Cyclone and Storm Surge - Iczmpwb.org

2.19
consecutive HWL or LWL is termed the “Period of Tidal Circle” which is on averages is 42 hours 24
minutes, The tidal cycles are represented graphically by tidal curve.
With the advent of flow tide, the velocity of current which is in the inland direction starts increasing,
reaches a maximum at about the middle of the flow tide and beginning to decrease thereafter being
zero at the HWL which is known as “High Water Slack”. Thereupon, the ebb tide commences and the
current velocity which is in the seaward direction starts increasing once again and after attaining a
maximum value begins to diminish gradually becoming zero at LWL which is known as the “Low
water Slack”. Two tides called “Semi-diurnal tides” occur in course of every lunar day. The tidal
ranges of the two semi-diurnal tides are also found to differ from each other. Table 2-5 gives the list
of highest High Water Level (HWL) recorded at Sagar Islands.
Table 2-5. Year-wise High Water Levels (HWL) at Sagar Island for the period from 1934 to 1976.
All levels are in Meters and refer to G.T.S. Datum.
Year H.W.L. YEAR H.W.L.
1934 3.47 1956 4.33
1935 3.72 1957 3.92
1936 3.77 1958 3.92
1937 3.47 1959 3.74
1938 3.51 1960 3.64
1939 3.72 1961 3.72
1940 3.44 1962 4.11
1941 3.41 1963 3.64
1942 5.61* 1964 3.79
1943 3.57 1965 3.62
1944 3.59 1966 3.59
1945 3.62 1967 3.45
1946 3.36 1968 3.05
1947 3.41 1969 3.14
1948 3.51 1970 3.45
1949 3.72 1971 3.36
1950 3.77 1972 3.63
1951 3.57 1373 3.13
1952 3.92 1274 3.13
1953 3.95 1975 3.25
1954 3.74 1976 3.61**
1955 3.69
* The H.H.W.L. of 1942 could not be recorded on the gauge but was estimated from flood marks.
** The H.H.W.L. of 1976 during the severe cyclone of September 1976 could not be recorded on the
gauge and the stated value excludes the H.H.W.L. of September.