Abstract:
Tide is the rhythmic rising and falling of sea levels caused by gravitational forces
from the moon and the sun occurring regularly under various astronomical
settings. Tidal data
are standard elevation levels defined by a certain phase of
the tide derived from
long-term observations. This study aimed to investigate
the variation of the long-term mean sea level (MSL) and chart datum (CD) at
Colombo, Sri Lanka over a 37-year period from 1981. Here, it is utilized both the
tide gauge data and satellite altimetry data obtained from the Sri Lanka Port
Authority and AVISO database respectively. Then, TOTIS tidal software was
used to analyze the hourly tidal data and S-Tide MATLAB package was used to
analyze altimetry data. However
, it did not identify a clear pattern in the
relationship between MSL and CD variation in Colombo from 1981 to 2017.
Nevertheless
, when considering
the value of annual observed MSL, the
lowest was recorded as 0.46 m in 1986 and the highest value was 0.63 m in 2016
with respect to the published MSL of Colombo tide gauge. Further, there was a
slight increase in the values of MSL and CD in long rum analysis. The value
adopted as the CD by the national hydrographic office is the Lowest
Astronomical Tide (LAT) and the standard value at Colombo is 0.47m below the
MSL. Nonetheless, the LAT value derived from the hourly tidal data for Colombo
is lower than the published value and the LAT value derived from satellite
altimetry data is slightly higher than that value. However, the exact details of the
derivation of the original CD could not be found and further details on that to be
explored from the respective authorities. Further, the missing data existing in the
tide record may also affect
the final results as well as the altimetry data may
not be applicable
interval.
