Cyclone and Storm Surge - Iczmpwb.org

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through this trough into the deeper part of the Bay of Bengal. The shallower part of southern continental
shelf off the coast of the Sunderbans, Patuakhali and Noakhali is covered by silt and clay, and extensive
muddy tidal flats are developed along the shoreline. The ‘Sunda Trench’ runs parallel along the
Westside of the Andaman-Nicobar islands which extends northward upto 10°N into the Bay and joins the
eastern limit of the Himalayan range. The ‘Ninety East ridge’ runs in a north-south direction
approximately along the 90°E longitude which lie immediately outboard the Sunda trench between the
Bengal fan and the Nicobar fan.
4.6.2. Hydrological and Oceanographic characteristics
The hydrological conditions in the Bay of Bengal are determined by the monsoonal wind system and
also by hydrological characteristics of the open part of Indian Ocean. Discharge of fresh water from
rivers largely influences the coastal northern part of the Bay. Physical oceanographic parameters
pertaining to temperature, salinity and density of water in the southern part of the Bay of Bengal is similar
to the open ocean. In the coastal region of the Bay and in north-eastern part of the Andaman Sea where
significant influence of river water is present, the temperature and salinity are found different from the
open part of the Bay.
4.6.3.Temperature
The mean annual temperature of the surface water is about 28°C. The maximum temperature is
observed in May (approx. 30°C) and minimum of 25°C in January-February month. The variation in
temperature is about 2°C in the southern end and about 5°C in the northward limits of the Bay of
Bengal.
4.6.4. Salinity
In the open part of the Bay the salinity varies from 32‰ to 34.5‰, and in coastal region the variation is
from 10‰ to 25‰. At the river mouths, the surface salinity decreases to 5‰ or even less. The coastal
water is significantly diluted throughout the year, although the river water is greatly reduced during
winter. Along the Ganges-Brahmaputra deltaic region there is decrease in salinity about 1‰ during
summer which increases to 15‰ - 20‰ in winter. Salinity variations increase from the coast towards the
open part of the Bay. On a vertical scale, the influence of fresh water discharge is experienced up to
depths of 200 – 300 meters