Dunes protected by a beach or embryo dunes higher than the water overflow were not eroded (Figure 4). On beaches lower than 2.5 m, every embryo dune that had developed since 2010 was eroded. The higher the form, the greater the volume of sand that was removed. Only embryo dunes located on beaches over 3 m

amsl were safe. Erosion was the strongest on beaches lower than 2 m. Erosion understood as dune retreat was greater when a beach was lower (coefficient 0.8). Foredune sections of the coast that had hitherto been accumulative witnessed dune foot erosion at a rate of 2–9 m after described storm surges (Table 2), i.e. from 2 to 4 times more than the annual rate of retreat of the Polish coast (1 m per year). Figure 5 presents selected profiles representing different types of foredune erosion XL184 mouse forced by the beach height during the events described. The mean rate of dune erosion was 2.5 m3 with an average Y-27632 clinical trial toe retreat of 1.4 m. The volumetric erosion of sand per square metre of dune exceeded 0.3 m3. On seriously threatened sections of the coast, the volume of sand washed off the dune ridge was larger than 1.0 m3 per square metre. This was a typical situation on the coastal section where the beach was lower than 2.5 m. The rate of sand washout was higher when a foredune was higher than 6 m. Throughout the study area, the largest loss of sediment from a

dune was estimated at 1.2–1.4 m3 per square metre. Figure 6 illustrates examples of dune damage on the monitored sections of the coast. On the lower sections of the coast washover fans 5-FU were formed that encroached on to the land up to 200 m from the beach, for example, on the Hel Peninsula and the Karwia Sandbar. The mouths of the channels connecting lakes with the sea were reformed and enlarged by waves flowing back into the lakes. After the storm, beaches were narrower by 10 to 20 m. The strongest storms, with force 10–12 winds, are produced by NE winds (after Zeidler et al. 1995). All autumn-winter storms have caused erosion and a southward retreat

of the coast at an average rate of 0.1 m year−1 over the last 100 years and 0.5 m year−1 from 1960 to 1983 (Zawadzka-Kahlau, 1999 and Zawadzka-Kahlau, 2012). On the southern Baltic coast the sea level during a storm may rise to 1.5–2 m amsl (Zeidler 1995); water flows on to the land, however, can reach 3.5 m amsl (Łabuz, 2009 and Łabuz, 2013), and such events can cause flooding in these areas. The lower the beach, the greater the dune erosion (Figure 7). The retreat of a dune foot is also related to the beach height (Table 3). Water overflows low dune ridges, artificial paths and depressions up to 3.5 m amsl, causing washover fan development (Łabuz 2009). All relief forms below this level are abraded, and dune ridges in the beach hinterland are subject to regression.