Now showing 1 - 7 of 7
  • Publication
    Extreme wave overtopping at ecologically modified sea defences
    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. Approaches for protecting our coastal areas have traditionally relied on the development and ongoing maintenance of ‘hard’ defences. 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.
  • Publication
    Effectiveness of Eco-retrofits in Reducing Wave Overtopping on Seawalls
    (Coastal Engineering Research Council, 2020-12-28) ; ; ;
    Terms such as 'nature-based', 'living shoreline', 'green infrastructure' and 'ecological engineering' are increasingly being used to reflect biomimicry-based engineering measures in coastal defences. Innovative interventions for nature-based sea defences have included the retrofitting of man-made water filled depressions or 'vertipools' to existing seawalls (Hall et al., 2019; Naylor et al., 2017) and the addition of artificial drill-cored rock pools to intertidal breakwaters (Evans et al., 2016). Through their capacity to retain water, such measures serve to enhance biodiversity in the built environment (Browne and Chapman, 2014). Evans et al. (2016) for example, experimentally demonstrated that the introduction of artificial rock pools to an intertidal granite breakwater enhanced the levels of species richness compared to those observed on plain surfaces of the breakwater. Notwithstanding these biological benefits, the impetus for incorporation of ecologically friendly measures to existing defences remains low (Salauddin et al., 2020a). This situation could potentially change should it be shown that the addition of 'green' measures to sea defences could enhance wave attenuation and reduce wave overtopping as well as wave pressures on the coastal defence structures. This paper describes small-scale physical modelling investigations of seawalls and explores reductions in wave overtopping that could be realised by retrofitting sea defences with 'green' features (such as 'vertipools'). Surface protrusions of varying scale and density are used in the physical modelling to mimic 'green' features and the results from measurements of overtopping are benchmarked to reference conditions determined from tests on a plain seawall.
  • Publication
    Distribution of Individual Wave Overtopping Volumes on a Sloping Structure with a Permeable Foreshore
    (Coastal Engineering Research Council, 2020-12-31) ; ; ; ;
    Maximum wave overtopping volumes on sea defences are an indicator for identifying risks to people and properties from wave hazards. The probability distribution of individual overtopping volumes can generally be described by a two-parameter Weibull distribution function (shape and scale parameters). Therefore, the reliable prediction of maximum individual wave overtopping volumes at coastal structures relies on an accurate estimation of the shape factor in the Weibull distribution. This study contributes to an improved understanding of the distribution of individual wave overtopping volumes at sloping structures by analysing the wave-by-wave overtopping volumes obtained from physical model experiments on a 1V:2H sloped impermeable structure with a permeable shingle foreshore of slope 1V:20H. Measurements of the permeable shingle foreshore were benchmarked against those from an identical experimental set-up with a smooth impermeable foreshore (1V:20H) of the same geometry. Results from both experimental set-ups were compared to commonly used empirical formulations, underpinned by the assumption that an impermeable foreshore exists in front of the sea structure. The effect on the shape factor in the Weibull distribution of incident wave steepness, relative crest freeboard, probability of overtopping waves and discharge are examined to determine the variation of individual overtopping volumes with respect to these key parameters. A key finding from the study is that no major differences in Weibull distribution shape parameter were observed for the tested impermeable and permeable sloped foreshores. Existing empirical formulae were also shown to predict reasonably well the Weibull distribution shape parameter, b, at sloping structures with both impermeable and permeable slopes.
  • Publication
    Assessment of source apportionment and composition of trace elements in rainwater in the south-eastern region of Bangladesh  
    Rainwater is considered as a dependable potable and non-potable water source, used for domestic purposes as well as for human consumption in many cases. While it is usually believed that rainwater is safe for drinking purposes, many studies have explored the existence of trace metals in harvested rainwater, which can impose a serious health risk to human beings when present in relatively high concentrations. The concentration of trace elements in atmospheric precipitation including rainwater also provides a good indication of the environmental pollution caused by anthropogenic activities.
  • Publication
    The effects of wave impacts on toe scouring and overtopping concurrently for permeable shingle foreshores
    Recent studies by the Intergovernmental Panel on Climate Change indicate that sea level will continue to rise in many low-lying areas due to the global climate change that would potentially cause the occurrence of more frequent extreme meteorological events and storm surges in future years. Concurrently, the damage to the critical infrastructures and surrounding properties from extreme climatic events such as wave overtopping, and scouring are expected to be exacerbated in future. Reliable prediction tools for wave overtopping and toe scouring characteristics at sea defences are therefore significantly important for climate resilience of coastal infrastructures. To date, however, most parametric studies regarding these aspects have tended to focus either only overtopping or scouring at sea defences, with investigations on the effects of wave impacts on both overtopping and scouring characteristics simultaneously, particularly for permeable shingle beaches in front of the structure being less well-studied. This limitation and research gap have driven the need to carry out a comprehensive suite of experimental investigations on the influence of wave impacts on toe scour and overtopping concurrently at sea defences with shingle foreshores.
  • Publication
    Spatial Distribution of Wave-by-Wave Overtopping at Vertical Seawalls
    (Coastal Engineering Research Council, 2020-12-28) ; ; ;
    Over the years, many physical and numerical modelling research has been carried out to investigate the wave-structure interactions and the resulting mean overtopping characteristics at sea defences. The most reliable empirical predication formulae for prediction of mean overtopping rates have been reported in the overtopping manual, EurOtop (2018). In addition to average overtopping rates, in recent years, the spatial distribution of overtopped water has become an important topic of research to understand the safe zone behind coastal defences. The existing empirical formulae for spatial distribution of overtopping provide conservative predictions, as it has been derived from the mean overtopping volumes. The extreme wave overtopping hazards in generally originate from individual overtopping events rather than the mean overtopping volumes. This study presents comprehensive laboratory investigations on the spatial distribution of wave-by-wave overtopping at vertical seawalls.
  • Publication
    Enhancing climate resilience of vertical seawall with retrofitting - A physical modelling study
    Coastal defence structures are playing a vital role in protecting coastal communities from extreme climatic conditions and flooding. With climate change and sea-level rise in the next decades, the freeboard of existing coastal defences is likely to be reduced and the probability of wave overtopping for these coastal defences will increase. The wave overtopping from coastal defences increases the probability of coastal inundation and flooding, imposing threat to the communities which are living in low-lying coastal areas. Retrofitting of existing seawalls offers the potential to enhance coastal resilience by allowing them to adapt and respond to changing climatic conditions. This study investigates a range of possible physical configurations and optimum retrofit geometry to maximize the protection of existing seawalls from wave overtopping. A comprehensive physical modelling study of four retrofit prototypes, including recurve wall, model vegetation, reef breakwater and diffraction pillars, was conducted to examine their performance in mitigating wave overtopping, when placed in front of a vertical seawall. All the tests were conducted on 1:20 smooth beach slope. Each test case consisted of approximately 1000 pseudo-random waves based on the JONSWAP spectrum. The physical modelling experiments were designed to include both impulsive and non-impulsive wave conditions. This study provides new predictive relations and decision support tool needed to evaluate overtopping risks from existing seawalls with retrofits under various hydrodynamic conditions. The analysis of experimental measurements demonstrates that wave overtopping from retrofitting structures can be predicted with similar relations for vertical seawalls, and by using a reduction factor which varies with geometric shapes. Statistical measures and sensitivity analysis show that recurve walls have the best performance in reduction of wave overtopping volume followed by model vegetation and reef breakwater. The measurements show the insignificance of diffraction pillars, at least for the selected configurations investigated, in mitigating wave overtopping.
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