Joan Pau Sierra

Wind waves off the Ebro Delta, NW Mediterranean

Abstract A descriptive investigation on the wind wave climate off the Ebro delta has been conducted on the basis of time series of data collected after 1978. Sea states have been classified into phenomenological cathegories according to available directional data. For selected records, illustrating the different wave conditions, statistical and spectral analyses have been performed so as to assess the short-term characteristics of the wave climate. Regarding the longer-term evolution, correlations among the main wave parameters have been established. Theoretical probability distributions have been fitted to the observed frequency histograms in order to complete the description of the average wave climate. Furthermore, some statistics of extreme wave heights have also been considered.

SEDIMENT TRANSPORT NUMERICAL MODELLING IN THE SWASH ZONE

A numerical model of sediment transport in the swash zone has been recently developed. The followed approach relies on the solution of the vertical distribution of suspended sediment concentration and incorporates the horizontal advection of suspended sediment from the bore collapse and local pickup using a Lagrangian computing scheme. Computed sediment transport rates are compared to measurements on a reflective beach on the central east coast of Australia. The model has proved to contribute to the explanation of the sedimentary process in the swash zone, predicting accretion on a reflective beach where classical swash sediment transport concepts would give erosion. Copyright ASCE 2006.

Composite modelling of interactions between beaches and structures

An overview of Composite Modelling (CM) is presented, as elaborated in the EU/HYDRALAB joint research project Composite Modelling of the Interactions Between Beaches and Structures. An introduction and a review of the main literature on CM in the hydraulic community are given. In Section 3, the case studies of CM of the seven partners participating in this project are discussed. The focus is on the methodologies used and their impact on the modelling approach, rather than the results of the experiments per se. A further section presents reflections on key elements in CM, as they emerged in the various case studies. The related subject of Good Modelling Practice is summarized in Section 5. Then guidelines are given on how to decide if CM may be beneficial, and how to set up a CM experiment. It is concluded that CM in the hydraulic community is still in its infancy but involves challenging research with significant potential.

Future wave-driven coastal sediment transport along the Catalan coast (NW Mediterranean)

Abstract In the context of climate change, this study evaluates the impact on the long-shore and cross-shore sediment transport (LST and CST) along the Catalan coast (NW Mediterranean Sea) derived from climate projections obtained from five combinations of regional and global circulation models (RCMs and GCMs). Special emphasis is given to how inter-model variability translates from wave projections to wave-driven coastal impacts, which is still poorly known. Results show that the uncertainty is in general larger, especially for LST, for which the discrepancies among regional models are more relevant than those associated with the forcing wave parameters. Such increase in the uncertainty can be explained by the nonlinear processes involved, and the role of the forcing wave parameters having sometimes competing effects (e.g. wave height vs. wave direction). This illustrates that the performance of each RCM–GCM can vary from forcing to impact parameters; hence, the suitability of a particular RCM–GCM to evaluate a certain impact should be assessed based on its ability to properly simulate such impact. In this regard, LST and CST rates computed using empirical formulae that integrate several wave climate parameters, as in this study, can be used as a non-computationally expensive tool to assess the suitability of a given RCM–GCM to project changes in coastal dynamics.

COASTAL DYNAMICS AROUND A SUBMERGED BARRIER

Submerged barriers are one of the most promising kind of shoreline protecting structures. The advantages offered vs. the conventional emerged structures are somehow off set because they are much more difficult to project. This decreases their use and limits their application potential. The paper presents some results, obtained by using numerical models on the hydro-morphodynamic behaviour of such structural concept. They illustrate the observed interactions between the freeboard of the structure, its distance to the coast and the resulting wave field, induced circulation and sediment transport patterns.

A review of potential physical impacts on harbours in the Mediterranean Sea under climate change

Abstract The potential impact of climate change on port operations and infrastructures has received much less attention than the corresponding impact for beach systems. However, ports have always been vulnerable to weather extremes and climate change could enhance such occurrences at timescales comparable to the design lifetime of harbour engineering structures. The analysis in this paper starts with the main climatic variables affecting harbour engineering and exploitation. It continues with a review of the available projections for such variables first at global scale and then at a regional scale (Catalan coast in the western Mediterranean) as a study case for similar environments in the planet. The detailed assessment of impacts starts from downscaled projections for mean sea level and wave storms (wind not considered in the paper). This is followed by an analysis of the port operations and infrastructure performance that are relevant from a climate perspective. The key climatic factors here considered are relative sea level, wave storm features (height, period, direction and duration) and their combined effect, which is expected to produce the highest impacts. The paper ends with a discussion and some examples of analyses aiming at port adaptation to future climate change.

Modelling the sensitivity to various factors of shipborne pollutant discharges

Most of the marine pollution attributable to ship actions is associated with the illicit discharge of oily residues or ballast water, in what is commonly termed operational pollution. In the particular case of ballast water, careless disposal can lead to severe ecological damage, including the irreversible establishment of communities of invasive species. In its 2004 Convention on ballast water management, the International Maritime Organisation defined the measures to be followed to prevent these environmental issues, including the exchange with mid-oceanic water at a minimum distance from the shore. This paper uses two numerical models to analyse the effects of several factors on the dilution of a discharge from a ship moving in the Spanish Mediterranean waters, in order to determine under which conditions the environmental impact of the discharge will be minimum. The results highlight the dual role played by a freshwater plume, which may contribute either to decrease or to enhance the onshoreward transport of the discharged substance, and the relevance of the ships speed in determining the dilution rates.

Short communication: Numerical model for wave overtopping and transmission through permeable coastal structures

In this paper, an energetic wave propagation model that reproduces shoaling, refraction, diffraction, wave-current interaction, bottom friction and wave breaking is modified to simulate also the processes of overtopping and wave transmission over and through permeable coastal structures. This enhances the capabilities of the model and allows to obtain, at a low computational cost, a better reproduction of the wave field (and as a consequence currents and beach response) behind a coastal structure, especially if it is permeable and/or low crested. Model results are compared with laboratory data, showing a good agreement and the suitability of the followed approach.

Numerical assessment of the dispersion of overspilled sediment from a dredge barge and its sensitivity to various parameters.

Marine dredging operations are not uncommon in coastal waters since they are necessary for several beneficial uses, such as harbour maintenance, beach nourishment or removal/capping of pollutants, amongst others. They also constitute a significant risk for the environment, changing its physical, chemical and biological characteristics, as evidenced by many authors. In this study, two numerical models are used to simulate the dispersion pattern of fine suspended sediment spilled from a dredge barge, considering different hydrodynamic scenarios, particle sizes and dredging tracks in a mesotidal environment. The results show that, in this particular case, the currents (largely induced by the tide) are the main responsible for the final disposition of the settled particles, being the other variables of secondary importance.

Climate Impact Assessments

This chapter highlights key climate impacts, hazards and vulnerabilities and associated indicators that have been used to assess current (recent) climate impacts at each of the case-study sites. The aim is to illustrate some of the wide range of information available from individual case studies and highlight common themes that are evident across multiple case-study locations. This is used to demonstrate linkages and sensitivities between the specific climate impacts of relevance for each case-study type (urban, rural and coastal) and the key climate hazards and biogeophysical and social vulnerabilities representing the underlying drivers and site conditions. For some impacts, there are clear, direct links with climate events, such as heat stress and flooding, while for others, such as energy supply and demand, the causal relationships are more indirect, via a cascade of climate, social and economic influences. Water availability and extreme temperatures are common drivers of current climate impacts across all case studies, including, for example, freshwater supply and heat stress for urban populations; irrigation capacity and growing season length for agricultural regions; and saltwater intrusion of aquifers and tourist visitor numbers at coastal locations. At some individual case-study locations, specific impacts, hazards and/or vulnerabilities are observed, such as peri-urban fires in Greater Athens, infrastructure vulnerability to coastal flooding in Alexandria, groundwater levels in Tel Hadya and vector-borne diseases in the Gulf of Oran. Throughout this chapter, evidence of current climate impacts, hazards and vulnerabilities from each of the case studies is detailed and assessed relative to other case studies. This provides a foundation for considering the wider perspective of the Mediterranean region as a whole, and for providing a context from which to assess consequences of future climate projections and consider suitable adaptation options.