Estimate of Wave Overtopping Rate on Vertical Wall Using FUNWAVE-TVD Model

This study established a numerical model capable of calculating the wave overtopping rate of coastal structures by nonlinear irregular waves using the FUNWAVE-TVD model, a fully nonlinear Boussinesq equation model. Here, a numerical model was established by coding the mean value approach equations of EurOtop (2018) and empirical formula by Goda (2009), and adding them as subroutines of the FUNWAVE-TVD model. The verification of the model was performed by numerically calculating the wave overtopping rate of nonlinear irregular waves on vertical wall structures and comparing them with the experimental results presented in EurOtop (2018). As a result of the verification, the numerical calculation result according to the EurOtop equation of this model was very well matched with the experimental result in all relative freeboard (Rc/Hmo) range under non-impulsive wave conditions, and the numerical calculation result of empirical formula was evaluated slightly smaller than the experimental result in Rc/Hmo < 0.8 and slightly larger than the experimental result in Rc/Hmo > 0.8. The results of this model were well represented in both the exponential curve and the power curve under impulsive wave conditions. Therefore, it was confirmed that this numerical model can simulate the wave overtopping rate caused by nonlinear irregular waves in an vertical wall structure.

Eco-Engineering of Seawalls—An Opportunity for Enhanced Climate Resilience From Increased Topographic Complexity

In the context of “green” approaches to coastal engineering, the term “eco-engineering” has emerged in recent years to describe the incorporation of ecological concepts (including artificially water-filled depressions and surface textured tiles on seawalls and drilled holes in sea structures) into the conventional design process for marine infrastructures. Limited studies have evaluated the potential increase in wave energy dissipation resulting from the increased hydraulic roughness of ecologically modified sea defences which could reduce wave overtopping and consequent coastal flood risks, while increasing biodiversity. This paper presents results of small-scale laboratory investigations of wave overtopping on artificially roughened seawalls. Impulsive and non-impulsive wave conditions with two deep-water wave steepness values (=0.015 and 0.06) are evaluated to simulate both swell and storm conditions in a two-dimensional wave flume with an impermeable 1:20 foreshore slope. Measurements from a plain vertical seawall are taken as the reference case. The seawall was subsequently modified to include 10 further test configurations where hydraulic effects, reflective of “eco-engineering” interventions, were simulated by progressively increasing seawall roughness with surface protrusions across three length scales and three surface densities. Measurements at the plain vertical seawall compared favorably to empirical predictions from the EurOtop II Design Manual and served as a validation of the experimental approach. Results from physical model experiments showed that increasing the length and/or density of surface protrusions reduced overtopping on seawalls. Benchmarking of test results from experiments with modified seawalls to reference conditions showed that the mean overtopping rate was reduced by up to 100% (test case where protrusion density and length were maximum) under impulsive wave conditions. Results of this study highlight the potential for eco-engineering interventions on seawalls to mitigate extreme wave overtopping hazards by dissipating additional wave energy through increased surface roughness on the structure.

COASTAL CONCRETE STRUCTURE DESIGN AGAINST DESTRUCTION BY IMPULSIVE WAVE

The design method for impulsive wave pressure with very short duration time is important to prevent material destruction but is not establish yet, though there is a possibility that the coastal concrete structures will be destroyed by waves or tsunami. In this study, we proposed a simple method to design structure for impulsive wave pressure and confirmed the validity of this method by large flume experiments. A simple evaluation of impact response in a single mass system problem was applied. The ratio of duration time and natural period determines whether to examine by impulse damage or dynamic expansion. In the latter case, Mstatic times Lmax is compared with the bending strength. By this method, we can evaluate simply without dynamic analysis.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/4h5pOHM-Jco

Extreme wave overtopping at ecologically modified sea defences

&lt;p&gt;Damage to coastal structures and surrounding properties from wave overtopping in extreme events is expected to be exacerbated in future years as global sea levels continue to rise and the frequency of extreme meteorological events and storm surges increases.&amp;#160; Approaches for protecting our coastal areas have traditionally relied on the development and ongoing maintenance of &amp;#8216;hard&amp;#8217; defences. &amp;#160;However, the longer-term sustainability of coastal flood management that is underpinned by such defences is increasingly being questioned both in terms of dealing with climate change and in the environmental/ ecological consequences and associated losses of biodiversity that comes with these structural defence lines in coastal areas.&lt;/p&gt;&lt;p&gt;The term 'nature-based' has emerged in recent years to describe biomimicry-based engineered interventions in coastal defences. For example, the addition of artificial water-filled depressions on coastal structures e.g. &amp;#8216;vertipools&amp;#8217; on seawalls and the use of &amp;#8216;drill-cored rock pools in intertidal breakwaters that enhance biodiversity and species richness on sea defence surfaces and in adjacent coastal zones. While the ecological benefits of such interventions are increasingly being investigated, the additional roughness they bring to sea defences and the role of this roughness in wave energy dissipation and in the mitigation of wave overtopping remains less well studied.&lt;/p&gt;&lt;p&gt;Here we investigate the wave overtopping characteristics of artificially roughened seawalls in a suite of laboratory experiments conducted in a two-dimensional wave flume at the University of Warwick, UK. &amp;#160;An impermeable sloping foreshore with a uniform slope of 1 in 20 was constructed in front of a vertical seawall. The seawall was subsequently modified by including 10 no. different test combinations of surface protrusions of varying scale and surface density, replicating &amp;#8216;green&amp;#8217; measures suitable for retrofitting to existing seawalls.&amp;#160; Wave overtopping was measured for each test.&amp;#160; All tests comprised approximately 1000 JONSWAP pseudo-random wave sequences. Both impulsive and non-impulsive wave conditions were considered in experiments with two constant deep-water wave steepness values of 2% and 5%.&lt;/p&gt;&lt;p&gt;Results from benchmark (plain seawalls) experiments showed an overall good agreement with predictions from new overtopping manual, EurOtop II, the European empirical design guidance for wave overtopping of sea defences and related structures. &amp;#160;However, test results for the ecologically modified sea defences under impulsive (breaking) wave conditions showed significant reductions (up to factor 4) in overtopping compared to predictions from EurOtop codes. &amp;#160;Reductions in overtopping for artificially roughened defences under non-impulsive wave conditions were less conclusive.&amp;#160; Overall, results indicate that there can be a dual benefit in retrofitting sea defences with ecological features, the first being enhanced biodiversity in the coastal zone and the second being reduced flood risk in coastal areas from reductions in overtopping, particularly for breaking wave conditions.&lt;/p&gt;&lt;p&gt;The work in this paper is being undertaken as part of the Interreg funded Ecostructure project (www.ecostructureproject.eu), part-funded by the European Regional Development Fund through the Ireland Wales Cooperation Programme 2014-2020.&lt;/p&gt;