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Beach profile evolution under storm sequence forcing presents an emerging research topic that has only been investigated at a limited number of sites. The occurrence and effects of storm sequencing on beach profile evolution are studied at Hasaki Beach, Japan, using weekly beach profile and two-hourly offshore wave measurements. During the 25-year study period, the supratidal beach at Hasaki is subjected to long-term accretion and steepening while the shoreline shows a long-term oscillation. In addition, oscillations of the supratidal beach volume and the shoreline at semi-annual and annual intervals are identified, which are largely controlled by the variability of the wave height. Hasaki Beach is subjected to frequent storms that often cluster in sequences, especially during the extra-tropical cyclone season (January to March). The majority of storms and sequences generate erosion of the beach above the low water level but some also lead to recovery. Despite a tendency for storms and storm sequences with larger power to cause more erosion, the present data does not demonstrate increased beach erosion by storm sequences. Following these findings, the tendency of the beach to evolve towards equilibrium and the importance of the antecedent beach morphology are demonstrated. • Accretion and steepening of the supratidal beach at Hasaki during the 25-year study period. • Annual and semi-annual oscillations of the shoreline, supratidal and intertidal beach volume are controlled by the wave energy. • Storms and storm sequences are quantitatively defined for Hasaki Beach and the definitions are discussed. • No indication for increased erosive effect due to storm sequences compared to individual storms of equivalent power • The antecedent beach morphology and the evolution of the beach towards equilibrium are found to be important. [ABSTRACT FROM AUTHOR]

New large-scale experiments on the influence of storm sequencing on beach profile evolution are presented. The experiments comprised three sequences that commenced from the same initial beach profile. Each sequence consisted of two storms of different energy, with each storm followed by a recovery phase. A specific focus of the experiments was the influence of storm chronology as well as the influence of the recovery wave energy and duration on beach evolution. The breaker bar and the shoreline are studied as indicators for the beach response. Both evolve towards an equilibrium location for each wave condition where the breaker bar reaches its equilibrium much faster than the shoreline. Overall, no enhanced beach erosion due to storm sequencing is observed. Despite a similar cumulative wave power of the three sequences, the final beach configuration of each sequence seems to be determined by the last wave condition instead of previous storms. However, storm sequencing is important when the beach profile has not yet fully recovered before being disrupted by the subsequent storm. In this case, the second storm does not necessarily cause further erosion but can result in onshore sediment transport and hence, form part of the recovery. The bulk onshore sediment transport as well as the shoreline recovery rate vary depending on the wave condition and the profile disequilibrium and show a maximum value for a recovery condition with an intermediate wave energy. The very low energy condition that was performed for a long duration (24 hours) generated a near-stationary beach profile with typical features of a reflective beach. • New large-scale experiments on storm sequencing and beach response. • The beach evolves towards an equilibrium state under the performed storm sequences. • The rate of beach change varies depending on the antecedent beach morphology. • Largest bulk onshore sediment transport occurs for intermediate low energy conditions. • A very low energy condition of long duration (24 h) results in a reflective beach profile. [ABSTRACT FROM AUTHOR]

The evolution of different initial beach profiles towards the same final beach configuration is investigated based on large-scale experimental data. The same wave condition was performed three times, each time starting from a different initial profile morphology. The three different initial profiles are an intermediate energy profile with an offshore bar and a small swash berm, a plane profile and a low energy profile with a large berm. The three cases evolve towards the same final (equilibrium) profile determined by the same wave condition. This implies that the same wave condition generates different sediment transport patterns. Largest beach changes and differences in hydrodynamics occur in the beginning of the experimental cases, highlighting the coupling between morphology and hydrodynamics for beach evolution towards the same profile. The coupling between morphology and hydrodynamics that leads to the same final beach profile is associated with differences in sediment transport in the surf and swash zone, and is explained by the presence of bar and berm features. A large breaker bar and concave profile promote wave energy dissipation and reduce the magnitudes of the mean near-bed flow velocity close to the shoreline limiting shoreline erosion. In contrast, a beach profile with reflective features, such as a large berm and a small or no bar, increases negative velocity magnitudes at the berm toe promoting shoreline retreat. The findings are summarised in a conceptual model that describes how the beach changes towards equilibrium from two different initial morphologies. [ABSTRACT FROM AUTHOR]