Cyclone and Storm Surge - Iczmpwb.org

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2.6 The most destructive element associated with an intense cyclone is storm surge. Past history indicates that loss of life is significant when surge magnitude is 3 metres or more and catastrophic when 5 metres and above. As mentioned in the previous section, cyclones have resulted in rather high damage, especially to the coastal areas. A list of the available data on losses due to cyclones in West Bengal has been provided by the Department of Relief, Government of West Bengal, and is attached as Annex – I. The cause of losses in rural and urban areas due to tropical cyclones is presented in the following sections. There are secondary hazards too. Some of these are: • Spread of epidemics – The wet environment in the aftermath of a tropical cyclone, combined with the destruction of sanitation facilities and a warm tropical climate, can induce epidemics of disease which claim lives long after the storm passes. Infections of cuts and bruises can be greatly amplified by wading in sewage polluted water. Large areas of standing water caused by flooding also contribute to mosquito-borne illnesses. Drinking water also gets polluted resulting in diseases like gastro-enteritis. • Power cuts – Tropical cyclones often knock out power to an area prohibiting vital communication and hampering rescue efforts. • Damages to communication links – Tropical cyclones often destroy key bridges, overpasses, and roads, complicating efforts to transport food, clean water, and medicine to the areas that need it. 2.3. Areas under the threat of damage from tropical cyclones The regions of West Bengal that may suffer the possible impact of tropical cyclones come belong to the following districts: 1. East Midnapore 2. 24 Parganas-South 3. 24 Parganas-North 4. Howrah 5. Hooghly Of course, the areas prone to devastation under each district vary according to the location. For example, the Blocks along the coastal region of West Bengal (Figure 2-5), being low lying, are
2.7 affected most. Here, the the landfall of the cyclone occurs and the dangers of inundation by storm surges as well as destruction of low-cost houses due to strong winds reign supreme. Also, the geographical location of this region is such that it has high chances of cyclone landfall. Though the Blocks of the East Midnapore are as close to the Bay of Bengal as those of the 24 Parganas-South, the alignment of the coastline here and the geographical location makes the probability of landfall rare. Of course, the rise in ocean level caused by a storm track grazing close by, may nevertheless cause inundation. Some portions of the Districts of 24 Parganas-North and Howrah though not coming very close to ocean, still suffer from the impending threat of river level rise due to a rise of the ocean level caused by a cyclone induced storm surge. The District of Hooghly is much inland, but as the event of 1737 had proved, a probable track of a tropical cyclone being incidentally aligned with the axis of the river Hooghly may cause a violent upsurge, especially since the water rushing up from the estuary would have to move up through the river where the width is relatively narrow. In most of the Blocks in the coastal West Bengal, and especially in the District of 24 Parganas-South, the land is rather low lying and the habitation areas along with the neighbouring agricultural fields are protected by embankments. The adjoining region to the east is the world famous mangrove forest of the Gangetic delta – The Sundarbans. In order to appreciate the magnitude of the cyclonic hazard and the means adopted to mitigate consequential damages, it is necessary to review the geographical and historical situations in these areas before and after the establishment of substantial habitation from its pristine characteristics of a marshy and swampy land. The State capital Kolkata also falls in the cyclone prone region, as stated before. However, the urban characteristics of Kolkata and its surroundings distinguish the damages here from that of the typical rural countryside of the Districts. The types of problems facing Kolkata and its neighbouring urban regions have been discussed separately in Chapter 3. In the present chapter, discussion is restricted to the region other than Kolkata. 2.3.1. Geographical extent The coastal region of the State of West Bengal is prone to the effects of cyclonic storms. Broadly, the West Bengal coast can be divided into two parts, on either side of the mouth of the river Hooghly. This may be seen from Figure 5 which illustrates the Development Blocks of the districts of Medinipur east and 24 Parganas South that hug the Bay of Bengal. Towards the east are the Gangetic deltaic tracts which are mostly shoals, sand spits, mud flats and tidal swamps and flats and towards the east are the Medinipur coastal plains which comprise of mostly sandy beaches. The geophysical nature of
Page 2 and 3: HAZARD ASSESSMENT AND DISASTER MITI
Page 4 and 5: Project Team Though the outcome of
Page 6 and 7: Preamble The State of West Bengal,
Page 8 and 9: 1.2 IMD, in its website (http://www
Page 10 and 11: 1.4 5. Proposals for location of cy
Page 12 and 13: 2.2 region is that which struck the
Page 14 and 15: 2.4 Figure 2-2. Track of the 1970 B
Page 18 and 19: 2.8 the two regions is rather diffe
Page 20 and 21: 2.10 2.4. The eastern coastal zone
Page 22 and 23: 2.12 velocity is first checked. As
Page 24 and 25: 2.14 Strong winds known as cyclones
Page 26 and 27: 2.16 2.4.6. Soil characteristics Th
Page 28 and 29: 2.18 All rivers have in general sou
Page 30 and 31: 2.20 Another interesting feature of
Page 32 and 33: 2.22 formed does not pose so much o
Page 34 and 35: 2.24 2.4.11. Forest composition The
Page 36 and 37: 2.26 Canning (Bidyadhari Outfall in
Page 38 and 39: 2.28 Administrative information Pop
Page 40 and 41: 2.30 Mangrove plantation beyond the
Page 42 and 43: 2.32 A retired embankment of river
Page 44 and 45: 2.34 The beaches are flattened by s
Page 46 and 47: 2.36 of a doiminant tidalbasin of t
Page 48 and 49: 2.38 primary mode is centered on th
Page 50 and 51: 2.40 Aquaculture ponds located betw
Page 52 and 53: 2.42 All the islands are situated w
Page 54 and 55: 2.44 • Transport the water to the
Page 56 and 57: 2.46 The other type of failure may
Page 58 and 59: 2.48 channel floor, some of the riv
Page 60 and 61: 2.50 embankments. Crops and propert
Page 62 and 63: 2.52 2. To reduce the average dista
Page 64 and 65: 3.2 a storm surge caused by a tropi
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3.4 these merchants may have been t
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3.6 Figure 3-1. Map of India during
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3.8 larger volume of sewage and dra
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3.10 receive, at least during the r
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3.12 3.9. Drainage scheme of Dr. B.
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3.14 3.10. CMPO and KMDA (originall
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3.16 Flows are diverted to the loca
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3.18 the Bhangar region through the
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3.20 the ocean level as a result of
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3.22 Table 3-6. Major pumping stati
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3.24 Table 3-9. Drainage basin area
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3.26 will lead to significant impro
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3.28 locks, one at Chitpur and anot
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3.30 Respectively. The discharge of
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3.32 Figure 3-6. The downstream of
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3.34 Figure 3-10 shows the tail end
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3.36
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3.38
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4.2 In US, there is a steady decrea
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4.4 This shows that Orissa (with 10
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4.6 30 25 20 15 10 Severe Cyclone C
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4.8 Table 3: Return periods of cycl
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4.10 Table 5: The number and return
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4.12 work station (the Automated Tr
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4.14 through this trough into the d
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4.16 Mean Low water 1.51 1.39 1.34
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4.18 τx,τy : x and y components o
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4.20 formulation. However, the rete
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4.22 ∂u ~ ∂ ~ ~ ∂ ~ ~ ∂ζ 1
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4.24 Δ p p(r) = p( ∞) − [1+ (r
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4.26 maximum surge for this event w
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4.28 U-Component of Velocity (Surfa
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4.30 ## ## ## #### ### ## ########
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4.32 V-component of Velocity (Surfa
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4.34 U-component of Velocity (Surfa
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## ################################
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4.38 V-Component of velocity (Surfa
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5.2 particular human settlement to
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5.4 The Composite Vulnerability Ind
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5.6 (2004 prices) prevalent in dist
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5.8 Moyna 0.6280 0.1592 0.542286 0.
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5.10 5.4.2. Social infrastructure H
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5.12 Budge-Budge(Part-II) 0.0000 0.
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5.14 secondary and tertiary activit
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5.16 F i Fˆ i ⎛ Total no. of =
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5.18 Table 5-4: Composite Index of
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5.20 M ′ = H M ′′ = I . S whe
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Chapter Six Mitigation Strategies a
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6.3 Beside these differences in lev
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6.5 • to reduce the destructive f
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6.7 6.2.4. Methods of Construction
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6.9 is attached to the structure. T
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6.11 (b) Medium rivers to armour th
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6.13 Likewise, in all the embankmen
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6.15 Figure 6 -5 Figure 6 -6 Figure
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6.17 Benefit cost ratio Area benefi
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6.19 Location and cost of proposed
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6.21 Swaraupnagar Swaraupnagar 100
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6.23 Gobadia Kakdwip Dk Kasiabad &
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6.25 Location and cost of proposed
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6.27 " Jagaddal " 800 6400000 " Jag
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6.29
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6.31
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6.33
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6.35 Figure 6 -11 Figure 6 -12
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6.37 Figure 6 -15 Figure 6 -16
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6.39 Figure 6 -19 6.2.7. Recommenda
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6.41 4. Rajraj Swarup & Ramnagar Ab
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6.43 project. Such sediment deficit
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6.45 paludosa, Rhizophora apiculata
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6.47 15. Ceriops tagal 0.22 0.40 0.
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6.49 shelterbelt (average 100 m wid
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6.51 (assuming land acquisition cos
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6.53 location are missing reducing
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7.2 resulted in large scale waterlo
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7.4 5. No adverse effect in drainin
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7.6 15 LT Panel L.S. 2,200,000 16 I
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7.8 Bagjola, Kestopur and SWF chann
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Executive Cost Summary of Recommend
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References Kanjilal (2005) “Sunde
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“……………….Designingadis
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