Filipa S. B. F. Oliveira

Improvement on open boundaries on a time dependent numerical model of wave propagation in the nearshore region

An improvement on the simulation of outgoing waves on a time dependent numerical model for water wave propagation in the nearshore region is presented. The governing equations consist of a system of first order partial differential equations (PDEs), the equation of continuity and the equation of motion. A comparative study of first order radiation boundary conditions (BCs) and first order radiation BCs combined with sponge layers is presented for cases where outgoing waves leave the numerical domain of calculation through the open boundary. A reduction of spurious reflections from the numerical open boundaries can be obtained with an irrelevant increase in terms of computational cost.

Wave climate modelling south of Rio de Janeiro in Brazil

A verified accurate numerical model for wave propagation in nearshore regions is used to study wave transformation and to predict the wave climate in the coastal area south of Rio de Janeiro in Brazil. The sea state is represented by a group of monochromatic waves. The existence of several groups of islands in the nearshore region adds complexity to the physical processes of wave transformation when waves travel shoreward. Such complexity requires the application of an adequate numerical model like the one used in this study. Results obtained reveal the effects of the islands in the process of wave propagation and the resulting variation of exposure to wave action along the beach.

Characterisation of the dynamics of Figueira da foz beach, Portugal

ABSTRACT The characterisation of the dynamics of Figueira da Foz beach, in the West coast of Portugal, is presented based on the analysis of previous studies and results obtained from the application of a numerical model. Advances on the understanding of the beach dynamics have been achieved by the quantification of the annual and seasonal longshore transport and several beach profile parameters. An evaluation of the contribution of the wave climate components on the longshore transport was also obtained. The results allow sustaining a prediction of the effect of a future change of the wave climate on the longshore transport. Figueira da Foz shoreline change was simulated based on different conceptual scenarios and the results, although not quantitatively conclusive, allow the understanding of the influence of the neighbouring beach hard rock outcrops on the recent evolution.

Scale effects in numerical modelling of beach profile erosion

ABSTRACT Oliveira, F.S.B.F. and Contente, J., 2013. Scale effects in numerical modelling of beach profile erosion. The beach profile morphodynamic processes can be relatively well reproduced in large scale physical models. However, the cost associated to their use makes this methodology not always practicable. As alternative, it is desirable to explore and apply smaller scales laboratory infrastructures with confidence, despite the different scaling laws, that is, the impossibility to simulate all relevant variables in correct relationship to each other. The combination of physical and numerical modelling can be a methodology to improve the required confidence (HYDRALAB III European Programme). Scale effects in a numerical process-based beach profile model, applied to simulate beach profile evolution under erosive wave conditions, were investigated in the present study. The numerical model was applied at laboratory and prototype scales, first with the default settings and then calibrated. Its performance was evaluated using the Brier Skill Score. The numerical results of the profile evolution in both scales were compared after reducing the results from the prototype scale to the laboratory scale. The profile erosion prediction was overestimated in the laboratory scale and underestimated in the prototype scale. Despite the calibration parameter that causes the largest modifications of the beach profile being the same in both scales, the Gamma2 wave parameter, the most efficient parameter was different. For most of the calibration parameters, the value for the best case was not coincident in both scales. It was concluded that there are scale effects using the Litprof model.

Coastal Erosion Management in Algarve (Portugal) — A Beach Nourishment Case Study

ABSTRACT PROENÇA, B., OLIVEIRA, F.S.B.F and SANCHO, F., 2011. Coastal Erosion Management in Algarve (Portugal) — a Beach Nourishment Case Study. In: Micallef, A. (ed.), MCRR3-2010 Conference Proceedings, Journal of Coastal Research, Special Issue, No. 61, pp. 328–334. Grosseto, Tuscany, Italy, ISSN 0749-0208. In the Portuguese southern coast, national and international appeal turns it into a highly relevant area concerning the countrys economy. Vale do Lobo is a resort located in the centre of this coast, where the beach has been suffering from erosion problems for several years now. Local interventions have been executed in order to prevent the erosion of the beach, yet the efficiency of such strategy has not been verified. This studys main purpose is to enable a better understanding of the evolutionary trends of the coastline between the Quarteira and Ancño inlet and to analyse the efficiency of the beach nourishment interventions as a protection technique for a coastal environment with the wave energy exposure and geomorphologic characteristics of the present one. The study focussed on a 10-year period, during which, 700×10 and 370×103 m3 of sand with D50=0.76 mm (slightly larger than the D50 of the native beach) were extracted from offshore, and deposited in the foreshore. The wave climate in the study area was processed, analysed and used as input for modelling the nearshore processes. In addition, beach profiles measured alongshore have been analysed to obtain the representative beach profile. Coastlines of different dates have been derived from aerial photographs. The longshore transport model Litdrift and the coastline model Litline were applied to study the sediment dynamics. Litdrift was used to estimate the longshore transport capacity of the beach for the hydrodynamic series considering the representative beach profile previously obtained. These results were then used to calculate the evolution of the coastline due to the incident wave climate with Litline model. Aerial photographs were used to verify the model. The analysis of the two beach nourishments performed allowed inference on the efficiency of this coastal protection technique to delay the erosion process.

A Simple and Efficient Methodology to Assess Long Term Shoreline Evolution – Case Study

The present chapter describes an efficient methodology to predict the impact of a marina on the adjacent indented beaches planform: initially, the impact of the marina on the hydrodynamic agents that induce sand transport in the adjacent indented beaches; finally, the beaches planform response to the modification of the hydrodynamic conditions. The innovative aspect of this analytical methodology concerns the process of estimating the dominant wave energy flux in front of the beaches, which is based on a statistical analysis of the incident wave regime. The methodology was successfully validated through the comparison of the shoreline configurations obtained analytically with the ones extracted from aerial photographs, before and after the construction of the marina.

A Case Study of Wave Climate Changes due to Nearshore Morphological Evolution

Abstract Seabed accretion, formation of a local irregular shoal as the result of disposal of dredged sediment, and modifications of the coastline configuration from anthropogenic action have introduced significant changes in the physical processes involved in wave propagation, and consequently on the wave climate, in the nearshore area of Hac-Sá Bay, Macau. Statistical analysis of the wave data recorded at a wave-rider station located offshore the study area revealed seasonal, energetic, and directional variation tendencies of the wave regime and facilitated schematization of a representative offshore wave regime. Numerical modelling of propagation and transformation of the components of the representative offshore wave regime, including processes of shoaling, refraction, diffraction, reflection, and breaking, was applied to assess the nearshore wave climate before and after the major coastline and seabed morphological changes. An advanced and accurate numerical model, suitable for the case study, was applied. Comparison of the results obtained for both situations showed that significant changes occurred in the wave climate due to the morphological evolution.