Simulating Destructive and Constructive Morphodynamic Processes in Steep Beaches

Abstract

Short-term beach morphodynamics are typically modelled solely through storm-induced erosion, disregarding post-storm recovery. Yet, the full cycle of beach profile response is critical to simulating and understanding morphodynamics over longer temporal scales. The XBeach model is calibrated using topographic profiles from a reflective beach (Faro Beach, in S. Portugal) during and after the incidence of a fierce storm (Emma) that impacted the area in early 2018. Recovery in all three profiles showed rapid steepening of the beachface and significant recovery of eroded volumes (68–92%) within 45 days after the storm, while berm heights reached 4.5–5 m. Two calibration parameters were used (facua and bermslope), considering two sets of values, one for erosive (Hm0 ≥ 3 m) and one for accretive (Hm0 < 3 m) conditions. A correction of the runup height underestimation by the model in surfbeat mode was necessary to reproduce the measured berm elevation and morphology during recovery. Simulated profiles effectively capture storm erosion, but also berm growth and gradual recovery of the profiles, showing good skill in all three profiles and recovery phases. These experiments will be the basis to formulate event-scale simulations using schematized wave forcing that will allow to calibrate the model for longer-term changes.

Biotic and abiotic factors governing dune response to storm events

“…tidal range, wave climate, and sediment availability) were considered to be stationary. It is also important to highlight that the beach width mapping was performed on images from the end of the spring season, suggesting that the berm could already have reached its maximum robustness, given the fact that beach recovery is very fast in the study area (Kombiadou et al, 2021; Malvarez et al, 2021). Thus, berm robustness or backshore volume was computed as the product of the backshore width (measured from the satellite images as the distance between the wet/dry and the vegetation lines) and the berm height (constant within each sector).…”

“…tidal range, wave climate, and sediment availability) were considered to be stationary. It is also important to highlight that the beach width mapping was performed on images from the end of the spring season, suggesting that the berm could already have reached its maximum robustness, given the fact that beach recovery is very fast in the study area (Kombiadou et al, 2021;Malvarez et al, 2021).…”

Modeling of Coastal Erosion in Exposed and Groin-Protected Steep Beaches

“…9 and 12). As the present work only focused on destructive processes induced by storms, these settings might not be appropriate to simulate constructive morphological processes in the long term, as found by Kombiadou et al (2021). The comparison between the 1D and 2D hydrodynamic and morphological outputs for the high-energy Storm Emma demonstrated that the higher erosion simulated by the 1D model was related to the higher infragravity wave height simulated in the 1D model (Fig.…”

Modeling the Morphodynamics of Coastal Responses to Extreme Events: What Shape Are We In?

“…(Cohn et al 2019a). Although aeolian transport plays a minor role relative to the wave-driven processes in storms, even during the recovery phase (e.g., Kombiadou et al 2021), the inclusion of these processes will improve simulations on timescales of years to decades. The effects of wave growth due to local winds can also be included.…”