Journal of Global Resources
Volume 6 (01)August 2019-January 2020
Page 148-153
UGC –CARE Listed Journal in Group D
ISSN: 2395-3160 (Print), 2455-2445 (Online)

23DELINEATION AND ZONATION OF FLOOD PRONE AREA IN LOWER AJOY RIVER BASIN
Hasibur Rahaman Molla
Assistant Professor, Department of Geography,
Sivanath Sastri College, Kolkata, India
Email: hasiburmollavb@gmail.com
Abstract: River Ajoy is notorious for its flood fury in central Bengal. It is a rain fed river andduring the monsoon period it frequently inundates its floodplain causing havoc to the bankdwellers. The lower Ajoy river basin, which extends from Pandabeswar (23˚44' N, 87˚ 17' E) toKatwa (23˚39' N, 88˚ 08' E), is much more susceptible to flood. On the basis of flood frequency
and duration of inundation the whole lower Ajoy river basin has been demarcated by four zones
i.e. severe flood prone zone, moderate flood prone zone, Low flood prone zone, and Flood freezone. The nature of damages caused by floods distinctly varies from one zone to another. Thepaper deals with the delineation of flood prone areas in the basin giving emphasis on the basisof demarcation of different zones, their type and characteristics. It is one of the most important
soft approaches by which we can mitigate the flood hazard effectively without any structuralintervention.
Key words: Inundation, Floodplain, Bank Dwellers, Flood Frequency, Hazard.
Introduction
Flood can be defined as a body of water which rises to overflow the land which is normally notsubmerged (Ward, 1987). Flood is a serious environmental hazard in West Bengal particularly
in monsoon and post monsoon period. The Lower Ajoy river basin is a well-known flood prone
area. Almost every year a large tract of the river basin gets inundated and brings about great
geomorphic and socio-economic consequences. Directorate of Irrigation and Waterways
Department, Govt. of West Bengal, has made attempts to control flood problems by embanking
the river. But floods continue to occur defying the embankments or other engineering
constructions. The flood hazard comprises many aspects including structural and erosional
damage, loss of life and other materials, disruption of socio-economic activities includingtransport and communication system and spoiling of agricultural land and so on ( Hewitt andBurton 1971 ). Flood plain zonation and delineation of flood prone area may be an importantmeasure to mitigate the flood hazard along with awareness of the people. The major objectiveof the study is to understand the flood intensity, periodicity, seasonality, and its spatio-temporalvariations and to delineate the different zones on the basis of present flood character of thebasin.
Materials and Methods
The major sources which have helped to identify the zones are the Survey of India top sheets(73 M/6, 73 M/10, 73 M/11, 73 M/14 ,79 A/2 ), flood demarcation maps of the Irrigation and Waterways
Directorate , Govt. of West Bengal. Remote Sensing data (IRS – IC & ID, LISS – III) for
mapping the extent of flood affected areas. Ground reality of the flood affected areas has beenchecked by the extensive field surveys conducted from time to time. Co-relation co-efficient has
been calculated to show the relationship between flood affected areas and number of affectedmoujas areas (Figure: 3). The study area i.e. the Lower Ajoy river basin geographically extends
from 23030’ N to 23045’ N latitudes and from 87020’ E to 88015’ E longitudes (Figure:1). Itoccupies an area of about 2816.65 sq.km. The river Ajoy is a right bank tributary of theBhagirathi River. The total length of the Ajoy River is about 299 km but only 145 km fall underthe study area. The Lower Ajoy river basin covers 7 blocks in Burdwan district and 5 blocks in
Birbhum district (W.B.). There are 619 moujas in under 12 C.D. blocks and out of the total 493
moujas are flood prone. Extensive field surveys have been conducted to acquire primary data.
Secondary data have been collected from Directorate of Irrigation and Waterways Department,Govt. of West Bengal, Zilla Parishad Offices of Burdwan and Birbhum districts.

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Figure 01: Key Map

Results and Discussion
Table-1 shows that the trend of flood affected area has gradually been increased since 1956.
The minimum affected area was in the flood of 1984 and about 305.72 square kilometres areasof the basin was flood affected, which accounts for 10.85 per cent of the total Lower Ajoy Basin.
On the contrary, the maximum inundation has been taken place in the flood of 1978 and about
1680 square kilometres areas was flood affected, which accounts for about 59.64 per cent of
the total area. The flood occurred in the year of 2000 was also notorious. About 1488 square
kilometres areas comprising total 369 mouzas were affected by the flood of 2000 and it
accounts about 52.82 per cent of the total Lower Ajoy Basin.

Year
1956
1959
1970
1971
1973
1978
1984
1995
1999
2000
2008
2015

Table 01: Spatio-Temporal Pattern of Flood in Lower Ajoy Basin
Flood Affected Mouzas
Affected AreasPercent to the(sq.km)
total basin
Entirely PartiallyTotal
153
32
185
680.0
24.14
120
27
147
584.38
20.74
186
36
222
812.24
28.83
130
31
161
624.71
22.81
124
36
160
639.02
22.68
307
67
374
1680.0
59.64
78
20
98
305.72
10.85
227
49
276
1380.82
48.99
237
60
297
1408.0
49.98
263
106
369
1488.0
52.82
136
39
175
706.54
25.08
152
46
198
764.23
27.12

Source: Irrigation and Waterways Department, Government of West Bengal, 2017

In the Lower Ajoy river basin ten major floods have been recorded since 1956 ,which
occurred in 1956 , 1959 , 1970, 1971 , 1973 , 1978 , 1995 , 1999, 2000, 2008 and 2015 . The
individual maps for the major floods have been prepared. All the maps have beensuperimposed over each other in two sets (five year each) to identify the area under maximum,moderate and minimum number of occurrences (Figure 04). By this way four zones (Table 03)
have been demarcated on the basis of frequency of flood occurrences.
High / severe flood prone zone (F1).
Medium / moderate flood prone zone (F2).
Low flood prone zone (F3).
Flood free zone (F0).+149

Figure 02: Inundation of Lower Ajoy Basin (IRS P6 LISS-III 2008)

Figure 03: Relationship between Flood Affected rea

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Table 02: Highest Flood Level in Different Gauge Station (1956- 2015)
Gaugestation

DangerLevel

Actual flood height ( metres ) in different flood year

Beta(metres)
57.90

Satkahonia

51.75

54.41

MaliaraGheropara

41.70
39.14

Nutanhat

19.19

1956

1959

1970

1971

1973

1978

1995

1999

2000

2008

2015

61.05

No
spilling
53.50

59.60

61.14

59.75

60.70

61.50

61.19

53.10

No
spilling
53.48

55.44

54.42

54.68

54.90

45.37
40.89

NospillingNo
spilling
45.58
41.31

44.17
40.51

44.47
40.29

43.16
40.63

45.71
42.82

45.72
42.50

44.46
43.22

45.86
42.79

No
spilling
44.76
41.10

21.02

21.84

20.40

20.62

20.00

22.42

22.30

22.89

23.21

21.34

No
spillingNo
spilling
43.10
No
spilling
20.21

Source: Irrigation and Waterways Directorate, Govt. of West Bengal-2017

Severe Flood Prone Zone
It covers an area of about 624.46 square km, which accounts 22.17 per cent out of the total
Lower Ajoy Basin. This is highly flood affected zone and runs almost parallel to the river basin.
But in the right bank it extends up to 8 km (in Ausgram block). In Ketugram block this zone isbroadened towards the east and extends 3 to 4 km from the river bank. It is estimated that outof the total 619 moujas 144 moujas are highly flood prone, which faced flood almost in every
flood occurrences. The frequency of occurrences of flood in this zone is more than 60
percentages. Sandsplays, Ox-bow lakes, Meander scrolls, etc. are the major geomorphicfeatures in this zone. The river in this zone is predominantly characterized by elevated riverbanks (levee). This is a result of either man made intervention in the form of embankment or
built up natural levees by sediment laden water. Multiplicity of abandoned channels, decadentrivers and depressions due to fluvial erosion are the natural consequences. In this zone thedanger level of flood height at some gauge stations like Beta, Satkahonia, Maliara, Gheropara
and Nutanhat are 57.90, 51.75, 41.70, 39.41, and 19.19 metres respectively but the actual
flood height in 2000’s flood were 61.50, 54.90, 45.86, 42.79, and 23.21 metres respectively(Table:2). The loss of agricultural land and crops due to sands play caused by breaching ofembankment becomes a great threat to the dwellers living in highly flood prone zone. This zone
is characterized by deep and long lasting inundation (Figure: 2)Moderate Flood Prone Zone
This zone occupies 528.00 square km and covers 18.75 per cent out of the total Lower Ajoy
river basin area. Out of total 619 moujas 130 falls under this zone. In this zone the frequency ofoccurrences of flood is 40 – 60 percentages. The predominant geomorphic features of thiszone are abandoned channels, cut-off channels, back swamps, etc. Gradual depositions of silton the back swamps have turned them into shallow swampy and ‘beel’ areas. During the rainyseason over-flooding of areas adjoining the ‘beels’ become a common feature. The coverage ofmedium flood prone zone is more on the right bank of the river than the left bank. In this zone
the houses, livestock and other assets have been lost more than agricultural crops.
Low Flood Prone Zone
This zone extends between the medium flood prone zone and the flood free zone. It occupies
576.30 square km, which accounts 20.46 per cent out of the total Lower Ajoy river basin. It isestimated that about 219 moujas are located in this zone. It is characterized by less than 40
percentages of frequency of flood occurrences. The geomorphic features are slightly varies
from western part to the eastern part of the basin particularly on the left bank side of the river.
In this zone particularly in the western portion, there are appearances of isolated terraces andhighland flood plain. Some old channels courses are found in the form of abandoned andmorbid channels which are now filled with water, forming swamps and ‘beels’. In this zone theflood induced devastation is quite little.
Flood Free Zone
Next to low flood prone area, there is another zone which is still totally free from flood. Thiszone covers 1087.89 square km which accounts 38.62 per cent out of the total Lower Ajoy riverbasin. About 126 moujas are located in this zone. Beyond this zone in the north, there isMayurakshi river basin and in south, there is Damodar river basin. The flood free zone consistsof micro-geographic features like terraces, slight dissected land, highland features. This zone ishaving marked characteristics of high relief, undulations, rolling and gently level topography
with the preponderance of rills, sheet wash, and gullies which are typical in its landform pattern.
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Table 03: Status of flood affected zones in Lower Ajoy Basin#12Zone

Area
2
(km )
624.46528.00No. of affected
Mouja
144
130

% of thebasin area
22.17
18.75

High/severe flood prone
Medium/moderate floodprone3
Low flood prone
576.30219
20.46
4Flood free
1087.89
12638.62
Source: Block Development Offices of Burdwan and Birbhum districts-2017

Frequency ofoccurrences ( % )>60
40 - 60<40--Figure 04: Flood Intensity Map

Proposed Remedial Measures
The traditional management response to a severe flood was typically an ad hoc reaction to thenatural process. The quick implementation of a project that considered both the problem and its
solution to be self-evident, and that gave no thought to the consequences for upstream anddownstream flood risks. Thus, flood management practices have largely focused on reducing
flooding and reducing the susceptibility to flood damage. Traditional flood management has
employed structural and non-structural interventions, as well as physical and institutional
interventions (Let, 2012). These interventions have occurred before, during and after flooding,and have often overlapped.
Conclusion
It is quite natural that every river has of its own ‘river arena’ in which the river performs its
various natural processes, like bank erosion, meandering, shifting of river channel etc. But inthe name of ‘flood control’ we are consciously or unconsciously destroying the ‘river arena’.
This is the only reason of flood fury in most of the river basins. The Lower Ajoy river basin ischaracterized by very gently sloping floodplain. Most of the time the river flows within its
normal course but during monsoon period because of the hydrological factors like heavy
runoff and geomorphic factors like plain and low lying area, it overflows beyond the normal
channel and thus causing great harm to human activities and properties. It can be mentionedthat extent of flood prone area is more on the right bank of the river than the left bank. However
it can be concluded that the flood damage is a function of the extent of flood affected area,
depth of inundation, duration of submergence, frequency of flooding, standing crop area
affected and its value, value of public and private properties and utilities affected and nonphysical damages . In the study area flood control is being practiced since centuries. As floodcannot be totally controlled and it is not possible to provide protection against all magnitude offlood, we have to adjust with the flood and implementation of proper flood management
programmes become very much necessary. Along with the structural measures likeconstruction of reservoirs, embankments, detention basins, river channel and drainage
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improvement diversions of flood water etc., proper weightage must be given to the nonstructural measures like flood forecasting and warning system, flood plain zoning, disaster
preparedness, relief and rehabilitation, etc. Thus the traditional sectoral planning approach forcomplete flood control should be changed to sustainable flood plain development policy (Haqueet. al. 1993). Preparation of floodplain zoning map (Figure: 4) is an important non-structural
measure to mitigate flood hazard. Degree of vulnerability of flood can be identified bydemarcating the high, medium, and low flood prone zone and proper planning of land-use of
the individual zone can be made accordingly. Government may launch different insurance
packages for the people living in different flood prone zone. Instead of making trifle attempts toprotect floods, we should try to adjust with floods keeping the view that flood is a natural
phenomenon and our relationship with rivers should be reciprocal in nature.
Strategy
Reducing Inundation

Reducing Susceptibility to Damage

Mitigating the Impacts of Flooding

Preserving the Natural Resources of Flood Plains

Options
Dams and reservoirs
Dikes, levees and flood embankments
High flow diversions
Catchment management
Channel improvements
Floodplain regulation
Development and redevelopment policies
Design and location of facilities
Housing and building codes
Flood proofing
Flood forecasting and warning
Information and education
Disaster preparedness
Post-flood recovery
Flood Insurance
Floodplain zoning and regulation

References
1. Bhattacharjee, N.G. (1995) Mitigation of Flood Problem in West Bengal, Directive Initiative,Calcutta.
2. Haque, C. Emdad and Zaman, M.Q. (1993) Human Response to Riverine Hazard inBangladesh A Proposal for Sustainable Flood Plain Development , World Development,
vol-21,
3. Hewitt, K. and Burton, I. (1971) The Hazardness of place: A Regional Ecology of Damaging
Events, University of Jorants, Dept. of Geography, Research publication.
4. Kar, S. (1999) The Flood Situation in West Bengal, Agenda for Action, Directive Initiative,
Calcutta.
5. Kazi, Md. F. Haq and Bhuiyan R.H. (2004) Delineation and Zonation of Flood Prone Area: ACase Study of Tangail District, Bangladesh, Indian Journal of Regional Science, vol.
XXXVI.
6. Let, S. (2012) Spatio-temporal changes of flood characteristics in the Dwarka River Basin,Visva-Bharati University.
7. Magura, L.M. and Wood D.E. (1980) Flood Hazard Identification and Flood Plain
Management on Alluvial Fan, Water Resources Bulletin.
8. Niyogi, M. (1987) Flood Frequency and Management Analysis of Lower Ajoy Basin, Indian
Journal of Landscape system and Ecological Studies, vol. 10 Calcutta.
9. Smith, K. and Tobin, G.A. (1979). Human Adjustment to the Flood Hazard, Longman,London.
10. Ward, R. (1978) Floods, A Geographical Perspective, Macmillan Press Ltd. London.

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