Climatic Drivers of Potential Hazards in Mediterranean Coasts

This paper studies climatic drivers (air and water temperature, precipitation rates, river discharge, sea level and storm patterns) in four Mediterranean regions: the Catalan-Valencia Coast (Spain), the Oran (Algeria) and Gabe`s (Tunisia) Gulfs and the western Nile Delta (Egypt). The paper also considers the potential hazards that these drivers can induce. It first analyses climatic trends in the drivers, taking into account the available time series of recorded and simulated meteo-oceanographic data from different sources. Next, it presents the general framework to assess biogeophysical hazards (flooding, erosion, droughts and water quality), followed by a simple and yet robust evaluation of those hazards for the four studied coastal sites. Assuming climate change projections under different scenarios and considering the observed trends in drivers, the resulting erosion rates due to sea-level rise and wave storm effects have been estimated. The Nile and Ebro Deltas, together with the Oran Gulf, are more vulnerable than the Gulfs of Valencia and Gabe`s. Regarding water quality in terms of (a) precipitation and dissolved oxygen in the water column and (b) sea surface temperature, the results show that the most vulnerable zones for the projected conditions (a) are the Gulfs of Oran, Valencia and Gabe`s, while the Nile Delta is the region where the decrease in water quality will be less pronounced. For the projected conditions (b), the most vulnerable zone is the Ebro Delta, while the impact in the other three cases will be smaller and of comparable magnitude. Finally, the overall future impact of these hazards (associated to climatic change) in the four sites is discussed in comparative terms, deriving some conclusions

Use of a hydrodynamic model for the management of water renovation in a coastal system

In this contribution we investigate the hydrodynamic response in Alfacs Bay (Ebro Delta, NW Mediterranean Sea) to different anthropogenic modifications in freshwater flows and inner bay–open sea connections. The fresh water coming from rice field irrigation contains nutrients and pesticides and therefore affects in multiple ways the productivity and water quality of the bay. The application of a nested oceanographic circulation modelling suite within the bay provides objective information to solve water quality problems that are becoming more acute due to temperature and phytoplankton concentration peaks during the summer period when seawater may exceed 28 ∘C, leading to high rates of mussel mortality and therefore a significant impact on the local economy. The effects of different management “solutions” (like a connection channel between the inner bay and open sea) are hydrodynamically modelled in order to diminish residence times (e-flushing time) and water temperatures. The modelling system, based on the Regional Ocean Modeling System (ROMS), consists of a set of nested domains using data from CMEMS-IBI for the initial and open boundary conditions (coarser domain). One full year (2014) of simulation is used to validate the results, showing low errors with sea surface temperature (SST) and good agreement with surface currents. Finally, a set of twin numerical experiments during the summer period (when the water temperature reaches 28 ∘C) is used to analyse the effects of proposed nature-based interventions. Although these actions modify water temperature in the water column, the decrease in SST is not enough to avoid high temperatures during some days and prevent eventual mussel mortality during summer in the shallowest regions. However, the proposed management actions reveal their effectiveness in diminishing water residence times along the entire bay, thus preventing the inner areas from having poor water renewal and the corresponding ecological problems.info:eu-repo/semantics/publishedVersio

Comparison of wave-current interaction formulation using POLCOMS-WAM wave-current model

Ocean processes do not take place in isolation but interact with one another to form a complex system. This paper focuses on these processes by using and developing the POLCOMS-WAM model. The Stokes’ drift and radiation stress effect on currents have been included, following state of the art formulations. The system is evaluated in the NW Mediterranean and the Irish Sea. Due to oceanographic properties of the Catalan coast, currents are typically less than 20 cm/s and therefore the modification of waves due to the effect of currents is minimal. However, the wave induced currents, mainly caused by enhanced wind drag due to waves, produce a current of about the same magnitude as the ambient one and thus become an important source of mass transport. For the Irish Sea an improvement of storm surge modelling by considering a wave modified wind stress is presented

Numerical Simulation of water mixing and renewal in the Barcelona harbour area.

Quantification of water quality in harbours is an important issue. Harbours are typically characterized by the presence of complex coastline and anthropogenic structures and reduced circulation. Often, microbe contamination from urban sources and over-enrichment by nutrients from agricultural sources is present in the harbour. Moreover, the presence of ships, combined with the water shallowness, may produce resuspension of polluted sediments degrading even more the quality of water. The combined effects may produce biological transformations and create a source of very polluted waters, that, once moved out of the harbour may affect the water quality of the surrounding sites. On the other hand, the use of prognostic models to evaluate water renewal and quality in these sites is complicated by the geometric complexities and by the interaction between different physical processes. For example the presence of submerged jets interacting with the picnocline and geometrical features, makes standard prognostic models based on simple closure schemes for turbulent mixing of momentum temperature and scalars (pollutants) hardly applicable. In the present joint research project we intend to analyze water quality under typical external forcing in the harbour of Barcelona (ES). We use a state-of-art numerical model (LES-COAST) recently developed for the analysis of water mixing in semi-closed or closed bays (Roman et al., 2011)

Measuring wave impact induced pressures with a pressure mapping system

The use of a pressure mapping system for measuring wave impact induced pressures is evaluated in this paper. A set-up and a calibration methodology are suggested and employed for this work. The system is validated against pressure transducer and load cell measurements and for a range of waves breaking on a vertical seawall. For a large number (120 measurements for each case considered) of breaking and broken waves interacting with the wall, the peak pressure (Ppeak) profiles and the pressure distribution maps reported by the system agree well with results acquired using pressure transducers. Although the pressure mapping system tends to underestimate Ppeak, differences on the mean of the 3, 5 and 10 highest Ppeak rangewithin±10%, while for the majority of the measurements the error on the integral of the acting pressures (the acting force compared with the force measured by the load cell) ranges within ±20%. It is concluded, that through careful calibration and set-up the pressure mapping system has the capacity to provide pressure distribution maps with a good accuracy. It is not, however, considered to constitute the absolute alternative to pressure transducers and thus a combined use is suggested for applications where a very high level of accuracy is required

Numerical Simulation of Water Mixing and Renewals in the Barcelona Harbour Area: The winter season.

In the present paper, we use numerical simulation to investigate currents, mixing and water renewal in Barcelona harbour under typical conditions of wind forcing for the winter season. This site is of particular importance due to the interplay between touristic and commercial activities, requiring detailed and high-definition studies of water quality within the harbour. We use Large Eddy Simulation (LES) which directly resolves the anisotropic and energetic large scales of motion and parametrizes the small, dissipative, ones. Smallscale turbulence is modelled by the anisotropic Smagorinsky model (ASM) to be employed in presence of large cell anisotropy. The complexity of the harbour is modelled using a combination of curvilinear, structured, non-staggered grid and the immersed boundary method. Boundary conditions for wind and currents at the inlets of the port are obtained from in-situ measurements. Analysis of the numerical results is carried out based on both instantaneous and time-averaged velocity fields. First- and second-order statistics, such as turbulent kinetic energy and horizontal and vertical eddy viscosities, are calculated and their spatial distribution is discussed. The study shows the presence of intense current in the narrow and elongated part of the harbour together with sub-surface along-shore elongated rolling structures (with a time scale of a few hours), and they contribute to the vertical water mixing. Time-averaged velocity field reveals intense upwelling and downwelling zones along the walls of the harbour. The analysis of second-order statistics shows strong inhomogeneity of turbulent kinetic energy and horizontal and vertical eddy viscosities in the horizontal plane, with larger values in the regions characterized by stronger currents. The water renewal within the port is quantified for particular sub-domain regions, showing that the complexity of the harbour is such that certain in-harbour basins have a water renewal of over five days, including the yacht marina area. The LES solution compares favourably with available current-meter data. The LES solution is also compared with a RANS solution obtained in literature for the same site under the same forcing conditions, the comparison demonstrating a large sensitivity of properties to model resolution and frictional parametrization

Effects of Ultra-Porous 3D Printed Reefs on Wave Kinematics

Present 3D printing technology allows the efficient design and construction of structures with complex shapes and high porosity satisfying biological and coastal protection demands. In this case, an array of ultra-porous tetrahedron shaped 3D printed artificial reef (UPTSAR) is proposed to be used as a submerged breakwater for both environmental enhancement and wave protection. The aim of this study is to analyse the wave-structure interaction effects and the resulting velocity and wave height fields. For this, two-dimensional small scale tests (1:15) using irregular waves were carried out in a wave flume facility at BarcelonaTech. The influence of wave steepness, relative freeboard, relative water depth and the porosity on wave Kinematics have been analysed. The paper will describe in detail the results obtained for the different tests. These results are used to evaluate the functionality of the UPTSAR as coastal protection structures

Wave propagation over posidonia oceanica: large scale experiments

Posidonia oceanica meadows are considered to be of high importance to the environmental conservation in the Mediterranean Sea, supporting a highly biodiverse habitat and protecting from coastal erosion. In the CIEM wave flume of LIM/UPC (Barcelona, Spain) large scale experiments have been conducted for measuring wave attenuation, transmission and energy dissipation over artificial P. oceanica in intermediate and shallow waters. The effects of submergence ratio hs/D (hs = height of seagrass, D = water depth) and seagrass density (number of stems per squared meter) on the above characteristics are investigated. Mean velocities above and within the simulated P. oceanica are measured and the wave induced flow within the seagrass, which influences processes such as nutrient uptake, waste removal and larval dispersion, is estimated. A meadow with a total length of 10.70 m was constructed using polypropylene artificial plants. Measurements of wave height at different locations along the meadow indicate attenuation of waves for three different submergence ratios (hs/D), two seagrass densities (stems/m2) and various wave conditions. Results are also analysed with regard to the wave induced flow within the field and the effects of hs/D and seagrass density on mean flow characteristics are investigated based on measurements of mean velocities taken within the meadow.Peer Reviewe