An estimate of the impact of vessel wakes on coastal processes: A case study for Aegna, Estonia

Abstract

The purpose of the study is to quantify the remote impact of wakes from fast ferries on the relocation of coarse gravel (diameter 1-2.5 cm), pebbles (2.5-5 cm) and cobbles (5-10 cm), The study site is at the coast of the island of Aegna in Tallinn Bay. Experiments were performed in the calm season (JuneJuly 2013) when the majority of gravel and pebbles were set into motion by vessel wakes. A few thousands of painted sediment grains were laid along a straight line (perpendicular to the waterline) to the subaerial beach until the observed highest wave run-up line and in batches at depths of 0.5-10 m. The location of each painted grain visible in the swash zone was positioned daily with the RTK-GPS device for nine subsequent days and once after three months in October. The relocation of the center of mass and dispersion of each size class and the skewness of the entire painted grain set was evaluated daily. Simultaneous measurements of vessel wakes in the nearshore made it possible to relate the properties of sediment transport with the properties of incoming waves.