The current study presents the effects of seasonal variations in the depth-of-closure (Dc) on shoreline evolution using a numerical, one-line shoreline model. Beach erosion of the southern beach of the Nha Trang Coast, which is located in south central of Vietnam, is selected as the study area. This study area is immensely influenced by the tropical monsoon climate that has a clear pattern of large waves in the northeast monsoon season and calm waves in the non-monsoon season. The analysis of the long-term measured shoreline variations from a video-camera system has found a strong correlation of these variations to the monsoon-dominated wave characteristics in the Nha Trang Bay. Therefore, a new approach for determining the depth-of-closure with consideration of the seasonal wave climate changes is purposed in the current study. By implementing this new approach into a numerical, one-line shoreline model, it is found that the seasonal variations of Dc appear to better describe the periodical shoreline evolution due to the monsoon-dominated wave characteristics for the Nha Trang Coast. Such important findings are considered to commonly apply for monsoon-dominated coastal regions in general. These findings are useful information not only for scientific readers but also for the coastal authorities and managers in order to make better countermeasure plans against this kind of erosion mechanism in the future.
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