Session: 06-01-01 Computational Mechanics and Design Applications

Submission Number: 180627

Post-Overtopping Wave Impacts on Vertical Breakwaters 

Composite vertical breakwaters are large monolithic structures widely employed to protect port basins, particularly in deep-water, microtidal environments. Their design traditionally relies on Goda’s (2010) formulae, incorporating Takahashi’s (1996) impulsive breaking conditions, and on the probabilistic design framework PROVERBS by Oumeraci et al. (2001). While wave loads on vertical walls in shallow water have been extensively studied (Cooker & Peregrine, 1990; Bullock et al., 2007), optimization of composite breakwaters in deep water remains underexplored. Because of the size and cost of these structures, even small improvements in hydraulic performance—reducing wave loads, reflection, or overtopping—can yield substantial economic benefits.

A promising design approach involves retreating the concrete crown wall relative to the caisson front. This modification alters the timing and nature of wave-induced loads, potentially reducing reflection and changing overtopping dynamics. However, such configurations significantly affect wave-structure interaction, making existing empirical design tools inadequate. Recent experimental studies (Romano & Bellotti, 2023; Romano et al., 2024) showed that while total loads on the caisson decrease with wall retreat, loads on the wall itself tend to increase, often due to impulsive impacts. These findings highlight the importance of post-overtopping flow hydrodynamics across the structure’s crest.

Post-overtopping flows—termed “green water” in naval and offshore engineering—have been classified by Fontes et al. (2021) into three types: Dam Break (DB), Plunging-Dam Break (PDB), and Hammer-Fist (HF), corresponding to increasing wave steepness. The present study extends this framework to vertical breakwaters with retreated walls through a 2D physical modeling campaign at Roma Tre University. Tests were conducted in a 20 m long, 0.605 m wide, and 1.0 m high wave flume using regular waves with active reflection compensation. Ninety-seven tests, at a scale of about 1:55, explored how wall retreat and flow type influence wave-induced pressures and post-overtopping dynamics.

The methodology involved two stages. First, 52 tests without the wall characterized the formation of DB, PDB, and HF events under varying wave conditions. Then, 45 tests with different wall retreats reproduced representative cases for each flow type. Advanced image-clustering techniques (Centorami et al., 2025) were used to quantify intra-wave processes such as air entrainment, while pressure sensors measured loads on the caisson and superstructure.

Results showed that flow type, aeration level, and wall position strongly influence impact pressures. A comprehensive parameter map was developed, linking post-overtopping flow regimes to geometric and hydraulic parameters. Inspired by the PROVERBS framework, this map provides practical guidelines for optimizing deep-water composite breakwaters. The study enhances understanding of the complex hydrodynamics governing retreated-wall configurations and offers a new foundation for performance-based design of next-generation coastal defenses.

REFERENCES
Bullock, G., Obhrai, C., Peregrine, D., Bredmose, H. (2007). Violent breaking wave impacts. Part 1: Results from large-scale regular wave tests on vertical and sloping walls. Coastal Engineering.
Centorami, F., Romano, A., Cecioni, C., Bellotti, G. (2025). Experimental analysis of post-overtopping flows on composite vertical breakwaters with retreated wave walls: Mapping of the hydrodynamic parameters. Coastal Engineering.
Cooker, M., Peregrine, D. (1990). Computations of violent motion due to waves breaking against a wall. Proc. 22nd Int. Conf. on Coastal Engineering.
Fontes, R. F. C. et al. (2021). On the evolution of different types of greenwater events. Water.
Goda, Y. (2010). Random Seas and Design of Maritime Structures. World Scientific.
Oumeraci, H. et al. (2001). Probabilistic Design Tools for Vertical Breakwaters (PROVERBS). CRC Press.
Romano, A., Bellotti, G. (2023). Wave forces on vertical caissons with retreated wall: A first experimental insight. Coastal Engineering.
Romano, A., Centorami, F., Cecioni, C., Bellotti, G. (2024). A physical model study on the hydraulic performances of vertical breakwaters with retreated wave walls. Coastal Engineering.
Takahashi, S. (1996). Design of vertical breakwaters. Short Course, Int. Conf. on Coastal Engineering, Orlando.

Presenting Author: Giorgio Bellotti Roma Tre University

Presenting Author Biography: Giorgio Bellotti is full professor of Coastal and Harbour Engineering at Roma Tre University, Italy. Graduated in Civil Engineering (1997) at Sapienza University of Rome, and earned his Ph.D. in Hydraulic Engineering (2002) at University of Naples Federico II.
His main research topic is that of the wave induced hydrodynamic processes in coastal areas, with focus on the wave-structures interaction, on the long waves amplification in harbours and bays, and on the numerical models for the short and long waves propagation.
Since January 2024 serves as Associate Editor of the journal Coastal Engineering (Elsevier), formerly member of the editorial board (2017-2023). He has been the coordinator of the Local Organizing Committee for the International Conference on Coastal Engineering held in Rome in September 2024. Member of the board of professors of the PhD schools in Civil Engineering, Roma Tre University and tutor/co-tutor of 9 PhD students. Formerly Director of the Civil Engineering courses (2016-2022) at Roma Tre University.
Visiting researcher/professor at the Center for Applied Coastal Research, University of Delaware (USA, 2000), Department of Civil Engineering, The University of Nottingham (Nottingham, UK, 2011), Universidad Catolica de la Santisima Concepcion and CIGIDEN, Centro Nacional de Investigacion para la Gestion Integrada de Desastres Naturales (Cile, 2016).
Author of more than 60 peer-reviewed scientific papers published on Scopus/ISI-indexed international journals.

Authors:

Giorgio Bellotti Roma Tre University
Matteo Centorami Roma Tre University
Alessandro Romano Roma Tre University
Claudia Cecioni Roma Tre University