Cyclone and Storm Surge - Iczmpwb.org

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6.43 project. Such sediment deficit ultimately prevents accretion that is so much necessary for the stability of sea wall or embankments. Mangroves at the foreshore of the creeks cause narrowing of creek orifices that result in increase of the velocity of water and helping the river channel to maintain the depth which helps in navigation. For mass plantation of mangroves, normally Ganwa (Excoecaria a gallocha) short poles are driven to support vegetative palisades on the riverside slope. The quick sprouting Genwa helps to sustain the brushwood palisade initially. Then the seedlings of other naturally regenerated mangrove species take the charge of maintaining the stability of the embankments. Usually, 2 to 3 lines of palisades along the toe line are structured in a staggered fashion. Seeds of Baen (Avicennia spp) are sown in the palisade which sprouts to stabilise the embankment. On the upper part of the slope Hental (Phoenix paludosa) and Genwa seeds are to be sown. In case of very gentle slopes three lines of mangrove plantations may be raised on the foreshore to protect the embankment. Hental being monocot have fibrous roots and will protect the embankments if the seeds are sown on the slope by dibbling. On the leeward side again Phoenix and Coconut should be encouraged to stabilise the embankments. These two species being freshwater monocot again have fibrous roots, which are likely to render stability to the embankments. Application of Geojute and planting of Kaora (Sonneratia apetala) have been extremely successful in Nayachar Island. In fact on the higher slopes of V-shaped channels terracing the slope and planting the mangrove prefers application of Geojute. The steeper long slopes at Nayachar were excavated to form the 1m wide terraces at 2m vertical gaps. The terraces were then covered with tar treated jute having proper perforations to accommodate the plant saplings. The transplanted mangrove saplings and hypocotyles found their way upwards through the artificial perforations made on the treated jute cover. The process helps the plants and hypocotyles from being washed away. In case of gentler slopes, geo jute is less used. But there can be a use if it is felt that the seeds are likely to be washed away by the currents or may be vulnerable to grazing damage. To day the initial geo-jute plantations of Sonneratia apetala of Nayachar has not only made the embankment extremely stable but also has given rise to natural regeneration of other mangroves like Rhizophore, Bruguiera and Excoecaria spp. Raising of mangrove plantation in the char lands that is available in between the embankments and the river face may help to reduce the impact of wave dash at the time of storm surges generated due to cyclones. However, such land is not readily available for all the embankments since most of the embankments have been constructed very close to the river. It is estimated that at most about 10
6.44 percent of the embankments (around 3,00,000 meters) have enough space (at least 100 meters) strip of land between itself and the riverbank which may be planted with mangrove saplings. Thus, Area available for planting mangrove saplings: 3,00,000 x 100 = 30000000 sq. meters. = 3000 hectares. As per the estimate of the Sunderban Development Board, plantation of mangrove saplings costs around Rs. 6500 per hectare. Therefore, Cost of mangrove plantation: 3000 x 6500 = Rs. 1,95,00,000 Apart from this, an additional area that would be available after retirement of the embankments (as given in Section 8.2) may be planted with mangrove saplings, at least on a part of the area, if not on the whole. Thus, Area available for planting mangrove saplings after retiring 55 kms of embankments is 1947 hectares. Therefore, Cost of mangrove plantation: 1947 x 6500 = Rs. 1,26,55,500 Thus the total cost of mangrove plantation comes to about Rs. 3,21,55,500, Say, Rs. 3 Crores. 6.4.1. The process of making mangrove plantation from various seeds The following information regarding the growing of mangroves from seeds is included for completeness. This has been prepared from the note of Assistant Forest Officer, 24-Parganas South Division, Sundarban Development Board, West Bengal. 1. Survey: Survey, Demarcation and also making map of the area of Mangrove plantation are made in February to March and through discussion is made with public arid members of panchyet about the purpose of mangrove plantation in the region so that the public are encouraged for protecting the Mangrove plantation. 2. Soil Work: Soil work starts from April and continues till June. This includes: a) Digging contour trench of size 30cm x 30cm x length, 2 mt. apart and dug out soil is deposited on the upper side of the trench towards the river - embankment. b) Digging pits of size 30cm x 30cm x 30cm, 2mt apart in between contom trench. Alluvial soil is deposited in the pits & Trench during high tides and low-tides in the river & they become fit for sowing seeds. 3. Seeds: Avicennia (alba,marina,officinalis) Bruguiera (Gyrnnorhiza, parviflora) Ceriops (decandra, tagal), Xylocarpus(Granatum, makongensis), Heritiera fomes, Phoenies
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HAZARD ASSESSMENT AND DISASTER MITI
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Project Team Though the outcome of
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Preamble The State of West Bengal,
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1.2 IMD, in its website (http://www
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1.4 5. Proposals for location of cy
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2.2 region is that which struck the
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2.4 Figure 2-2. Track of the 1970 B
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2.6 The most destructive element as
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2.8 the two regions is rather diffe
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2.10 2.4. The eastern coastal zone
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2.12 velocity is first checked. As
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2.14 Strong winds known as cyclones
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2.16 2.4.6. Soil characteristics Th
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2.18 All rivers have in general sou
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2.20 Another interesting feature of
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2.22 formed does not pose so much o
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2.24 2.4.11. Forest composition The
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2.26 Canning (Bidyadhari Outfall in
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2.28 Administrative information Pop
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2.30 Mangrove plantation beyond the
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2.32 A retired embankment of river
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2.34 The beaches are flattened by s
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2.36 of a doiminant tidalbasin of t
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2.38 primary mode is centered on th
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2.40 Aquaculture ponds located betw
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2.42 All the islands are situated w
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2.44 • Transport the water to the
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2.46 The other type of failure may
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2.48 channel floor, some of the riv
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2.50 embankments. Crops and propert
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2.52 2. To reduce the average dista
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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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Page 224 and 225: References Kanjilal (2005) “Sunde
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