The use of different wave overtopping models has been analysed. These overtopping models were applied to vertical walls with different geometries built for the protection against storm surges in the harbour of Hamburg (Germany). A comparison of existing overtopping test data and results from specific hydraulic model tests for existing geometries in Hamburg was also performed. A simple design diagram to predict both the overtopping rate q and the required freeboard Rc is presented. Furthermore, a simple engineering approach is proposed for the reduction of the horizontal wave load of the harbour walls due to wave overtopping. Finally, conclusions are drawn to come up with a "general overtopping formula" and further research work is outlined.

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Application of Overtopping Models to Vertical Walls against Storm Surges

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SPH Modeling of Solitary Waves and Resulting Hydrodynamic Forces on Vertical and Sloping Walls

The beach drainage can be included among the soft engineering methods aimed to counteract the shoreline retreat related to the sediment redistribution along the beach profile. The idea that the groundwater table plays a role in the mobilization of the sediment grains underlies the application of the beach drainage system (BDS) as a tool able to modify the natural dynamics of groundwater table at sandy beaches. Indeed, BDS consists of a series of alongshore buried drains aimed to lower the groundwater table. Due to the drainage, the thickening of the layer of dry sand makes the solid grains less prone to be mobilized by the action of the waves at the swash zone, where interaction phenomena between the percolating and the incoming water lens take place. This tool had a troubled history. Its first applications were encouraging. Since then, controversial performances of both experimental and prototype scale experiences have been observed around the world. This paper aims to present an up-to-date full review of the studies and experiments carried out so far, in order to provide the reader with a complete perspective on its strength and weakness as well as open challenges to be faced in the near future.

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Beach Drainage System: A Comprehensive Review of a Controversial Soft-Engineering Method

Coastal ecosystems, such as seagrass meadows, have been heralded as a nature-based solution for coastal protection. However, the functions of seagrass meadows, including wave attenuation and sediment stabilisation, have typically been measured offshore and do not directly translate to coastal protection at the shoreline. In contrast, the protective effects of conventional submerged structures, such as breakwaters and artificial reefs, on adjacent shorelines have been well described and are predictable. Importantly, these artificial structures often cause erosion in adjacent areas. This study examines how seagrass may affect shoreline morphodynamics by making inferences from existing knowledge of conventional submerged structures. Both conventional submerged structures and seagrass meadows affect wave height and direction, yet this effect on longshore sediment transport has only been considered within the context of coastal defence structures. From the conventional literature on submerged structures, it is known that a constant rate of longshore sediment transport will result in a constant shoreline shape. Therefore, a change in the rate of longshore sediment transport, or gradient, generates changes in the shoreline shape and, hence, the shoreline morphodynamics. We propose that seagrass also has spatially heterogeneous effects on shoreline morphodynamics, with protection occurring in some locations and downstream erosion likely in others. Empirical and modeling research is required to test this hypothesis. In the meantime, this review suggests contexts under which seagrass may affect shoreline morphodynamics and provide shoreline protection. This research bridges the gaps in knowledge across marine ecology, physical oceanography and coastal engineering to overcome some of the challenges of interdisciplinary coastal science. 

Contextualising shoreline protection by seagrass using lessons from submerged breakwaters

We consider the issue of wave-breaking closure for the well-known Green–Naghdi model and attempt at providing some more understanding of the sensitivity of some closure approaches to the numerical set-up. More precisely and based on Kazolea and Ricchiuto (Ocean Model 123:16–39, 2018), we used two closure strategies for modeling wave-breaking of a solitary wave over a slope. The first one is the hybrid method consisting of suppressing the dispersive terms in a breaking region and the second one is an eddy viscosity approach based on the solution of a turbulent kinetic energy model. The two closures use the same conditions for the triggering of the breaking mechanisms. Both the triggering conditions and the breaking models themselves use case depended/ad/hoc parameters which are affecting the numerical solution while changing. The scope of this work is to make use of sensitivity indices computed by means of analysis of variance to provide the sensitivity of wave-breaking simulation to the variation of parameters such as the mesh size and the breaking parameters specific to each breaking model. The sensitivity analysis is performed using the UQlab framework for uncertainty quantification (Marelli et al., UQLab user manual—sensitivity analysis, Technical report, Chair of Risk, Safety and Uncertainty Quantification, ETH Zurich, Switzerland, 2019). 

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Parameter Sensitivity for Wave-Breaking Closures in Boussinesq-Type Models

A concept for the design of high water protection (HWP) walls under storm surge conditions has been developed and is applied to the geometry found in the harbour of Hamburg, Germany. However, the design methods used have been generalized so that they may be used for a wide range of cases with similar geometries. Many gaps in standard design formulae have been filled by developing engineering approaches or formulae as reflection by steep berms, new breaker criterion, design formulae for impact breakers, reduction of loads by overtopping and soil pressure distribution in front of the wall.

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C. Miller

Papers

Design of Vertical Walls Against Storm Surge