Coastal flood risk Belgium
The Belgian coast
The Belgian coastline is 65 km, of which 33 km are dunes and the rest is built-up area and harbours (protected from the sea by a dike). 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 (2,3).
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 (2,3).
Sea level rise in the past
In Belgium, observations for the period 1937-2003 in Ostend show an increase in mean sea level estimated at 16 cm/century, with no sign of recent acceleration (4). A more recent (CLIMAR) study, however, gives a completely different message: in Ostend between 1927 and 2006, an annual increase in sea level of 1.69 mm was observed, a value higher than those reported until now (1). Other regression models show a possible acceleration of the sea level rise during recent decades. Since 1992 an annual increase of 4.41 mm has been recorded (as opposed to 1.4 mm per year during previous years) (1).
Sea level rise in the future
An average sea level rise for the Belgian coast from 1990 to 2100 of 9 to 88 cm is projected (based on all IPPC SRES scenarios). In addition, the Belgian hinterland is projected to subside by 5 cm in this period (2).
Storm surges and waves in the past
Recent research suggests that there has been a reduction in the frequency of storms in the Southern Bay of the North Sea. A slight reduction in significant wave height seems apparent at Westhinder, but the temporal series are too short to be able to provide a definitive response. Similarly, wind speed on the Belgian coast has shown a slight reduction, in particular since 1990-1995. However, no clear trend has yet been observed in the measurements of significant wave height over the last 30 years (1).
Storm surges in the future
There is a lot of information available on projected storm surges along the Dutch, Danish and German coast (see the coastal flood risk pages for these countries). One of the projections for these countries, including the Belgian coast, shows an increase of storm surge elevations for the continental North Sea coast of between 15 and almost 25 cm at the end of the 21st century (14).
Global sea level rise
For the latest results: see Europe Coastal floods
For the latest results: see Europe Coastal floods
Extreme water levels - Global trends
More recent studies provide additional evidence that trends in extreme coastal high water across the globe reflect the increases in mean sea level (11), suggesting that mean sea level rise rather than changes in storminess are largely contributing to this increase (although data are sparse in many regions and this lowers the confidence in this assessment). It is therefore considered likely that sea level rise has led to a change in extreme coastal high water levels. It is likely that there has been an anthropogenic influence on increasing extreme coastal high water levels via mean sea level contributions. While changes in storminess may contribute to changes in sea level extremes, the limited geographical coverage of studies to date and the uncertainties associated with storminess changes overall mean that a general assessment of the effects of storminess changes on storm surge is not possible at this time.
On the basis of studies of observed trends in extreme coastal high water levels it is very likely that mean sea level rise will contribute to upward trends in the future.
Extreme waves - Future trends along the Western European coast
Recent regional studies provide evidence for positive projected future trends in significant wave height and extreme waves along the western European coast (12). However, considerable variation in projections can arise from the different climate models and scenarios used to force wave models, which lowers the confidence in the projections (13).
The large natural variability has a greater impact on the local North Sea wind field than potential anthropogenic-induced trends. For the North Sea region reliable predictions concerning strongly wind- influenced characteristics such as local sea level, storm surges, surface waves and thermocline depth are still impossible (28).
Vulnerabilities - Potential coastal damage
In the situation as it stands at present, three weaknesses have been identified in relation to the scope of the flooding: Mariakerke, Ostend and Wenduine. The most critical point is Ostend because of a greater concentration of buildings and population. In the event of an extreme storm, damage is assessed at 410 million EUR and the number of victims at 10. In the ‘worst case’ scenario for 2100, breaches are expected to occur in more than 50% of profiles. Total damage is assessed at 17 billion EUR and could result in up to 6,700 victims (1). Floods could reach 20 km inland and could pose a threat to over 200,000 people (3).
Climate change exposes the coastal region to three main types of impact: floods during storms, coastal erosion, and deterioration to or loss of natural ecosystems, including wetlands (1,2). Climate change may increase coastal flood risk to some 200,000 people and their houses near the coast, and an additional number of tourists in the summer. It may also cause damage to nature reserves and the natural flood protection (dunes), and reduce the attractiveness of the coastal zone for tourists. Besides, it may cause damage to agriculture (floods and salt intrusion), shipping and fishery (3).
Vulnerabilities - Coastal flood protection
There are currently 3 large projects off the Flemish Coast, designed to bring the level of protection up to the level of a 1000-year storm: The Integrated Coastal Safety Plan, the Public Works Plan in Oostende and the Zwin project. The protection against a 1000-year storm (incl. factoring in the rise in sea level to 2050 of 30 cm at the high water level) is a minimum acceptable level of protection. Some zones where the risk of flooding is large (risk = chance x consequence), as a result of severe consequences, for example construction immediately behind the sea defences, need to be protected against an even bigger storm in a 2nd phase (1).
The centre of Oostende, which forms the weakest link in the Flemish Coast, will in future require protection against a 4000-year storm, due to the position of the town centre (average sea level) and its close proximity to the sea compared to the rest of the coastline, and as a result of the large risk of flooding. The Beach that was constructed in front of the dyke in Oostende in 2004, a precursor of the Public Works plan, was required due to the urgency of increasing the level of protection (previously only offered protection against a 25-year storm, after construction and maintenance there is a level of protection against a 100-year storm) (1).
Antwerp and the Scheldt Estuary
In the Scheldt estuary, effective sea- level rise is up to 15 mm per year since 1930. This is a much higher rate than sea-level rise at the coast: wetland embankment has triggered extra sea-level rise, because storage area for flood waters is lost, causing water levels to rise faster in the remaining channels of the estuary (25). New nature- based engineering solutions should include the restoration of large wetlands between rivers and human settlements, which can provide extra water storage, slow down flood propagation, and reduce flood risks in populated parts of a delta (25).
Flooding occurred in the past in the Scheldt estuary and its tributaries, leading to the adoption of the so-called ‘Sigmaplan’ several decades ago (after the flood of January 1976). In this framework, next to raising over 500 km of flood defences (3), 13 ‘controlled flooding zones’ were established. These zones are managed so that occasional flooding during very high tides is tolerable and helps lower the water level. Dykes protect the land behind the flood zone. With the current climate, the risk level is estimated at one flood every 350 years, but the risk is expected to rise to up to one in 25 years by the year 2100 due to climate change. The Sigma-plan has been revised. The plan, adopted in July 2005, involves new controlled flood zones. A 60 cm rise in sea level is now taken into account (1,2); without additional measures, 60 cm sea level rise would result in a fivefold increase in flood risk (15).
Belgium has adopted a new approach to flood protection, based on the management of acceptable levels of flood risk where economic and societal interests are weighed to find the optimum level of flood protection. A high level of protection for a large area, such as protection against a 10,000-year storm surge, is thus no longer strived for (3).
Economic impacts of sea level rise for Europe
The direct and indirect costs of sea level rise for Europe have been modelled for a range of sea level rise scenarios for the 2020s and 2080s (16). The results show:
- First, sea-level rise has negative economic effects but these effects are not particularly dramatic. In absolute terms, optimal coastal defence can be extremely costly. However, on an annual basis, and compared to national GDP, these costs are quite small. On a relative basis, the highest value is represented by the 0.2% of GDP in Estonia in 2085.
- Second, the impact of sea-level rise is not confined to the coastal zone and sea-level rise indeed affects landlocked countries as well. Because of international trade, countries that have relatively small direct impacts of sea-level rise, and even landlocked countries such as Austria, gain in competitiveness.
- Third, adaptation is crucial to keep the negative impacts of sea-level rise at an acceptable level. This may well imply that some European countries will need to adopt a coastal zone management policy that is more integrated and more forward looking than is currently the case.
Potential adaptation measures are the creation of artificial islands and reefs, active breakwaters and super-dykes. If needed, the volumes of sand that are nourished onto the beaches are raised (2). Where dykes need to be built, a 60 cm rise in sea level is taken into account (1).
For the 21st century, the cost of adaptation is regarded as moderate (5), but a further rise in sea level would make adaptation much more difficult. A lot of knowledge has been developed in the new EU project Safecoast, aimed at protecting North Sea coasts (6).
Though it is important to look far into the future when selecting alternatives, it is not necessary to design all the measures up to 2100 right now, as the (social) costs of designing everything until 2100 right now are greater than for re-evaluation and possible modification in 2050 (1).
The coastal zone
The Flemish Government approved a Master Plan Coastal Safety in June 2011 comprising calculations and safety assessments for the periods 2000–2050 and 2050–2100. A vision for further development of the Flemish coastal zone is on its way aiming at the integration of safety, natural values, attractiveness, sustainability and economic development including navigation and sustainable energy. This concept is referred to as ‘Vlaamse Baaien’ or ‘Flanders Bays 2100’ and includes conceptual plans for responding to climate change effects beyond 2050. Execution of the Master Plan Coastal Safety is a pre-condition that must be met before implanting the ‘Flanders Bays’ concept (27).
Antwerp and the Scheldt Estuary
The so-called ‘Sigmaplan’ for the Antwerp area at the Scheldt estuary may be adjusted to allow for a high level of flood protection in the future (aimed at 2030). Measures may be included to increase the wetted cross section of the Scheldt near Antwerp, and thus lower extreme flood levels, by adding additional flooding zones to the river (3). Around 4000 ha of historically embanked floodplains will be restored by 2030. These efforts should lower a 1-in-100-year storm surge by 60 to 80 cm and are more cost-efficient than conventional heightening of dikes (26). Another option may be to connect the Western and the Eastern Scheldt in the Netherlands, which also lowers peak flood levels near Antwerp. The combination of all these measures may result in a protection against a 10,000-year storm surge. Without the connection between the Western and the Eastern Scheldt, a protection against a 4,000-year storm surge is projected (3).
Disaster prevention, preparedness, response and recovery should become even more of a priority for Member States (7).
Adaptation strategies - The costs of adaptation
Both the risk of sea-level rise and the costs of adaptation to sea-level rise in the European Union have been estimated for 2100 compared with 2000 (17). Model calculations have been made based on the IPCC SRES A2 and B1 scenarios. In these projections both flooding due to sea-level rise near the coast and the backwater effect of sea level rise on the rivers have been included. Salinity intrusion into coastal aquifers has not been included, only salt water intrusion into the rivers. Changes in storm frequency and intensity have not been considered; the present storm surge characteristics are simply displaced upwards with the rising sea level following 20th century observations. The assessment is based on national estimates of GDP.
The projections show that without adaptation (no further raising of the dikes and no beach nourishments), the number of people affected annually by coastal flooding would be 20 (B1 scenario) to 70 (A2 scenario) times higher in 2100 than in 2000. This is about 0.05 - 0.13% of the population of the 27 EU countries in 2010 (17).
Without adaptation, damage costs would increase roughly by a factor of 5 during the century under both scenarios, up to US$ 17×109 in 2100. Total damage costs would amount to roughly 0.04% of GDP of the 27 EU countries in 2100 under both scenarios. Damage costs relative to national GDP would be highest in the Netherlands (0.3% in 2100 under A2). For all other countries relative damage costs do not exceed 0.1% of GDP under both scenarios (17).
Adaptation (raising dikes and beach nourishments in response to sea level rise) would strongly reduce the number of people flooded by factors of 110 to 288 and total damage costs by factors of 7 to 9. In 2100 adaptation costs are projected to be US$ 3.5×109 under A2 and 2.6×109 under B1. Relative to GDP, annual adaptation costs constitute 0.005 % of GDP under B1 and 0.009% under A2 in 2100. Adaptation costs relative to GDP are highest for Estonia (0.16% under A2) and Ireland (0.05% under A2). These results suggest that adaptation measures to sea-level rise are beneficial and affordable, and will be widely applied throughout the European Union (17).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Belgium.
- Ministry for Social Affairs, Health and Environment (2009)
- Van Ypersele and Marbaix (2004)
- d’Ieteren et al. (2003)
- MIRA (2004), in: Ministry for Social Affairs, Health and Environment (2009)
- Brouwers et al. (2004), in: Ministry for Social Affairs, Health and Environment (2009)
- Commission of the European Communities: Green paper (2007)
- Bindoff et al. (2007), in: IPCC (2012)
- Church and White (2011), in: IPCC (2012)
- Velicogna (2009); Rignot et al. (2011); Sørensen et al. (2011), all in: IPCC (2012)
- Marcos et al. (2009); Haigh et al. (2010); Menendez and Woodworth (2010), all in: IPCC (2012)
- Debernard and Roed (2008); Grabemann and Weisse (2008), both in: IPCC (2012)
- IPCC (2012)
- Woth (2005)
- Broekx et al. (2011)
- Bosello et al. (2012)
- Hinkel et al. (2010)
- Cazenave et al. (2014)
- IPCC (2014)
- Watson et al. (2015)
- Yi et al. (2015)
- Church et al. (2013), in: Watson et al. (2015)
- Shepherd et al. (2012), in: Watson et al. (2015)
- Church et al. (2013), in: Watson et al. (2015)
- Temmerman et al. (2013), in: Temmerman and Kirwan (2015)
- Meire et al. (2014), in: Temmerman and Kirwan (2015)
- Niemeyer et al. (2016)
- Schrum et al. (2016)