In such cases, the parameter k may reach a value close to 1. The parameter k, representing the nearshore wave energy in relation to the offshore wave energy for all encountered

wave conditions, is illustrated in Figure 6. Apart from coastal swell and wind waves, there may also be oscillatory motion of the water, characterized by longer periods. Such waves, called infragravity waves, are said to have a significant influence Copanlisib chemical structure on coastal morphodynamic processes (Aagaard and Greenwood, 2008, Coco et al., 1999, Coco et al., 2001 and Pruszak et al., 2007). The study of Pruszak et al. (2007) concerns the southern Baltic coast, and includes the Lubiatowo site considered in the present paper. It appears that both standing and progressive infragravity waves can occur in a multi-bar dissipative coastal zone. These latter waves are generally much smaller than gravity waves, and decrease rapidly in height seawards of the shoreline. Infragravity waves are

therefore likely to create and modify rhythmic shoreline forms, but are unlikely to affect the onshore and offshore movement of the entire shoreline (Pruszak et al. 2007). An important indicator of beach resilience, especially for dunes on the beach INCB018424 hinterland, is beach width. Owing to possible large variations at shorter time scales, the behaviour of beach width in the long term is of considerable importance. Long-term field data (1875–1979) collected from the ca 500 km long non-tidal coast of Poland suggest that a sandy seashore with dunes is relatively safe and stable when the beach width (ys–yd) is no less than 40 m ( Dubrawski & Zawadzka (eds.) 2006). Similar conclusions, defining the safety

of a sandy shore by a beach width of at least 40–50 m, can be drawn from investigations of other southern and south-eastern Baltic shores ( Boldyrev, 2008 and Bobykina and Boldyrev, 2008). Observations of the shore at Lubiatowo, comprising measurements of shoreline and dune toe positions carried out since 1983, indicate that this coastal section has been rather stable in the long term. Nevertheless, beach safety criteria are different for tidal shores where the hydrodynamic loads are more complicated. On tidal coasts, the mean beach width during the Thalidomide ebb tide can be 2–3 times larger than at high tide. Moreover, unlike dissipative non-tidal shores, the beach width is bigger in winter than in summer ( Quartel et al. 2008). Previous surveys at CRS Lubiatowo have shown that it is difficult to make out any clear seasonality of variations in the parameter (ys–yd): this can be assumed as evidence that the randomness of morphological processes plays a more important role than seasonal climatic fluctuations. A certain regularity is discernible only for the autumn months (decrease of beach width): this can probably be explained by the storms and other extreme events that usually occur at that time and cause periodic intensification of beach erosion and shoreline retreat.