Belgium

Coastal erosion Belgium

Vulnerabilities

The Belgian coastline is 67 km, of which 33 km are dunes and the rest is built-up area and harbours (protected from the sea by a dike) (2). A large part of the coastline has been subject to erosion for several decades. Groynes have been built to restrict the erosion by currents and waves. Since 1960 beach nourishments have been carried out regularly to compensate for the erosion at almost 20 km of the coastline (4,5).

The coastline is characterized by a high building and population density, an important source of income from tourism, important harbours, a lot of fishery, a hinterland dominated by agriculture, and some valuable nature reserves (4,5).

Beaches and dunes also have an important role in protection against flooding. Beach erosion is variable: some beaches are stable, a small fraction is growing, but the majority (around a third) has been eroding continuously for a long time (3).

Until the ‘70-’80s hard sea wall measures were mainly used. At that time people realized that these hard structures eroded the beach even further as a result of wave action. Since the ‘90s Belgium has mainly used beach nourishments, so that the beach causes the waves to break further away from the dyke and on the beach (as a result of the shallower water depth) (3). Higher amounts and/or a higher frequency of beach nourishments will be necessary in the future because of sea level rise (5,6).

Beach erosion may negatively affect tourism. It is estimated that as a result of the rise in sea level, around 17% of beaches in the average scenario and up to 50% in the ‘worst case’ scenario will disappear (3).

Nature Reserve ‘Het Zwin’

Nature reserve ‘het Zwin’ is a small wetland area along 2.3 km of the Belgian coastline at the border between Belgium and the Netherlands. The area is a remnant of a former tidal inlet. The nature reserve was all that was left in the second half of the 19th century after parts had silted-up and were reclaimed from the sea. The reserve is separated from the hinterland by a flood defence dike, built in 1872: the dunes in this area, therefore, do not serve for flood protection. It is a particularly important case that illustrates the complexity of the impacts of a rise in sea level (3,4).

The ecological value of this natural zone is connected with the fact that seawater regularly enters the area, while there is no freshwater input. Its natural evolution would result in a slow filling of the water input channel by sand. However, this invasion by sand has accelerated in recent decades, probably due to the sand that is brought to the nearby beaches to counteract erosion. In the near future, it may be expected that the major problem will still be this silting-up process. If the rise in sea level reaches one or more metres, however, the nature reserve would probably be lost. In addition, increased temperatures may cause drying of the soil (3,4).

Adaptation strategies

In essence, the Belgian defence approach is best characterized by massive hard engineering (groins, breakwaters and seawalls), but artificial nourishment (on 22% of the Belgian coast (1)) has become a preferred strategy in recent decades. Dune stabilization is part of the shore protection strategies and is achieved through vegetation planting, access limitation and fence construction (2). The Flemish authorities aim to keep the protection line at the Belgian North Sea coast (6). The Flemish authorities are anticipating a SLR of about 6 mm year^-1 by 2050 and 10 mm year^-1 between 2050 and 2100 at the Belgian coast, and these values have been considered for planning and construction targeted at safety levels for 2050 (6).

References

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