Short-term observations of beach Morphodynamics during seasonal monsoons: two examples from Kuala Terengganu coast (Malaysia)

摘要

This paper describes the morphodynamic changes that took place along Kuala Terengganu coastline over daily periods during seasonal monsoons (onset of Northeast Monsoon in October 2014 and during Southwest Monsoon in May 2015). Cross-shore beach profiles had been determined and foreshore sediments were sampled from two selected beaches; north of Kuala Terengganu at Pengkalan Maras (PM) and another to the south at Kuala Ibai (KI). Based on the beach classification scheme, PM appeared to be a spilling breaker type beach (xi(b)) with an Intermediate state (omega), whereas KI belonged to the plunging breaker type (xi(b)) with Intermediate-Dissipative state (omega). The beaches were dominated by coarse and fine sands at PM and KI, respectively. The wave hydrodynamics on the southern beach (KI) was characterised by higher H-b values, when compared to that in the north (PM). This study investigated the impact of morphodynamic changes during seasonal monsoons, regardless of the presence of coastal defence structures. Without any coastal defence structure (revetment), the PM beach exhibited attainment of equilibrium state, when compared to the KI beach. Therefore, coastal structures, such as revetments, directly modified the morphodynamics at KI beach. The PM beach displayed the tendency for occurrence of erosion during the Northeast Monsoon, while exhibited accretion during the Southwest Monsoon. This scenario differed from that noted at the KI beach, which signified erosion during both seasonal monsoons. The study outcomes may assist in formulating an effective coastal zone management plan for monsoon-dominated coasts, particularly sandy beaches.