Forma en planta de equilibrio estático y dinámico en playas encajadasnuevos avances e influencia del clima marítimo direccional

Resumen

The main objectives of this study were to: (i) investigate the influence of the directional variability of the wave climate on the shape of the equilibrium planform of embayed beaches, (ii) to determine the representative direction of wave energy flux that dictates the orientation of beaches in static equilibrium conditions, and (iii) to model and fit the dynamic equilibrium planform of headland bay beaches characterized by net littoral drift rates. Most of the work presented in this thesis is based on the analysis of directional wave climates impacting prototype beach cases in equilibrium conditions. The study employed field date from several beaches in Spain and Latin America and utilized vertical aerial images of the selected beaches. Moreover, the Coastal Modeling System (SMC) was used as a helpful tool for different purposes within this thesis such as the modeling of wave transformation in the lee of headland breakwaters, estimation of net sediment transport rates and plotting the equilibrium planform shape of the beaches over vertical images. An extensive review of the research topic was addressed in Chapter 2. Next, the effect of beach sediment size and the Shape of the Directional Distribution (SDD) of the energy flux of the wave climate on the direction that dictates the static equilibrium beach orientation was investigated in Chapter 3. Field data from 32 beaches along the Spanish coast and available long-term databases of directional wave climates were employed. Moreover, initiation of sediment motion due to wave action was taken into account in order to filter the directional wave climate to consider only waves that are capable of moving the sediment. The results indicated that the direction of the mean energy flux of filtered waves is more appropriate for the determination of the (SEBO) than that of whole waves. This direction was identified as the morphologically representative direction of the wave energy flux. Chapter 4 investigated the methodology for locating the down-coast control point (Po) point of the SEP of embayed beaches, exploring the role of wave climate directional spreading and employing 44 HBBs in Spain and Latin America. It correlated the planform shape in the long term with the directional variability of the wave climate at the diffraction point. Additionally, an extensive series of numerical simulations using a spectral wave model was carried out to model the combined effects of refraction-diffraction in the lee of a breakwater, defining the part affected by the coastal structure under different wave conditions. The results clarified the importance of wave directional spreading in locating the (Po) point. Additionally, a new formula was derived to locate the down-coast control point (Po) of the parabolic part of the shoreline as a function of the directional variance of the wave climate and the location of the diffraction point with relation to the straight shoreline. The planform shape of embayed beaches in dynamic equilibrium conditions was explored in Chapter 5, proposing a new derived formula to obtain the DEP of (HBBs). The model represents a general form of the Parabolic Bay Shape Equation (PBSE) with modified C coefficients as a function of both the wave obliquity (β) and the net littoral drift rate that is passing through the bay. The angular difference (γd) between the direction of the mean wave energy flux at the diffraction point of the headland and the beach orientation down-coast is utilized in the proposed model as the driver of the net longshore sediment transport rate. The model was verified against natural HBBs in dynamic equilibrium characterized by various net littoral drift rates along the Brazilian coast, producing good results. Furthermore, a design procedure was presented in Chapter 6 to be used for stability studies and design of pocket beaches in dynamic equilibrium conditions. The proposed methodology employs the net sediment transport rate passing through the bay together with the time series of the wave climate impinging on the beach in order to compute the angle (γd) in order to plot and identify the DEP. Furthermore, the design methodology can be employed in coastal management and in the assessment of shoreline changes in situations where the sediment supply rate changes or is reduced from its originating source (e.g. fluvial discharges, sand bypassing, or from an updrift source).