The Netherlands coast covers circa 350 km along the North Sea and is primarily a sand barrier coast, backed by low-lying land. These low-lying areas are polders, locally extending to 8 m below Mean Sea-Level. Close to the coast, the North Sea bottom is mostly sand, so that the Netherlands coast has a large sand reservoir on its doorstep. It is probably the only European country in such a situation. The major part of the coast consists of dunes, which together with the beach and shoreface; represent a natural sand defence against the sea. The year 1953 marked an important turning point in coastal defence management. A disastrous flood struck large parts of the south-western delta, causing much damage and over 1,850 casualties. Areas further south showed continued erosion, as sediment supply lagged behind the increase in coastal lagoon size located behind the narrow coastal barrier in Zealand and along the Wadden Sea.