Coastal erosion is caused by various factors, such as harbor development along coastal areas and climate change. Erosion has been accelerated recently due to sea level rises, increased occurrence of swells, and higher-power storm waves. Proper understanding of the complex coastal erosion process is vital to prepare measures when they are needed. Monitoring systems have been widely established around a high portion of the Korean coastline, supported by several levels of governments, but valid analysis of the collected data and the following preparation of measures have not been highly effective yet. In this paper, we use a drone to obtain bed material images, and an analysis system to predict the representative grain size of beach sands from the images based on artificial intelligence (AI) analysis. The predicted grain sizes are verified via field samplings. Field bed material samples for the particle size analysis are collected during two seasons, while a drone takes photo images and the exact positions are simultaneously measured at Jangsa beach, Republic of Korea. The learning and testing results of the AI technology are considered satisfactory. Finally, they are used to diagnose the overall stability of Jangsa beach. A beach diagnostic grade is proposed here, which reflects the topography of a beach and the distribution of sediments on the beach. The developed beach diagnostic grade could be used as an indicator of any beach stability on the east coast of the Republic of Korea. When the diagnostic grade changes rapidly at a beach, it is required to undergo thorough investigation to understand the reason and foresee the future of the beach conditions, if we want the beach to function as well as before.

Yoo, H.J.; Kim, H.; Lee, J.L., and Park, J.Y., 2021. Asymmetry between accretional advance and erosional retreat of shoreline position in on-offshore direction. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 6–10. Coconut Creek (Florida), ISSN 0749-0208. Episodic shoreline retreat often slowed recovery in low frequency periods (weeks or months). The asymmetry between wave energy rise and collapse is closely related to the asymmetry of shoreline advancement and retreat, but the latter is more pronounced due to the different profile adjustment processes. Long-term wave time series data and shoreline time series data were analyzed at Won-pyeong beach located on the east coast of Korea. When waves such as storms come into the beach, the shoreline quickly retreated, and in relatively quiet times, the beach slowly recovered to it's original position. Also, the asymmetry of the shoreline position with respect to time is stronger than that of the wave height. A methodology is proposed here, and the envelope rope curve can be used to predict profile and average shoreline changes in the reference section for erosion steps such as storms.The proposed equation was in good agreement for shoreline asymmetry position, and is satisfactory. Empirical formular are slightly different in the relatively calm period, this is an artificial change formed by external pressure conditions such as artificial nourishment. Several variables were used as correction factors. It`s important for future research to propose standardized correction factors and ranges by applying them at various sites.

The edge wave on a uniform-sloped seabed was described by the velocity-potential function by Mok and Yeh in 1999. Edge waves cannot be extended above a certain level from the still-water level, and the upper limit of the run-up of the edge waves for given conditions is found here. In this study, quantitative mass transport by the edge waves of the beach is introduced. The maximum run-up height is decided from the wave’s amplitude at shoreline, and the maximum run-up distance from the shoreline is proportional to the wavelength of the edge waves. The fluid alongshore-mass-transport profile shows that the strongest mass transport rate corresponds to the position offshoreward multiplied by 0.0362 times the wavelength, and its magnitude is 1.23 times the mass-transport rate at the shoreline. The maximum cross-sectional total mass-transport rate is 0.214 times the mass transport at the shoreline, multiplied by the wavelength for the maximum run-up condition. This study suggests that edge waves cannot be increased infinitely and that there is a maximum run-up on the coast.

Vertical diffusivity of suspended sediment with wide size distribution is concerned. The sediment size is expressed by ϕ scale, and the ϕ values are assumed to be normally distributed. The suspended sediment concentration is divided into two groups, 2% of fine side, and 98% of the rest, and single representative settling velocity for median size is used to calculate the vertical diffusion coefficient of the suspended sediment. The computed distribution of the vertical sediment diffusion coefficient is larger than the distribution of the vertical fluid eddy viscosity. A set of equations is proposed for description of the distribution of the vertical suspended sediment diffusion coefficient for engineering purposes. The new equation improves correlation with a set of measured diffusion coefficient values by Barton and Lin.

The Leibniz integral rule for the first derivative with variable limits of integration is expanded for the second and the third order derivatives by using the chain rule here. Water wave propagation equation in the x-z plane containing second derivatives is depth-integrated by using the Leibniz rule. The integrated wave equation is then applied to wave transmission and reflection over an inclined step, and the computed reflection coefficients agree well with those from existing theories such as full linear equation, mild slope equation, and modified mild slope equation.

Physical properties are important for the selection of concrete armour units (CAUs) for a specific site. Geometric properties are closely linked to physical properties. Here, new concepts in geometric properties that may be related to structural stability are proposed. Void ratio, overall slenderness, member slenderness, mass distribution with the distance from the gravity centre, and moment of inertia with respect to the gravity centre or pivot line are measurable, and we focus on geometric properties of several CAU structures. All CAUs have the same mass of 32 t. Hexacone has exceptionally high mass density near the leg tips, which helps to increase the moment of inertia. The moment of inertia of a Hexacone with respect to the horizontal pivot axis at the bottom line of the units is also the largest of the four tested. Hexacone is the most resistant to external torques when standing on its own. There is a possibility that a layer of Hexacones could be the most stable of the four types of units, especially when Hexacones are randomly placed or regularly placed with mixed vertical and horizontal columns. Future development of CAUs will aim to achieve a larger moment of inertia, raising the interlocking level and strengthening member endurance at the same time.