Directional characteristics of waves in the nearshore waters of the eastern Arabian Sea

Directional characteristics of the waves at a coastal location in the eastern Arabian Sea are studied based on the data measured from April 2008 to December 2020. The multiple-scale variations; daily, monthly, intraseasonal, seasonal, and interannual; in the directional characteristics are examined. The variations in mean wave direction (D-p), and peak wave period (T-p) during monsoon, pre- and post-monsoon are inspected. The study also investigates the influence of cyclones on D-p. Annually 97.9 % of the time, the waves measured at 9 m water depth fall in intermediate water depth. Waves are predominantly swells, and short-period waves are more during January-March. The waves during monsoon are mainly from 240 degrees to 270 degrees. During the pre-monsoon, a frequent occurrence of multiple waves originating from the northwest, characterised by a relatively short-period (T-p<8 s) is noted. The T-p and D-p collectively exhibit a distinctive tri-modal sea-swell configuration. Waves of low frequency, similar to 0.05 Hz, with a direction spanning 180 degrees-210 degrees, are more prominent during the post-monsoon. Since D-p varied significantly (similar to 175 degrees) in a day, it is vital to take the observations at hourly intervals while researching coastal dynamics. The directional spread of waves at primary peak (27 degrees) is much less than that at the secondary (37 degrees) peak.