Assessment of potential beach erosion risk and impact of coastal zone development: a case study on Bongpo–Cheonjin Beach

In many parts, coastal erosion is severe due to human-induced coastal zone development and storm impacts, in addition to climate change. In this study, the beach erosion risk was defined, followed by a quantitative assessment of potential beach erosion risk based on three components associated with the watershed, coastal zone development, and episodic storms. On an embayed beach, the background erosion due to development in the watershed affects sediment supply from rivers to the beach, while alongshore redistribution of sediment transport caused by construction of a harbor induces shoreline reshaping, for which the parabolic-type equilibrium bay shape model is adopted. To evaluate beach erosion during storms, the return period (frequency) of a storm occurrence was evaluated from long-term beach survey data conducted four times per year. Beach erosion risk was defined, and assessment was carried out for each component, from which the results were combined to construct a combined potential erosion risk curve to be used in the environmental impact assessment. Finally, the proposed method was applied to Bongpo–Cheonjin Beach in Gangwon-do, South Korea, with the support of a series of aerial photographs taken from 1972 to 2017 and beach survey data obtained from the period commencing in 2010. The satisfactory outcomes derived from this study are expected to benefit eroding beaches elsewhere.

FORMATION OF CUSPATE FORELAND BEHIND AN ISLAND UNDER WAVES INCIDENT FROM TWO OPPOSING DIRECTIONS

Long-term shoreline changes of a cuspate foreland behind Okinoshima Island located in Tateyama Bay were investigated, and a beach survey was carried out using an RTK-GPS on May 2, 2018. Then, numerical simulation of the formation and deformation of a cuspate foreland between 1941 and 2012 was carried out using the BG model (a model for predicting 3-D beach changes based on Bagnold's concept). It was found that sand, which was deposited on the shallow sea associated with the increase in ground level during the Kanto Great Earthquake that occurred in 1923, accumulated to form a cuspate foreland.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/4SDfN9xp9hE

Numerical Modeling of Beach Morphological Change: A Case Study of Kaanapali Beach, Maui, Hawaii

This case study reports results from field observations and numerical simulations of waves and morphological changes along a portion of Kaanapali Beach on West Maui, Hawaii, which is protected by a hard coral reef and experiences shoreline changes from season to season. The SWAN spectral wave model shows reasonable agreement with ADCP observations of wave-heights for the winter months. Simulated beach profile change over one-month time frame was able to reasonably capture the trend of beach face migration (accretion or erosion); the modeled shoreline also shows satisfactory agreement with beach survey data. This case study suggests that Delft3D is able to capture key features of sediment transport along a narrow beach protected by a fringing reef.

Seaweed Species Composition, Abundance and Diversity in Drini and Kondang Merak Beach, Java

The different characteristics of subtrate might give influence on species composition, abundance and diversity of seaweed. Kondang Merak and Drini Beach are two beaches in Java Island which have different subtrate characteristic. The aim of this study is to investigate seaweed composition, abundance and diversity in Drini Beach and Kondang Merak Beach. Survey method and quadrant transect sampling technique were applied in this study. The result showed that 13 species of seaweed were found at Drini Beach and 18 species of seaweed were found in Kondang Merak Beach. The composition of the seaweed at Drini Beach and Kondang Merak Beach were dominated by Rhodophyta (69% and 56%). Enteromorpha flexuosa was the most abundant seaweed at Drini Beach, while at Kondang Merak Beach was dominated by Chaetomorpha crassa. The seaweed diversity index of Kondang Merak Beach (2,08) was higher than Drini Beach (1,27). Physical and chemical parameters were categorized as the optimal for the growth of the seaweed.

QUANTIFICATION OF SHORELINE RHYTHMICITY

The study of beach morphology, for example, its changes with wave and tide conditions, is facilitated by the development of simple numerical values which characterize the morphology. Multivariate (EOF) analysis of topographic contour data is a means for determining important morphologic components which vary independently. If these components correspond to familiar shoreline features the researcher considers important, then the development of each component can be quantified by its significance, or weighting, in each sample. Alternatively, the components may be complicated and not useful in quantifying beach morphology. A study of these morphologic components, however, can provide insights into the dynamics of the beach system. If multivariate analysis produces complicated components, an alternative approach, of subjectively identifying shoreline characteristics of interest, can be taken. The characteristics may be the same as those frequently used in past studies, such as beach slope or sand volume. It is likely, though, that EOF analysis of topographic data will suggest more sophisticated characteristics which should be used. Some of these, for example, mean shoreline position or amplitude of a rhythmic shoreline, may be easily quantified, whereas, others such as longshore position of rhythmic features or cusp width relative to embayment width, may be more difficult to quantify. Both of these analysis approaches were applied to beach survey data obtained over a period of ten months (including the El Nifto winter of 1982/83) on Siletz Spit, Oregon. The shoreline was rhythmic with an 800-850 m wavelength throughout the duration of the study. Rhythmic topography has been associated with significant past beach and dune erosion at this site. Hence, it is of interest to describe the beach morphology quantitatively, and relate three dimensional beach changes to wave and tide conditions.