Cyclone and Storm Surge - Iczmpwb.org

2.12
velocity is first checked. As the spilling proceeds away from the river banks, the silt content of the
spilled water and consequently the depth of silt deposited is less and less. The area lying midway
between two adjacent flood carriers is lower than the two banks. But the tides by their constant
movement distribute the unconsolidated silt charge uniformly over the entire basin and raise the
inside valley almost to same level as that the bank. Thus the general topography is very flat.
The North Eastern area (Haroa-Minakhan-Sandeshkhali) area being close to Calcutta had been
prematurely reclaimed much earlier than the south West area (Kakdwip – Sagar – Pathar-protima
area) by marginal embankment and hence has been deprived of natural raising by flood and tide.
The average ground level in above mentioned North-eastern and South-Western area is around 1.2m
and 2.0m above Mean Sea Level respectively against mean high water level of 2.75m (H.F.L at sea
wall zone is approximately 3.5m).
2.4.3. Rainfall, Temperature and Humidity
The total average rainfall in the area is 1625 mm. In some abnormal years this exceeds 2000mm and
in some subnormal years it is as low as 1300 mm. South Westerly Monsoon generally breaks up on
8th June and recedes on 20th October. Approximately 73.2 percent of the annual rainfall occurs in 53
days within 124 days monsoon season. Though the maximum daily rainfall during the monsoon
seldom exceeds 300 mm a rainfall of as high as 800 mm in a period of four consecutive days was
recorded in September, 1900. The pattern of rainfall in the district of 24-Parganas (North and South)
where Sundarban is situated is given in Table 2-2 below: -
Table 2-2. Average monthly precipitation in Sundarban area of West Bengal
Month
Average monthly rainf Monthly rainfall
(mm)
percentage
average Rainfall
Average Rainy days
month
January 5.59 0.3 0.49
February 19.05 1.2 0.45
March 34.80 2.1 1.78
April 63.00 3.9 1.73