A schematised numerical model of beach cusp evolution in My Khe beach, Da Nang, Vietnam

The formation, maintenance, and development of beach cusps are among the most challenging morphological and physical processes in hydrodynamics and coastal morphology. Many unanswered questions remain despite extensive research, data collection, measurement, and modeling of these coastlines. A study of the My Khe coastal region revealed that beach cusps, ranging from 150 to 200 meters, mainly form during the transitional period from the southwest monsoon to the northeast monsoon. To gain further insight, a two-dimensional numerical experiment model for beach cusp formation was constructed using the elevation and hydrodynamic data of the area in the Xbeach model. Simulation results show the crescent-shaped cusps' initial formation and subsequent development trends from an initially flat state during the transitional period. The horn and bay features of the beach cusps first formed in the offshore area. The size and spacing of these cusps match the observed scales in reality. The initial period, when the water level first rises, is when the formation and development of the cusps seem most pronounced. As the water level increases, the cusps shift gradually towards the shore. This process is hypothesized to repeat when the sea level drops in the next cycle. As a result, a series of cusps gradually moves towards the shore.