Groin impacts on updrift morphology: Physical and numerical study

Abstract

Groins interfere with coastal dynamics and sediment transport, leading to sediments accumulation at the updrift side, while at downdrift, the erosive process is anticipated due to the lack of sediments. To improve numerical modeling capacity to simulate the groins impacts, it is necessary to totally understand the shoreline evolution along time and its relationship with the cross-shore profiles shape. The main goal of this work was to analyze and compare the performance of physical and numerical studies on evaluating the evolution of updrift crossshore profiles geometry and shoreline position after the construction of a groin. This study analyzed a coastal stretch updrift of the groin, at a prototype and model scales, considering the analytical formulation of Pelnard-Considère, the numerical model LTC (Long-term Configuration) and the laboratory tests. The laboratory tested scenario was designed with the aim to gather results, which could be analyzed and compared with numerical simulations from LTC (Coelho, 2005), allowing its improvement, and with the Pelnard-Considère (1956) analytical formulation, both at model scale. The developed study shows an important difference between LTC and Pelnard-Considère (1956) approaches because the analytical solution for the shoreline in equilibrium does not include the wave refraction effects over the updated bathymetry. LTC observed trend of the equilibrium shoreline is not parallel to the initial shoreline, and this behavior was confirmed in the laboratory tests. It was also observed that the sediment transport capacity has very small impact on the LTC shoreline configuration, despite the refraction effects over the updated bathymetries along time. The profile shape obtained in laboratory includes bed forms difficult to reproduce in longterm numerical modeling evaluation of cross-shore profiles because LTC transversal behavior is only based on geometrical considerations and does not represent cross-shore sediment transport and its impact on profile geometry.