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The prediction of wave impact loads on prototype caisson breakwaters from the results of physical model tests is considered, with particular attention given to the effects of air, breaker shape, structural response and scale. A review of related literature is presented from which it is concluded that the different aspects of the problem may be related through the force impulse. Large scale soliton impacts are used to show the importance of entrapped air in determining the form of the load time history. Small scale waves with artificially high levels of entrained air and highly controlled drop impacts are used to show and quantify an inverse relationship between entrained air and impact load maxima. Specially developed aeration probes and analysis techniques are used to show the influence of entrapped air on pressure maxima and quantify entrained air levels in small scale fresh water breaking waves. A definition of the force impulse is proposed and used to investigate its variation with breaker shape. The impulse magnitude is shown to be relatively invariant for regular wave impacts compared to a large scatter in impulse form. A numerical model of caisson dynamics is used to predict structural motion and to calculate a series of dynamic amplification factors. The prediction of structural response to obtain effective static loads through the use of these factors is investigated and achieved through the adoption of an 'equivalent impulse' concept. The scatter in impulse form is found to cause large variations in effective static loads between nominally identical impact events. The equivalent impulse concept is used to solve this problem. A comparison is made between the form and magnitude of the force impulses of the small and large scale waves. The results indicate that the impulse magnitude may be relatively free of scale effects. An example is given in which the results of a small scale test are interpreted, scaled and processed to account for the effects of entrained air and structural response in order to predict large scale effective static loads. These are shown to compare well with predictions made using measured large scale force time histories and the numerical caisson model.

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Engineering design considerations of artificial coastal structures were tested to resemble as far as possible the nearest natural equivalent habitat, ecologically valuable rocky shores, as a potential management option. Coastal areas around the world attract urbanisation but these transitional areas between sea and land are inherently vulnerable to risk of flooding and erosion. Thus hard structures are often built in sensitive coastal environments to defend assets such as property and infrastructure (roads, railways, ports) against rising and stormy seas. The design, construction and maintenance of hard defences should wherever possible incorporate ecological considerations to enhance biodiversity, including maintaining or restoring natural habitats and wild species to ensure favourable conservation status. Artificial habitats are less topographically complex than natural rocky shores, at millimetre scales in terms of surface roughness, centimetre to meter scales for crevices and pools to tens, hundreds and occasionally thousands of meters for variation in tidal height and wave action gradients. The habitat value of design features of an existing seawall and breakwater, such as areas of different slope and orientation, and the presence of crevices and pools, that are analogous to habitat created by topographical features on a natural shore, were demonstrated by their ability to support distinct assemblages of species. X Furthermore, evidence is provided that a greater variation in the type of design features led to a higher species diversity occupying the structure, and included species that would otherwise not be present on the structure. The long term succession on artificial structures and the biodiversity reached on intertidal coastal defence structures is described to inform understanding of timescales over which successional processes operate. As a consequence of succession, artificial structures of large extent eventually resemble natural rocky shores of the same exposure. Increased surface heterogeneity of concrete armour units on Plymouth Breakwater by drilling holes was effective in adding habitat and increasing local species diversity. These can be added at the construction stage or post construction. In a real case study, added recessed pools, holes and surface texture during the construction of a tidal defence sea wall at Shaldon made heterogeneous surfaces to add habitat and influence species diversity, without compromising the engineering function or aesthetics of the structure. This study provides coastal engineers and decision makers with well researched practical design options to inform future construction and maintenance of coastal defence structures that will encourage specific outcomes to mitigate the negative environmental impact of artificial structures and contribute to conservation priorities.