Abstract
Abstract. 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.
Highlights
In recent years, erosion of sandy beaches has intensified in many countries due to the complex effects of climate change (i.e. 25 global sea-level rise), reduced coastal sediment budgets, and deterioration of coastal environments
The change in the amount of sand is due to the law of conservation of matter, and the littoral drift characteristic of sand is interpreted as a change in the main crest line at the breaking point, and the response characteristics of shoreline position is interpreted as change in the erodibility and recovery 15 characteristics of beach sand. This quantitative method was applied to Bongpo-Cheonjin Beach of erosion grade D in Gangwon-do, Korea to identify the cause of erosion and evaluate the detailed applicability of this method. It was interpreted using a series of aerial photographs taken from 1972 to 2017 and survey data obtained from the erosion rating project started in 2010
The former occurs when there is an imbalance in the sand budget and the amount of incoming sand becomes smaller than the 40 amount of outflow, while the latter is caused by (1) a decrease in the beach width in the region where the equilibrium shoreline retreats due to wave field changes which generate transport of longshore sediment, and (2) a decrease in the beach width in the section where the equilibrium shoreline retreats due to a change in the wave field, or a temporary retreat of the shoreline due to the influence of sand suspension and offshore transport under the storm wave incidence
Summary
Erosion of sandy beaches has intensified in many countries due to the complex effects of climate change (i.e. 25 global sea-level rise), reduced coastal sediment budgets (e.g. due to changes in watershed environment), and deterioration of coastal environments (e.g. caused by artificial structures and human interference). It is assumed that the longshore sediment transport alters the feature of shoreline, but does not change the quantity of sand in the littoral cell This results in deposition in some areas, but at the same time, erosion in some areas. 60 observations and studies have been conducted to estimate the correlation of longshore sediment transport rate to wave and sand environments (Komar and Inman, 1970; CERC, 1984; Kamphius, 2002; Bayram et al, 2007) It is still mostly dependent on the empirical models in estimating the equilibrium shoreline in the vicinity of harbor breakwaters or coastal structures. It is expected that this quantitative method for identifying the risk to beach erosion could be applied to similar coastal environments on the eastern coast of the Korean Peninsula, as well as elsewhere in the 100 developing and developed countries
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