Author(s): Miguel-Angel Reyes-Merlo; Christian Jesus Montero-Llerandi; Fernando De La Torre-Fernandez; Jose Ramon Martinez-Cordero

Linked Author(s):

Keywords: Maximum Flooding Level; Breakwater; Overtopping; Semi-empiric formulation; Computational Fluid Dynamics model

Abstract: Flood assessment is an ongoing issue in coastal areas. Ordinary Maximum Flood Level (MFL) computations consider storm surges, astronomical tides and run-up levels. However, the presence of infrastructures along the coast hinders this assessment, especially regarding the overtopping of breakwaters in harbour areas. To fulfil the obligations laid down in the Spanish Coastal Law, this MFL must account for the tidal and the storm surge level reached at least five times in a period of five years. This work addresses the assessment of this MFL in Puerto de Vega (Northern Spain), developing a methodology to calculate the overtopping in breakwaters, considering the Spanish regulations’ criteria. This work uses two different sources of bathymetry: multibeam bathymetry provided by the regional government for shallow and intermediate waters, assembled with data from Navionics electronic nautical charts for deep waters. Tidal and wave information are provided by the Spanish Authority Puertos del Estado (REDMAR network and SIMAR records from high resolution modeling, respectively). Wave states are propagated through the MOPLA module of the SMC 2.5 numerical model. The employed methodology uses collected measurements from an extreme coastal event, including photographic documentation and DTM techniques, in order to calibrate and calculate the overtopping volume in the breakwater. The combination of forcing agents that is most likely to provide the appropriate MFL is reduced before the propagation, synchronising each wave state to the recorded water level. The proposed method sorts these provisional MFLs through an iterative process, with Ahrens formulation for the run-up, and Longuet-Higgins for the set-up. Then, the overtopping over the breakwater is computed through two different approaches. The first one considers the division of the breakwater in subsets, since the alignment is composed of more than one typology. Nearshore values in the representative breakwater sections are computed with Longuet-Higgings and Stewart equations, for the set-up, and Van der Meer and Janssen formulation, for the run-up and the overtopping. The second one estimates the fluid-structure interaction through a CFD model based on the Lattice Boltzman approach. In this case, nearshore values for the overtopping are obtained with a particle-based method. Although the computational time is longer than in the first case, the semi-empiric parameters to be estimated are less. Despite slightly differences, both methods provide realistic MFL values. Therefore, this work proposes the combination of both techniques to assess the MFL in the presence of coastal structures, encouraging the use of the numerical model approach. The reason is that results show the reliability on the CFD method compared to semi-empiric traditional formulation, and computational times are constantly shortened due to the development of cutting-edge equipment and solving schemes.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022711

Year: 2022