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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, tina.mertens@mow.vlaanderen.be

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

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(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).