An analytical model for beach erosion downdrift of groins: case study of Jeongdongjin Beach, Korea

Changbin Lim,Jung Lyul Lee,Soonmi Hwang

doi:10.5194/esurf-10-151-2022

Changbin Lim, Jung Lyul Lee + Show 1 more

Open Access

https://doi.org/10.5194/esurf-10-151-2022

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Journal: Earth Surface Dynamics	Publication Date: Mar 8, 2022
Citations: 3	License type: CC BY 4.0

Affiliation: Sungkyunkwan University

Abstract

Abstract. Beach erosion at the unprotected downdrift end of a groin is common with waves approaching the structure obliquely. This phenomenon has often occurred on the downdrift side of natural groins on the east coast of South Korea during high waves in winter months. The resulting planform assumes a distinctive crenulate shape with a maximum indentation point landward of the erosion. An analytical model is employed to study the beach erosion at the downdrift end of a natural rock groin at Jeongdongjin Beach in Korea, using mathematical equations derived from the parabolic model for headland-bay beaches in static equilibrium, to predict the downdrift control point and maximum indentation of the eroded shoreline. These equations are solved using the prevailing wave height, wave angle at breaking and wave direction derived from analyzing NOAA's wave data over 40 years and the longshore sediment transport rate calculated from the wave data. The location of the calculated maximum indentation is also verified using shoreline video monitoring data and compared with the result of a one-line numerical model for shoreline change. The limitation of the proposed analytical model is discussed as is the effect of sediment bypassing the groin.

Highlights

Groins of moderate dimension running from the beach into the sea at right angles or at an incline have produced unwanted beach erosion, despite them being installed to intercept or accumulate sediment on the updrift side
This type of beach erosion at the downdrift end of shore-based coastal structures, which is known as beach flanking, is common, but it is rarely taught in the classroom or well documented in the literature
The aims of this paper are threefold: (1) to derive mathematical equations for calculating the position of the maximum indentation in the eroded beach, (2) to demonstrate the applicability of an analytical model derived from the parabolic model and (3) to apply the mathematical equation to downdrift erosion at Jeongdongjin in Korea

Summary

Introduction

Seawalls of vertical or sloping (revetments) have been used for many decades as a purported protection in an erosive situation, it is unfortunate that they have often promoted further erosion, to the beach in front of them and on the downdrift side, where a seawardconcave planform is produced (Kraus and McDougal, 1996). Groins of moderate dimension running from the beach into the sea at right angles or at an incline have produced unwanted beach erosion, despite them being installed to intercept or accumulate sediment on the updrift side This type of beach erosion at the downdrift end of shore-based coastal structures (e.g., seawalls, revetments and groins), which is known as beach flanking, is common, but it is rarely taught in the classroom or well documented in the literature. On the east coast of Korea (Fig. 1), low waves from an east–northeasterly direction prevail in summer and high waves from the northeast dominate in winter This causes seasonal change in shoreline orientation (Kim and Lee, 2015) as well as localized beach erosion up to 30 m on the downdrift side of some natural groins due to high waves in the winter months.

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