Hydraulic performance of different non-overtopped breakwater types under 2D wave attack

Maritime structures, and particularly breakwaters, must be designed to satisfy the project requirement and to control wind-wave actions. Depending on their typology, breakwaters reflect, dissipate, transmit, and radiate incident wave energy. Thus, wave transformation (i.e. wave reflection, modulus, and phase) plays an important role in defining the oscillatory regime in front of, near (seaward and leeward), and inside the breakwater. The superposition of incident waves and of those generated and transformed by the presence of breakwaters constitutes the set of oscillation patterns that affects the performance of the structure. Nowadays, maritime engineering design tools are usually based on independent formulas for each breakwater type, structural elements, and failure modes. To compare the performance of different breakwater designs and to make a decision accordingly, engineering methods and procedures must be physically and mathematically comparable. They must also be equally certain/uncertain and bounded. In the current state-of-the-art procedure, the design of coastal structures and breakwaters has a high level of uncertainty. Such uncertainty is difficult to assess, and this can ultimately jeopardize the engineering design process.

The paper puts forward a new methodology to evaluate the hydraulic performance generated by the interaction of incoming water waves and different breakwater typologies. Accordingly, a full spectrum of oscillatory regimes was specified for the most frequent breakwater types. It was thus possible to obtain complex wave reflection and transmission coefficients as well as the overall dissipation rate caused by the structures, in terms of dimensionless parameters, representing breakwater geometry, granular materials, and the incoming wave train. A logistic sigmoid curve was used to define the values of these coefficients, depending on the scattering parameter, an independent variable, and other parameter that describe the breakwater typology and wave conditions. The fitted curves can be used to determine the performance of the most popular types of breakwater. The results of this research show that when the characteristics of the wave train are modified, most of the structures transit smoothly (sometimes abruptly) between the following regimes: (a) the standing oscillatory regime (full wave reflection); (b) partial standing oscillatory regime (partial wave reflection); (c) dissipative regime (either by wave breaking or because of frictional forces inside the porous medium); and (d) transmitted oscillatory regime (wave transmission, either through the breakwater or by overtopping it). Indeed, all of the breakwater types cover a full spectrum of oscillatory regimes, depending on incoming wave steepness.

The curves proposed can be used as a first option in breakwater design. They contribute to the rational exploration of the entire parametric map with very few resources and in a very short period of time. In this way, it is also possible to analyze the sensitivity of the breakwater type to different agents, materials, and geometries, determine its viability, and estimate construction costs.

The results obtained in this study open the door to the development of new engineering methods and procedures, which are physically and mathematically comparable as well as equally certain/uncertain and bounded. They permit an accurate comparison of different types of breakwater with a view to evaluating their performance, safety, serviceability, and operationality in response to wave action. To achieve this aim, the prediction of the characteristics of wave height in front and face of breakwaters is crucial. This has been the objective of a new manuscript (submitted in Coastal Engineering) which focuses on the estimation of the statistical behavior of the wind waves interacting with different breakwater types in terms of its hydraulic performance.