Dimensioning and numerical modeling of the breakwater embankment of Hernesaari marina in Helsinki

A new regional development site is being constructed on Hernesaari and a large marina is planned. The southern tip of Hernesaari is the southernmost point of the Helsinki Peninsula and is highly susceptible to wave action. Therefore, a breakwater is necessary to attenuate wave entering the marina. The marina breakwater is a wave energy barrier designed to protect the marina from the effects of waves, with the purpose of ensuring the safety of vessel navigation. Understanding wave behavior is one of the most critical considerations in breakwater design. However, real sea waves are complex, and modeling them is not straightforward. A numerical wave modeling is required to determine the breakwater dimensions and understand its impacts. REEF3D, an open-source computational hydrodynamics software, was used to simulate wave attenuation of the breakwater. The potential flow solver NHFLOW was chosen as the best compromise between performance and speed in this work. Waves were generated as multidirectional irregular waves using a frequency spectrum extracted from Hernesaari measurements. Experiments were performed to first verify the fidelity of REEF3D to analytical results, and then measure the wave attenuation performance of a simplified version of the planned breakwater. Fidelity to analytical results was acceptable, and the capacity of wave attenuation of that simplified version was demonstrated, with attenuation until $5-10$\% of the original wave height. Nevertheless, more experiments need to be performed with 1) a more faithful breakwater shape, 2) different wave incidence angles, 3) severe storm waves, and 4) the effect of future sea level rise incorporated.