Analysis of relationships between near-shore hydrodynamics and sediment movement on Osmussaar Island, western Estonia

Abstract

Based on field studies, hydro-meteorological data and wave hindcasts, coastal developments and their hydrodynamic forcing conditions are studied on the limestone relict island of Osmussaar. Areal growth of Osmussaar Island, which emerged from the Baltic Sea 2000–3000 years ago and has grown ever since, has practically stopped as the current global sea level rise nearly balances out the local isostatic post-glacial uplift; yet it continues on the southern shores of the island as a result of gradual accumulation of the matter eroded by waves from the north-westerly exposed Osmussaar cliff and the submarine limestone bench in front of it. Based on analysis of old maps, photographical material, and levelling surveys from coastal study sites on Osmussaar, the island as a whole is slowly migrating to the south-east. Compared to the 1960s and 1970s, the rate of coastal changes has increased from 0.2 m2 y-1 to 1.2 m2 y-1 per shoreline meter. A painted sediment experiment conducted in 2011 revealed the nearshore feeding zones for beach ridges. Storminess and high sea level events have increased on the windward, westerly exposed coast. Wave climate has undergone some cyclical changes with the last high phase in the 1990s and a new cycle probably started again 2010.