Coastal Processes and Research
Our beaches are always changing. Under the influence of wind, waves and tides, the Dutch coasts can develop considerably in over a short period of time. When more sand is washed away than is supplied, there is beach eroding; vice verse the beach is accreting.
Coastal erosion and recovery
The Netherlands is very prone to windy days. During storms, wind speeds at sea increase enormously. This can generate large waves in a short period of time. Combined with the onshore wind, these waves make the water level rise along the coast. This increased water level drives a strong offshore undertow. The sand that is stirred up by the breaking waves is therefore transported seawards rapidly and in large amounts.
It often takes a long time before the beaches are recovered. This recovery happens during mild conditions; when the waves are no bigger than about 1 meter. Those waves drive circular water movement on the seabed; it sways forwards and backwards to the rhythm of the waves. The landward current is slightly more dominant. As a result, wave by wave, small amounts of sand are returned to the beach.
Below you will find a short lecture (in English) about these natural beach dynamics.
After the sand has reached the beach, the wind takes over. When part the beach is not covered with water during low tide, the sand slowly dries up. When the wind blows, the dried grains are then carried away by the wind and moved towards the dunes. Beach vegetation such as marram grass, which grows higher up the beach and covers a large part of the Dutch dunes, absorbs part of the sand grains that blow past, causing the beach to accrete locally. In this way the upper part of the beach and the dunes slowly start to grow.
Below you will find a video about our research into dune development.
Nourishments and maintenance
Naturally, Dutch beaches experience more erosion than accretion. If we didn't do anything, the shoreline would therefore slowly move inland, at the expense of the dunes and the land behind. This is why Rijkswaterstaat, which is responsible for the Dutch public works and water management, maintains the Dutch coast by means of sand nourishments: large quantities of sand from the deep North Sea that are placed off the coast where it is needed. These sand nourishments are usually carried out underwater, in the surf zone. Under the influence of natural processes, this sand then slowly, over a period of months to years, moves towards the beach and dunes.
CoastSnap enables the researchers (from Utrecht University) to track the change of our beaches along the coast and to correlate this change to the natural and human-influenced dynamics. Read more about how you can contribute here.