RAJKUMAR POREL, M.SC , WBSU , BHAIRAB GANGULY COLLEGE

4. Geography And Climate Of West Bengal
West Bengal is on the eastern bottleneck of India, stretching from the Himalayas in the north to the
Bay of Bengal in the south. The state has a total area of 88,752 square kilometres (34,267 sq mi).The
Darjeeling Himalayan hill region in the northern extreme of the state is a part of the eastern Himalayas
mountain range. In this region is Sandakfu, which, at 3,636 m (11,929 ft), is the highest peak in the
state. The narrow Terai region separates the hills from the North Bengal plains, which in turn
transitions into the Ganges delta towards the south. The Rarh region intervenes between the Ganges
Many areas remain flooded during the
heavy rains brought by a monsoon.
delta in the east and the western plateau and high
lands. A small coastal region is in the extreme south,
while the Sundarbans mangrove forests form a
geographical landmark at the Ganges delta.
The main river in West Bengal is the Ganges, which
divides into two branches. One branch enters
Bangladesh as the Padma, or Podda, while the other
flows through West Bengal as the Bhagirathi River and
Hooghly River. The Farakka barrage over the Ganges
feeds the Hooghly branch of the river by a feeder
canal. Its water flow management has been a source
of lingering dispute between India and Bangladesh.
The Teesta, Torsa, Jaldhaka, and Mahananda rivers are
in the northern hilly region. The western plateau
region has rivers like the Damodar, Ajay, and
Kangsabati.

5. The Ganges delta and the Sundarbans area have numerous rivers and creeks. Pollution of the Ganges
from indiscriminate waste dumped into the river is a major problem. Damodar, another tributary of the
Ganges and once known as the "Sorrow of Bengal" (due to its frequent floods), has several dams under
the Damodar Valley Project. At least nine districts in the state suffer from arsenic contamination of
groundwater, and as of 2017 an estimated 1.04 crore people were afflicted by arsenic poisoning.
West Bengal's climate varies from tropical savanna in the southern portions to humid subtropical in the
north. The main seasons are summer, the rainy season, a short autumn, and winter. While the summer
in the delta region is noted for excessive humidity, the western highlands experience a dry summer like
northern India. The highest daytime temperatures range from 38 °C (100 °F) to 45 °C (113 °F). At
night, a cool southerly breeze carries moisture from the Bay of Bengal. In early summer, brief squalls
and thunderstorms known as Kalbaisakhi, or Nor'westers, often occur. West Bengal receives the Bay of
Bengal branch of the Indian Ocean monsoon that moves in a southeast to northwest direction.
Monsoons bring rain to the whole state from June to September. Heavy rainfall of above 250
centimetres (98 in) is observed in the Darjeeling, Jalpaiguri, and Cooch Behar district. During the arrival
of the monsoons, low pressure in the Bay of Bengal region often leads to the formation of storms in
the coastal areas. Winter (December–January) is mild over the plains with average minimum
temperatures of 15 °C (59 °F). A cold and dry northern wind blows in the winter, substantially lowering
the humidity level. The Darjeeling Himalayan Hill region experiences a harsh winter, with occasional
snowfall.

6. Evolution of the Bengal Delta and Its
Prevailing Processes :-
INTRODUCTION:-
The Bengal Delta is the largest delta in the world (Gupta, 2007). It drains almost all of theHimalayas,
themost sedimentproducing mountains in the world, through the three main river systems: the Ganges,
Brahmaputra, and Meghna. These systems (Figure 1) carry the world’s largest sediment load,
more than 1 billion tonnes of sediment every year, of which nearly 80% is delivered during the four
monsoon months (Goodbred and Kuehl, 2000b). Bangladesh, with more than 2% of the world’s
population and a density of more than 1080 people/km2 (Steckler et al., 2010), has a highly vulnerable
coastal environment (Minar, Hossain, and Shamsuddin, 2013). Sea level rise (SLR) of 1 m would cause
inundation of 17% to 21% of the total area of Bangladesh (Choudhury, Haque, and Quadir, 1997; IPCC,
2001). Because more than half of the area is less than 5 m above mean sea level, according to the digital
elevation model, it could be more vulnerable for higher SLR and a high rate of subsidence. Differences in
opinions are found in the literature on the impacts of climate change and subsidence. To address these
impacts in the coming decades, it is necessary to review the varieties of ideas on different processes
acting on the delta and seek to find some sustainable solution. Furthermore, many research studies
have been carried out on river-dominated deltas, but few have focused on tide-dominated deltas,
where tide plays the key role in shaping the delta. Even existing practices of delta models rarely include
the interaction amongst rivers, floodplains, and tidal plains, because the processes in the delta system
are complicated. Most delta models consider a static river system when they assess the long-term
effects of climate change. Therefore, the related literature has been reviewed to outline the present
understanding with a view towards finding knowledge gaps intending for further research.

7. STUDY AREA:-
This section describes the geological setting and the fluvial setting of the study area. In the geological
setting, the main physical features that influence the development of the Bengal Delta have been
figured out. Hydromorphological descriptions have been given in the fluvial setting section.
Geological Setting of the Study Area: Bengal Delta Several million years ago, the NE portion
of the Indo- Australian plate fractured and sank below what was then sea level. This depressed basin
then attracted all rivers to meet the sea. In the course of time, this depression filled with the sediment
to form the present Bengal Basin. The basin is prograding from a NE hinge line (Goodbred and Kuehl,
2000b). Deposition of 4 km of deposits at the hinge and more than 10 km at the shelf break (Lindsay,
Holiday, and Hulbert, 1991) has made the world’s largest fan deposits (Goodbred and Kuehl, 2000b),
with a volume of approximately 1.25 x 10⁷ km3 for approximately 3 x 10⁶ km2 of area (Curray, 1994),
mainly carried by the Ganges–Brahmaputra (G-B) Rivers from the foreslope and backslope of the
Himalayas, respectively (Goodbred and Kuehl, 2000b).
Fluvial Setting of the Rivers in the Delta: Three large rivers, the Ganges, Brahmaputra, and
Meghna, are the main fluvial sources of the basin . The Ganges River, with an average of 1200 mm of
rainfall over about 1,000,000 km2 of catchments, produces an annual average discharge of about
11,300 m3/s, along with producing sediment at 550 million tonnes/y (CEGIS, 2010). The Brahmaputra
River covers 573,000 km2 with an average rainfall of 1900 mm, and it results in an annual average
discharge of 20,200m3/s with 590 million tonnes/y sediment. A total of 1 trillion (1012)m3 of water
and sediment at a rate of 1 billion (109) tonnes/y, as the combined flow of the Ganges, Jamuna (the
downstream continuation of the Brahmaputra), and Meghna Rivers, are delivered to the Bay of Bengal
through the Lower Meghna River. The hydromorphological details, including catchments areas and
fluvial inputs of the different contributors to the basin, are given in Figure 3 for comparison.

8. Location map of the Ganges, Brahmaputra, and Meghna catchments.

9. The sediment carried by the Ganges, Brahmaputra, and Meghna Rivers has contributed to the present
size of the delta, which is about 100,000 km2.
The average flood discharges of the
Jamuna, Ganges, Padma (the main
branches of the Ganges and
Jamuna), and Upper Meghna Rivers
are 70,000, 52,000, 95,000, and
13,700 m3/s as measured at
Bahadurabad, Hardinge Bridge,
Mawa, and Bhairab Bazar,
respectively (Sarker et al., 2003).
The average low flow discharges are
4250, 600, and 4800 m3/s for the
Jamuna, Ganges, and Padma Rivers.
The mean sizes of the bed material
in the Jamuna, Ganges, Padma,
Upper Meghna, and Lower Meghna
Rivers are 0.20, 0.15, 0.12, 0.14, and
0.09 mm, respectively.
The planform of the rivers varies from meandering to braiding over space and time (the Jamuna is
braided, the Ganges is meandering, and the Padma is a wandering river). The Upper Meghna is
anastomosing, and the LowerMeghna is anabranching (Sarker et al., 2003). Along with the sediment
transported by these main rivers, the other two major
Figure 3. Hydromorphological characteristics of the three main
rivers of Bangladesh.

10. distributaries, the Gorai and the Arial Khan, contribute in transporting fluvial inputs to the delta
system. The Gorai River delivers annually about 30 billion m3 of water and 30 million tonnes of
sediment to the bay (EGIS, 2001), and the Arial Khan River supplies about 30 billionm3 of flow and 25
million tonnes of sediment every year. The Arial Khan River is connected to the Lower Meghna River,
which contributes to the present delta building process. This process is continuing in the Meghna
estuary area. There are three major distributaries, the Shahbajpur, Hatiya, and Tentulia Channels,
through which most of the water and sediment enter the Bay of Bengal. Tides are semidiurnal, with a
slight diurnal inequality, along the coast of the Bengal Delta (including the Indian part), and the average
tidal range varies from 1.5 m in the west to more than 4 m at the NE tip of the Meghna estuary.
However, the Meghna estuary is a mesotidal estuary, where the tidal range varies between 2 and 4 m
(MES II, 2001).
Tectonic Settings of Bengal Basin:-
The Bengal Basin is an asymmetric polycyclic tectonic basin on the eastern margin of the Indian shield.
Evolution of the Bengal Basin took place in different phases through plate movements in space and
time. The Indian plate started moving with a velocity of approximately 10 cm/yr initially in a N-NE
direction and collided with the Eurasian plate, then started moving in the N-NW direction at 4 cm/yr
(Rangin, 2012). After the collision of the Indian plate with the Eurasian plate, the Indian plate rotated
clockwise to become prominent in the north south direction (Kundu and Gahalaut, 2013). The tectonic
evolutionary stages of Bengal Basin are (i) the Pre-Rift stage (Permo-Carboniferous), (ii) the Rift-Drift
stage (Late Jurassic-Early Cretaceous), (iii) the Post-Rift stage (Mid Cretaceous-Paleocene), and (iv) the
Depositional stage (Mid Pliocene to Quaternary) (Pahari et al., 2008). The Pre-Rift stage, in which the
Indian plate was associated with the Australian plate, is located in the southern hemisphere (Stamofli
and Borel, 2001).

11. The Rift stage of the Bengal Basin, evidenced by the Gondwana sediments in block faulted troughs, is
associated with Rajmahal volcanism and the breakup of the Gondwana land, while the Post-Rift stage is
evidenced by the differentiation of the basin into the shelf slope and rise (Pahari et al., 2008).
According to the tectonic geodesy, the Burma plate behaves as the sliver line between the Indian and
the Sunda plate (Maurin and Rangin, 2009). The eastern block moves slower than the western block of
the Indo-Burmese Wedge (Kundu and Fallout, 2013). The Indian plate moves northward with a velocity
of 36 mm/yr, out of which about 20 mm/yr is accommodated across the Sunda fault in the east and the
remaining motion is accommodated in the Indo-Burmese wedge (Kundu and Gahluat, 2013).
Tectonic Divisions of Bengal Basin:-
The Bengal Basin is tectonically disturbed due to the proximity of major faults like the Main Boundary
Thrust (MBT), the Main Central Thrust (MCT), the Main Frontal Thrust (MFT) in the north of the Bengal
Basin and the Dauki Fault, the Oldham Fault marking the boundary of the strikingly elevated Shillong
plateau (Guha et al. 2010) as shown in Figure 2.1(a). Besides these, the Garhmoyna-Khandaghosh
Fault, the Jangipur-Gaibandha Fault, the Pingla Fault, the Debogram-Bogra Fault, the Rajmahal Fault,
the Malda-Kishanganj Fault, the Eocene Hinge, the Sainthia-Bahmani Fault, the Purulia Shear Zone, the
Tista Lineament and the Purulia Lineament are the major faults and lineaments of the Bengal Basin as
depicted in Figure 2.1(a) (Nath et al. 2014). The broad shelf zone of the basin is marked by the
Precambrian outcrops in the west and the Eocene Hinge Zone in the east. The tectonic units of the
Bengal Basin have been divided into (i) the Shelf Zone, (ii) the Hinge, (iii) the Deep Basin, and (iv) the
Western Shear Zone from west to east (Mukherjee and Hazara, 1997; Khan and Agarwal, 1993; Alam et
al., 2002; Guha et al., 2010).

12. Tectonic elements of the Bengal Basin: (a) Tectonic divisions of the Bengal Basin with major faults and
lineaments with seismic events of Mw≥4.5 (modified considering Dasgupta et al., 2000; USGS-BGAT,
2001; and GSB, 1990), and (b) E-W geological cross section depicting the Lithostratigraphic and structural
settings of the Bengal Basin (Nath et al., 2014).

13. 1. The Shelf Zone:-
The Shelf Zone denotes the west and the northwest region of the Basin. It has an elongated shape
extending from north to south and bounded by the basin margin fault like the Oldham Fault, the Dauki
Fault, the Jamuna Fault and the Tista Fault (Mukherjee and Hazara, 1997). The Shelf Zone has further
been subdivided into the Baharampur Terrace, the Baidyapur depression, the Contai terrace from
north to south, the Dinajpur slope, the Rangpur Saddle and the Bogra slope from west to east. The
Dinajpur slope represents the broad elongated depression with a sediment column of 200 m to 800 m.
The Rangpur saddle is an uplifted land surface, which is bounded by two faults from the western and
the eastern margin of the Garo-Rajmahal gap. The Bogra slope represents a monocline plunging fold
gently sloping towards the southeast of the Hinge Zone and the width of it varies from 60-125 km
(Guha et al., 2010).
2. The Hinge Zone or Calcutta Mymensingh Gravity High:-
The most prominent tectonic feature in the Bengal Basin is the NE-SW trending Eocene Hinge Zone
(EHZ), also known as Calcutta-Mymensing Hinge Zone as shown in Figure 2.1(a). It is ‘S’ shaped
alignment, which swings at Jagli and Contai areas marked by a system of conjugate lineaments and
possibly tectonically related to a deep seated basement fault (Guha et al., 2010). The Eocene Hinge
Zone has a width of 25 km and covered by upper Paleozoic to Holocene sedimentary fill to a maximum
thickness of about 7.5 km (Nath et al., 2014). The subsidence pattern differs across the Hinge Zone
(Morgan and McIntire, 1959; Alam et al., 2003). The gravity pattern revealed a steep change across the
Eocene Hinge Zone, so that the Eocene Hinge Zone marked a continental Ocean Boundary (COB)
beneath the Bengal Basin in the west and the Barisal-Chandpur gravity High in the east (Dehlinger,
1978; Alam et al., 2003).

14. 3. The Deep Basin:-
The deep basin or the Geosynclinal basin in the southeast is filled with huge clastic sediments and the
thickness of the sediments increasing towards S-E as depicted in Figure 2.1(a) and (b). The eastern part
of the basin is much deeper than the western part and is occupied by the sub basins viz. the Sylhet
Trough, the Faridpur Trough and the Hatiya Trough. The Bengal Basin and its adjoining region emphasize
the tectonic mobility or instability of the area, causing rapid subsidence and high sedimentation in a
relatively short span of geological time. The Geosynclinal basin is further classified into (i) the Faridpur
Trough, (ii) the Barisal-Chandpur High, (iii) the Hatiya Trough, and (iv) the Madhupur High (Khan and
Agarwal, 1993; Guha et al., 2010).
The Hatiya Trough exhibits the deepest trough in the Bengal Basin with its thickest clastic sedimentary
deposits as depicted in Figure 2.1(a) at the S-E margin of the Basin. The Hatiya Trough consists of
offshore anticlinal structures with their oil reserves (Guha et al. 2010). TheMadhupur High or
Pleistocene terraces, separating the Faridpur Trough from the Sylhet basin are slightly elevated from the
adjacent flood plain. A series of en-echelon fault flanks the western side of the uplifted Madhupur tract
(Alam et. al., 2003).
4. Western Shear Zone:-
The western boundary of the Bengal Basin is marked by the Indian shield as depicted in Figure 2.1(a).
The western shield region of the Bengal Basin has nearly 100 km long narrow tectonic zone named
Tamar-Porapahar Shear Zone (TPSZ) trending in WNW-ESE direction. The TPSZ is recognized by the
visible surface feature as cataclastic movement resulting in brecciation, grinding, fracturing, shearing
and mylonitisation. An E-W trending zone within Chhotanagpur Gneiss Complex (CGC) is named as
North Purulia Shear Zone (NPSZ) located in the Belma-Panrkidih-Nowahara area in Purulia district. This
NPSZ is recognized by the silicified rocks, fault breccia, baryte, apatite and Rare Earth Elements (REE)
mineralization, numerous Quartz reef of varied dimensions are also encountered in the ductile to
brittle shear zone.

15. Geomorphology:-
Geomorphology of the region is the expression of surface or subsurface lithostratigraphy. The entire
Bengal Basin is divided into four geomorphic unit’s viz. the northern hilly region, the central river
terrace, the foredeep basin zone and the southern geosynclinal zone. The Himalayan region represents
the convergent region of two plates from the northern margin and from eastern margin ridge and the
valley topography of Tripura fold belt evidenced of plate convergent. The rivers of the Himalayan
region deposited their sediments and formed the alluvial plains/fans with gently undulating
topography as depicted in Figure 2.19. The geomorphic units of the Basin are the coastal plains,
floodplain, piedmont alluvial plain, pleistocene uplands, terrace deposits, shillong plateau, tertiary hills,
active and inactive Ganga-Brahmaputra-Meghna delta, tidal delta and rajmahal hills as depicted in
Figure 2.19. These units of the basin can be classified as geomorphic features of the northern zone and
the southern zone of Bengal Basin.
Geomorphic Features of Northern Zone of Bengal Basin
The northern zone of the Bengal Basin is bordered by the Tertiary hills. Vertical erosion is much greater
than lateral erosion in the northern zone due to a high gradient of slope. The eroded sediments are
deposited by the rivers to the south of the foothills and form the alluvial fans as shown in Figure 2.19.
The distinct geomorphic features of the northern zone are the mountains, the piedmont plains, the
alluvial plains, the flood plains, Shillong plateau, Pleistocene uplands and depression.
1. The Mountains
The northern mountain ranges of the Basin are the part of the Himalayan mountain system and
extended upto Darjeeling and the Cooch Behar district. The hills in this region are highly dissected and
covered with thin sediments over the Granite-Gneisses rocks. The Teesta River and its tributaries cut
the entire geological formations as illustrated in Figure 2.19. In Bangladesh the hills are confined to a
narrow strip along the southern margin of the Shillong Plateau.

16. Geomorphological units of the Bengal Basin and its adjoining region with the Liquefaction sites
triggered by the 1897 Shillong earthquake. Major drainage pattern is also depicted (modified after
Shamsudduha and Uddin, 2007; Ambraseys and Bilham, 2003a).

17. 2. The Piedmont Plains
The Piedmont zone is characterized by a low gradient and undulating surface expression to the south
of the Tertiary hills as shown in Figure 2.19. The piedmont plains of north Bengal comprises of the
Bhabhar-Terai belt. The Piedmont zone is a narrow striped land between the mountains and the Great
Plains.
3. The Alluvial Plains/Fans
The alluvial plains covered a large spatial extent in the southern front of the mountain region, after the
piedmont plain as depicted in Figure 2.19. The lithofacies of the alluvial plains show high porosity of
rocks. The region comprises of younger and older alluvial fans, the older fan material much oxidized
than the younger fan and occupy a narrow width. Samsing formation is the oldest alluvial fanformation
of this zone and Baikunthpur formation represents the youngest fan in the region. The sand and gravel
deposits of the Mahananda and Karatoya Rivers may possibly be as old as late Pleistocene or as early as
the Holocene. The alluvial plains gently slope to the south from about 96 m down to 33 m above MSL
(www.banglpedia.org).
4. Flood Plain
The flood plains are made up of silty sediments near the river bank and unsorted material away from
the river in the monsoon season. The spatial extent of the flood plains is shown in Figure 2.19. The
northern flood plains have an extension from west to east and are characterized by less vertical and
high lateral erosion of the river due to low gradient. In the southern flood plains, meander loops often
cut off from the main channel stream and form Oxbow. These flood plains are further divided on the
basis of river basins and their encroached areas, as the Tista Floodplain, the Old Brahmaputra
Floodplain and the Jamuna Floodplain. The northern flood plain has developed by filling the shallow
inland water body and the southern riverine plain has developed as deltas by pushing out sea water
from the shallow continental shelf. The Teesta and the Brahmaputra rivers changed their path towards

18. east, while the Mahananda and the Mechi have not changed their course and merged in the Ganga
River. This behavior of rivers indicates the presence of some subsurface structures.
5. Shillong Plateau
In the N-E of the Bengal Basin, the Shillong plateau represents a large geomorphic unit with an up
arch of Precambrian metamorphic rocks characterized by the basement Gneissic complex with a
structural trend of NE-SW. The Assam plains marked the northern boundary and the alluvial plains
sharply marked the southern boundary of the Shillong plateau. The structural hills show various
degrees of dissections to the prominent parallel trend to the structural strike along NE-SW (Talukdar
and Talukdar, 2012).
6. The Pleistocene Uplands
The Pleistocene uplands are also known as the Barind and the Madhupur uplands. These uplands are
made up of ferralitic soils. These uplifted regions are associated with an east-west trending Horst
block (Singh et al., 1998) and highly dissected by several rivers. In the eastern part of the zone, the
Mahananda and the Kalindi Rivers have removed the surface expression of the ferralitic formations
and covered it with alluvial sediments.
7. Depression
The Depression or Haor basins are the left depressions filled with water in between the streams of the
north of Barind in India and Sylhet in Bangladesh. These units covered very small region and noticed
that the water bodies in Barind had not been totally filled up before the rivers started cutting through
the ferralitic formations. The Chalan beel of Rajshahi in Bangladesh is a wellknown example of such
depressions. The major part of this zone lies in Bangladesh whereas the southern part of West
Dinajpur district and some part of the western Malda district located in West Bengal.

19. Geomorphic Features of Southern Zone of Bengal Basin
The southern Bengal Basin has a very low gradient which provides suitable conditions for rivers to
deposit sediment. Although the major part of the southern zone of the basin is covered by the flood
plains and Delta, the western margin of the zone exhibits peninsular region marked by the Ayodhya
Plateau and the undulating Purulia High Plain. In the eastern part of the Bengal Basin, the Syllhet
depression is a significant feature as shown in Figure 2.19. The southern zone of Bengal Basin can be
divided into the Peninsular region, the Ganga-Brahmaputra-Meghna delta and the Tidal delta.
1. Peninsular Region
On the western margin, the Bengal Basin is bounded by a plateau region. The micro-geomorphic units
in the peninsular region are the Rajmahal hills, the Ayodhya plateau, the Purulia Highlands and the
Rarh uplands. The Ayodhya Plateau is a block of highland in the south-western part of the Purulia
district in West Bengal, also known as the Baghmundi hills. The Ayodhya plateau represents the
extension of the Ranchi surface and is characterized by similar Granite-Gneisses of Chhotanagpur
Gneissic Complex (CGC) (Nag, 2005). The Subarnarekha River flows from north to south in this tract
through some structural weak planes and separates the Ayodhya Plateau from Ranchi Plateau. In this
manner it appears as a residual hill. The similar feature as of Purulia high plain has been noticed in
some parts of the Bankura, Medinipur and Birbhum district in the western part of the Bengal Basin. In
Purulia High plain metamorphic rocks like Gneiss, Schist and varieties of Phyllites are dominant. The
southern margin of the zone is marked by the east-west oriented metamorphosed rocks, which are
nearly parallel to the Dalmaorogenic belt. The northern margin is marked by the Gondwana rift valley.
Many residual hillocks scattered on the high plain evidenced ancient volcanism in the terrain. The east
Purulia high land, which is made up of ferralitic soil is known as the Rarh uplands. The Rarh uplands are
characterized by a variety of rocks, deposited during the Miocene period through repeated marine
transgression. This zone covers the western part of Burdwan district in the Bengal Basin.

20. The Rarh uplands are characterized by the undulating landform which is subjected to
extensive soil erosion (Jana and Majumdar, 2010).
2. The Ganga-Brahmaputra-Meghna Delta
The southern part of the Bengal Basin is characterized by Delta deposits. On the basis of the
deposition pattern the delta is divided into an inactive and an active delta system (Shamsudduha and
Uddin, 2007). The southern riverine delta has developed through alluviation, where river sediments
have pushed away the sea front from a shallow offshore zone. The river gradient has decreased to the
southward of the zone and Oxbow lakes, acute meander loops formed profusely and conspicuously on
the outward margins of the Deltas (Jana and Majumdar, 2010). This zone covers the eastern part of
the district Murshidabad, where the largest Delta is formed by the Ganga River. The Ganga delta
extends southward upto the border of the districts of Nadia and North 24-Paraganas. The Delta of the
Ajoy and the Damodar Rivers in the south-west of the Ganga delta covers the eastern Bardhman
district and the northern Hooghly district. The spatial extent of the Delta system has been shown and
marked as GBM I-II in Figure 2.19.
3. Tidal Delta
The Tidal delta or marine delta is developed by the interlacing tidal channels. The Tidal influx, scouring
the shallow continental shelf, supplies the sediments to carve the landscape of the region as shown in
Figure 2.19. The Tidal delta land provides favorable conditions for the mangrove forest and exhibits
world’s largest mangrove forest in the Sundarban region.

21. 4.2 Problem Of Flood, Drought And
Ground Water Contamination

22. Disaster
• Disaster is a natural or human ,
caused phenomenon, which causes
serious disruption of the
functioning of a community or a
society causing widespread human,
material, economic and
environmental losses which elicited
the ability of the affected
community, society to cope using
its resources.
• Floods are a common feature in
the country that occur every year
in many parts including South
India.

23. INTRODUCTION:-
A flood occurs when the Geomorphic Equilibrium in
the river system is disturbed because of intrinsic or
extrinsic factors or when a system crosses the
geomorphic threshold.
(a) Flooding in a river due to aggradation of river bed
(intrinsic threshold);
(b) Flooding in a river due to heavy rainfall (extrinsic
threshold)
Floods in major cities especially during rainy season
are proving to disastrous not only to the environment
but also have serious implications for human life and
property.
TYPES OF FLOODS:-
 Types of floods •Flash floods •River floods •Coastal Floods •Urban Flood
Types of Flood-
It is a temporary inundation of large regions as a result of an increase in reservoir, or of rivers flooding
their banks because of heavy rains, high winds, cyclones storm surge along coast, tsunami, melting
snow or dam bursts.
Flash Floods
It is defined as floods which occurs within six hours of the beginning of heavy rainfall, and are usually
associated with cloud bursts, storms and cyclones requiring rapid localized warning and immediate
response if damage is to be mitigated. In case of flash floods, warning for timely evacuation may not
always be possible.

24. According to their duration flood can be divided into different categories:
•Slow-Onset Floods: Slow Onset Floods usually last for a relatively longer period, it may last for one or
more peeks, or even months.
•Rapid-Onset Floods: Rapid1Onset Floods last for a relatively shorter period, they usually last for one
or two days only.
•Flash Floods: Flash Floods may occur within minutes or a fe1w hours after heavy rainfall, tropical
storm, failure of dams or levees or releases of ice dams. And it causes the greatest damages to society.
River Floods
Such floods are caused by precipitation over large catchment’s areas. These floods normally build up
slowly or seasonally and may continue for days or weeks as compared to flash floods.
Coastal Floods
Some floods are associated with the cyclonic activities like Hurricanes, tropical cyclone etc.
Catastrophic flooding is often aggravated by wind-induced strom surges along the coast.
Floods
Natural
Man made
Storm Surge, Tsunami, Glacial
Melt, Landslide, Riverine,
Estuarine & Marine Flood
Breach of Dam/ Barrage/
Embankment Release from
Reservoir, Urban Flood
Eg: bursting of landslide
blockades in the catchment
areaof the Bhagirathi River in
August 1978
Eg: In the year 2009,Almatti and
Naryanpur dams on the Krishna River in
Karnataka. This water along with rain
water reached Andhra Pradesh near the
Srisailam dam. It causes a hevy floods in
andhrapradesh

25. The time from peak rainfall to peak
discharge is the LAG TIME.
The discharge
starts to fall slowly
as water is added
from through flow
and groundwater
flows which are
much slower.
The base flow
supplies the river
with water
between storms
and keeps it
flowing in summer.
Rainfall is intercepted or
infiltrated into the
soil moisture store
Start of the storm there is a
slow rise in discharge, as only
a small amount of water falls
into the channel
The soil becomes
saturated and
overland flow and
through flow
reach the river and
Discharge
increases.
Overland flow
arrives first.

26. Causes of floods
i. Excessive rainfall in river
catchments or concentration of
runoff from the tributaries and river
carrying flows in excess of their
capacities.
ii. Backing of water in tributaries at
their confluence with the main river.
iii. Synchronization of flood peaks of
the main rivers and tributaries.
iv. Landslides causing obstruction to
flow and change in the river course.
v. Poor natural drainage.
vi. Cyclone and very intense rainfall.
vii. Intense rainfall when river is
flowing full.

27. FACTORS
VEGETATION COVER
This varies seasonally. The type and
amount will affect interception and
stemflow/throughfall. Overland flow is
reduced. Lag time will be increased.
CLIMATE
The distribution of rainfall over the
year and the temperatures will
affect the lag times.
SLOPES
Steep slopes will encourage
overland flow and gentle
slope will slow run off down.
RAINFALL INTENSITY &
DURATION
Intense rain will increase overland
flow and reduce lag times. Gentle
rain over a longer time will allow
more infiltration.
LAND USE
Impermeable surfaces created by
urbanisation will reduce infiltration
and encourage overland flow.
Different types of crops affect
interception rates e.g. cereals 7-
15%.
SOIL TYPE & DEPTH
Deep soils store more water, pipes
in the soil encourage through flow.
Soils with small pore spaces will
reduce infiltration and increase
overland flow.
LAKES & RESERVOIRS
These will store floodwater and
thus reduce lag time and control
river response to heavy rainfall.
ROCK TYPE
Impermeable rocks prevent
groundwater flow and encourage
through flow and overland flow. These
rocks will decrease lag time.
Permeable rock will have the opposite
effect.

28. The floods of West Bengal have special characteristics. Heavy rainfall at origin or catchment’s areas of
main flooding rivers of this state cause flood, but these areas are mainly lying outside this state. The
West Bengal is flooded by water from adjoining states or countries.
Major contributing factors to flood in Northern regions are the run-off because of heavy local rainfall,
discharge of upper basin areas and also out fall condition in the neighbouring countries. The
Mahananda and most of the rivers of Uttar and Dakshin Dinajpur districts get stagnated when the
Ganga upstream and downstream of Farakka Barrage rules high there by not allowing draining of flood
discharge during that period. Flooding Malda is caused by the rivers Fulhar-Mahananda-and Ganga.
The Ganga, forming the southern boundary of the district, brings flood water from eleven states and
Nepal. The Fulhar meets the Ganga upstream of Farakka.
The rivers of rivers of Bhagirathi-Hoogly basin generate flood because of high rainfall and limited
carrying capacity of the river Bhagirathi from Jangipur in Murshidabad to Kalna in Bardwan. In this
reach the Bhagirathi has discharge carrying capacity of maximum 1.3 lac. Cusec. But all these rivers if
receive rainfall simultaneously in their catchment areas can generate run-off volume of any amount
between 4-6 lac. Cusec. In this vast tract of land there is only the Massanjore dam to interfere with
the natural flow of flood water.
The basic reason of flood in this zone is the shape of the catchment area, its steep slope from a high
level plateau area sloping sharply down to aflat terrain near the outfall and also adverse outfall
condition because of its limited intake capacity. This feature is again adversely affected by the tidal
condition as is generally noticed in the month of September, when the Hoogly is in high tide condition.
Delay in drainage causes more accumulation resulting in spread of flood in the upstream of the river
system in the west and beyond Berhampur. Generally part of Murshidabad and Nadia suffer from
flood because of three reasons –

29. 1. High intensity rainfall in the basin area of Bhairabi-Jalangi-Sealmari itself,
2. Inflow of flood water from Ganga-Padma at its high spate and
3. Drainage congestion at its outfall because of the high stage of Bhagirathi.
Traditionally, Damodar basin was known to be a curse. The basin of river Damodar has a very special
shape and this influences its flood pattern. The river has about 70% of its basin just upstream of
Durgapur town. This upper catchments of Jharkhand plateau, above Durgapur, generates heavy run-off
during high rainfall and is carried to Durgapur in a short time. From here, this discharge travels through
the river, bifurcating at Beguahana. One branch, the lower Damodar with very small capacity, reaches
the Hoogly on the west bank. The major discharge passes through the Mundeswari to meet the
Rupnarayan. Any major discharge along the downstream of Durgapur Barrage may cause flood
depending upon the outfall condition of the Mundeswari at Harinkhola. In Kangsabati river system, the
Kangsabati Dam has a limited flood storage capacity which is very nominal. Any major spillway
discharge from Kangsabati Dam may cause flood at lower areas downstream of Medinipur town
depending on tide and downstream rainfall.

30. The Flood Problem
The flood problems of the state are of different nature at different regions. The rivers Teesta, Torsa,
Jaldhaka, Raidak-I, Raidak-II etc. flowing through the districts of Jalpaiguri and Cooch Behar originate
in the neighbouring country of Bhutan and the state of Sikkim and flows down to Bangladesh, another
neighbouring country to meet the Bramhaputra at different locations. The rivers of the districts of
Uttar Dinajpur and Dakshin Dinajpur originating at Bangladesh passes through these districts and then
joins the Ganga-Padma at downstream of Farakka in Bangladesh. Both the places of origin and also
the outfall of most of these rivers are in Bangladesh. The district of Malda through which the river
Ganga flows receives its flood water from about 11 (eleven) States and is battered by the run-off flow
generated from these vast areas. Ultimately the river flows down the Farakka Barrage to Bangladesh.
Another portion of the Malda district receives floodwaters of the Mahananda, which again originates
in the hills of the neighbouring country of Nepal and has some catchment area in the neighbouring
state of Bihar and then passes through the district to join the Ganga-Padma at downstream of Farakka
Barrage in Bangladesh.Major contributing factors to flood in North Bengal regions are the run-off
because of heavy local rainfall, discharge of upper basin areas and also outfall condition in the
neighbouring countries. The Mahananda and most of the rivers of Uttar and Dakshin Dinajpur districts
get stagnated when the Ganga upstream and downstream of Farakka Barrage rules high thereby not
allowing drainage of flood discharge during that period.
River System In West Bengal
The Ganga-Padma river artery divides the state in two parts, north and south. Being a part of Ganga-
Bhrammhaputra-Meghna basin, North Bengal is extremely flood prone. The rivers Teesta, Torsa,
Jaldhaka, Raidak-I, Raidak-II and their numerous tributaries belonging to the Brammhaputra basin and
flowing through a part of Darjeeling, Jalpaiguri and Coochbehar originate in the Himalayas of Sikkim
and Bhutan and flows south-east to Bangladesh.

31. A part of Darjeeling and the districts of Uttar Dinajpur, Dakshin Dinajpur and Malda are drained
through the rivers of Mahananda, Dauk, Tangon, Nagar, Atreyee, Punarbhaba and their tributaries.
These are part of Ganga basin. Except the Mahananda, all other rivers originate in the plain of West
Bengal and Bangladesh and join the Ganga-Padma at downstream of Farakka in Bangladesh. The
Mahananda emerges from the Nepal Himalayas. Malda through which the river Ganga Flows receives
its flood water from about eleven states and batters by the run-off flow generated from these vast
areas. In central and southern part of this state, there are certain distinctive features of drainage
condition which gives rise to flood situation. Basin-wise there are a number of rivers on the right bank
of the Bhagirathi-Hoogly. These are Pagla-Bansloi, the Dwarka-Bramhani, the Mayurakshi-Babla-
Uttarasan, the Bakreswar-Kuye and also the Ajoy. They emerge from the Jharkhand Plateau an flow
southeast to meet Bhagirathi-Hoogly. These rivers drain an area of 17,684 km. spread over the State
Jharkhand and Birbhum, western part of Murshidabad and Burdwan. Originating from Ganga-Padma,
the Bhairab-Jalangi-Sealmari system of rivers drain the eastern part of Murshidabad and meet the
Bhagirathi at Swarupnagar in Nadia. Nadia is drained partly by Jalangi and partly by the Churni which is
a part of Mathabhanga-Churni-Ichamati system, taking off from Ganga-Padma flowing southwest, to
meet Bhagirathi on the east bank at Ranaghat. The other part viz. the Ichamati flows east through
Bangladesh enters the district of Uttar 24 Paraganas, flows in the south direction to fall into the tidal
creek of the Raimangal. Part of Howrah and Uttar and Dakshin 24 Paraganas are drained mainly by the
Hoogly and its tidal creeks and other internal drainage canals. Burdwan, Howrah and Hoogly districts
are mainly drained by Damodar and Bhagirathi-Hoogly Rivers. In the Damodar-Barakar basin system,
the rivers originate at Chotanagpur plateau and flow down the plains of West Bengal to meet
Bhagirathi. The Ajoy forms the border between Birbhum and Burdwan. Purulia and Bankura are
drained by the rivers of Kangsabati, Kumari, Shilabati, Keleghai, Dwarakeswar and their tributaries. The
Keleghai also drains Paschim Medinipur and a part of Purba Medinipur. These rivers originate from the
western highland of the state and flow in southeast direction to form the tidal rivers of the
Rupnarayan and the Haldi to meet the Hoogly on the west bank. The Rupnarayan forms the boundary

32. Analysis of Area Flooded against Years of Occurrence
Flood affected area (in sq. km) Years during which the flood
occurred
Total No. of
Below 500 1985, 89, 92, 94 & 97 5
Between 500 – 2000 1962, 63, 64, 65, 66, 72, 75 & 96 8
2000 - 5000 1960, 61, 67, 69, 70, 74, 76, 80,
81 & 82
10
5000 - 10000 1973, 77, 93, 95 & 98 5
10000 - 15000 1968, 79, 83, 90 & 99 5
15000 – 20000 1971, 86, 87 & 88 4
Above 20000 1978, 84, 91 & 2000 4
between Hoogly and Purba Medinipur. A part of Purba Medinipur is drained by the river Subarnarekha
originating from the Jharkhand Plateau and flowing in southwest direction to meet the Bay of Bengal in
Orissa.

33. Blue Areas depict Flood Affected Area
Flood North Bengal South Bengal
Districts
Affected by
Flood
Cooch Behar,
Jalpaiguri,
Uttar Dinajpur,
Dakshin
Dinajpur,
Malda;
Nadia,
Howrah,
Murshidaba,
North 24
Parganas,
South 24
Parganas,
Hooghly,
Burdwan,
Birbhum,
Paschim
Medinipur,
Purba
Medinipur
Relatively
scare
Districts
affected by
Flood
Darjeeling Puruliya &
Bankura

34. Flood Among natural hazards, occurrence of flood ranks first in West Bengal which has become annual
festival in the State. Almost all the districts are affected by flood from July to October. But flood is
relatively scarce in Darjeeling in North Bengal and Bankura & Purulia in South Bengal. The detail is
depicted in the following matrix. According to the Irrigation Department, 37.6 lakhs Ha of West Bengal
(42.4% of the total geographical area and 69% of its net cropped area) has been identified as flood
prone area; of this 29.8 lakh Ha ( i.e., 58% of the flood prone area) is Protected Area. Strong monsoon,
rivers and floods are an integral part of Bengal’s characteristic ecology that shaped its civilization and
culture and at the same time, cause of flood hazard and disasters for the society as a whole.
Followings are the records of large FLOODS in West Bengal
Period Description
1978 Major Flood
1986 Flooding due to heavy rains in some areas of Kolkata, Hooghly, Howrah, Parganas and Midnapore
1988 Monsoonal rains caused flooding in areas of Balurghat and Dinajpur lying under the purview of the
Ganges and Churani rivers
1991 Flash floods caused damage 35,000 houses
1995 Flooding triggered by heavy rains caused erosion, severe agricultural damage and outbreak of diseases
1998 Monsoon rains caused flooding of the Ganges River
1999 Tropical cyclones caused destruction of an estimated number of 1500 villages. Floods due to brief
torrential rains affected areas of Kolkata, Burdwan and Birbhum

35. Period Description
2000 Besides flash floods triggered by incessant torrential rains, disaster is also accredited to the opening of
sluice gates of dams. The fatalities counted to the tune of 1262, besides affecting millions of people.
2002 Flooding in Jalpaiguri, Cooch Behar and Jalpaiguri in north Bengal due to monsoonal rains. Flash floods
swamped ten villages, causing four deaths and 11,000 displacements
2003 Monsoonal rains caused floods affecting the regions of Darjeeling, Jalpaiguri, Malda and Murshidabad
2004 Heavy monsoonal rains affected several districts
2005 Heavy rains caused floods in many areas. About 3000 coastal villages were inundated and 60,000 huts
and many roads washed away. Heavy monsoon rains triggered flash floods and landslides
2006 The regions of Birbhum, Burdwan and Murshidabad were affected mainly from continuous monsoonal
downpour Monsoonal rains and tropical cyclone-driven storms in the Bay of Bengal hit India and
Bangladesh. West Bengal recorded 50 deaths, 300 were injured and 30,000 mud houses destroyed.
Heavy rains left large parts of Kolkata city under water; subsequently 2000 people were evacuated from
the city.
2007 Heavy rain from tropical depression in the Bay of Bengal caused flooding leading to 51 deaths, and
affecting 3.2 million people.
2013 Heavy rainfall & water release from various dams by DVC led to widespread flooding in the districts of
Paschim & Purba Medinipur, Howrah, Hooghly, Bardhaman and Bankura Causing 17 deaths, 8790
villages affected, and affecting 2.1 miillion people

36. FLOODS IMPACTS
• Human Loss
• Property Loss
• Affects the Major Roads
• Disruption of Air / Train / Bus services
• Spread of Water-borne Communicable Diseases
• Communication Breakdown
• Electricity Supply Cut off
• Economic and Social Disruption
• Increase in Air / Water Pollution

37. Disaster mitigation and management for West
Bengal, flood:
Floods
Approximately 55.8% of the region is susceptible to floods. Furthermore, complicacy is implicated by
the origination of major flood-producing rivers beyond the state jurisdictional limits. Table 1 provides
historical records of large floods in the state.
An outline of flood management
A monograph on flood management prepared on the basis of hands-on experience of the State
Government officials recommends a standard operating procedure (Figure 1). Three phases of actions
are specified: pre-flood, during flood and post-flood.
The pre-flood phase activities consist of preparatory measures, which involve vulnerability
assessment, personnel and organizational database development, viable emergency action plan such
as deployment of early warning system, training of personnel for rescue and evacuation, verification
and updating of existing search, rescue and evacuation plans, and inventories of essential
commodities and relief materials.
A district disaster management committee is expected to be coordinated before the onset of the
monsoon season to ensure adequate preparedness. Participation of various government and non-
governmental organizations is anticipated in knowledge and expertise sharing. Strategic planning
focuses on hazard elements and formulates actions such as construction, restoration or improvement
of drainage channels, and removal of human encroachment along the riverbanks. On the very onset of
the hazard, the highest priority is on ‘search, rescue and evacuation’, in addition to ‘organization of
relief facilities’. Quick and correct damage assessment would enable speedy restoration and

38. rehabilitation in terms of physical, economic and social aspects. The disaster related information
should be well documented to enable future management plans.
Post – flood
Assessment of damage.
Verification of loss of life.
Rehabilation.
Animal care.
Documentation.
Pre -flood
Preparedness
Vulnerability assessment.
Database preparation.
Early warning dissemination system.
Stocking of essential commodities.
Coordination.
Activating control rooms.
Maintenance of essential service.
Responsibilities and accountability.
Preparedness and emergency response.
Mitigations
Planning and capacity building.
During – flood
Role of local government
representatives.
Local coping mechanisms.
Control room operation.
Coordination.
Disposal of carcass and
death bodies.
Figure 1. Standard operating procedure for managing flood
hazard depicted in a nutshell.

39. The overall impetus at the national and global level is on preparedness and mitigation7,8. Several
recent commissions have been formed at the national level, such as National Water Policy, 1987;
National Commission for Integrated Water Resource Development Plan, 1996 and Regional Task Forces,
1996, and the ensuing recommendations adopted. However, effectiveness of recommendations seems
to be lacking in several cases9. The National Commission for Integrated Water Resources Development,
1999, recommended management approach rather than control, emphasizing failure to render
complete protection. The strategies include flood-plain zoning, flood proofing, forecasting, disaster
preparedness, response planning and insurance, etc. In respect of flood-plain zoning, the National
Commission on Floods–1980 proposed a legislation to classify flood-prone zones according to
occurrence and intensity. However, in West Bengal, the problem is rather vexing due to high population
density and large flood-prone areas. While it is imperative to prevent encroachment of river beds, it is
not feasible to relocate structures and developmental activities from all the hazard-prone areas. In
recent times, flood forecasting is advancing with utilization of satellite and remote-sensing techniques.
If the approaching flood can be predicted/ observed, evacuation through monitoring and warning is
possible.

41. What is a Drought? :-
Drought is defined as a period in which a region has a deficit in its
water supply whether surface or underground water. It can last for
months or years, or even days….. Though droughts can persist for
several years, even a short, intense drought can cause significant
damage and harm to the local economy.
Definition of Drought :-
Drought is a period of below-average precipitation in a given region, resulting in prolonged shortages
in its water supply, whether atmospheric, surface or ground water.
A drought can last for months or years, or may be declared after as few as 15 days.
It can have a substantial impact on the ecosystem and agriculture of the affected region and harm to
the local economy.
TYPES OF DROUGHT :-
Meteorological drought
Hydrological Drought
Agricultural Drought
1) Meteorological:- Meteorological drought is brought about
when there is a prolonged time with less than average precipitation.
This happens when the actual rainfall in an area is significantly less than
the climatological mean of that area. The country as a whole may have
a normal monsoon, but different meteorological districts and sub-divisions can have below normal
rainfall. The rainfall categories for smaller areas are defined by their deviation from a meteorological
area's normal rainfall.

43. 2)Hydrological:- drought is brought about when the
water reserves available in sources such as aquifers, lakes and
reservoirs fall below the statistical average. It is associated with
the effects of periods of precipitation shortfall on surface and
sub surface water supply rather then with precipitation shortfall.
A marked depletion of surface water causing very low stream
flow and drying of lakes, rivers and reservoirs.
3)Agricultural :-It is drought occurs when there is not enough
water available for a particular crop to grow at particular time. it
doesn't depend only on the amount of rainfall but also on the
correct use of water. it is affected crop production.
Inadequate soil moisture resulting in acute crop stress and fall
in agricultural productivity.
Socioeconomic :- it is associates the supply and demand of sum economics good or service with
element Hydrological, Meteorological, Agricultural.
1. Less rainfall: if there is an above average presence of dry, high pressure air system, less moisture is
available for produce rain.
2. High Air pressure: When there is high air pressure, air falls instead of rising. With the air pressing
down in a high pressure zone, no currents of water vapor are carried upward. As a result, no
condensation occurs, and little rain falls to earth.

44. Common causes and impact of drought

45. 3. Low air pressure: Low-pressure systems see more cloudy, stormy weather. Usually, however, we
experience both high- and low-pressure systems.
4. Monsoon role: Usually, summer winds known as monsoons carry water vapor north from the Indian
Ocean inland, providing desperately needed rain. Sometimes, however, instead of blowing from north to
south, they blow east to west. When that happens, the vapor doesn’t leave the Indian Ocean and many
people suffer from the resulting droughts.
5. Water Vapor role: Droughts occur because water vapor is not brought by air currents to the right
areas at the right times. Water that evaporates from the oceans is brought inland by wind to regions
where it is needed. However, sometimes those winds are not strong enough.
6. Moisture: In some states, moisture is carried up from the ocean by blowing winds. This moisture is
then pushed by other winds until it reaches the location. However, if the winds don’t blow at the right
time, in the right direction, or with enough force, the moisture falls in other areas and suffers from
drought.
7. Mountains region wind: Mountains can prevent wind from blowing moisture to needed regions. As
air is moving past a mountain range, it is forced to rise in order to pass over the peaks. However, as the
air rises, it becomes colder and the vapor condenses into rain or snow. When the air mass finally makes
it over the mountain, it has lost much of its vapor. This is another reason why many deserts are found on
the side of a mountain facing away from the ocean. This phenomenon is known as the rain shadow
effect.
8. Rainfall pressure: Generally, rainfall is related to the amount of water vapor in the atmosphere,
combined with the upward forcing of the air mass containing that water vapor. If either of these are
reduced, the result is a drought.
9. Global warming: Human activity can directly trigger exacerbating factors such as over farming,
excessive irrigation, deforestation, and erosion adversely impact the ability of the land to capture and
hold water.

46. No Drought / Drought Condition

47. 10. Decline in groundwater : India has seen a sharp decline in groundwater levels, leading to a fall in
supply, saline water encroachment and the drying of springs and shallow aquifers. Around 50% of the
total irrigated area in the country is now dependent on groundwater, and 60% of irrigated food
production depends on irrigation from groundwater wells.
11. Depletion of forest : The rapid depletion of forest cover is also seen as one of the reasons for water
stress and drought. India has a forest cover of 76 million hectares, or 23% of its total geographical area –
much lower than the prescribed global norm of 33%.
12. Rainwater harvesting : Combined with these and a host of other factors – poor irrigation systems,
pressure from the increasing industrial use of water is the appalling indifference displayed towards
rainwater harvesting. Little has been done over the years to droughtproof the country, when community
based rainwater harvesting measures could easily accomplish this feat.
CONSEQUENCES OF DROUGHT
Effects of droughts can be divided into three groups:
Environmental
Economic
Social consequences
In environmental effects: lower surface , lower flow
levels, increased pollution of surface water, the drying out
of wetlands, more and larger fires, losing biodiversity, worse
health of trees and the appearance of pests.
Economic losses include lower agricultural, forest, game and fishing output, higher food production
costs, lower energy production levels in hydro plants, losses caused by depleted water tourism , and
disruption of water supplies for municipal economies.

48. social costs include the negative effect on the health of people, possible limitation of water supplies
and its increased pollution levels, high food costs, stress caused by failed harvests.
Effects:-
Diminished crop growth and carrying capacity for livestock.
Dust bowls and Dust storms, themselves a sign of erosion.
Famine due to lack of water for irrigation.
Habitat damage, affecting both terrestrial and aquatic wildlife.
Hunger , Malnutrition, dehydration and related diseases.
Reduced electricity production due to reduced water flow through hydroelectric dams.
Shortages of water for industrial users.
Snake migration, which results in snakebites.
Social unrest.
War over natural resources, including water and food.
Wildfires, such as Australian bushfires.
Drought
Management
System
in
India

50. Drought Management Strategy

52. Drought risk management cycles

53. Analysis of Meteorological Drought: The Scenario of West Bengal
Introduction
Being the most important environmental problems affecting our earth, drought has been ranked by Hass
(1978) as the ‘third most costly geophysical phenomena’ (Oladipo, 1993). Based on its nature, droughts
may be divided into four different categories, viz., meteorological, hydrological, agricultural and socio-
economic (Mishra and Singh, 2010). Of these, the meteorological drought signifies the paucity of rainfall
over a region for a considerable period of time. Climatic conditions / factors like high temperature and
high wind can only worsen its intensity. It should also be noted that a detailed analysis of drought also
requires understanding of several other factors like, soil moisture, potential evapo-transpiration,
vegetation condition, surface and ground water levels, and etc. Existing literature on drought largely talks
about drought intensity and frequency in various regions like Nebraska in US (Oladipo, 1985), Colorado in
US (McKee et al, 1993), Sabah and adjacent parts of northern Borneo (Walsh, 1996), Sahel in northern
Africa (Agnew and Chappell, 1999), northern China (Zhiew et al, 2003) and Aravalli in India (Bhuiyan et
al, 2006).
A number of different indices have been formulated to quantify the nature of drought. These include
Rainfall Anomaly Index (RAI), Palmer Drought Index (PDI), Bhalme and Mooley Drought Index (BMDI),
Surface Water Supply Index (SWSI), Standardized Precipitation Index (SPI), Reclamation Drought Index
(RDI) etc. Mishra and Singh (2010) have provided a neat review of commonly used drought indices along
with their relative advantages and limitations.

54. Study Area
Physiographically, West Bengal is unique containing almost all the physical features. It has three distinct
meteorological seasons, viz., summer (March-May), rainy season (June- October) and winter (November-
February). During the hot and dry summer, it experiences localized thunderstorms associated with strong
winds and short duration rain. Rainfall is largely due to the south-west monsoons. The Indian
eteorological Department (IMD) M long period data (1900-2005) shows increasing trend in the annual
frequency of severe tropical cyclones that crossed West Bengal coast. About 2.65 million ha of land in
the state is prone to flood (Attri and Tyagi, 2010). IMD has divided this state into two meteorological sub-
divisions, viz., Sub-Himalayan West Bengal (SHWB) and Gangetic West Bengal (GWB). In order to get a
holistic and real spatial analysis of drought, the geographically well-distributed 15 meteorological / rain
gauge stations have been taken into consideration (Table-1 and Fig.1)
Table-1: Meteorological/Rain Gauge Stations of Study Region
Meteorological Sub-division Meteorological/Rain Gauge Stations
Sub-Himalayan West Bengal (SHWB) Darjeeling, Cooch Behar, Jalpaiguri,
Balurghat and Malda
Gangetic West Bengal (GWB) Berhampore, Shantiniketan, Bankura,
Purulia, Bagati, Krishnanagar, Uluberia,
Midnapore, Sagar Islands and Alipore
Source: Climatological Tables of Observatories in India, 1961-1990, 6th Ed., IMD.

55. Percentage Rainfall
Departure
Condition
99.99-90 Normal rainfall
89.99-74 Deficient
73.99-50 Moderate Drought
<50 Severe Drought
Table-2:Drought Categories
Database and Methodology
Monthly rainfall data for each station for the
period, 1973 – 2005 has been collected from IMD
Data Centre, Pune. However, due to lack of data,
the monthly rainfalls of Balurghat and Sagar
Islands have been taken for the period, 1969 –
2001, and that of Purulia for the period, 1970 –
2002. Climatological Tables, showing long period
normal rainfall data (1961-1990) have been
obtained from the IMD, New Delhi. For
understanding rainfall dynamics, ‘coefficient of
variation’ has been used. Besides, to calculate
drought intensity, ‘percentage of rainfall
departure’ (IMD) and ‘standardized precipitation
index’ (SPI) have been used. IMD defines

56. ‘meteorological drought’ as ‘a situation when the seasonal monsoon (June-September) rainfall is less
than 75% of its long-term average value’ (Attri and Tyagi, 2010). Hence, ‘percentage of rainfall departure’
variable has been considered to identify the drought categories (Table 2). Due to non-availability of data
for all stations, the study has been restricted within 2005.
For a particular station, SPI is calculated
on the basis of long term rainfall record for a
desired period. This long-term record is fitted to a
probability distribution, which is then
transformed to a normal distribution so that the
mean SPI for the location and desired period is
zero (Mishra and Singh, 2010).
SPI = (a – b) / c
where, a = individual Gamma cumulative
distribution value, b = mean, c = standard
Deviation.
It can be calculated for various time scales;
however, different length of rainfall record
and use of different probability distribution yield varying results in SPI (Mishra and Singh, 2010). For the
present study, the following drought categorization has been taken into consideration (Table – 3).
Table-3: Drought Categories
according to SPI values
SPI values Drought Category
0 to -0.99 Mild Drought
-1.00 to -1.49 Moderate Drought
-1.50 to -1.99 Severe Drought
<= -2.00 Extreme Drought
Source: McKee et al (1993)
Analysis
(a) Rainfall Dynamics:-
As in West Bengal rainfall mostly depends on vagaries of south-west monsoon, its spatiotemporal
variation is very prominent. IMD long period normal data (1961-1990) reveals that annual average
rainfall is highest in Cooch Behar (288.9 mm) and lowest in Krishnanagar (98.9 mm). Although, extreme
northern and southern parts (adjacent to Bay of Bengal) of the state receive more rainfall, the central

57. and western parts receive less rainfall. Coefficient of variation, a relative measure of dispersion, is
computed to get seasonal and annual variability of rainfall for all stations. During pre-monsoon
(February-May) and post-monsoon season (October-January), most of the stations report high
variability of rainfall. During pre-monsoon season, rainfall variability is quite high in Berhampore, Sagar
Islands, Purulia, Malda and Darjeeling. In monsoon season (June-September), all the stations (excluding
Krishnanagar) report less than 36% variability. However, in post-monsoon season, some stations like
Krishnanagar, Midnapore, Purulia, Jalpaiguri, Darjeeling, Malda and Balurghat exhibit higher rainfall
variability. In general, few stations like Krishnanagar, Balurghat, Malda and Sagar Islands report higher
rainfall variability.
(b) Drought Frequency and Intensity — analyzing rainfall departure:-
Rainfall dynamics is very helpful in assessing meteorological drought. During pre-monsoon season,
Balurghat, Darjeeling, Malda, Krishnanagar, Berhampore, Sagar Islands and Bagati have experienced
higher number of ‘severe droughts’. In this season, ‘moderate drought’ frequency is found to be higher in
Darjeeling, Balurghat, Alipore, Uluberia and Bagati. On the other hand, Jalpaiguri, Shantiniketan, Bankura
and Purulia show normal rainfall condition during this season.
However, monsoon season is characterized with variable rainfall across the state. ‘Normal rainfall’
occurred in Cooch Behar, Jalpaiguri, Berhampore, Purulia, Midnapore and Bagati. However, higher
number of years of ‘deficient rainfall’ has been experienced in Darjeeling, Berhampore, Uluberia, Alipore
and Sagar Islands. Only Krishnanagar has experienced higher number of ‘severe droughts’ in this season.
In post-monsoon season, meteorological drought appears more prominently. Higher frequency of severe
droughts has been reported in Darjeeling, Balurghat, Berhampore, Krishnanagar, Malda and Sagar
Islands. Moderately higher frequency of ‘severe droughts’ has been observed in Bankura, Purulia, Malda
and Jalpaiguri. Malda, Balurghat, Jalpaiguri, Berhampore and Krishnanagar also report higher frequency
of ‘moderate droughts’ (Fig.5).

58. It should be noted that Krishnanagar has the unique experience in higher frequency of ‘severe droughts’
in all three seasons. Apart from this, Balurghat has experienced higher frequency of ‘moderate droughts’
in all three seasons. The seasonal data also reveals that Darjeeling, Malda, Berhampore, Uluberia and
Sagar Islands have reported higher frequencies of high intensity (severe and moderate) droughts. Here,
we must remember that rainfall variability is quite higher in Krishnanagar, Balurghat, Malda and Sagar
Islands.
(C) Periodicity of Drought:-
If drought occurs continuously for years, the water balance situation gets hampered, thereby affecting
water resources, natural vegetation and crops. But if the drought is intermittent, then other rainfall-led
wet years keep soil moisture recharged. That’s why periodicity of drought is important. It has been
observed that Balurghat and Krishnanagar have continuous ten years drought period.
Even, Krishnanagar, Bankura and Puruliya have poor experiences of five-year prolonged drought.
Continuous Four-year drought has happened in Bankura, Midnapore, Uluberia and Sagar Islands. Even
Jalpaiguri has experienced such four-year prolonged drought twice.
Conclusion:-
Drought frequency and intensity analysis shows that the western (Bankura and Purulia) and central parts
(Balurghat, Malda and Krishnanagar) are more affected by this hazard. This may be attributed to
considerable variability of rainfall. South-West Monsoon (Bay of Bengal Branch) practically provides
plenty rainfall in northern and southern parts of the state. However, extreme northern part has also
been found to be drought affected in recent years. IMD long period data (1961-1990) shows that
Krishnanagar, Malda and Purulia have experienced relatively lower rainfall (< 1333 mm) as compared to
Darjeeling and Cooch Behar (> 2500 mm). Fortunately, Darjeeling and Cooch Behar is well endowed with
abundant rainfall, glacier-fed fluvial system and grey black Terai soil. Unfortunately, the central and
western parts are characterized by shallow and reddish lateritic soil having low moisture retention
capacity. Besides, its interior location and rugged undulating terrain have also prompted persistent dry

59. conditions. Thus, even a smaller fluctuation in rainfall would largely affect moisture availability conditions
in Krishnanagar, Malda and Purulia as compared to Darjeeling and Cooch Behar. Therefore, an integrated
planning approach, addressing regional climatic conditions, soil, natural vegetation, hydrology and
topographical characteristics, can help in agricultural and landuse planning.

61. PRESENTGROUNDWATERSCENARIOOF WESTBENGAL
Introduction:-
Groundwater is prime natural resources in the earth .Not only it supported almost all types of life form to
evolve, but also helped in growth of human civilization. It quenches thirst and meets the household
demands. Used in the fields for production of food grains .Lastly the industries catering to the various
needs and luxuries of human being have started consuming voluminous quantity of Water .Groundwater
is therefore a precious national asset and planning, development and Management of water resources
need to be governed by national perspectives.
In the beginning, water from rainfall and snow and rivers were only source of water to mankind. As these
surface water sources were dependent on rainfall, localized shortage was often witnessed. With primitive
technologies men was not able to build sustainable water reservoir to see them through the drought
period .But once man came to know of groundwater, his dependence on it increased with the advent of
civilization. At present about two billion people in the world is dependent on groundwater. Fortunately,
groundwater is a renewable resource that is recharged every year through rainfall. However, this
recharging process is not entirely dependent on rainfall but on various other natural factors that differ
from region to region and within space and time. Therefore, recharge of groundwater is never a constant
factor .When the average quantity of draft exceeds recharge for repeated years we face the situation of
over exploitation.
The manner and the scale in which the use of groundwater has accelerated, human being has become so
much dependent on the assured source that no sign of the over increasing demand for groundwater
stabilizing.
Beginning of 20th century witnessed demand for groundwater in industrial sector rising phenomenally at
a faster rate than that in agriculture and domestic sector.
West Bengal is the only state in India that stretches from Mountain to the Sea and truly a “Asamudra
himachalam” state as the meaning goes. West Bengal has a very good groundwater potential. The reason

62. of such affluence is due to her geographical location, high rainfall and favorable geological setting .The
state have land area of about 2.7% but have about 6% of total replenishible groundwater resources of
India. Groundwater is the most exploited resource in west Bengal particularly in agriculture sector With
the introduction of water intensive high yielding variety , the need for groundwater have skyrocketed.
Quinquennial census of minor irrigation structures indicated a 64% growth in number of STWs over last
16 years,@4% annually. Table Showing Number of Groundwater Structures from 1986 to 2001
Hydrogeological Condition:-
Geologically West Bengal can be divided into two broad units (A) Consolidated or semi consolidated
formation occurring in the northern most and western part of West Bengal and (B) Unconsolidated
formation in the rest of West Bengal.
(A) Consolidated/ semi consolidated formations:
These formations cover the western and the northern part of the state. These are comprised of
Archaean crystalline rocks and Gondwana group of rocks including Rajmahal traps covering part of
Purulia, Bankura Paschim Medinipur, Birbhum and Burdwan.. Archaean metamorphics, Siwalik and
Gondwana covers part of Darjeeling and Jalpaiguri District. In the western part and in some part of
Darjeeling district , these hard and semi consolidated rocks are overlain by weathered residuum and
laterite capping.
(B) Unconsolidated formations:
These formations belonging to the Tertiary and Quaternary age and covering rest of West Bengal. These
formations may be subdivided into (a) Secondary laterite (b) Older alluvium and (c) Recent alluvium.
Secondary laterite occurs at the marginal area between the Consolidated/ semi-consolidated rock and
older alluvium mainly in the districts of Bankura, Paschim Medinipur, Burdwan and Birbhum. Older
alluvium occurs mainly in the elevated terraces fringing the lateritic margin of the Chhotonagpur plateau
in Bankura, Pascim Medinipur, Burdwan, Birbhum, Hoogli and Murshidabad district and in the Barind
region of North Bengal. Recent sediments occupy the river courses and flood plains.

63. Arsenic as a Chemical:-
Arsenic is a steel-grey semi-metallic element and present in Group 15 in the periodic Table. Abundance of
arsenic is 1.8 ppm in the earth’s crust by weight. Arsenic does not present in its elemental state but
commonly presents as sulphides (As₂S₃) and sulfosalts such as arsenopyrites, FeAsS. All arsenic
compounds are poisonous. Arsenic is a very redox-sensitive element and its mobility is controlled by pH
and redox potential in the groundwater. Arsenic is stable in four oxidation states (+5, +3, 0, -3) under the
normal redox potential conditions in aquatic systems. However, predominant forms are trivalent arsenite
(As3+) and pentavalent arsenate (As5+). The toxicity of different arsenic species varies in the order
arsenite ˃ arsenate ˃ monomet hylarsonate (MMA) ˃ dimethylarsinate (DMA). As5+ exists in solution as
arsenate ion and arsenic acid which forms salt such as sodium arsenate. The element arsenic is insoluble
in HCl and dil. H₂SO₄ but soluble in concentrated HNO₃. Arsenic is not an essential element for human
body, although it is found in very small quantities in tissues. Elemental arsenic is not absorbed in human
body but its salts are readily absorbed through the food and water.
Source of Arsenic in Ground Water:-
The cause of arsenic contamination in ground water is still debatable topic. The source of arsenic in
ground water was traced out by geological survey of India and the Central Ground Water Board.
According to them the present drainage pattern of Ganga-Bramhaputra are responsible for sedimentation
in West Bengal. The affected area of West Bengal is a part of the Ganga- Bramhaputra delta having
sediments of varying thickness of deposition. The source of arsenic could be from the coal fields to bring
arsenic minerals form the mine working to the sediments. The source of arsenic in groundwater of lower
gangetic delta is considered to be the arsenic-rich sediments which has transported from the
Chotonagpur-Rajmahal highlands[6-7]. Some research workers believe that the leaching of arsenic in
ground water is due to maximum use of ground waters for irrigation. During the 80’s there was a
remarkable change in irrigation sector by cultivating of summer paddy expanded in the seven districts in
West Bengal. The Boro cropping is depended on the use tube wells for ground water. The Boro irrigation
lowers the ground water level at high rate. The ground water occurring mainly with the shallow zone

64. (20 – 60 M) where the principle source of arsenic in the arsenic sulphites minerals deposited with the clay
in the reducing environment. The lowering of ground water level at a rapid rate during summer session
cause aeration and oxidised the arsenic sulphides and make it in water soluble.
STRETCH OF ARSENIC POLLUTION IN
WEST BENGAL:-
From the overall study on As in West Bengal and
Bangladesh, it is revealed that the magnitude of
the groundwater contamination is severe (Pearce,
1998; Smith et al., 2000). Groundwater arsenic
contamination in the Lower Ganga basin of West
Bengal, India, was first identified in July 1983 (Saha
KC. Unpublished data). Garai et al. (1984) reported
16 patients in three families from one village of 24
Parganas District. Saha (1984) further reported
127 patients with arsenical skin lesions. In the
combined areas of West Bengal and Bangladesh
(Ganga-Padma–Bramhaputra delta), around 150
million people are at risk from arsenic-
contaminated groundwater. According to the
reports of SOES, Jadavpur University, India, has
identified tube wells with arsenic concentrations ≥
50 μg/L in more than 3,000 villages. Based on
Arsenic concentrations, West Bengal was classified
into three zones:

65. highly affected 9 districts (Malda, Murshidabad, Nadia, North-24-Parganas, South-24-Parganas,
Bardhaman, Howrah, Hoogly and Kolkata, mainly in eastern side of Bhagirathi River) where average
arsenic load is > 50 μg/L (upto 300 μg/L) can be found in tube-wells;
mildly affected 5 districts (in northern part) where average Arsenic load in tube-wells was below 50 μg/L
(a few above 50 μg/L but all < 100 μg/L) and
Arsenic-safe 5 districts (mostly <3 μg/L) in western part. The estimated population drinking Arsenic-
contaminated water above 10 and 50μg/L were ~9.5 and ~4.6 million respectively. In West Bengal alone,
26 million people are potentially at risk from drinking Arsenic-contaminated water above 10 μg/L
(Chakraborti, 2003).
There is no generalized mitigation method applicable for all the affected regions due to
(i) geographical and geomorphological variations, (ii) differing socio-economic and literacy conditions of
people.
But whatever be the approach, for success at field level, awareness among the people and their
wholehearted participation is need (Das et al., 2009).
Problem in West Bengal :-
During 1980’s some cases of skin disorder in the districts of North 24 Parganas, South 24 Parganas, Nadia,
Murshidabad and Burdwan were report from where it is known that the disease is due to use of arsenic
contaminated groundwater. Out of the twenty districts in West Bengal, 9 districts Malda, Murshidabad,
Nadia, North-24-Parganas, South-24-Parganas, Bardhaman, Howrah, Hoogly and Kolkata are affected by
arsenic contaminated groundwater (Fig. 1). Ground water having higher concentration of arsenic
generally occurs within 20 – 80 M depth zone[8]. In West Bengal more than 26 millions of people are
potentially at risk for drinking arsenic contaminated water. The other six districts in the northern part of
West Bengal and 5 districts in western part of West Bengal are arsenic safe-zone.

66. Health Problem:-
Although the arsenic contamination in ground
water problem is about four decades old but still
it is deeply concerned with arsenic
contamination of drinking water[9-10]. The
irrigated water containing arsenic can enter to
the bodies of human through vegetables and
food grains. The complex nature of arsenic
increases the severity of the health problems in
West Bengal. Chronic poisoning by arsenic
compounds leads to diarrhoea, gastrointestinal
problems, anemia, renal defects, neurological
defects, skin cancer etc. It also blocks the thiol
function of the enzymes. Arsenic (+3) exerts its
toxic action by attacking –SH groups of an
enzyme and thereby inhibits enzyme action. It
inhibits the function of thioredoxin reductase
and pyruvade dehydrogenase enzymes. Arsenic
inhibits ATP synthesis by replacing the phosphate
group. Due to the chemical similarity between
arsenic and phosphorous, arsenic interferes
some biochemical process of ATP (Adenosine
Triphosphate). Arsenic can induce oxidative
damage of DNA, altered DNA methylation and
altered regulation of DNA-repair.

67. Social Problem and Awareness:-
Arsenic affected people are also facing serious social problems. The affected villagers are living in very
poor conditions[11-12]. A few people are aware of arsenic pollution and its impacts on the human health.
A large number of people are ignorant of arsenic pollution. They suffer from arsenic diseases and become
the victim of arsenic contamination of water but they do not think of it. When the impact of arsenic
becomes serious and people suffer from black foot disease then only they can realize that they are
suffering from arsenic poison. When people suffer from different skin diseases, the body looks very
rough, black spots are found on the hand and foot. Therefore, awareness is needed among the rural
people and make them free from arsenic diseases. It is essential to develop management plans involving
adequate medical and infrastructural support for them. A change in tapping of newer water resources is
essential. The general antidotes for arsenic poisoning are chemicals having –SH groups e.g. 2, 3
dimercapto propanol.
Mitigation Measures:-
There is an acute scarcity of medicine to cure chronic Arsenic toxicity. Safe water, nutritious food and
some physical exercise are only the proven measures to fight chronic Arsenic toxicity (Maeda, 1994).
Proper watershed management and cost-effective utilization of available surface water along with the
education of the villagers and their active participation appear to be the only solutions to resolving the
present Arsenic crisis in the gangetic delta (Tripathi et al., 2005).
Inorganic Arsenic can undergo microbially mediated biochemical transformation, i.e., the hydroxyl group
of arsenic acid is replaced by the CH3 group to form MMA, DMA, and TMA, thus get transferred into
relatively non-toxic form (Frankenberger and Losi, 1995). The pathway of As5+ methylation initially
involves the reduction of As5+ to As3+, with the subsequent methylation of As3+ to dimethylarsine by
coenzyme S-adenosylmethionine (Pierce and Moore, 1982). Methylation is often enhanced by sulfate-
reducing bacteria. Several fungal species also have shown ability to reduce Arsenic (USDHHS, 2000).
Some of the existing arsenic removal technologies can be reduced in scale and conveniently be applied at

68. household and community levels for the removal of arsenic from contaminated water drawn by tube
wells.
1. Oxidation: Arsenite can be oxidized by oxygen, ozone, free chlorine, permanganate, hydrogen
peroxide etc. Atmospheric oxygen, hypochloride and permanganate are commonly used for oxidation in
developing countries. Air-oxidation of arsenic is very slow but chemicals like chlorine and permanganate
can rapidly oxidize arsenite to arsenate under wide range of conditions (Wegelin et al., 2000).
2. Solar Oxidation: It is a simple method of solar oxidation of arsenic in transparent bottles to reduce
arsenic content of drinking water (Young, 1996). Ultraviolet radiation can catalyze the process of
oxidation of arsenite in presence of other oxidants like oxygen (Ahmed et al., 2000). Experiments show
that the process on average can reduce arsenic content of water to about one-third.
3. Co-precipitation and Adsorption processes: Water treatment with coagulants such as aluminium
alum, activated alumina, ferric chloride and ferric sulfate are effective in removing arsenic from water.
Ferric salts have been found to be more effective in removing arsenic than alum on a weight basis and
effective over a wider range of pH. In both cases pentavalent arsenic can be more effectively removed
than trivalent arsenic (Pierce and Moore, 1982).
Conclusion :-
Arsenic contamination of ground water is an alarming problem in West Bengal. Millions of peoples in
nine districts are drinking ground water with the arsenic contamination. The affected people do not have
alternative sources of safe drinking water. The only way is to stop consumption of arsenic contaminated
drinking water. Therefore, it is necessary to organise awareness camps regularly in the affected area. It is
also needed desperately to increase awareness and educate the people about the serious problem.
Besides, the maximum surface water resources such as rain water should be used. So rain water
harvesting followed by proper purification can be used as low cost effective arsenic free water. Still there
is not enough technology to encounter to the arsenic exposed people. The general awareness by
Government, Semi-Government agencies, NGOs and other individual are needed and collective efforts is
the only solution of this problem.