Cyclone and Storm Surge - Iczmpwb.org

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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