Environmental Engineering Reference
In-Depth Information
Table 1.6
Cyclonic storms which crossed the Sundarban
coast (1907
-
1997)
Year
during this time rises above 100 km/h and is
usually accompanied by gigantic tidal waves
causing much loss of lives, damage to properties,
forests and habitats of animals and plants thriv-
ing in this area. Sea waves in this region rarely
become destructive except during cyclonic
storms. When the cyclonic incidences coincide
with the spring tides, wave height sometimes
exceeds over 5 m above the mean tide level.
Ripple waves appear in the months of Octo-
ber
Duration of storm
Maximum wind
speed (km/h)
1907
17
19 June
95
-
1907
24 and 25 June
95
1909
17 and 18 October
126
1912
5 and 6 September
81
1913
23
25 July
126
-
1916
21 and 22 September
68
1916
9 and 10 November
81
December, when wind-generated wave
height varies approximately from 0.20 to 0.35 m.
In the months of April
-
1917
3 May
126
1917
30 and 31 October
45
August, when the normal
wind speed ranges between 15 and 40 km/h,
large wavelets are formed in the shelf region,
which starts breaking as they approach towards
the coastal margin. In this condition, the wave
height rises up to 2 m that causes maximum
scouring action to adjoining of landmasses.)
-
1919
24 and 25 September
126
1920
21
-
23 July
81
1921
26 and 27 July
68
1925
27 and 28 June
81
1927
28 and 29 July
126
1928
18
20 July
126
-
1929
15
-
17 July
56
1932
23 and 24 May
126
1.2.2 Tides
1933
20 and 21 September
56
1935
8 and 9 July
126
Tides may be de
ned as the periodic rise and fall
of the sea level and occur as a result of the
gravitational pull of the sun and the moon. The
magnitude of this attraction varies directly as the
product of the mass of attracting bodies and
inversely as the square of the distance between
them. Though the sun
1936
26
28 May
113
-
1937
28 and 29 September
126
1940
30 June and 1 July
-
1940
7 and 8 July
-
1940
2 and 3 August
-
1940
21 and 22 October
-
10
6
times
bigger than that of moon, the ratio of the square
of the distance from the sun to the earth and that
from the moon to the earth is roughly 58
'
s mass is 26
×
1941
9 and 10 July
81
1941
8 and 9 August
-
1942
9 and 10 July
81
10
6
.It
×
1945
1 and 2 July
81
is because of this, the moon
s pull is about 2.2
times stronger than that of the sun. Depending on
the position of the heavenly bodies, the tides may
be of two types (Fig.
1.21
).
Spring tides: These tides are witnessed dur-
ing the new moon condition, when the sun, the
moon and the earth are in a line (linear align-
ment) leading to maximum tidal range.
Neap tides: These tides occur when the sun
and the moon are at right angles to each other
during the
'
1946
4 and 5 October
81
1950
10 and 11 June
95
87
1952
4 July
-
1956
30 May to 2 June
-
29 May
74
76
1962 20 and 21 September
93
80
1965 10 and 11 May 74
1997 20 and 21 August 120
(
-
) means not recorded; Source Mitra (
2013
)
1960
27
-
rst or third quarter of the lunar cycle.
In Indian coasts, the tides are
semi-diurnal
in
