Morphodynamic Evolution of Post-Nourishment Beach Scarps in Low-Energy and Micro-Tidal Environment

Gen Liu,Feng Cai,Hongshuai Qi,Jianhui Liu,Chao Cao,Jun Zhu,Shaohua Zhao,Gang Lei

doi:10.3390/jmse9030303

Abstract

Beach scarps are commonly associated with nourishment. Large and persistent beach scarps not only affect the performance of beach nourishment, but also are safety hazards to tourists. In this study, the morphological evolution of beach scarps was examined at a nourished beach in a low-energy and micro-tidal environment. Topographic surveys of nine beach profiles were carried out every 3–6 months after nourishment, lasting for nearly 4.5 years, combined with observed and simulated hydrodynamic data. The results showed that beach scarps were extensively developed after nourishment and migrated landward gradually. The formation of beach scarps was attributed to the higher designed berm, while the migration was possibly initiated by the subsequent higher total water level connected with the irregular tides. However, scarps were completely removed by the first post-nourishment severe storm and had been long absent ever since although two other energetic storms approached. This was different from the result of previous studies, which could be attributed to the much gentler upper beach slope. These results highlighted that the first post-nourishment storm played a key role in the evolution of beach scarps at low-energy and micro-tidal nourished beaches. This study also proposed two methods of determining berm elevation in beach nourishment according to China’s experiences, which would be helpful for other countries’ beach nourishment projects.

Highlights

Beach scarps are defined as a nearly vertical discontinuity in the foreshore slope
Since Hato, no beach scarps had been observed at ML beach in spite of two other energetic storms attacking ML beach (Figure 7f–h)
Wave energy dissipated completely and the backflow took away part of the sediment on foreshore, leading to the formation of a steep scarp in the seaward of the berm (Figure 11a). It showed that the formation of beach scarps at ML beach was attributed to the much higher designed berm, which was confirmed by Dean and Dalrymple [15] and Jackson et al [12] who found that an inadequate design of the nourished beach profile could lead to the formation of beach scarps

Summary

Introduction

Beach scarps are defined as a nearly vertical discontinuity in the foreshore slope. As a distinctive morphological feature of many shorelines [1], they are often associated with coastal erosion [2,3]. A beach scarp was defined as a feature with a slope larger than the critical angle of repose of 32◦ and a minimum height of 0.25 m [4]. They can be as high as 3 m [5] and extended for thousands of meters along the shoreline [1]. Higher beach scarps cause inconvenience and pose serious safety hazards to beach users [4,6]. Beach scarps have been reported around the world [3], along natural shorelines [6,7,8], and on nourished beaches shortly after implementation [3,4,9,10,11,12,13]

Methods

Results

Discussion

Conclusion