Abstract
Understanding of the reflection characteristics of coastal seawalls is crucial for design. Wave reflection can cause difficulties in small vessel manoeuvring at harbour entrances; this can cause damage to the toe of coastal structures by scouring. Previous studies have examined the reflection characteristics of coastal seawalls under random wind-generated waves without considering the effects of wave bimodality created by the presence of swell waves. This present study focuses on the influence of random wave bimodality on the reflective characteristics of coastal seawalls. 823 experimental tests were conducted to examine the reflection performance of impermeable sloping seawalls under bimodal waves. Reflection coefficients were computed from each test. The analysis of the results suggests that both unimodal and bimodal waves give similar reflection characteristics. However, the reflection coefficient in bimodal sea states seems to be more prolonged than in the unimodal sea states. It was found that the reflection coefficients of coastal seawalls are strongly influenced by the seawall slope, the wave steepness, the relative water depth, and the surf similarity parameters. A new empirical reflection equation to describe the influence of wave bimodality on the reflection characteristics of coastal seawalls has been formulated based on this study.
Highlights
Waves incident on coastal seawalls will be partially reflected unless they are fully absorbed by the structure
This study examined the reflection performance of a smooth sloping impermeable aluminium seawall in bimodal sea states
An array of four wave gauges positioned around the centre was applied to effectively capture both incident and reflected wave elevations
Summary
Waves incident on coastal seawalls will be partially reflected unless they are fully absorbed by the structure. The reflected wave component will interact with the incoming wave, creating interference. This can lead to wave amplification, wave breaking, and standing waves according to Lykke Anderson [1]. Existing literature provides little guidance on reflection characteristics in this situation, which Hawkes et al [3] consider as constituting the worst-case scenario in terms of wave conditions. There remains a gap in our understanding of seawall performance under bimodal wave conditions. This paper presents the results of laboratory experiments of bimodal waves impinging an impermeable seawall
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