Influence of Mild Bottom Slopes on the Overtopping Flow over Mound Breakwaters under Depth-Limited Breaking Wave Conditions

Patricia Mares-Nasarre,Josep R Medina,M Esther Gómez-Martín

doi:10.3390/jmse8010003

Patricia Mares-Nasarre, Josep R Medina + Show 1 more

Open Access

https://doi.org/10.3390/jmse8010003

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Abstract

The crest elevation of mound breakwaters is usually designed considering a tolerable mean wave overtopping discharge. However, pedestrian safety, characterized by the overtopping layer thickness (OLT) and the overtopping flow velocity (OFV), is becoming more relevant due to the reduction of the crest freeboards of coastal structures. Studies in the literature focusing on OLT and OFV do not consider the bottom slope effect, even if it has a remarkable impact on mound breakwater design under depth-limited breaking wave conditions. Therefore, this research focuses on the influence of the bottom slope on OLT and OFV exceeded by 2% of incoming waves, hc,2% and uc,2%. A total of 235 2D physical tests were conducted on conventional mound breakwaters with a single-layer Cubipod® and double-layer rock and cube armors with 2% and 4% bottom slopes. Neural networks were used to determine the optimum point to estimate wave characteristics for hc,2% and uc,2% calculation; that point was located at a distance from the model toe of three times the water depth at the toe (hs) of the structure. The influence of the bottom slope is studied using trained neural networks with fixed wave conditions in the wave generation zone; hc,2% slightly decreases and uc,2% increases as the gradient of the bottom slope increases.

Highlights

Mound breakwater design criteria are evolving due to climate change effects and increasing social pressure to reduce the visual impact of coastal structures
Overtopping is an increasing risk on coastal structures because of the rising sea levels caused by climate change and social demands to reduce the visual impacts
Few studies are focused on overtopping layer thickness (OLT) and overtopping flow velocity (OFV) estimation on coastal structures

Summary

Introduction

Mound breakwater design criteria are evolving due to climate change effects (e.g., sea level rise) and increasing social pressure to reduce the visual impact of coastal structures. Lorke et al [15] carried out physical model tests on dikes (horizontal bottom and 0.1 ≤ Hs/hs ≤ 0.3) focused on the effect of currents and wind on overtopping Using this dataset, the authors proposed new empirical coefficients for the hc,2% formulas obtained by Schüttrumpf and Van Gent [8] as a function of the seaward slope of the dike, α. Mares-Nasarre et al [9] adapted the formulas given by Schüttrumpf and Van Gent [8] to estimate hc,2%(xc = B/2) on mound breakwaters with m = 2% and 0.2 ≤ Hs/hs ≤ 0.7 These authors proposed new empirical coefficients and roughness factors for three armor layers (Cubipod®-1Layer, randomly placed cube-2Layers, and rock-2Layers). Overtopping discharges were collected and measured using a collection tank and a weighing system behind the model during each test

Wave Analysis

Findings

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