Vicente Gracia

Processes reshaping the Ebro delta

Abstract Due to the limited supply of sediment from the Ebro river, its delta is mainly subject to reshaping processes in the form of alongshore alternation of erosive and accretive coastal stretches, without a significant change in the overall subaerial surface of the delta. The main agents presently forcing these processes (waves and mean water-level oscillations) are analysed in detail as a function of their contribution to coastal processes. In this manner, waves are characterised in terms of short-term/seasonal changes, longshore sediment transport pattern, long-term cross-shore transport at the shoreface and storm impacts. Although the study area is a microtidal one, and waves are the main agent forcing coastal evolution at yearly scales, mean water-level oscillations (meteorological tides and long-term relative mean sea-level variations) play a non-negligible role. Additionally, a joint analysis of waves and storm surges has been done in order to characterise conditions inducing an ‘impulsive’ type of coastal response. At last, the classical ternary classification of deltas has been applied in a ‘dynamical way’ by considering the river vertex in terms of the variation in sediment supply. Moreover, the effects of considering mean water-level variations (other than tides) on the deltaic classification has also been tested. The inclusion of RSLR influence becomes relevant for ‘river-independent’ deltas since it indicates the inability of the delta to withstand it. The main problem to include this agent in the ternary classification is that RSLR is more of a ‘passive’ factor, whereas the other considered agents are ‘active’ in the sense that they induce more perceivable morphological processes.

Managing coastal environments under climate change: Pathways to adaptation

This paper deals with the question of how to manage vulnerable coastal systems so as to make them sustainable under present and future climates. This is interpreted in terms of the coastal functionality, mainly natural services and support for socio-economic activities. From here we discuss how to adapt for long term trends and for short terms episodic events using the DPSIR framework. The analysis is presented for coastal archetypes from Spain, Ireland and Romania, sweeping a range of meteo-oceanographic and socio-economic pressures, resulting in a wide range of fluxes among them those related to sediment. The analysis emphasizes the variables that provide a higher level of robustness. That means mean sea level for physical factors and population density for human factors. For each of the studied cases high and low sustainability practices, based on stakeholders preferences, are considered and discussed. This allows proposing alternatives and carrying out an integrated assessment in the last section of the paper. This assessment permits building a sequence of interventions called adaptation pathway that enhances the natural resilience of the studied coastal systems and therefore increases their sustainability under present and future conditions.

Breaching of a barrier under extreme events. The role of morphodynamic simulations

ABSTRACT Gracia, V., García, M., Grifoll, M. and Sánchez-Arcilla, A., 2013. Breaching of a barrier beach under extreme events. The role of morphodynamic simulations A study of three breaching episodes of the Trabucador barrier beach (Spanish Mediterranean coast) is presented. The analysis is done from a modeling perspective using XBEACH and SWAN. The morphodynamic model (XBEACH) has been validated with the available information. The so obtained Brier Skill Score index has been 0.44 which can be considered as acceptable. Results indicate that in all cases breaching was taking place after 8 hours of wave action (storm) or less. Besides, four main parameters control the final morphodynamic response of the barrier: the storm intensity, the water level and the initial emerged topography and the storm duration. Major breaching occurs when swell waves are in coincidence with high water levels whereas if they are uncoupled the barrier tends to be breached by a diversity of smaller channels.

Multivariate statistical modelling of future marine storms

Extreme events, such as wave-storms, need to be characterized for coastal infrastructure design purposes. Such description should contain information on both the univariate behaviour and the joint-dependence of storm-variables. These two aspects have been here addressed through generalized Pareto distributions and hierarchical Archimedean copulas. A non-stationary model has been used to highlight the relationship between these extreme events and non-stationary climate. It has been applied to a Representative Concentration Pathway 8.5 Climate-Change scenario, for a fetch-limited environment (Catalan Coast). In the non-stationary model, all considered variables decrease in time, except for storm-duration at the northern part of the Catalan Coast. The joint distribution of storm variables presents cyclical fluctuations, with a stronger influence of climate dynamics than of climate itself.

Influence of benthic boundary layer dynamics on wind‐induced currents in the Ebro delta inner shelf

Measurements taken by two instrumented tripods deployed on the Ebro delta inner shelf at 8.5- and 12.5-m depth were used to characterize low-frequency currents under the action of a moderate eastern storm. Results show that inner shelf currents respond very rapidly to wind action with along-shelf currents dominating over the across-shelf ones. Mean along-shelf velocities of 0.35 and 0.24 m s -1 at the inner and outer position, respectively, were recorded during the event, and they were highly correlated with the along-shelf wind stress. The measured current profiles were used to derive wind drag coefficients, assuming a balance between the along-shelf components of the wind and current bottom stresses. Since under eastern wind events, wave action in the Ebro inner shelf is significantly enhanced, wave-current interaction processes controlling the current bottom stress and sediment mobilization can affect the current structure. During the event, depth-averaged concentrations in the lower meter of the water column larger than 1 g L -1 were recorded that were also accompanied by the generation of vertical concentration gradients larger than 1 g L -1 m -1 . When the bottom drag coefficient was obtained from velocity profiles without considering the presence of these gradients, the required wind drag coefficients to fulfil the along-shelf balance were much higher than the ones derived from wind data, and they vary across the inner shelf. However, when bottom drag coefficients are obtained including stratification effects, the wind drag coefficients fulfilling the along-shelf balance were of the same order of magnitude as the ones derived from wind data and without any difference at both locations.

Suspended sediment observations in the Barcelona inner-shelf during storms

ABSTRACT Grifoll, M., Gracia, V., Fernandez, J. and Espino, M. 2013. Suspended sediment observations in the Barcelona inner-shelf during storms. This contribution describes in detail the Suspended Sediment Concentration (SSC) obtained from an observational set at 24 m depth in the Catalan inner-shelf (North-western Mediterranean Sea) analysing the dominant processes affecting sediment dynamics during storm events. A clear correlation between SSC, energetic waves, and along-shelf currents events has been found. Peaks in river discharge associated to rainy events are also correlated with SSC measurements. Measured conditions highlight the different sediment dynamic situations present during short-term events such as “wet” and “dry” storms with similar wave height. SSC observed during “dry” conditions are correlated with wave action. On the other hand, SSC peaks during “wet” conditions are primarily caused by wave action, along-shelf current, and river discharge. Observed sediment fluxes during storms are larger in spring than during fall. Although the observations present similar characteristics to other inner-shelf regions in the NW Mediterranean Sea, the results reveal a non-negligible influence of the along-shelf current in sediment dynamics. The results presented here contribute to advance in the understanding of sediment dynamics in wave-dominated regions such as the Catalan shelf.

SHORT-TERM RELATIVELY DEEP SEDIMENTATION ON THE EBRO DELTA COAST. OPENING THE CLOSURE DEPTH

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

SUSPENDED SEDIMENT MIXING IN THE SURF ZONE

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

Effects of ultra-porous 3D printed reefs on wave kinematics

ABSTRACT Frau, L.; Marzeddu, A.; Dini, E; Gracia, V.; Gironella, X.; Erioli A.; Zomparelli, A., and Sánchez-Arcilla, A., 2016. Effects of ultra-porous 3D printed reefs on wave kinematics. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 851–855. Coconut Creek (Florida), ISSN 0749-0208. 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.

Chapter 10 – Sustainability of Artificial Coasts: The Barcelona Coast Case

Coastal Zones: Solutions for the 21st Century bridges the gap between national and international efforts and the local needs for actions in communities where coastal zone challenges are faced daily. The solution-oriented approach covers issues of coastal zone management as well as responses to natural disasters. This work provides ideas on how to face the challenges, develop solutions, and localize management of common-pool resources. Coastal Zones targets academic stakeholders and coastal stakeholders who have local knowledge and experience but need a theoretical framework and a greater range of skills to make use of this experience.