Beach morphodynamic classification in different monsoon seasons at Terengganu beaches, Malaysia

TL;DR: In this article, two main morphodynamic characteristics are used to define a reflective, intermediate and dissipative beaches such as the surf similarity index (ξb) and the dimensionless fall velocity (Ω).

Abstract: Wave climate, topography and sediments are the main forcing factors that influence beach morphodynamics. This paper characterise beach morphodynamic classification along the Terengganu coast during seasonal monsoons (the onset of southwest monsoon in June 2009 as calm conditions and northeast monsoon in December 2009 as storm conditions). Two main morphodynamic characteristics are used to define a reflective, intermediate and dissipative beaches such as the surf similarity index (ξb) and the dimensionless fall velocity (Ω). In order to estimate morphological changes, repetitive beach profiles were acquired and averaged. The morphodynamic characteristics are also supported with wave data collected from the European Centre for Medium-Range Weather Forecasts (ECMWF) database and modeled in Spectral Wave Flexible Mesh of Mike-21 module, in order to investigate the wave propagation along the Terengganu coast. According to the beach morphodynamic classification scheme, the southern Terengganu coast showed a reflective beach state with high wave energy and coarser sand. In contrast the northern part with low wave energy, due to sheltering by many islands, demonstrated an intermediate beach state and finer sediment. However, the trend of sediment mean grain size (D50) reveal finer to coarser during southwest and northeast monsoons respectively. The results of this study are helpful in formulating and preliminary observation on effective coastal zone management plan for monsoon-dominated coast especially in sandy beach.