The coast is vulnerable to forces from the sea – and coastal protection and maintenance is an ongoing challenge.
Information and knowledge about wind, waves, depth conditions and sediment types is key in the decision-making process on how to protect the coasts.
Coastal erosion: how it happens
Waves and currents stir up the sediment in the seabed, and move the suspended material in the flow direction.
This is what we call sediment transport.
One of the most important types of sediment transport occurs when the waves approach the coast with an angle, and break close to shore. Looking at the coast from a distance, we clearly see that the shoreline is changing its position from year to year.
This is due to longshore transport picking up and settling out sediment in different patterns along the coast.
This molding and erosion of the coast by the waves and the currents is called ‘coastal morphology’.
It poses a huge problem for coastal engineering projects and for coastal communities.
How to prevent coastal erosion
Historical attempts to prevent erosion is by adding coastal structures.
But whenever a construction is put on the coast, it will tend to block the natural sediment transport. Sand will be held back on one side, but on the other side, the sand will be missing and increased erosion is now a problem there.
The overall erosion cannot be stopped by hard structures. Positive effects are often only temporary or local. In reality, the erosion problem is in most cases just exported downstream.
Another important way of dealing with erosion is by using sand nourishment.
If we artificially add sand to the coast at the same pace as the coast is being eroded, we can neutralise the erosion in a very simple way. The sand will be eroded so new sand has to be added periodically – say once a year – to keep up with the erosion.
You might compare this with painting a house to protect it against the sun and the rain.
Using simulation models
Structures are sometimes needed, and we need to develop a design for sand to pass around it in the best possible way.
This is most efficiently done by using computer models to simulate the sand movement for different layouts. And from these results, decide on which one has the desired effect.
Computer models can be used to simulate the behaviour at the actual coastal area using information about wind and waves, depth conditions and sediment types in that area.
It is the only tool available for predicting impacts on the coast due to anticipated climate change – and to study mitigation measures.
There is an increased need for coastal protection, maintenance and coastal development in the future. And also to develop computer models that support design and decision making in the increasingly demanding future.