impacts of climate change on coastal geomorphology

A large proportion of the coastline of the UK and Ireland is currently suffering from erosion (17% in the UK; 19.9% in Ireland) and of the 3700 km coastline of England and Wales 28% is experiencing erosion greater than 10 cm per year. In Scotland, 78% of the coast is considered ‘hard or mixed’, and is unlikely to erode at perceptible rates, 19% is ‘soft/erodible’, whilst 3% has artificial defences. Since the 1970s, 77% of the soft/erodible coast in Scotland has remained stable, 11% has accreted seawards and 12% has eroded landwards

Role of atmospheric indices in describing shoreline variability along the Atlantic coast of Europe

The data set consists of time series atmospheric indicates, wave conditions and beach morphology for three sites on the Atlantic coast of EuropeThe project investigate the connections between atmospheric indicates, wave conditions and beach change over a 15-20 year period for three beach on the Atlantic coast of Europ

A new climate index controlling winter wave activity along the Atlantic coast of Europe: The West Europe Pressure Anomaly

International audienceA pioneering and replicable method based on a 66-year numerical weather and wave hindcast is developed to optimize a climate index based on the sea level pressure (SLP) that best explains winter wave height variability along the coast of western Europe, from Portugal to UK (36–52 ∘ N). The resulting so-called Western Europe Pressure Anomaly (WEPA) is based on the sea level pressure gradient between the stations Valentia (Ireland) and Santa Cruz de Tenerife (Canary Islands). The WEPA positive phase reflects an intensified and southward shifted SLP difference between the Icelandic low and the Azores high, driving severe storms that funnel high-energy waves toward western Europe southward of 52 ∘ N. WEPA outscores by 25–150% the other leading atmospheric modes in explaining winter-averaged significant wave height, and even by a largest amount the winter-averaged extreme wave heights. WEPA is also the only index capturing the 2013/2014 extreme winter that caused widespread coastal erosion and flooding in western Europe

REPEATABILITY OF MORPHOLOGICAL CHANGE ON A SANDY BEACH ACROSS MULTIPLE TIMESCALES

The swash zone is a highly dynamic region of the nearshore in terms of both hydro- and sediment dynamics. Previous work has demonstrated that the majority of swash events transport only small amounts of sediment and net beachface volume change over several hours tends to be small. However, a small number of individual swash events can deposit or remove hundreds of kilograms of sediment per metre width of beach. These events are typically associated with swash flows that involve one or more highly turbulent swash-swash interactions, causing enhanced suspension and transport of sediment (Blenkinsopp et al. 2011). The timing and location of these interactions is complex and small changes in either can lead to very different local flow conditions. The complexity of these flows make sediment transport prediction on a swash-by-swash basis very challenging, and raises the question whether deterministic physical and numerical modelling of swash sediment transport is warranted. </jats:p

Detailed investigation of overwash on a gravel barrier

This paper uses results obtained from a prototype-scale experiment (Barrier Dynamics Experiment; BARDEX) undertaken in the Delta flume, the Netherlands, to investigate overwash hydraulics and morphodynamics of a prototype gravel barrier. Gravel barrier behaviour depends upon a number of factors, including sediment properties (porosity, permeability, grain-size) and wave climate. Since overwash processes are known to control short-term gravel barrier dynamics and long-term barrier migration, a detailed quantification of overwash flow properties and induced bed-changes is crucial. Overwash hydrodynamics of the prototype gravel barrier focused on the flow velocity, depth and discharge over the barrier crest, and the overwash flow progression across and the infiltration through the barrier. During the BARDEX experiment, overwash peak depth (0.77 m), velocity (5 m s−1 ) and discharge (max. 6 m3 m−1 ) were high, especially considering the relatively modest wave energy (significant wave height = 0.8 m). Conversely to schemes found in the literature, average flow depth did not linearly decrease across the barrier; rather, it was characterised by a sudden decrease at the crest, a milder decrease at the barrier top and then propagation as a shallow water lens over the backbarrier. The barrier morphological evolution was analysed over a series of 15-min experimental runs and at the timescale of individual overwash events. Overall, the morphological variation did not result from an accumulation of many small consistently erosive or accretionary events, but rather the mean bed elevation change per event was quite large (10 mm) and the overall morphology change occurred due to a small imbalance in the number of erosive and accretionary events at each location. Two relationships between overwash hydrodynamic variables were deduced from results: (1) between overwash flow depth and velocity a power-type relation was obtained; and (2) a linear relation was observed between overwash flow depth and maximum overwash intrusion distance across the barrier top (i.e. overwash intrusion). Findings from this study are useful to enhance the knowledge of overwash processes and also have practical applications. On the one hand, results shown here can be use for the validation of overwash predictive models, and additionally, the simple empirical relations deduced from the dataset can be used by coastal managers to estimate overwash intrusion distance, which in turn can assist in the location of areas under risk of overwash and breaching.N/

Performance of a dynamic cobble berm revetment for coastal protection, under increasing water level.

In a changing climate, sea level rise and projected regional-scale changes in storminess may increase the vulnerability of sandy coastlines to coastal erosion and flooding. As a result, there is increased interest in the development of adaptable, sustainable and effective coastal protection measures to protect these highly variable sandy coastlines. One such example is a dynamic cobble berm revetment; a "soft-engineering" solution (i.e., not fixed) consisting of a cobble berm constructed around the high tide wave runup limit, that has the potential to stabilise the upper beach, provide overtopping protection to the hinterland and translate with water level rise. However, there have been limited applications of dynamic cobble berm revetments to date, and there is a lack of understanding about the efficacy of this coastal protection to current and changing waves and water levels. This study details a prototype-scale experiment conducted to test the behaviour and performance of a dynamic cobble berm revetment as a form of coastal protection against erosive waves and water level increase. Results from the experiment showed that the revetment was "dynamically stable" under wave action as a consistent global shape was retained even though individual cobbles were mobilised under every swash event. Although the front slope and the crest responded to the incident wave condition, the net rate of change was always an order of magnitude lower than the gross rate of change. Tracking of individual cobbles using Radio Frequency Identification (RFID) technology showed that stability of the revetment was likely maintained by rollover transport of cobbles onto the crest, as the revetment moved upward and landward under water level rise. The presence of the revetment reduced the vertical and horizontal runup as well as the retreat of the upper beach. The experimental results presented suggest that a dynamic cobble berm revetment could be a cheap, efficient and low environmental impact engineering solution for protecting sandy coastlines in a changing climate. Some preliminary design guidelines for coastal engineers are also drawn from this experiment

Coastal cliff ground motions and response to extreme storm waves

Coastal cliff erosion from storm waves is observed worldwide, but the processes are notoriously difficult to measure during extreme storm wave conditions when most erosion normally occurs, limiting our understanding of cliff processes. Over January–February 2014, during the largest Atlantic storms in at least 60 years with deepwater significant wave heights of 6–8 m, cliff-top ground motions showed vertical ground displacements in excess of 50–100 µm; an order of magnitude larger than observations made previously. Repeat terrestrial laser scanner surveys over a 2 week period encompassing the extreme storms gave a cliff face volume loss of 2 orders of magnitude larger than the long-term erosion rate. The results imply that erosion of coastal cliffs exposed to extreme storm waves is highly episodic and that long-term rates of cliff erosion will depend on the frequency and severity of extreme storm wave impacts

Coastal survey data for Perranporth Beach and Start Bay in southwest England (2006–2021)

Records of beach morphologic change and concurrent hydrodynamic forcing are needed to understand how coastlines in different environments change over time. This submission contains data for the period 2006 to 2021, for two contrasting macrotidal environments in southwest England: (i) cross-shore dominated, dissipative, sandy Perranporth Beach, Cornwall; and (ii) longshore-dominated, reflective gravel beaches within Start Bay, Devon. Data comprise monthly to annual beach profile surveys, annual merged topo-bathymetries, in addition to observed and numerically modelled wave and water levels. These data provide a valuable resource for modelling the behaviour of coastal types not covered by other currently available datasets