert them into park lands; and

Emergency preparedness and responseflood preparedness, forecasting, warning andcombat.

There are three concepts of floodplain management:

1. One-zone concept,2. Two-zone concept and3. In a few exceptional situations, a special policy area concept

Regardless of the concept applied, the overall intent of the policies governing public

health and safety should be assured.

(1) One-zone concept:Using this, planning authorities determine the flooding hazardslimit, and prohibit all development or site alteration within those boundaries. This is

the most effective way of minimizing threats to public health or safety or property

damage. Where the one zone concept is applied, the entire flood plain or the entire

flooding hazard limit defines the floodway.

(2) Two-zone concept:This concept identifies the floodway and the flood fringe. Thefloodway refers to that portion of the floodplain where development and site

alteration would cause a threat to public health and safety and property damage. The

flood fringe is the portion of the flood plain where development may be permitted

subject to certain established standards and procedures.

(3) Special Policy Areas: In some unique or exceptional situations, communities areallowed to continue uses in a flood plain if the area is officially designated as a Special

Policy Area (SPA). The application of the SPA concept is really limited to those areas,

which are essential for the continued viability of existing uses; e.g. historical sites or

old neighbourhoods built before flood plain policies came into effect.


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Flood management can be divided into five parts:Structural measurement

Non-structural measurement

Geologic or alternative solutions

Reduce of carbon emission

Usage of proper sanitation or dry toilet

(a) Structural measurements:Over the second part of last century flood managementstrategies adopted in the country have continuously evolved in three distinct phases of

their development, and with mixed experiences. At the beginning, the emphasis was

on structural measures through the implementation of some large-scale Flood control,

drainage and irrigation (FCDI) projects. After some time later it has been realized that

a huge amount of investment is required to implement the idea as well as it is going

to take more time to complete. It was then opted for the construction of small andmedium scale Flood and Coastal Defense (FCD) projects so as to provide early

benefits. After this, it was observed that other sectors related to water resources

development and utilization should also be taking care of like the way they do for

agriculture. Environmental protection has been given first priority. As a result, since

the 1960s 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 35% of the total area, the meaning is about

5.37 million ha of land.

Moreover, the back flow of flood water (the water enters from the three major river

will be transfer to Bay of Bengal) through drainage can be implemented and in that

case more drainage channels and pumping systems have to be established as

mentioned earlier above the investment involvement is high. But studies showed that

the fly-over bridges that are constructed in the capital city to reduce traffic jams cost

about USD 67million.

The government has invested for the flood management around USD 4 billion to the

water sector used mainly for the FCDI project during the last 40 years, meaning an

annual expenditure of 200 million USD.

To maintain drainage channels and structures and also to raise new improved

drainage channel with bigger structures will reduce the maximum amount of flood

affecting the capital city. It is also hoped that the other developing cities would

benefit this money and will utilize it for improved flood management.

(b) Non-structural measurements: It has been proven that structural measures aloneare not the only solution to improved flood conditions. Non-structural measures like

Flood Forecasting and Warning System (FFWS) have been introduced to share the


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flood problems. In early 70s the FFWS has been established in Bangladesh and was

modernized in 1996 and then again in the year 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 hours and 48 hours. The

FFWS is currently assisting Government, disaster managers and the communities livingin the flood prone areas in matters of flood preparedness, preparation of emergency

mitigation plans, rehabilitation and agricultural planning.

Furthermore, for the flood mitigation more emphasis is now put on other non-

structural means 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. However, a new

concept is being introduced of controlling the flood as per desire of the stakeholders,

instead of protecting some areas to make them completely flood-free.

Strategy for mitigating flood hazard, the concept of social adjustment, also known as

non-structural measures can be important. These include:

(1) Dissemination of meteorological forecasts, short and long range warning system

including the height to which the flood water is likely to rise in the next few hours or

so and a programme of speedy evacuation.

(2) Land management for reduction of runoff water. In this case a programme of

afforestation and reforestation together with animal grazing controls to increase

absorption and reduction of runoff water could be undertaken.

(3) Landuse change and enactment of building codes, diversification of agricultural

production, that is, identification and planting of flood resistant crops and adjustment

of planting season.

(4) Floodplain zoning, involving landuse zoning to control development and

restrictive development regulations, should ensure that any development meets

certain standards and that they take into consideration the threat to a site.

Non-structural measures can be implemented at nominal costs and in a very shorttime resulting in positive benefit to the floodplain users.

(c) Geologic solution: We need to understand the geologic processes before weexpress any kind of solutions that causes flood. In the entire region flooding in

Bangladesh is a part of the overall hydrodynamic process. 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.


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Further studies of 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. While safeguarding the environment a better understanding of all geologicprocesses can help us to solve the problem of flooding.

The geologic solutions of flood problem can be measured into 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.

Alternative solution includes-

(1) Dredging of rivers:To increase the capacity of the river and elevation of the landcontinuous dredging of the rivers and channels and dispersion of the dredged

sediments on the delta plain is necessary. These factors will in turn reduce the severity

of annual flooding. For accelerated growth of the Ganges-Brahmaputra delta

adequate sediment supply, accumulation and dispersion are primary requirements to

maintain the pace with the rising sea level.

From a volumetric calculation of sediment shows that 100,000 m3 of sediment can be

generate from a dredging process if a river increase 1 m in depth of a 1 km stretch

with a width of 100 m of a river. Now, if this amount of sediment is dispersed

constantly on the flood plains over a 1 km2 area on both sides of the river it 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. 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.

(2) Preventing land degradation: All the farmers in Bangladesh especially in the ruralarea should be advised to leave a few inches of stem remaining from their rice crops

during harvesting before the rainy season because suspended sediments adhere to the

stems of plants. They should also be taught and given more information about the

problem of soil erosion including correct tilling practices such as putting tall earthen

boundaries between large farm lands. Tilling at the edge of the boundary can preventsediments from precipitation water drained by streams out to the channels.


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(3) Flood preparedness: Every individual should prepare themselves and take somemeasures about the upcoming flood, which also includes shelters and food.

(4) Inter-basin cooperation: Any major inter-basin development activity is almostimpossible without regional cooperation between the co-riparian nations. Only

certain percentages of the river basin area fall within Bangladesh. To make a successful

inter-basin flood control projects it has to be designed to serve the common interests

of the people of the countries concerned. For example, construction of reservoirs in

the upstream regions of the Brahmaputra to hold excess water during rainy seasons

can reduce flood propensity in Bangladesh. During the summer months the trapped

water can be used to produce electricity to meet some of the irrigation demands for

Bangladesh.

(d) Reduce of carbon emission:The world gets warmer due to global warming and asa result the chances for flooding increase rapidly. Cutting down the carbon emissionscan also reduce flooding. One of the major sources of carbon emissions in the

atmosphere is the transportation in Bangladesh. Compressed Natural Gas (CNG)

could be used instead of petrol to all the vehicles. And the cost will be much less since

CNG is produced in Bangladesh naturally. The community involvement and the

government initiative should be strongly considered to implement this project.

(e) Usage of proper sanitation and dry toilet:Health is increasingly being regarded asa holistic and socio-cultural phenomenon rather than a purely medical matter. These

means that the four role of health management prevention, promotion, cure andrehabilitation have to be integrated both into so called complementary medical

procedures and into socio-economic development patterns that place the physical and

mental well-being of people as the first priority.

Water management instrumentsMany rules and acts have been introduced since the 19th centuries for the flood

management, for example, Embankment Act (EA), Drainage Act (DA) and Canal Act

(CA), etc. and also legal instruments were used from the ancient time for the

management of flood in Bangladesh. The government has found some inconsistenciesin these laws and has come up with some new acts to manage flood compared to the

practices of early sixties and has decided to publish a unified law and work which is

now going on in the form of a National Water Code (NWC).

Bangladesh has improved in good hydrological data collection system all over the

cities, as well as an integrated hydrological database with about 40 years of data.

There is also a real-time water level and rainfall data collection system from a selected

number of stations for FFWS during monsoon months. All these data are used for

planning and design of different types of hydraulic structures, construction of different

infrastructures.


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PolicyIn 1980, National Water Plan (NWP) was made for various aspects of water use and

demand and the interests of different stakeholders involved in the water sector. From

mid-nineties a Flood Action Plan (FAP) was implemented, on the basis of which a

National Flood and Water Management Strategy which was formulated in 1996

including policy guidelines for public participation in multi-criteria analysis and

Environmental Impact Assessment (EIA) during implementing process in all future

water sector projects.

In 1999 the National Water Policy (NWPo) was introduced, which guides all the

activities in the water sector. Subsequently, a National Water Management Plan

(NWMP) was prepared in 2001, cross-cutting different sectors of national economy in

the light of Integrated Water Resources Management, to address conflicting water

needs and to ensure equitable water use and balanced economic growth, into thenext 25 years. The Plan includes also the management of water-induced disasters, e.g.

floods, erosion and droughts. A Comprehensive Disaster Management Plan (CDMP)

and Disaster Management Guidelines were also prepared, in which the responsibilities

of different.

Agencies involved in disaster mitigation activities are delineated during pre-disaster

preparedness, rescue and evacuation operation during disaster and post-disaster relief

and rehabilitation.

Enforcement of Relevant Laws for Flood Plain ManagementBangladesh has many laws enforced at different times for flood plain and flood

management. There are some inconsistencies found in these laws. Considering the

importance of brining harmony and consistencies among the laws the Govt. has

decided to promulgate a unified law and work is now going on in this direction.

Work is now going on framing a National Water Code.

Community-based floodplain managementCommunity based resource management, is also found in Bangladesh as a

development strategy to promote the participatory resource management and ensure

traditional livelihoods. In the early 1990s several projects were implemented by the

government with community based resources management approach. Particularly,

community based fisheries management has developed well enough and this concept

scaled up the co-management strategy in other resource management including water,

forest, disaster preparedness and now in adaptation to climate change.


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Since flood management is an integral part of overall water resource management,

regional cooperation in this area will help create a better climate for the much-needed

joint strategies for sustainable utilization of the water ecosystem.

REFERENCESLiterature:1. H. BRAMMER. Floods in Bangladesh: II. Flood Mitigation and Environmental

Aspects. The Geographical Journal, Vol. 156, No. 2 (Jul., 1990) DOI:10.2307/635323

2. EDWARD A. KELLER. Environmental Geology, Eighth Edition, Chapters 5, 7&12,

pages 98, 112, 161, and 317. ISBN: 0-13-022466-9

3. AVIJIT GUPTA AND MUKUL G. ASHER. Environment and the developing world:

Principles, Policies and Management. Chapter 7, page 111. ISBN: 0-471-96604-5

4. PATRICK C. KANGAS. Ecological Engineering: Principles and Practice. Chapter 2,

page 25. ISBN: 1-56670-599-1

5. JAMES L. WESCOAT, JR. AND GILBERT F. WHITE. Water for Life: Water

management and Environmental Policy. Chapters 7, 8, pages 109, 129, 139.

ISBN: 0-521-36211-3.

6. ANDY D. WARD. STANLEY W. TRIMBLE. Environmental Hydrology, Second

Edition. Chapters 1, 3, 5&12, pages 4, 55, 119 & 339. ISBN: 1-56670-616-5.

7. CHRIS PARK. The environment: Principles and Applications, Second Edition. Part

IV, page 349. ISBN: 0-415-21770-9.

Other References (Electronic & Web):8. FLOOD PROBLEMS IN BANGLADESH. Earth and Environmental Science [Online].

[Cited: 23rd February 2007]. Available from World Wide Web:

http://www.springerlink.com/content/q46n04165005528x/.

9. WMO/GWP Associated Programme on Flood Management. [Online]. [Citied: 27th

February 2007]. Available from World Wide Web:

http://www.apfm.info/pdf/case_studies/bangladesh.pdf

10. BANGLADESH INFORMATION. Bangladesh, an Introduction [Online]. [Citied:

2nd March]. Available from World Wide Web:

http://www.southasianfloods.org/regional/bangladesh/banginfo1.html

11. BANGLADESH INFORMATION. Culture & Life styles [Online]. [Citied: 2nd March

2007]. Available from World Wide Web:

http://www.bangladeshinfo.com

12. www.wikipedia.com

All the maps are created by using Arc GIS-10 software.
http://www.bangladeshinfo.com/http://www.bangladeshinfo.com/

Documents

Flood and Floodplain Management of Bangladesh