1,720,970 research outputs found
Understanding defence failures and coastal flood events: a case study approach
No full textExtreme sea level events are a current global threat, whilst sea-level rise (SLR) and climate change over the 21st century will increase the frequency and severity of flooding in most coastal regions. Numerical model simulations can help to understand and predict coastal floods (e.g. flood mapping and forecasting) but in comparison to flood sources (waves and water levels) coastal flood pathways (defence failures and inundation) are presently less integrated within these models. This thesis develops and demonstrates a methodology to rapidly simulate and understand the consequences of coastal flood events, with an emphasis upon regions where the risks of flooding are not well understood and could change quickly with SLR. The Solent on the south coast of England is the case study, and is prone to frequent flooding. This region is currently differentiated from the UK east and west coasts by experiencing smaller storm surges, and is characterised by undefended sections of shoreline and small floodplains. Within the Solent is Portsmouth, a city of national flood significance (only London and Hull contain more people considered at risk of coastal flooding in the UK). However, life threatening floods have not occurred in living memory. An integrated modelling approach is developed, coupling loads and defence failures with two-dimensional simulations of floodplain inundation. Observations collated from a real storm surge and flood event are shown to generate a validation data set, which indicates that this model can predict floodplain water levels to a good level of accuracy, whilst highlighting implications of such data collection. Solent-wide analysis includes simulations of hypothetical coastal flood events based upon scenarios that cover the full range of coastal loadings (realistic waves and water levels) and defence failures (overflow, outflanking, overtopping and breaching). More detailed case-studies are also applied at two sites within the region (including Portsmouth). This analysis generates peak flood water depths and an overview of impacts across this spectrum of possible floods.This research improves the existing knowledge of coastal flooding in the case study, and highlights a number of generic concepts that should be applied to others. For example the combination of flood simulation methods with real flood event analysis is essential for optimising the interpretation of model outputs whilst supporting inferences about flood consequences associated with extreme loading events (including how these may change with SLR). Simple methods estimated that >24,000 properties are within a 1 in 200 year flood event outline; and incorporating defence failures, flood dynamics, validation and detailed case studies substantially refine the assessment of places likely to experience damages. Breach defence failures generate the worst flood impacts, although in the Solent this failure mechanism is presently less of a threat than outflanking, overflow and wave overtopping. The modelling system includes easily interpreted outputs, whilst being computationally fast; therefore with potential applications including supporting land-use and defence planning, and real-time flood forecasting and warning
Estimating the evolution of flood risk to coastal populations
No full textThe long term evolution of flood risk in a coastal area due to (a) Sea level rise and (b) Population rise is assessed. Historic maps and population data are used to estimate the spatial distribution of the coastal population through time, and extrapolated sea levels are used as a boundary condition in a hydrodynamic flood model to estimate the historic flood exten
Understanding a coastal flood event: the 10th March 2008 storm surge event in the Solent, UK
No full textExtreme sea-level events (e.g. caused by storm surges) can cause coastal flooding, and considerable disruption and damage. To understand the impacts or hazards expected by different sea levels, waves and defence failures, it is useful to monitor and analyse coastal flood events, including generating numerical simulations of floodplain inundation. Ideally, any such modelling should be calibrated and validated using information recorded during real events, which can also add plausibility to synthetic flood event simulations. However, such data are rarely compiled for coastal floods. This paper demonstrates the capture of such a flood event dataset, and its integration with defence and floodplain modelling to reconstruct, archive and better understand the regional impacts of the event. The case-study event comprised a significant storm surge, high tide and waves in the English Channel on 10 March 2008, which resulted in flooding in at least 37 distinct areas across the Solent, UK (mainly due to overflow and outflanking of defences). The land area flooded may have exceeded 7 km2, with the breaching of a shingle barrier at Selsey contributing to up to 90 % of this area. Whilst sea floods are common in the Solent, this is the first regional dataset on flood extent. The compilation of data for the validation of coastal inundation modelling is discussed, and the implications for the analysis of future coastal flooding threats to population, business and infrastructure in the region
Coastal flooding in the solent: an integrated analysis of defences and inundation
No full textThis paper demonstrates a methodology for integrating existing models for the rapid simulation of coastal flood events across a large and varied case study area on the UK south coast. Following validation against observations from real coastal floods, synthetic events driven by realistic waves and water levels and the full range of failure mechanisms were modelled for a range of loadings to generate peak flood water depths and an overview of impacts across this spectrum of possible floods. Overtopping is relatively important compared to breaching as coastal floodplains are small. This modelling system supports multiple potential applications, such as planning flood warnings, coastal defence upgrade, and land use, including under sea-level rise. The concepts drawn from this study are transferable to similar coastal region
Coastal flooding in the Maldives: an assessment of historic events and their implications
No full textWith many inhabited islands only at about 1 m above mean sea level, the Maldives is among the nations most threatened by coastal flooding and sea level rise. However, the understanding of recent coastal flood events in the Maldives is limited and is important to understanding future flood threats. This paper assesses (1) the sea level and wave climate of the Maldives, (2) the sea level and wave conditions during recent coastal flood events, and (3) the implications for flood management and future research. The analysis uses observed still water levels (1987–2015) and hindcast wave conditions (1979–2015). Two significant flood events on 10–13 April 1987 and 15–17 May 2007 are examined in detail. This shows that coastal flooding in the Maldives occurs due to multiple interacting sources. These include long-period (up to 20 s) energetic waves generated in the Southern Ocean combined with spring tides. Wave run-up (mainly wave set-up) appears an essential mechanism for a flood, but is currently poorly quantified. However, as sea levels continue to rise the conditions that produce a flood will occur more frequently suggesting that flooding will become common in the Maldives. This analysis is a starting point for future research and highlights the need to continue research on flood sources, pathways and receptors, and plan adaptation measures. Priorities include monitoring of waves, sea levels and flood events, and a better understanding of set-up (and other shallow water processes over reefs)
High-frequency sea level variations and implications for coastal flooding: A case study of the Solent, UK
No full textThis study examines the occurrence and characteristics of high-frequency (<6 h) sea level variations in the Solent, UK – a mesotidal estuarine strait located in the central English Channel. A 14-year time series (2000–2013) of sea level observations sampled at 15-min intervals from the Southampton tide gauge was analyzed. The 8 highest-energy events have a mean amplitude of approximately 0.6 m and a dominant period of around 4 h. These events correspond with periods of enhanced meteorological activity, namely a marked reduction in air pressure and onset of strong southwesterly-southeasterly winds. Sea level observations from tide gauges around the Solent and the wider English Channel region (23 in total) were used to assess the spatial characteristics of these events. Analysis of time series and phase information indicates the occurrence of standing waves oscillating across the English Channel between southern England and northern France. This study provides a unique example of standing waves generated by extra-tropical cyclones over a large basin (the English Channel) with implications for flood inundation. The event of 28th October 2013 – the highest-amplitude (1.16 m) event in the record – was associated with minor coastal flooding at Yarmouth, Isle of Wight. This flood occurred during a neap tide, when such events are widely thought to be impossible. Hence, our findings emphasize the relevance of high-frequency sea level variability for regional sea level forecasting and flood risk management
The impact of temperate reefs on 34years of shoreline and vegetation line stability at Yanchep, southwestern Australia and implications for coastal setback
No full textCoastal setbacks are used to protect populations and infrastructure, and involve determining baselines and historic trends in shoreline movements. Assessing these movements can be difficult on coasts with especially complex geomorphology, such as due to rock and coral reefs. Reefs are often assumed to provide coastal protection and stability. However, little is known about the spatial variability of beach dynamics on beaches with reefs, over inter-annual and decadal time-scales. Spatial variability in inter-annual vegetation line and shoreline stability was assessed on three adjacent beaches at Yanchep, southwestern Australia, using 34 years (1974–2008) of aerial photographs. Over 96% of the study area, beach width narrowed over the 34 years. This trend was statistically significant on 83% of the middle beach, 43% of the northern beach, and only 29% of the southern beach. The maximum mean annual change in beach width was 1.7 m yr.? 1 at the south end of the southern beach, the first mode of the Empirical Orthogonal Function (EOF) explained 45% of the variability alongshore, and correlated significantly (p < 0.05) with the 90th percentile of annual wave height and annual mean sea level. Beach rotation and reef-controlled currents resulted in cellular beach morphodynamics, and vegetation line and shoreline movements varied greatly alongshore. On one occasion, the beach widened by more than 50 m inter-annually while other areas eroded by 50 m. The southern beach that was fronted by the most continuous and highest (supratidal) section of reef was the most temporally variable. Even the vegetation line here moved by up to 20 m inter-annually, so cannot be assumed to be a ‘stable’ baseline for setback. The impact of reefs on inter-annual shoreline and vegetation line stability should be considered in future guidelines for determining coastal setback
Coastal flood analysis and visualisation for a small town
No full textExtreme sea levels and floods are a widespread threat to coastal communities, and sea-level rise is increasing the probability of such events. This paper describes how inundation modelling was used to engage local stakeholders about climate change and adaptation, for a town (Yarmouth) on the UK south coast. This included a participatory visualisation exercise using three extreme sea level scenarios, informed by a recent flood event. Further analysis, informed by the repeated floods during the 2013/14 storm surge season, placed these scenarios in a broader perspective across a range of events. Results indicate that coastal flooding may become a significant issue during this century due to sea-level rise, unless there is adaptation. These methods engaged the interest of the community, and this paper presents practical considerations for future studies. A similar approach could be applied widely at the community level and form an important component of coastal flood management, including planning responses to sea-level rise
Spatial and temporal analysis of extreme sea level and storm surge events around the coastline of the UK
Full text linkIn this paper we analyse the spatial footprint and temporal clustering of extreme sea level and skew surge events around the UK coast over the last 100 years (1915-2014). The vast majority of the extreme sea level events are generated by moderate, rather than extreme skew surges, combined with spring astronomical high tides. We distinguish four broad categories of spatial footprints of events and the distinct storm tracks that generated them. There have been rare events when extreme levels have occurred along two unconnected coastal regions during the same storm. The events that occur in closest succession (< 4 days) typically impact different stretches of coastline. The spring/neap tidal cycle prevents successive extreme sea level events from happening within 4-8 days. Finally, the 2013/14 season was highly unusual in the context of the last 100 years from an extreme sea level perspective
An improved database of coastal flooding in the United Kingdom from 1915 to 2016
No full textCoastal flooding caused by extreme sea levels can produce devastating and wide-ranging consequences. The ‘SurgeWatch’ v1.0 database systematically documents and assesses the consequences of historical coastal flood events around the UK. The original database was inevitably biased due to the inconsistent spatial and temporal coverage of sea-level observations utilised. Therefore, we present an improved version integrating a variety of ‘soft’ data such as journal papers, newspapers, weather reports, and social media. SurgeWatch2.0 identifies 329 coastal flooding events from 1915 to 2016, a more than fivefold increase compared to the 59 events in v1.0. Moreover, each flood event is now ranked using a multi-level categorisation based on inundation, transport disruption, costs, and fatalities: from 1 (Nuisance) to 6 (Disaster). For the 53 most severe events ranked Category 3 and above, an accompanying event description based upon the Source-Pathway-Receptor-Consequence framework was produced. Thus, SurgeWatch v2.0 provides the most comprehensive and coherent historical record of UK coastal flooding. It is designed to be a resource for research, planning, management and education
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