Comparison of wave hindcasting of linear wave theory and SWAN modelling at Batu Pahat River Estuary

Abstract

Estuary, like other coastal systems, is ephemeral; undergo continuous geological evolution and very active coastal region. Batu Pahat river estuary is chosen, togather information on wave conditions nearshore. Estuary of Sungai Batu Pahat is exposed to high energy wave conditions from the Strait of Melacca. Offshore wave data is analyzed for design wave nearshore and wave height is the most important parameters observed. Wave height transformation nearshore was predicted from linear wave theory and SWAN nearshore wave modeling. Regular Waves theory of small-amplitude or linear wave theory developed by Airy (1845) and numerical wave models SWAN (acronym for Simulation Waves Nearshore) developed by the Delft Institute of Technology in the Netherlands using spectral method of Irregular Waves theory are adopted for wave hindcasting. Linear wave theoiy is often used due to its simplicity and easily applied. SWAN (acronym for Simulation Waves Nearshore) is a phase averaging wave model designed to obtain realistic estimates of wave parameters in coastal areas, lakes and estuaries from given wind, bottom, and current conditions. SWAN is one of the most widely applied spectral wave models at present in coastal engineering studies and is freely available for both research and consultancy studies. Offshore wave data are analyzed for various wave heights of average one third of maximum wave heights (H1/3 ) and extreme value of Gumbel and Weibull statistical distribution with three wave scenarios of Annual, Northeast Monsoon and Southwest Monsoon. The differences in the analysis are inspected. Both mefliods agreed well with the theoiy where wave heights decreases when it reach estuary, but SWAN gives smaller results of wave height at shallower location. Waves are irregular in nature; linear wave theory is based on Regular Waves theory while SWAN based on spectral methods and deal with complex bathymetry nearshore from Irregular Waves theory. Thus, SWAN gives more dependable answer compared to linear wave theory for design purposes.