1 Reliability of Beaches as Defence Against Storm Impacts Under a Climate Change Scenario (original) (raw)
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Ocean Engineering, 2014
This study assesses three different approaches for evaluating coastal vulnerability using indicators. We began by establishing a procedure for binding three codes to simulate realistic or idealized climates. The procedure was validated in terms of hydrodynamics and beach morpho-dynamics. We then defined and studied the vulnerability of the coast on the basis of in situ observations and model results taken from a set of simulations based on different scenarios. We present three simple indicator methods developed to analyze the vulnerability of a sandy beach based on the results of simulations for different wave climate scenarios. The first method is based on the wave energy, and specifically how it differs as a function of climate change scenario. The second method consists of estimating the maximum grain size mobilized. Note that the calculation of stress at the sea bottom is routinely estimated solely on the basis of simulated velocity post-wave. Here, we calculate the maximum grain size potentially mobilized with a simpler approach, based on analysis in different points along the cross-shore profile. The third method presented is the analysis of the time-course evolution of cross-shore sea bed profiles in response to different climate change scenarios.
An approach to assess flooding and erosion risk for open beaches in a changing climate
Coastal Engineering, 2014
This paper examines the vulnerability to flooding and erosion of four open beach study sites in Europe. A framework for the quantitative estimation of present and future coastal flood and erosion risks is established using methods, data and tools from across a range of disciplines, including topographic and bathymetric data, climate data from observation, hindcast and model projections, statistical modelling of current and future climates and integrated risk analysis tools. Uncertainties in the estimation of future coastal system dynamics are considered, as are the consequences for the inland systems. Different implementations of the framework are applied to the study sites which have different wave, tidal and surge climate conditions. These sites are: Santander, Spain-the Atlantic Ocean; Bellocchio, Italy-the Adriatic Sea; Varna, Bulgaria-the Black Sea; and the Teign Estuary, UK-the northern Atlantic Ocean. The complexity of each system is first simplified by sub-division into coastal "impact units" defined by homogeneity in the local key forcing parameters: wave, wind, tide, river discharge, run-off, etc. This reduces the simulation to that of a number of simpler linear problems which are treated by applying the first two components of the Source-Pathway-Receptor-Consequence (S-P-R-C) approach. The case studies reveal the flexibility of this approach, which is found useful for the rapid assessment of the risks of flooding and erosion for a range of scenarios and the likely effectiveness of flood defences.
Forecasting the impact of storm episodes on beaches: present limitations
2015
The application of credible morphodynamic forecast models to provide evidence-based information for coastal managers making decisions for re-profiling the beach and thus increase coastal resilience by restoring the sediment balance and providing space for coastal processes is a relevant issue since the future risk of coastal storm impacts is likely to increase. The study exposes the practical limitations and inevitable uncertainties found in the application of two state-of-the-art process-based morphodynamic numerical models to an Atlantic urban sandy beach under extreme wave energy and surge conditions. The erosion of the foreshore and backshore of this particular beach was characterised as function of the intensity and duration of the hydrodynamic forcing parameters. The models performance was evaluated and compared. A major conclusion achieved was that in order to obtain reliable simulations of the morphodynamics during high energy coastal events it is necessary to further develop and apply non-intrusive monitoring techniques, which enable accurate monitoring in such adverse environments, to capture the physics in those conditions and load correctly the numerical models. There is an urgent need to overcome the present limitation in order to achieve a higher level of reliability in beach erosion impact forecasts.
Flooding of Sandy Beaches in a Changing Climate. The Case of the Balearic Islands (NW Mediterranean)
Frontiers in Marine Science, 2021
The fate of the beaches around the world has paramount importance as they are one of the main assets for touristic activities and act as a natural barrier for coastal protection in front of marine storms. Climate change could put them at risk as sea levels rise and changes in the wave characteristics may dramatically modify their shape. In this work, a new methodology has been developed to determine the flooding of sandy beaches due to changes in sea level and waves. The methodology allows a cost-effective and yet accurate estimation of the wave runup for a wide range of beach equilibrium profiles and for different seagrass coverage. This, combined with regional projections of sea level and wave evolution, has allowed a quantification of the future total water level and coastline retreat for 869 beaches across the Balearic Islands for the next decades as a function of greenhouse gases emission scenario. The most pessimistic scenario (RCP8.5) at the end of the century yields an averaged percentage of flooded area of 66% under mean conditions which increases up to 86% under extreme conditions. Moreover, 72 of the 869 beaches of the region would permanently disappear while 314 would be completely flooded during storm episodes. Under a moderate scenario of emissions (RCP4.5), 37 beaches would permanently disappear while 254 would disappear only during storm episodes. In both cases, the average permanent loss of beach surface at the end of the century would be larger than 50%, rising over 80% during storm conditions. The results obtained for the Balearic Islands can be extrapolated to the rest of the Mediterranean as the beaches in all the regions have similar characteristics and will be affected by similar changes in sea level and wave climate. These projections indicate that adaptation plans for beach areas should be put in place as soon as possible.
Vulnerability of sandy coasts to climate variability
Climate Research
The main objective of the VULSACO (VULnerability of SAndy COasts to climate change and anthropic pressure) project was to investigate present day and potential future vulnerability of sandy coasts at the 2030 horizon, i.e. on a time scale related to climate variability. The method, based on a multidisciplinary approach bringing together geologists, geographers, physicists, social psychologists, engineers and stakeholders, was structured around 4 axes: field data analysis; numerical modelling; analysis of governance and stakeholder perceptions; and develop- ment of vulnerability indexes. This approach was designed to investigate vulnerability at a local scale and was applied to 4 contrasting beaches located in France: Sète Lido (Mediterranean Sea), Truc Vert and La Tresson beaches (Atlantic Ocean), and Dewulf (English Channel). The results focus on decadal and multi-annual beach trends at the Truc Vert beach site. There is almost no trend in beach volume at Truc Vert beach, although there is a variation in this parameter on a cycle of 2 to 3yr, with variations related to wave energy and probably to indexes of climate variability. Numerical modelling identified the sensitivity of beach responses to changes in wave height and direction, especially in terms of subtidal morphology and the potential development of shoreline instability. Together with the observed offshore wave angle at the Biscay Buoy, these model results suggest that a potential change in wave angle due to climate variability could significantly modify the bars’ morphology. The combination of data analysis and numerical modelling contributed to the development of vulnerability indexes designed for sandy coasts, which take into account climate-dependant variables such as waves. This allowed the differentiation of the sites in terms of vulnerability to erosion: Sète Lido and Truc Vert beach were the most and least vulnerable sites, respectively. These indexes help in identifying the dominant components of beach vulnerability, and provide potential for the study of how anthropogenic factors affect vulnerability. The study of stakeholder perceptions and decision-making with regard to climate-related risk also highlighted potential anthropogenic effects on beach vulnerability, and identified possible site-specific outcomes.
Storm-induced damages along the Catalan coast (NW Mediterranean) during the period 1958–2008
Geomorphology, 2012
The temporal and spatial patterns of storm-induced damage along the Catalan coast (NW Mediterranean) during the last 50 years have been analyzed to identify main climatic and non-climatic forcings. In the absence of systematic data, a storm-induced damage database compiled from press news has been built, which together with an intensity scale has allowed us to characterize the frequency and intensity of damage. Although no temporal trend has been detected in storm-induced hazards, coastal damage has increased at a rate of about 40% per decade during the last 50 years along the Catalan coast. The main non-climatic factors identified controlling this trend were the urban growth along the coastal fringe and the generalized erosive behavior of beaches. The first one increased values at risk and the second one increased their exposure to storm-induced hazards. In spite of the importance of non-climatic factors to modulate coastal damage, an exponential dependence of damages on storm-induced inundation and erosion was detected. In addition to this, storm-induced geomorphic changes along the Ebro delta coast have also been analyzed. During the period analyzed, "harmful" storms seem to be clustered, with most of the events being present in the late 1990s and especially from 2001 to 2004, resulting in frequent events of intense beach/barrier breaching, massive overwash and flooding. They are mainly expressed in sensitive areas which are subject to long-term erosional processes and comprise a low-lying profile and a narrow beach. This reflects the role of coastal morphology in controlling the intensity of storm-induced hazards along the deltaic coast. Shoreline evolution rates calculated during this period were significantly larger than the previously recorded ones, reflecting a pulsating erosion behavior where large pulses occur during stormy periods and are reduced during post-storm periods. Under the present scenario of maximum coastal development, storm-induced damage has been reported almost every year which could indicate that the present overall beach configuration status along the Catalan coast has reached its limit for protecting the hinterland against storms.
Storm-induced beach erosion potential on the Catalonian coast
Journal of Coastal Research, 2006
The impact of storms in the Catalonian coast is analyzed by classifying storms terms of their beach erosion potential. This follows a two-step procedure in which, first, the storm-induced erosion is simulated using a beach profile evolution model (SBEACH). The coastal response is characterized using two simple parameters, beach retreat and eroded volume from the inner part of the profile. The second step involves looking for a beach erosion potential parameter that when fed with synthetic information on storm characteristics yields erosion values (beach retreat and eroded volume) similar to those calculated with the SBEACH model. To do this, several beach profile change predictors were tested and, although some of them gave reasonable results, it was found that the inclusion of the storm duration within each predictor significantly improved their performance. Thus, the storm duration was identified as a key variable in parametric prediction of storm-induced erosion. Moreover, to predict beach erosion on different profile types, predictors that explicitly include beach slope have to be used. Here we propose one parameter combining wave storm and beach characteristics (wave height, period and storm duration, sediment grain size and beach slope). This was used to estimate beach erosion induced by each of the recorded storms. From this, a 5-class storm scale based on the erosion potential (eroded volume and induced beach retreat) was produced.
Frontiers in Marine Science
In this study, we estimate the shoreline retreat, the vulnerability and the erosion rates of an open beach-dune system under projected sea level rise (SLR) and the action of wind-waves (separately and in combination). The methodology is based on the combination of two state-of-the-art numerical models (XBeach and Q2D-morfo) applied in a probabilistic framework and it is implemented in an open sandy beach in Menorca Island (Western Mediterranean). We compute the shoreline response to SLR during the 21st century and we assess the changing impacts of storm waves on the aerial beach-dune system. Results demonstrate the relevant role that the beach backshore features, such as the berm, play as coastal defense, reducing the shoreline retreat and dune vulnerability rates in the near-term (a few decades ahead) and highlighting the importance of simulating the beach morphodynamic processes in coastal impacts assessments. Our findings point at SLR as the major driver of the projected impacts over the beach-dune system, leading to an increase of ∼25% of the volume eroded due to storm waves by the end of the century with respect to present-day conditions.