Un modelo numérico para la simulación de la evolución del fondo marino en la zona cercana a la costa

En este artículo se presenta un modelo numérico que simula la evolución del fondo marino en la zona cercana a la costa. El modelo está dividido en tres módulos que calculan la propagación del oleaje, las corrientes inducidas por oleaje y viento y el transporte de sedimentos y los cambios morfodinámnicos asociados al mismo. Para calibrar y validar el modelo se han utilizado algunos ejemplos extraídos de la literatura, así como datos de campo. Los resultados del modelo muestran que éste estima adecuadamente tanto las magnitudes como las tendencias de la evolución del fondo marino bajo distintas condiciones hidrodinámicas, por lo que puede ser considerada una herramienta útil para propósitos ingenieriles.Peer Reviewe

Circulación baroclínica e inducida por viento en el puerto de Tarragona (España)

The sustainability of harbour management from an environmental standpoint is a current concern for port authorities. It includes dealing with problems that may affect the quality of in-harbour waters. In semi-enclosed basins, the characteristics of the circulation pattern are one of the main factors influencing the water quality, since they determine the residence time of pollutants inside the basin and govern the interaction between inside waters and the cleaner outside waters. Although harbour hydrodynamics are affected by the constant traffic of vessels and the physical constraints imposed by harbour structures, the water dynamics in ports are generally governed by three mechanisms: tidal forcing, wind surface stress, and baroclinic effects. This study presents the characterisation of winter circulation features in Tarragona harbour (northeast Spain), based on both field data and numerical simulations. Due to the microtidal nature of the Mediterranean Sea, three-dimensional water density distribution and local wind are expected to be the most relevant driving mechanisms. The results obtained suggest that, although wind effects may be important in determining the water flow in and out of the harbour for small time-scales, in the long term the most important water exchange mechanism is related to the waterbody’s baroclinic structure, with wind forcing playing only a second-order role. La gestión sostenible de los puertos desde un punto de vista ambiental es un tema de interés actual y un objetivo para las autoridades portuarias. Este tipo de administración incluye el tratamiento de problemas que pueden afectar a la calidad de las aguas interiores del puerto. En cuerpos de agua semicerrados, uno de los factores que más influye en la calidad del agua son las características del patrón de circulación, puesto que gobiernan la interacción entre aguas interiores y aguas exteriores más limpias, y determinan el tiempo de residencia de contaminantes dentro del recinto. Si bien las corrientes dentro de los puertos se ven afectadas continuamente por el tráfico de buques y por las restricciones físicas impuestas por las propias estructuras portuarias, la hidrodinámica general está dominada por tres mecanismos distintos: mareas, tensión de viento, y efectos baroclínicos. Este estudio presenta la caracterización de la circulación invernal en el Puerto de Tarragona (España), basada en datos de campo y en simulaciones numéricas. Debido al carácter micromareal del Mediterráneo, se espera que los forzamientos más relevantes sean el viento local y la distribución tridimensional de la densidad del agua. Los resultados obtenidos sugieren que, si bien los efectos del viento pueden ser importantes para determinar el flujo de agua hacia el interior del puerto para escalas de tiempo reducidas, a largo plazo el mecanismo más importante de intercambio de agua con el exterior está asociado a la estructura baroclínica del cuerpo de agua, siendo el forzamiento por viento un agente secundario

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

ARTEMIS: A complete mission architecture to bridge the gap between humanity and near-Earth asteroids

Asteroid retrieval missions have recently attracted increasing interest from the community and could provide opportunities for scienti c exploration, resource utilisation and even the development of planetary defence strategies. This paper was developed as a result of a 6-month MSc group project, realised by a total of 14 students at Cran eld University pursuing the Astronautics & Space Engineering degree. An overall system design is proposed for a technology demonstrator mission to move a near-Earth asteroid into an easily-accessible location where it could be further explored by future missions. The target nal orbit is a southern halo orbit around the Lagrange point (L2) on the Sun-Earth system. ARTEMIS (Asteroid Retrieval Technology Mission) abides by ESAs constraints for a Large (L) mission call: realised in only one launch with Ariane 64, an operational duration of less than 15 years and a cost at completion of at most e1100M. The proposed mission combines the design of optimal trajectories, employs advanced solar electric propulsion and introduces a be tting level of spacecraft autonomy. The target is the 2006 RH120 asteroid, with an approximate diameter of 6.5 m and mass of roughly 350 tons. To re ne existing data, the ARROW CubeSat mission (Asteroid Reconnaissance to Research Object Worthiness) is to be launched a year prior to the main mission to probe the asteroid via a y-by. ARROW will provide valuable information, such as the asteroids spin rate, rotational axis and better mass estimate, increasing the overall chance of mission success. The main mission will then capture and secure the asteroid using a mechanism of arm-like booms with xenon- lled VectranTM bags. To allow for proper adaptability to the objects shape and mass distribution, as well as preserve the asteroid unaltered, the mechanism is fully contained in fabric that encapsulates the asteroid. The paper concludes that such a mission is conditionally feasible, and summarises the design process resulting in the nal overall mission baseline design. It also examines the practicality of the suggested design for future missions such as space debris removal or its ability to retrieve celestial bodies with variable mass and shape. Proper adaptation of the design could allow for retrieval of similar size or smaller objects. The future implementation of this mission may further the understanding of the origin of the solar system and act as a catalyst to a new celestial body exploitation industry

Tsunami hazards in the Catalan Coast, a low-intensity seismic activity area

The final publication is available at Springer via http://dx.doi.org/10.1007/s11069-017-2918-zThe potential impacts of tsunamis along the Catalan Coast (NW Mediterranean) are analysed using numerical modelling. The region is characterized by moderate to low seismic activity and by moderate- to low-magnitude earthquakes. However, the occurrence of historical strong earthquakes and the location of several active offshore faults in front of the coast suggest that the possibility of an earthquake-triggered tsunami is not negligible although of low probability. Up to five faults have been identified to generate tsunamis, being the highest associated possible seismic magnitudes of up to 7.6. Coastal flooding and port agitation are characterized using the Worst-case Credible Tsunami Scenario Analysis approach. The results show a multiple fault source contribution to tsunami hazard. The shelf dimensions and the existence of submerged canyons control the tsunami propagation. In wide shelves, waves travelling offshore may become trapped by refraction causing the wave energy to reach the coastline at some distance from the origin. The free surface water elevation increases at the head of the canyons due to the sharp depth gradients. The effects of potential tsunamis would be very harmful in low-lying coastal stretches, such as deltas, with a high population concentration, assets and infrastructures. The Ebro delta appears to be the most exposed coast, and about the 20% of the delta surface is prone to flooding due to its extremely low-lying nature. The activity at Barcelona port will be severely affected by inflow backflow current at the entrance of up to 2 m/s.Peer ReviewedPostprint (author's final draft

Potential of Transplanted Seagrass Meadows on Wave Attenuation in a Fetch-Limited Environment

In this paper, the effectiveness of transplanted (either created or restored) seagrass meadows as a coastal protection measure is assessed through a five-step methodology. The analysis is focused on a stretch of the Catalan coast (NW Mediterranean) which is a fetch-limited environment. The results show that even considering conservative values for the meadow parameters (plant diameter, meadow density and canopy height), significant reductions of the annual average wave heights reaching the beach may be obtained, reducing flooding and erosion risks. Therefore, the investment in the conservation and restauration of seagrass meadows for protecting coastal areas from erosion and flooding is a measure that must be considered, due to the multiple benefits that they provide including ecosystem services. In addition, the proposed methodology may be a useful tool for coastal managers to help them in the design of seagrass meadows for coastal protection

Sediment quality and resuspension rate in Mangueira Bay, Brazil

Mangueira Bay is located in southern Brazil (between 30_ and 32_ south latitude). It is a significant regional resource that lends itself to activities such as tourism, fishing, and fish and shellfish breeding. Studies performed by Rio Grande University (FURG) have demonstrated that, due to its natural conditions, Mangueira Bay is an area of shelter and feeding for the local biota. As a result, the possibility of implementing intensive shrimp breeding has been analyzed. It is therefore important to study the hydrodynamics, water quality and sediments of this water body. This paper describes the spatial and temporal distribution of heavy metals in sediments during monitoring campaigns carried out in October 2002 and June 2003 as a part of the ‘‘Estuaries and Coastal Areas. Basis and Tools for a More Sustainable Development’’ (ECOSUD) project. The distribution of metals in the bed was estimated as well as the potential for resuspension due to the waves caused by typical storm conditions similar to those measured in the May 2003 campaign. This sediment resuspension in the seabed can repollute the water column. Classic expressions were used to estimate the wind-induced water waves, the resuspension rate and the concentration of suspended material. The results show differences in spatial distribution between the two campaigns, but in both cases the south of Mangueira Bay was found to be the proper area for aquaculture. Furthermore, in all of the sediment samples analyzed, the different metals were present in concentrations under the limits stipulated by the Canadian Environmental Quality Guidelines of the Canadian Environmental Protection Agency (CEPA). The calculation of sediment resuspension demonstrated that conditions favor shrimp breeding along the southwest coast under typical winds from the west, especially in the southern part of Mangueira Bay

Modelado del penacho del río Ebro. Validación con medidas de campo

The spreading of the plume induced by the freshwater discharge from the Ebro River into northwestern Mediterranean coastal waters was modelled using two numerical codes. The coastal current field was obtained with a finite difference hydrodynamic model based on a steady-state version of the shallow-water equations, whereas the freshwater dispersion was calculated with a Lagrangian code that solves the 3D convection-diffusion equation and reproduces turbulent diffusion using a random-walk algorithm. The agreement obtained between numerical results, satellite observations and field measurements allows an analysis of the more relevant physical mechanisms and the corresponding tuning of the two models. The results show that local hydrodynamics near the river mouth, and consequently the spreading of the river plume, are highly dependent on the driving river discharge and wind field characteristics.Se presenta la simulación del penacho de agua dulce resultante de la descarga del río Ebro en el Mediterráneo mediante el uso secuencial de dos modelos numéricos. La hidrodinámica costera ha sido obtenida con un modelo en diferencias finitas, basado en una versión estacionaria de las ecuaciones para aguas someras, mientras que la dispersión del agua aportada por el Ebro se ha calculado con un modelo lagrangiano de partículas que resuelve la ecuación de transporte 3D. El ajuste obtenido entre los resultados numéricos, medidas de campo y observaciones desde satélite permiten analizar los mecanismos físicos más relevantes, así como realizar el correspondiente calibrado de ambos modelos. Los resultados muestran que la hidrodinámica local cerca de la desembocadura del río y, por consiguiente, la dispersión del penacho del río, dependen principalmente del volumen de descarga del río y de la características del viento dominante