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AN INTEGRATED MASTER PLAN FOR FLANDERS FUTURE COASTAL SAFETY
Mertens, T.1, DeWolf P.
1, Verwaest T.
2, Trouw K.
3, De Nocker L.
4,
Couderé K.5
This paper reflects the realisation of an Integrated Master Plan to protect the Flemish
coastline against erosion and flooding on a short and long term basis, looking ahead at
the year 2050. Different measures and alternatives to prevent present and future flooding
are being worked out on the basis of safety checks and flood risk calculations along the
entire coast. The different solutions will be subjected to a social cost - benefit analysis
and an environmental impact assessment. The final master plan is expected to be ready in
2010 and will detail the priorities and the needs for coastal protection investments along
the coastline.
THE BELGIAN COASTLINE
The Belgian coast is situated at the southern part of the North Sea. The
coastline is 67 km long consisting mostly of sandy beaches with sea walls in
front of the cities and dunes in between. There are 4 harbours at Nieuwpoort,
Oostende, Blankenberge and Zeebrugge and the Zwin (tidal inlet) (Fig. 1). In
the flood prone area live about 400.000 people.
Although Belgium has a small coast, every kilometre is intensively used.
Residential neighbourhoods, ports, industries and important nature reserves are
present. The pressure from tourism and recreation is immense. To balance the
needs of all these interests, at present and in the future, an integrated approach is
necessary. Nonetheless, special attention has to be given to coastal safety. Due to
climate changes (e.g. sea level rise, more severe storms with increased wave
energy) and continuing development of the coastal zone, protection against
coastal erosion and flooding will become increasingly difficult and costly to
guarantee. To counter this problem, good spatial planning, cooperation between
different governmental organisations and collaboration with neighbouring
countries will be essential.
1 Belgian Coastal Division, Vrijhavenstraat 3, 8400 Oostende, Belgium, [email protected]
2 Flanders Hydraulics Research, Berchemlei 115, 2140 Antwerp, Belgium
3 International Marine and Dredging Consultants, Coveliersstraat 15, 2600 Antwerp, Belgium
4 Flemish Institute for Technological Research (VITO), Boerentang 200, 2400 Mol, Belgium
5 Resource Analysis, Coveliersstraat 15, 2600 Antwerp, Belgium
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Figure 1. The Belgian coast is 67 km long and has 4 harbours at Nieuwpoort, Oostende, Blankenberge and Zeebrugge. At the borders two important nature reserves (Westhoek and Zwin) are located.
SET-UP OF A MASTER PLAN
In Belgium coastal protection is a regional responsibility. Up to now, the
Flemish government (Flemish region) has defined the minimum safety level of
the coastal protection at once in 1000 year. However, this safety standard is not
implemented in any law or decree. Every 5 years the safety of the entire coastline
is checked and yearly monitoring enables to update the achieved safety level.
Awaiting for the master plan to establish the desired safety level, every year
smaller beach nourishments are carried out. For several years no new sea walls
have been built, because these hard safety measures intervene with the natural
dynamic of the coastline whereas soft measures, like nourishments work together
with the accretion and erosion processes.
A lot of coastal communities however do not achieve the safety standard. So
far, a minimum safety level of once in 100 year is guaranteed along the entire
coastline. The yearly budget does not add up to meet the standard. There is a
need for long-term planning… Hence, for the first time, the Coastal Division of
the Flemish region started up a study to work out an ‘integrated master plan for
Flanders future coastal safety’. The aim of this study is to protect the Flemish
coast against erosion and flooding on a short and long term basis, looking ahead
at the year 2050, based on the principles of ICZM. Therefore the time aspects of
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investments, sea level rise, beach erosion, … are also taken into account. This
integrated master plan must in particular define the measures needed to develop
and guarantee a safe coastline.
The study started up March 1st 2007 and will last 40 months. A total budget
of € 1 million is extracted to set up the master plan. The infrastructure works that
will follow still need to be budgeted.
Within the preparation and the execution of the coastal policy in general and
the policy concerning coastal safety in particular there are four different
important angles to take into account:
• Policy angle: strategic vision development and foundation of it leading to
policy choices how to handle coastal safety, leading to vision documents,
policy plans and management plans.
• Operational angle: the implementation of the actual management and
maintenance (including matters such as monitoring, testing/inspection,
warning) and the execution of specific measures for improvement of the
coastal safety.
• Legal angle: the legal anchoring of the coastal safety policy in terms of
safety norms, touristic demands for broader sea walls and the tasks, roles
and responsibilities of the parties involved.
• Financial angle: the regulation of financing and the financial statement and
flows of funds between involved parties.
According to the expectations the term ‘master plan for coastal safety’ is in
the first place related to the policy angle. In the master plan the policy visions
should be developed and specifically translated in a policy plan for the further
development of the coastal area, the required protection of the hinterland and the
maintenance and/or the improvement of the natural and artificial sea walls that
are located in the coastal zone. The master plan is a plan on a higher abstraction
level and should offer the framework for the more specific management and
execution plans, which form the basis for the operational execution of the coastal
policy. On the other hand there are important relations between the master plan
and the legal and financial frameworks.
The different topics of the study are summarized in Fig. 2 and will be
addressed in the outline of this article.
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Figure 2. Different topics of the Integrated Master Plan.
SAFETY CHECK AND FLOOD RISK CALCULATIONS
To highlight weak links in the coastline a safety assessment of the existing
coastal protection systems (dikes, dunes, beaches, harbours) and flood risk
calculations are performed. Thus, not only the impact of extreme storm
conditions on the local infrastructure, but also the consequences for the
hinterland caused by flooding is being looked at. The return period of extreme
storm events resulting in serious flooding is of the order of magnitude of 1.000
years or more. In the framework of this master plan the impact of a 1000 and
4000 year storm event is envisaged and even worse credible storm events are
incorporated in the flood risk calculations.
To perform these calculations, seventy-five years of measurements of water
levels and twenty-five years of deep water wave measurements at the Belgian
coast are available. Important parameters are wind, wave and storm surge
statistics. The storm surge level of an extreme storm event is the most
determining storm characteristic with respect to the associated flooding. Wave
characteristics are also important, but found to be relatively well correlated with
the storm surge level.
Fig. 3 details the different steps of the safety assessment. Statistics on water
levels, wind velocity, wave heights and periods were established at deep water
measurement locations. These wave statistics have been transformed to near
shore wave characteristics using a calibrated numerical wave model (SWAN).
The results of this consist of wave parameters at a line along the coast, with a
water depth at about –5 m below low water, a position at which the bathymetry
will not change considerably during storms (depth of closure).
safety check flood risk calculations
measures/alternatives
SCBA
EIA
legal framework
MASTERPLAN COMMUNICATION
risk management
EU -projects
flood risk reduction
finalised
ongoing
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During a storm the beach in front of the dike will erode. Due to the lowering
of the bed level, waves will transfer more easily towards the toe of the dike,
hence to know the wave height at the toe of the dike, it is important to calculate
the erosion of the beach. The erosion of the beach during the storm was
determined with DUROSTA (Steetzel 1993). In principle, the wave height must
be determined at the toe of the dike. However, most wave models (Swan, Endec,
etc.) produce less reliable wave heights at very shallow water depths. Therefore
the wave height at a distance of 5 times the significant wave height at deep water
from the toe of the dike is used. Only for very steep slopes (<1:30) the waves
are determined closer to the dike.
As a final phase the failure mechanisms of the sea defence (dunes, dikes,
quay walls and sluices in harbours) are tested. To estimate the erosion risk of the
dunes, the Vellinga approach was used (Vellinga 1986). A breach is assumed to
occur if the dune volume above the maximum water level is smaller than a
critical volume. For dikes the overtopping discharge must not exceed a certain
limit (i.e. 1 liter/s/m) and the stability of the structure must be guaranteed. The
same goes for harbour infrastructure, bearing in mind that the crest of quay walls
must be higher than the storm surge level and sluices must withstand storm
conditions.
Figure 3. Different steps of a safety assessment. Statistics on water levels, wind velocity, wave heights and periods are established at deep water locations (1) and transformed to near shore wave characteristics (2) using a calibrated numerical wave model (SWAN). The erosion of the beach during the storm is determined with DUROSTA (3). As a final step the failure mechanisms of the sea defence (dunes, dikes, quay walls and sluices in harbours) are tested (4).
The safety assessment concluded all harbours to be weak links and in total
almost 30% of the entire coastline doesn’t meet the safety standard of long-term
protection against a 1000 year storm event (sea level rise included). The
overtopping discharges of dikes are too high and quay walls are too low, thus
forming key factors to counter in the set-up of protection measures.
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Once a coastal protection system fails and a breach occurs, it’s important to
look at the consequences for the hinterland. As one of the partners in the study to
prepare an integrated master plan for Flanders future coastal safety Flanders
Hydraulics Research performs flood risk calculations for the actual situation at
the Belgian coast as well as for alternative designs of measures to improve the
coastal safety.
Flemish water management today no longer chooses to prevent floods at all
costs, but instead seeks to limit the damage, or more general to limit the negative
consequences of floods. Therefore, Flanders Hydraulics Research developed a
customer-tailed flood risk methodology. Depending on available data and
customer needs this approach allows to determine the expected damage, the
possible human casualties and the associated flood risk. As a result flood maps
and flood risk maps are made up for several worst credible storm events.
Detailed information can be found in Verwaest et al. (2008).
SOFT AND HARD PROTECTION MEASURES
Different measures and alternatives to prevent present and future flooding
are being worked out on the basis of these safety checks and flood risk
calculations. Protection against 1000 and 4000 year storm events as well as the
possibility of a differentiated protection level is being looked at.
‘Soft’ and ‘hard’ protection measures will be examined. Soft solutions
(shore face, beach or dune nourishments) have the advantage of flexibility with
regard to sea level rise, positive impact on recreation and their overall impact is
relatively small, but the disadvantage of maintenance costs (local seaward
movement of the coastline). Hard constructions (increasing the height of existing
dikes, storm return walls, …) have a greater impact on the human side. The
possible measures can be classified as follows:
for sea walls in front of cities
• beach nourishments
• beach nourishments + storm return walls on the sea walls
• beach nourishments + stilling wave basin (= storm return wall on the slope
of the sea wall)
• increased roughness of slopes
for dunes
• dune nourishments
• beach nourishments
for harbours
• storm flood barrier
• storm return walls around the harbour
• increased roughness of slopes
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• floatable breakwater at entrance of harbour
Besides these permanent measures, maintenance costs (of nourishments) can
also be lowered by for example the construction of groins, the planting of
marram grass, the use of wind shields or shore face nourishments.
The design of the beach nourishment takes into account the available sand at
borrow areas, since the grain size determines the equilibrium beach slope and the
beach erosion. In the long shore direction a gentle transition of the beach
extension to the neighbouring coastline is necessary. The use of groins and
breakwaters is evaluated to decrease long shore sand losses.
Defence strategies as retreat, holding the line and seaward extension are
regarded as an option for mid-term and long-term strategy. Whereas the current
policy is based on a holding-the-line approach, retreat is a reasonable option in
broad dune areas and to increase the biodiversity.
In the first stage possible measures are worked out technically for one
location. All possible combinations of measures are examined and at the end
discussed in a workshop with coastal specialists. In a second workshop the
possible solutions are presented at specialists who will carry out the social cost
benefit analysis and who will be involved in the Environmental Impact
Assessment studies. Both workshops aim to obtain an optimal set of possible
measures to be examined more in detail for the whole coast.
For all measures both the initial as the maintenance costs have to be
examined as an input for the social cost benefit analysis.
EVALUATION OF MEASURES
The different solutions will be subjected to a social cost - benefit analysis
(SCBA) and an environmental impact assessment (EIA). Also the risk reduction
is considered, especially regarding human casualties.
Social cost – benefit analysis
The social cost – benefit analysis compares construction and maintenance
costs with the benefits. However, not only the technical costs and benefits are
important, also social, ecological and economic impacts and especially impacts
on recreation and tourism have to be looked at.
The overall cost-benefit framework follows the recommendations of the
OEEI guidelines, developed for the cost benefits analysis of transportation plans
(Eijgenraam et al. 2000). It is adapted to take account of the specificity’s of
flood protection analysis and nature development. Special attention is given to
take account of long time horizons and economic growth and discounting. The
approach is in line with current thinking on flood risk modelling and evaluation
(see e.g. guidelines from Ramsar (Barbier et al. 1977), guidelines from Defra
8
(MAFF 2000)). The approach however goes a step further in the detail of the
analysis in different fields (both technical and economic parameters), in the
scope of the analysis (esp. time horizon), sensitivity and uncertainty analysis.
The optimal scheme will be the result of the best balance between the extra
costs necessary to materialize the higher protection level, and the extra benefits
resulting from these investments as compared to the zero option.
On the cost side, the necessary investment costs for the flood protection
works have to be considered, and all necessary maintenance and operation costs
during project life time (considered 50 years). If the analyzed scheme implies
relocation of agricultural areas or forests, the corresponding costs are also
considered.
On the benefit side, the avoided flood risks (i.e. safety benefits) are
considered by comparing the remaining flood risks, after implementing different
measures, to the zero option (do nothing). Where necessary, avoided costs are
added. Where applicable, benefits resulting from nature development and
recreation have also been considered and translated in monetary values.
An important aspect in the SCBA is handling uncertainties in both the flood
risk modelling as in the normal future economical development (interest rates
…).
The social cost-benefit analysis results in an overview of all the costs and all
the benefits of a project. With this overview a ranking of all projects can be
made and it will be proven that the project has an added value for the society. It
will be input, together with the EIA, for decision makers to decide on the best
alternative.
Environmental impact assessment
The environmental impact assessment (EIA) is executed in parallel with the
SCBA since exchange of information between these two parts of the study is
necessary. In the EIA all possible effects on the environment are considered both
of soft and hard measures. Amongst others, results of a recent study on the
ecological effects of beach nourishments (executed by Ghent University and
commissioned by the Coastal Division) will be taken into account, but also the
social effects of e.g. a storm return wall on a dike.
The following are EIA operating principles of good practice and
performance amended from Sadler (1996). First of all a strategic-EIA is
executed in which the general possible solutions are compared and their effects
are studied without going in too much detail. Together with the social cost-
benefit analysis and other policy decisions this results in (some) “most desired”
alternatives. The alternatives are worked out in more detail and it is examined if
the strategic-EIA is sufficient or if project-EIA’s are necessary. Fig. 4 shows the
general scheme for the EIA-study.
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Figure 4. General scheme for the EIA-study.
The execution of project-EIA’s falls out of the scope of this master plan. It
is expected that some coastal zones won’t need a project-EIA to start
construction works in 2010 (after application for a building permit). Those zones
that do need a project-EIA will be investigated into detail afterwards, in parallel
with the first constructions.
Risk reduction for human casualties
Casualties can only be avoided partially by evacuation plans. Reference is
made to criteria for every individual in the region, as well as for groups that are
applied in other sectors of external safety. However, acceptability is still a topic
of debate.
FROM “MOST DESIRED ALTERNATIVE” TO MASTER PLAN
Once the “most desired” alternatives are known the implementation of these
measures needs to be further examined.
Legal framework (DeWolf and Berteloot 2006)
The juridical part aims at inventorying the license pathway for the presented
measures and their implementation alternatives by offering a step-by-step guide
under the form of a procedure handbook. It appears that plural licence pathways
have to be explored because of, among others, the nature, the scope and the
location of the presented measures; several permission procedures and/or
appraisals are employed.
Concrete solutions are formulated, thus investigating for example how the
coastal protection policy can come about (Flanders has no legally binding
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document that states how coastal protection has to be carried out), and if there
are spatial implementation plans (RUP’s) and existing legislation that must be
complied with.
This part will give an overview of the legal framework of the coastal
protection works and the implementation alternatives: the legal and
administrative procedures (required licenses), the appraisal of the sectors, the
determined sticking points and the possible solutions.
Project risk management
For all large infrastructure projects in Flanders the decree concerning
monitoring of large infrastructure projects applies. This decree has the aim to
prevent or at least restrict incidents (juridical problems, exceedings of
construction budget, technical problems during realisation, …) that might
jeopardize the realization of the objectives for a given project. The project risk
management has the following aims:
• Determination of the aims for the risk management
• Identification of the possible risks;
• Analysis of the possible risks;
• Management of the most important possible risks;
The final master plan will eventually summarize the entire evaluation
process, resulting in a programme which outlines the “most desired” alternative
and the realisation procedure (measures, finances, legislation). And last but not
least, the final instrument in the set-up of this master plan is the communication
part.
COMMUNICATION
In the course of the study special attention is given to the communication
with different stakeholders and the broader public (questionnaires, presentations,
brochures, digital newsletter…). Moreover, consultation of national and
international governmental institutes is essential.
In the framework of the European project Safecoast knowledge on climate
change and coastal flood and erosion management was shared and information
and ideas concerning master planning was exchanged. As a result, relevant
information from existing coastal zone master plans in neighbouring countries
will be integrated in Flanders master plan.
Another example of stakeholder involvement is a poll that was organised at
two coastal towns to evaluate the visual impact of possible protection measures.
300 surveys were performed by means of digital simulations (Fig. 5). The main
results were:
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• most people are in favour of ‘hard’ measures (e.g. storm return wall or
stilling wave basin);
• young people prefer larger beaches (perfect playground for children);
• old people complain about the ‘extra’ sand transport on the sea walls
(coming from beach nourishments).
The results of this poll will be imbedded in the evaluation process of the
different measures (SCBA and EIA).
Figure 5. Digital simulation of possible protection measures: a) a storm return wall and b) a stilling wave basin on top of an existing sea wall.
CONCLUSION
The Integrated Master Plan for the Flemish coast is expected to be ready in
2010 and will finally detail the priorities and the needs for coastal protection
investments along the coastline, so as to minimise the risk of flooding in the
nearby and distant future.
a)
b)
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REFERENCES
Barbier, E., M. Acreman, and D. Knowler. 1997. Economic valuation of
wetlands: a guide for policy makers and planners, Ramsar, Switzerland.
DeWolf, P., and M. Berteloot. 2006. Strategic and project environmental impact
studies for a combined harbour and coastal protection scheme at Ostend,
Belgium – the experience with European guidelines, Pianc-congress,
Estoril.
Eijgenraam, C., C. Koopmans, P. Tang, and A. Verster. 2000. Evaluatie van
infrastructuurprojecten en leidraad voor kosten-batenanalyse.
MAFF (Ministery of Agriculture, Fisheries and Food). 2000. FCDPAG5 Flood
and Coastal Defence Project Appraisal Guidance, pp. 69.
Mertens, T., K. Trouw, K. Bluekens, L. De Nocker, K. Couderé, C. Sauwer, P.
De Smedt, C. Lewis, and T. Verwaest. 2008. SAFECoast: INTEGRATED
MASTER PLAN FOR FLANDERS FUTURE COASTAL SAFETY, Coastal
Division of the Flemish Community, Belgium.
Sadler, B. 1996. Environmental Assessment in a changing world. Evaluating
Practice to Improve Performance, CEAA and IAIA.
Steetzel, H.J. 1993. Cross shore transport during storm surges, Thesis, Civil
Engineering, Delft University of Technology, Delft, The Netherlands.
Vellinga, P. 1986. Beach and dune erosion during storm surges, Ph.D. thesis
Delft University of Technology.
Verwaest, T., K. Van der Biest, P. Vanpoucke, J. Reyns, P. Vanderkimpen, L.
De Vos, J. De Rouck, and T. Mertens. 2008. Coastal flooding risk
calculations for the Belgian coast. Proceedings of 31st International
Conference on Coastal Engineering, ASCE (this publication).