Measuring and Modeling Coastal Morphology and Hydrodynamics

eng Sandy beaches are among the most vulnerable systems to mean sea-level rise, which is one of the most certain consequences of human-driven global change. The investigation of mean sea-level rise effects over sandy beaches has to be addressed at the regional scale and below. At the same time, new techniques need to be developed and more data needs to be measured, in order to improve these analyses. Within this context, the current dissertation aims to improve our knowledge of sandy beaches in the Balearic Islands, from a hydrodynamic and morphodynamic perspective. To this end, the study was divided into three different phases. The first phase dealt with the estimation of the coastal flooding and beach erosion induced by mean sea-level rise over and behind the sandy beaches of the Balearic Islands. Regionalized mean sea-level rise projections for different scenarios were used, considering mean sea-level rises up to 103 cm by 2100, in combination with marine extreme events caused by waves and storm surges, obtained from a historical hindcast. Under the worst case scenario, around 36.5 km² of the regional land surface may be permanently flooded by the end of the century, while the area intermittently flooded during extreme events may increase up to 41% with respect to that affected nowadays. Under the same conditions, up to 60% of the beaches within the region may lose more than half of their current emerged surface. This situation would correspond to a loss of recreational value accounting for 7.2% of the 2019 Balearic Islands GPD, affecting the regional economy based on tourism. The second phase of this doctoral thesis involved the development of new models to quantify the shoreline recession induced by mean sea-level rise, according to equilibrium beach profile theory. The development of such models was accompanied by a critical revision of preexisting models within the same theoretical framework (Bruun's rule and Dean's model) which were compared against the newly proposed models using a numerical equilibrium beach profile model named Q2Dmorfo (which computes sediment transport dynamically) as ground truth. The analysis demonstrated the importance of selecting the active profile limits when defining a shoreline recession model, based on the time series of instantaneous forcing. It also highlighted how the finite cross-shore width of beaches can result in a change of the shoreline recession trends, due to the limited sediment availability. This is particularly important to model the typical Balearic Island beach, which is narrow and backed by a hard physiographic control. The third phase of the doctoral thesis described the use of an X-band frequency-modulated continuous-wave radar for beach monitoring, and the development of a novel algorithm for the estimation of spatially-distributed wave spectra and bathymetry over the nearshore, without external calibrations. With the current setup, these variables can be obtained up to 500 m from the radar location, although the offshore limit could be extended in multiple ways, the use of antennae with narrower horizontal beamwidth being the most viable candidate. The algorithm proposed uses the non-coherent part of the measurements, and so suffers from several issues commonly reported for non-coherent radar wave measurements. These could be avoided analyzing the coherent part of the measurements, which is currently under investigation.