The role of gravel pocket beach on stability of urban rocky coastline

Gravel beaches provide natural coastal protection along other ecosystem services to many coastal areas. By dissipating wave energy, they can contribute to stability of cliffs and coastal structures behind them. This paper investigates the effectiveness of gravel pocket beaches (GPB) for protecting urban coastline in the city of Rijeka, Croatia. Two beach systems were studied, a natural system comprised of a beach and a cliff (Sablićevo) and a man-made system (Ploče) comprised of an artificial beach and a sea wall. The rocky coastline around Rijeka is predominantly formed in carbonates (Benac et al., 2013). A number of pocket gravel beaches can be found at locations of previously weakened carbonates, where a local erosion of coastal cliffs provides the sediment supply (Pikelj and Juračić, 2013). This is a micro-tidal environment with a tidal range between 20 and 50 cm. The coastline is exposed to wind-generated waves from the south-east (SE) to south-west (SW) directions, with the largest significant wave height of 3 m in the Rijeka Bay (Lončar et al., 2014). The highest waves from the SE direction are usually accompanied by storm surges. The heights water elevation of 1.27 m CVD was recorded at the nearby tidal gauge in Bakar Bay, east of Rijeka, on 29th October 2018.