Spatial variations of wave loads and closure depths along the coast of the eastern Baltic Sea; pp. 93–109

The closure depth is a key parameter in coastal processes as it characterizes the overall wave intensity in the nearshore and indicates the water depth down to which storm waves are able to maintain a universal shape of equilibrium coastal profiles. The properties and alongshore variations of the closure depth for the eastern Baltic Sea coast are evaluated at a coarse resolution (5.5 km) and for the vicinity of Tallinn Bay at a higher resolution (0.5 km). The study is based on numerical simulations of wind-generated wave fields. It is shown that, due to the small contribution of remote swell in the Baltic Sea, the typical ratio of wave heights in strongest storms and average wave heights is about 5.5, which departs considerably from that of open ocean coasts. A modification of the formula for the approximate calculation of the closure depth from the average wave height is derived. The estimates are based on four methods: from the wave heights of the strongest storms, from average wave heights based on a linear approximation, and using two versions of a second-order approximation. The greatest closure depth of up to 7.25 m was found to occur along the coast of the Baltic Proper near Hiiumaa, Saaremaa and the Kurzeme Peninsula. These areas also experience the largest wave intensities. Along other parts of the Baltic Proper coast the closure depth is typically 5–6 m, whereas in the Gulf of Riga and along the southern coast of the Gulf of Finland it is usually in the range of 3–4 m.