A Hybrid Monitoring-modelling Analysis on the Storm Induced Sediment Dynamics of a Structure-controlled Beach

Modeling Wave Overtopping on a Seawall with XBeach, IH2VOF, and Mase Formulas

“…Most of the country's urbanized marine fronts have been protected with coastal defense structures, such as groins and seawalls, since the 1970s, as is the case of Cova-Gala, the study site [34,35]. However, the rise of the mean sea level and the expected increase of frequency and intensity of maritime storms [1], added to the propagation of a southward erosive trend with large time and space scales, predominantly due to the lack of sediment supply [35], are factors that increase the shore exposure to erosion and wave overtopping, which leads to flooding and inundation [8].…”

“…To protect this maritime front and reduce the generalized beach erosion verified after the construction of the Mondego river mouth jetties in the 1970s, a combined groyne field and seawall defense scheme was built. In contrast to the sediment accumulation at the updrift side of the river mouth's north jetty, extended in 2008-2010, the southern beaches face serious erosion problems, particularly troublesome in Cova-Gala [8,33,35,36]. The seawalls, alongshore coastal defense structures, are located in backshore of a narrow beach, which, despite being emerged during the summer season, when it has an intense recreational and bathing occupation, becomes totally submerged under storm conditions that occur mostly between December and March [33].…”

“…The erosion rate was higher in the first 24-h period of the storm, as the representative equilibrium profile adapted to new highly energetic hydrodynamic conditions, and in the third 24-h period, when the storm reached its energy peak, with Hs reaching 8.60 m ( Figure 6). The scouring of the seawall may be overestimated by the model [36], but XBeach has been successfully applied to investigate the effects of hard elements on the erosion processes during storm surges [4,6,8,61]. The local scour hole developed due to the presence of the seawall that cuts off the sediment supply to the upper beach profile by increasing the energy dissipation on its toe [6].…”

“…The XBeach hydro-morphodynamic process-based numerical model application [4], for simplified coastal defense schemes, proved that it is capable of identifying the overall hydro-morphodynamic driving processes and allows the sensitivity assessment of certain parameters for the environmental test conditions [5,6]. Several recent one-dimensional (1D) and (quasi-) two-dimensional (Q2D) model applications in energetic environments, such as the Portuguese west coast [7,8], have brought new insight on the processes involved in the sea-structure-sediments interactions and how they affect the local morphodynamics. The quantification of how these effects vary with the hydrodynamic and geomorphologic characteristics of the coastal environment was built upon the consolidated knowledge on modeling approaches of the nearshore dynamics [9][10][11].…”

“…The quantification of how these effects vary with the hydrodynamic and geomorphologic characteristics of the coastal environment was built upon the consolidated knowledge on modeling approaches of the nearshore dynamics [9][10][11]. A recent study performed by [12], regarding the 1D and Q2D XBeach hydrostatic model performance for bed morphology evolution, revealed overall Brier Skill Scores that indicate similar performance of Q2D and 1D simulations in the inter-tidal and shoreline area, under storm conditions comparable to [7,8]. Still, as is the case for these applications and as collected by [2], most of the model validation studies regarding wave run-up and overtopping have been limited to the scope of morphological changes comparison (e.g., [13][14][15][16]).…”