Cyclone and monsoonal wave characteristics of northwestern Bay of Bengal: long-term observations and modeling

摘要

Long-term wave data play a crucial role in arriving the wave criteria for ports and harbors and shore protection structures. Seasonal and annual wave characteristics are studied based on wave data collected for the year 1994, 2008-2009 and 2013-2014 off Gopalpur, northwestern Bay of Bengal (BoB). The tropical cyclones ensued in BoB hit the coast frequently causing severe erosion due to extreme waves. The sea and swell waves are separated by wave steepness method, and the significant wave height (H (s)), zero-crossing period and mean wave direction are examined. The results indicate a distinct shift in sea direction by 90A degrees during mid-November to mid-February compared with rest of the year. Throughout the year, predominant swell direction is 160A degrees. In an annual cycle, the contribution of swells in wave height is slightly higher than that of the seas. Annual occurrences of single-, double- and multi-peaked spectra are 22, 40 and 38 %, respectively. The waves are predominant southerly during the southwest monsoon (June, July, August and September) and south-southeasterly for rest of the year, and the variations of wave parameters for three different years are trivial. The spectral wave model MIKE 21 is used to simulate wave characteristics using reanalyzed NCEP wind data for the period June 2008 to May 2009 which exhibits good agreement with a correlation coefficient (R) of 0.86 for H (s). The design significant wave height of 7.1 m and 7.8 m is calculated for 10 and 100 years of return periods, respectively, by Weibull distribution.