How to Deal with Flooding

How to deal with flooding

Preparations for drafting the flood risk management plans for the river basins of the River Dijle upstream of Leuven and the River Woluwe in Flanders. Park Jourdain along Kleine Maalbeek

Composition and editing Publisher ARCADIS Belgium NV Philippe D’Hondt, VMM D/2011/6871/037 Final editing Ivo Terrens, Annelies Haesevoets, More information Maureen Nuyts (VMM) Infoloket VMM [email protected] Photography +32 53 72 64 45 VMM www.vmm.be ARCADIS Belgium NV De Urbanisten (www.urbanisten.nl) Photo cover Conseil Général du Loiret Restructured Woluwe in the new Stadsarchief Leuven business park along the eastern Désiré Vanautgaerden Brussels ring road Stad Leuven Guido Lieben Carl Vandervoort Dienst Openbare Werken Zaventem

Maps VMM ARCADIS Belgium NV

Layout CIBE communicatie op maat van de publieke sector (www.cibecommunicatie.be)

2 Table of content

Foreword 4

❶ Two river basins with flood risk 6 ① Floods and measures in the basin of the River Dijle 13 ② Floods and measures in the basin of the River Woluwe 18 ③ Choice of project areas 23

❷ Approach 24

❸ Damage and impact caused by flooding 28 ① Methodology 31 ② Results 36

❹ Research on types of measures 48 ① Alleviation: protection against flooding 50 ② Avoidance: prevention of flooding and damage 64 ③ Awareness and capacity to respond 74 ④ Assistance before, during and after a flood 78

❺ Consultation with stakeholders 84

❻ The future, how will we continue this work? 98 ① Alleviation: protection from flooding 100 ② Avoidance: prevention of flooding and damage 106 Park Jourdain along Kleine Maalbeek ③ Awareness 111 ④ Assistance before, during and after a flood 114

Epilogue 118

Table of content • 3 Foreword

In the last few years Flanders repeatedly came into the news with reports on floods and flood damage. Flanders is susceptible to flooding. In Europe, and the rest of the world, more attention is being paid to problems with flooding. Floods occurred in the past and cannot be excluded in the future either. However, there is the impression that the impact of floods has increased. Therefore we should consider how we want to deal with these floods. How can we prevent or mitigate floods in Flanders and at what price? What is socially feasible and what can people do for themselves?

Because floods can wreak a great deal of damage, there have always been attempts to prevent them. This has generally been done through technical constructions to protect people from floods, such as deepening and widening waterways, and constructing dikes and flood reservoirs.

Because of the increase in hardened surface area in Flanders and the possible consequences of climate change, there may be more frequent and more extreme floods. Moreover, we are building more and more in the natural flood plains, so that the potential damage from flooding increases. This raises questions as for example, should we provide additional protection to avoid floods? And if so, what risk do we want to protect ourselves from? Do the costs and impact of a protective measure offset the risk of floods and damage?

More and more, the view is gaining ground that we cannot protect ourselves 100% against floods, but that we should make more effort to mitigate the damage caused by flooding. There is also more attention for source-targeted measures to reduce the probability of floods.

Recently the European ‘Flood Risks Directive’ came into force. Drawing up a flood risk management plan (FRMP) is the last step laid down by the European directive. The emphasis is on protection, prevention and preparedness, taking into account the specific characteristics of the river basin.

The Flemish Environment Agency (VMM) had this study done within the framework of the Euro- pean Interreg IVB NWE project ‘FloodResilienCity’ (FRC) as a preparation to drawing up a FRMP for the Dijle and for the Woluwe . The aim of this project is to ascertain to what extent we can protect urbanised centres along rivers in North-West Europe from floods. The starting point is that floods will occur more frequently and possibly more extremely because of climate change. At the moment a great deal of infrastructure, including city centres, is not protected and in practice such protection is also difficult to achieve. Therefore we have to develop an approach to deal in an appropriate and targeted way with the 'unavoidable' and become more resilient to floods.

4 What this document offers This document provides a summary of the project to prepare the drawing up of a flood risk management plan for the river basins of the Woluwe and the Dijle in Flanders.

This summary contains six main sections:

Chapter ❷ provides an ❶ overview of the working ❸ method and the approach of the project. A number of In Chapter ❶ 'Two river Chapter ❸ 'Damage and terms are explained, as well impact caused by flood- basins with flood risk' we as the assumptions made in ing' provides an explanation discuss the river basins of this project. the Dijle and the Woluwe about the methods we in Flanders and tell some- used to calculate economic thing about the floods that damage, social damage occurred in the past and and ecological impact. This the measures already taken ❷ chapter also shows the result against flooding. of those calculations for the river basins of the Dijle and the Woluwe in present conditions. ❹

In Chapter ❹ 'Research on types of measures' we look for various types of measures. Alleviation measures are assessed on the basis of an extensive cost-benefit analysis. In addition an overview is given of possible measures ❻ for avoidance, awareness and assistance. We consider to Chapter ❻ 'The future, how what extent these measures will we continue this work?' ❺ can avoid or reduce the provides an overview of the damage. measures which seem to be Chapter ❺ 'Consultation of promising for execution or stakeholders' is the result further study in the context of a series of workshops, of the entire process. For in which we presented the each measure there is a list outcomes of the previous of action points still to be chapters and discussed them undertaken to implement with various stakeholders. the measure in question.

Foreword • 5 ❶

Two river basins with flood risk

6 Two river basins with flood risk • 7 The Dijle and Woluwe rivers are both part of the Dijle-Zenne river basin, located in the centre of Flanders.

The Woluwe rises in the Brussels Region and enters the Flemish Region at the commune of Zaventem. This river flows through the urbanised area of Brussels and its surrounding municipalities. At many locations the river is embanked or covered over.

The Dijle rises in Wallonia and flows into Flanders south of the city of Leu- ven. The Dijle flows through Leuven The Dijle and Woluwe river basin city and then further on in the direction of the city Mechelen where it joins the Zenne river. Upstream of Leuven the Dijle valley remains fairly undevel- oped and agricultural lands and nature predominate. Once entering Leuven The basin of the River Dijle upstream of Leuven is char- the river is shut in by the city. acterised by fairly steep slopes. Over the years, the Dijle wore away a valley of around 50 metres depth. The river basin used to be virtually fully wooded. However, these woods had to largely give way to agricultural land. This leads to faster drainage of rain water, resulting in erosion. The Dijle as such was never straightened or embanked upstream of Leuven. Up to the present, the Dijle retains its meandering pattern and is therefore unique in Flanders.

8 Legend Urban buildings Other buildings Industry and trading infrastructure Other infrastructure Sea port infrastructure Airport infrastructure Green urban zones Arable farming Pasture Alluvial pasture Orchard Deciduous forest Coniferous forest Mixed forest Heath land Beach and dunes Water Highway District road

Use of land in the basin of the River Dijle upstream of Leuven

Two river basins with flood risk • 9 Meandering Dijle upstream of Leuven

Leuven is situated on the transition towards the low- lands of Belgium. At the level of Leuven a number of efflu- ents are formed that subsequently converge again. A large part of the Dijle, Dijle branches and tributaries (Voer, Vunt, Molenbeek) were vaulted over during the years. The vaults are a bottleneck for the flow of water through Leuven. The highly meandering pattern of the Dijle upstream of Leuven is unique in Flanders

10 Waterways in the centre of Leuven

The Woluwe river flows in the Zenne valley. This valley Parallel to the four major waterways in the area (Wolu- is traditionally a marshy and alluvial one. In the past several we, Kleine Beek, Kleine Maalbeek and Vuilbeek) there are waterways were moved, excavated, or modified to improve large main sewers in many places. In addition various col- drainage of the area or for the construction of water mills lectors were built in the area. The collectors and main sew- and ponds. Pressure on the waterways rose due to intense ers discharge rain, ground water and waste water. There are urbanisation and industrialisation in the area. On the one many interaction points between the waterways, collec- hand there was the augmented discharge of rain water tors and main sewers. On the waterways there are several because of the increase in hardened surface area, which overflow spillways of these mains. On the other hand the resulted in floods. On the other hand there was a need waterways as such also frequently overflow into the collec- to discharge waste water from households and industry. tors and main sewers. The result is a highly meshed network In order to deal with these issues, the decision was taken between the scarce open waterway sections and tubed to construct a system of collectors and main sewers. At mains, with the main aim of discharging rainwater into the the time the construction of such a system was pioneer- Zenne without flooding. ing work from an international perspective, also because of the enormous dimensions of the mains and the marshy subsoil.

Two river basins with flood risk • 11 Legend Navigable waterway Unnavigable water course – Cat.1 Unnavigable water course – Cat.2 Unnavigable water course – Cat.3 Unclassified water course

The major unnavigable waterways in the basin of the River Woluwe

Legend Navigable waterway Unnavigable water course – Cat.1 Unnavigable water course – Cat.2 Unnavigable water course – Cat.3 Unclassified water course Main sewers Modelled interaction points

The large collectors and main sewers in the river basin

12 In the past there were several floods in Leuven ① These pictures show the flood in 1891

Floods and measures in the basin far beyond its banks. Around one third of the city centre of the River Dijle was under water.

A second very severe flood took place in March 1947. That A history of floods time too the flood was the result of a sudden thaw with rain and melting snow that had fallen on frozen ground. Because of the steep slopes and historical deforesta- Damage in the city was limited thanks to a barrage at the tion upstream of Leuven, the Dijle reacts fiercely to pre- entrance of the city of Leuven, but in the upstream munici- cipitation with a quickly rising flow rate and water level. In pality a great deal of land was flooded. the past this frequently led to floods in the lower parts of the valley. In August 1996 a period of heavy rain caused the Dijle and a tributary to flood just upstream of Leuven. The damage Historical documents show that the most severe known was very limited. The flooding was the result of a rain storm flood occurred in January 1891. Because of the combination that apparently occurs once every 100 years. As much water of heavy rain and melting snow, the water of the Dijle rose as possible was diverted to a canal in the neighbourhood.

Two river basins with flood risk • 13 Floods in Leuven 1981

However, the water level remained very high. At a crisis meeting it was decided to prepare for closure of the locks at the barrage where the Dijle enters Leuven. This was a last resort to protect the inner city from flooding. The evacuation of people living in the neighbourhood was planned. At the last minute the water started to go down and flooding did not occur.

September 1998 saw major flood damage in certain parts of Floods in Leuven 1906 Flanders, but the Dijle valley was spared from flood problems. This was due to good steering of the control structures on the Dijle and the discharge of part of the water to a neighbouring canal. Discharge along the Dijle also followed the same scenario in the flood periods in 2000 and 2002.

Floods in Leuven 1947

14 Construction of the CFP in Egenhoven

Existing measures to protect against A detailed computer model of the Dijle was created and flood damage linked to a flood forecasting system. This allows for optimal control of the CFP in Egenhoven. In the last few years Down the centuries various technical measures have no flooding occurred during heavy rain in Leuven, and any been taken to protect the city centre of Leuven and the threat is indicated by the flood forecasting system. surrounding municipalities from flood damage. Examples are: deepening and straightening the waterways in the city, During the winter of 2010-2011, many places in Flanders suf- constructing levees, dikes and flood reservoirs and imple- fered from severe flood damage. In Leuven itself no floods menting adapted control of dams and locks. Many of these occurred, but the CFP in Egenhoven was filled to the brim measures are not very natural and shift flood problems to in November 2010. In the 'Doode Bemde' as well a great downstream areas. amount of water was stored in a natural way. At the same time the maximum allowable flow rate was discharged Recently measures were taken upstream of Leuven in the through Leuven. This demonstrates that, although various nature reserve 'Doode Bemde' in order to restore the natu- protective measures have been taken, we still have to be ral water storage in the valley. As additional protection for alert and assess whether additional measures are required Leuven a controlled flood plain (CFP) was constructed in in the future. Egenhoven, just upstream of Leuven.

Two river basins with flood risk • 15 ▲ ▼ Construction of the CFP in Egenhoven

16 ▲ ▼ During the high-water period of November 2010 the CFP in Egenhoven and the natural flood plain in the Doode Bemde were filled to the brim. In the centre of Leuven the Dijle reached the maximum allowable water level

Two river basins with flood risk • 17 Kleine Maalbeek at Laag-Kraainem ② Floods and measures in the basin of the River Woluwe

Measures already taken against flooding

In the past 30 years there has been an enormous in- lems in the case of winter storms, which tend to result in crease in urban sprawl. Consequently more water is dis- long-term wet periods without extreme peak flow rates. charged faster because of the high degree of surface Recently several large investments were done in order to hardening. During heavy summer storms, precipitation and increase buffer capacity in the discharge system, e.g. the discharge peaks lead to flooding. Main sewers and water- construction of flood reservoirs and storage sewers. ways cannot deal with the temporary high discharges and overflow on the streets. There are far fewer flood prob-

18 Kleine Maalbeek at Laag-Kraainem

Legend use of land Urban buildings Other buildings Industry and trading infrastructure Other infrastructure Sea port infrastructure Airport infrastructure Green urban zones Arable farming Pasture Alluvial pasture Orchard Deciduous forest Coniferous forest Mixed forest Heath land Beach and dunes Water Highway District road

scale: 1:16.000 Use of land in the Woluwe river basin

Two river basins with flood risk • 19 Kapelanebeek in wooded area at Burbure Estate

In the past various big collector works were executed in the Woluwe valley

20 Henneaulaan flood reservoir Outlet flood reservoir Henneaulaan

Open flood reservoir Trawool with pumping station

Two river basins with flood risk • 21 Flooding of the Woluwe at the level of the Henneaulaan in Zaventem

Permanent risk of flooding

In spite of the great efforts made to prevent flood prob- Recently, during the winter of 2010-2011, many places in lems, flooding still occurs during heavy (summer) storms. Flanders suffered from flood damage. The Woluwe river Up to 25 years ago, certain places in the municipality of Za- basin did not experience any problems, but the available ventem were regularly troubled by floods. These problems buffer capacity was almost completely taken up. have been virtually solved by the various measures that were taken. Only in case of extreme heavy summer storms or when two summer storms occur in rapid succession, are there still reports of water in the streets, although with lit- Over the years tle inconvenience. various measures At the intersection point of the municipalities of Kraainem, have been taken Wezembeek-Oppem and Sterrebeek there is still severe flooding during short, heavy rainfall. At this location the to protect the Vuilbeek collector flows into the Kleine Maalbeek collector. Woluwe valley In Machelen too there are still problems where the Woluwe River flows into the Woluwe collector. In the past five years from flood flooding with relatively great damage has occurred twice. damage

22 An often flooded road junction at Oudstrijderslaan in Laag-Kraainem ③ Choice of project areas

Although both river basins are located close to each other, watercourse as it will have problems discharging the runoff they have quite different characteristics and encounter water during and after a peak rain event. In this river basin different flooding problems that will need a different ap- there are several critical sites where such flooding events proach to define useful solutions. can occur. The Dijle river is characterized by its natural course running through agricultural and natural areas upstream of Leuven. Because of these issues, the two river basins were selected Once it enters Leuven it is shut in by urban developments. as part of the project aiming to examine possible solutions This is a major bottleneck for discharging water when high for the flooding problems. The project areas considered in water levels are experienced. this project are the Flemish part of the Woluwe basin and The Woluwe river flows through the urbanised area of the Flemish part of the Dijle valley from Leuven upstream Brussels and its surrounding communes. This high degree of to the Walloon border. pavement in the river basin causes a high pressure on the

Two river basins with flood risk • 23 ❷

Approach

24 Approach • 25 In this project we developed a meth- Flood risk odology to reach a set of measures In normal language, 'risk' is understood as a ‘probability’. for the prevention of extreme flood- However, 'flood risk’ consists of the combination of the ing and consequent damage. In a first probability that a given flood will occur and the corre- stage we evaluated the effects of ex- sponding damage. A flood that occurs very frequently but causes little damage therefore entails a small risk. Damage treme flooding, the so-called flood should be interpreted broadly: it does not only comprise risk. We determined the economic, tangible elements such as faulty electrical appliances, but social and ecological impact. Subse- also less tangible elements such as the upheaval that peo- quently we proposed a set of various ple undergo after having experienced flooding, or the tem- types of measures and elaborated porary shutdown of a company. The damage resulting from a methodology to assess them. The a flood is calculated on the basis of its economic, social and methods and measures used were dis- ecological impact. cussed with various stakeholders. Integrated set of measures Currently many areas are not protected from extreme In the context of this project we as- events and in many cases it is not possible to provide ad- sume that floods as a result of extreme equate protection either. Therefore an integrated approach storms will occur more frequently in should be employed, not only with the aim of preventing the future. We elaborate risks, dam- flooding, but also to optimally reduce damage as a result age and measures on the basis of such of floods. –– In the context of the European FRC project, the VMM extreme storms. We do not attribute (Flemish Environment Agency) was inspired by the any probability risks (return period) work of the Scottish authorities, who elaborated an in- to these extreme storms because the tegrated approach. The approach is based on the 4 As, degree of uncertainty is too high. For viz. Alleviation, Avoidance, Awareness and Assistance. nobody knows what the future may bring, or to what extent any climate We applied this approach to the river basin of the Dijle up- change will develop in the future. stream of Leuven and the Woluwe in Flanders. For the Dijle, the flood of 1891 was selected as an extreme event to be worked out further.

For the Woluwe river basin, a flood was modelled on the Components for the determination of flood risks basis of the hydrological and hydraulic modelling study that would take place in a storm occurring once every 100 Exposure Value receptors-at-risk receptors-at-risk Vulnerability years. A more extreme storm was also considered in or- Probability (depth, velocity, (market value, receptors-at-risk der to analyse the impact of an extreme event. No new duration, rise properties, WTP (susceptibility and rate, water avoidance heath resilience) modelling was performed for this purpose. The expected quality, ...) impacts, ...) flooded volume as a result of a storm occurring once every 100 years was increased by 50% in the new, more extreme Probability Consequence starting situation.

Flood risk We determined the impact and damage of these extreme events for the two river basins. Subsequently, various Source: Giron E., Sacre D., Hecq W., Coninx, I., Bachus K., Dewals B., Detrembleur S., Pirotton M., El Kahloun M., Meire P. De Smet L. measures that may help to mitigate the flood risk were and De Sutter R. (2008). ADAPT - Towards an integrated decision listed. These measures were grouped according to the 4 As tool for adaptation measures - Case study: floods. Final report phase I, Report for the Belgian Science Policy, Brussels, Belgium. concept.

26 We use an extensive cost-benefit analysis to determine The FRMPs have to be based on flood risk maps with dif- which alleviation measures we still can construct against ferent probabilities of occurrence (low, medium and high) future floods in the river basin of the Dijle or the Woluwe. and the corresponding flood risk maps. They also have to This should allow us to compare alleviation measures with comprise relevant aspects such as costs and benefits and each other. all aspects of flood risk management. Here the emphasis is on protection, preparedness (predictions) and the specific Participative consultation characteristics of the river basin. At this moment (January We discussed the various measures in a series of workshops 2012) the flood risk maps for the Dijle river basin are mod- with the involved stakeholders (e.g. municipalities, water- elled. way managers, the province, crisis managers). The aim was to reach an initial set of measures for each river basin, for The great difference between the directive and the ap- which there is broad support. We will further elaborate proach in this project is working with the probability of these measures in the future. floods. In this project the explicit choice was not to work with probabilities of floods, but with an extreme event. Flood risk management plans The methodologies and measures presented in the con- The European Flood Risk Directive came into force in No- text of this project may, after refinement, serve as input vember 2007. This directive obliges Member States to map for the drafting of the FRMPs. Good ideas can be derived out flood hazards and draw up a flood risk management plan from it, in particular for prevention and preparedness. The (FRMP). The FRMPs have to be ready by 22 December 2015. participative process to arrive at an underpinned package of measures was also a first exercise and will be applied The directive provides for three stages: throughout Flanders in an improved and adapted form. –– 22/12/2011: Preliminary flood risk assessment –– 22/12/2013: Flood hazard and flood risk maps –– 22/12/2015: Flood risk management plans

Objective 5 ST RAT EG Y E N CA PA C IT Y : T o Objective 2 d e AVOIDANCE: v e l To limit flood damage and o p

ease recovery t h by planning e

c Objective 4 and adapting a p ASSISTANCE: buildings, a c

i To provide surfaces and t y

support to economic t Objective 1 o

communities, AWARENESS: activities m proir to, during a

To enhance the n a

and after flood awareness of flood g e

events risk and the means of f l

managing it o

Objective 3 i n

ALLEVIATION: t

To reduce flood risk by implementing a

physical and technical measures for i

the management of water systems e

o b j 4 e - c 1

t i s v e

Concept of the 4 A’s as applied in the FRC project

Approach • 27 ❸

Damage and impact caused by flooding

28 Damage and impact caused by flooding • 29 Flooding of the Woluwe at Zaventem

A flood causes damage and has an im- First this methodology is described pact on many fronts. When a home and then its results are explained. For floods, it doesn’t only cause damage the Dijle river basin, this methodol- to the house itself. It also impacts ogy was applied to an extreme flood- on the physical and mental health of ing event in the city of Leuven. For the the occupants and on their financial Woluwe river basin, this methodol- situation. When nature reserves are ogy was applied to a flood caused by flooded, there may also be an impact a storm with a return period of once on the ecological value. Quantifying every 100 years and to a more extreme these various types of impact is not situation in which the flooded volume a simple matter. A methodology was was even increased by 50%. In the con- elaborated in the context of the pro- text of this project we chose not to ject to calculate the economic, social calculate the ecological impact of the and ecological damage of a flood. In floods in the Woluwe river basin. This order to be able to apply the meth- can still be integrated on further elab- odology in the whole of Flanders, only oration in the future. data that are uniformly available for Flanders were used.

30 Soil use map

FLOOD EXTENT Exposed economic systems

Relative damage Economic value (€) functions

WATER DEPTH Relative direct damage (%)

FLOOD MAP

Absolute direct economic flood damage (€)

Chart of economic damage calculation

① Methodology Flooding parameters Economic damage

To calculate the damage and impact of a flood, we have Financial consequences of floods to know which areas have been flooded and how high the A flood causes physical damage with financial consequenc- water was in various places (inundation depth). es. The damage as such doesn’t only reduce the financial value of a real estate or property, but also has financial con- This is determined by entering the flood contours in a GIS sequences because a building is temporarily out of use. (Geographic Information System). These flood contours The financial damage is highly dependent on the premises, can be determined on the basis of modelling or on the ba- the activity performed in it and the extent of the flood. sis of historical flood maps. For example, damage to a home does not entail the same These contour data can be combined in GIS with the Digi- financial consequences as damage to an industrial building tal Elevation Model (DEM) in order to determine through or a hospital. Neither does the damage of a flood with an interpolation the water levels (in mTAW [Belgian water inundation depth of 10 centimetres have the same financial level mark]) of the floods within the flood contours. In turn consequences as a flood with an inundation depth of one these water levels can be compared with the ground levels metre. of the DEM in GIS. In this way the inundation depth can be calculated anywhere within the flood contours.

Damage and impact caused by flooding • 31 1 0,9 0,8 0,7 Damage factor Damage 0,6 0,5 0,4 0,3 0,2 0,1 0 04 0, 0,8 1,2 1,6 2 2,4 2,8 3,2 3,6 4 4,4 4,8 Inundation depth (m)

Homes

Household effects

Industry

Vehicles

Roads In the context of this project these damage functions were applied to homes and household effects, industry, vehicles and roads

Damage function historical and heritage buildings (castles, historical buildings, museums and windmills) and buildings and infrastructure Determining economic damage is performed by using a with a special value (train stations, electricity plants, water so-called damage function. For a given type of land use catchment areas, airports and graveyards). The susceptibil- it describes the relationship between one or more flood ity of these sites and above all their value is difficult to parameters (inundation depth, flow rate, etc.) and the de- assess. Therefore we opted for recording the damage to preciation percentage. This depreciation percentage is the these entities separately in addition to the overall damage damage factor. calculated. In the context of this project, some damage functions were applied with flood depth as the parameter. The most ap- Land use map propriate damage function was selected for the following land use categories: homes and household effects, vehi- We drew up a land use map within the flood contours. This cles, industry, various types of non-residential buildings is a map on which the various types of relevant land use are and industrial buildings, roads and railways, agriculture and indicated. The map is drawn up by combining the following recreation. The combination of the damage factor and the basic data: economic value of a real estate or property leads to the –– Cadastral plots and buildings from CadMap (digital absolute economic flood damage. map with the cadastral plots), together with the description of the cadastral nature of the plots. We did not use the abovementioned damage functions to –– Linear infrastructure such as roads and railways from calculate the damage to special entities such as cultural- StreetNet.

32 –– Areas with an agricultural function from the agricul- a maximum damage of €1,367/m² was defined. tural use plots map. –– Vehicles: The average value used for a family car was –– Recreation areas determined on the basis of the Re- €4,788. gional Plan. –– Roads and railroads: depending whether the road is single or double track, electrified or not or for a Economic damage high speed connection, the value calculation ranges from €710/m to €26,598/ m² To calculate the economic damage, we combined the land use Apart from the main damage cat- map, the map with the water A flood causes egories described above, we also depths, the land use specific physical damage include shops, supermarkets, ser- damage functions and the finan- vice stations, gas stations, restau- cial values of the plots. The result with financial rants, bars, hotels, offices, thea- is a map with the spatial spread consequences tres, cinemas etc., sport centres, of the damage. Adding together educational institutes, hospitals, the damage over the entire flood town halls, libraries, religious contours gives the overall eco- buildings, fire and police stations nomic damage in euros. The ta- and prisons, recreational areas bles representing the economic and agriculture. damage per damage category are represented for both the Dijle and the Woluwe cases. Social impact

The following list gives an overview of the main damage The social effects of floods are the mental and/or physical categories that have been used in this project. consequences that people experience on various levels (as –– Houses and apartments: The value of a house or flat an individual, family and/or society). Examples of the ef- is highly dependent on the location. Information on fect a flood may have on people and their social networks house prices was obtained from the national institute include damage to the physical and/or mental health of of statistics. The price of an average house ranges people, disruption of their financial situation, loss of ob- from 204,000 euros in Vilvoorde to 346,000 euros jects with personal value, changes in risk perception, dif- in Kraainem. For a ficulties in providing for flat this ranges from basic needs, and problems 162,000 euros (in Social Impact Score = in getting the house in or- Leuven) to 233,000 a combination of der again. euros (in Tervuren). ➞ exposure index –– Furniture: The value ➞ susceptibility In the context of this pro- of furniture in hous- ject we mapped out the es and apartments ➞ ability to adapt social impact of floods was estimated as with the aid of the ‘So- 30% of the sales val- cial Flood Impact Tool ue of the properties, based on information provided (SFI tool)’ developed by HIVA - KULeuven. This method is by Assuralia, the professional organization of insur- based on linking the flood parameters of a particular flood, ance companies. with the habitation in the flooded area and the susceptibil- –– Industry: The calculation of the current value of an ity and ability of the people living in the affected area to enterprise is very difficult, not only the value of the adapt. The latter three elements are quantified on the basis buildings, machinery etc. has to be accounted for, but of three indices that take into account exposure, suscepti- also the future profit potential of the company has to bility and ability to adapt respectively. be included. Based on existing studies on this subject,

Damage and impact caused by flooding • 33 Buildings

FLOOD EXTENT Exposed social systems

Vulnerability Adaptive capacity Exposure of people to of man and society of people the consequences to the consequences of floods of floods

Social vulnerability of people to floods

WATER DEPTH Absolute social flood damage

FLOOD MAP Social damage calculation chart

The exposure index is determined on the basis of the inundation depth of the flood. This is divided into three categories: –– At an inundation depth of 0 cm the score is 0. –– At an inundation depth of 0 to 30 cm the score is 0.5. Not everyone –– At an inundation depth of over 30 cm the score is 1. has the same level A person's susceptibility may largely be ascribed to indi- of knowledge vidual characteristics that affect their knowledge and possibilities to deal with the consequences of floods. Older and possibilities people, the sick, the poor, single-parent families etc. have to control a different way of dealing with floods. This results in different susceptibility groups: the negative –– Resilient. –– Risk of social susceptibility. consequences of –– Socially susceptible. floods –– Very socially susceptible. Each group has its own score.

34 The ability of man and society to adapt indicates to what The nature target type as such also receives a biological rat- degree they can adapt to floods and thereby mitigate their ing score. This score is assigned on the basis of the Biologi- consequences. This index too is determined with the aid cal Rating Chart (BRC). The maximum score is 1 (very valu- of a set of indicators, such as the presence of a (social and able). The less valuable the nature target type, the lower financial) safety net, the existence of emergency plans, the the score. use of warning systems etc. In the context of this study, the ability to adapt is not evaluated on a personal level. For the To obtain the ecological impact score (EIS), the rating of social impact assessment, this study takes into account an flood compatibility is coupled with the biological rating average ability to adapt of 0.45 for the entire project area. score (on the basis of the BRC) as follows:

The combination of these three indices means that every EIS = compatibility score x biological rating score individual living in the affected area is given a score from zero to one. An individual with maximum exposure, maxi- The ecological impact score calculated is a number be- mum susceptibility and with minimum ability to adapt will tween 0 and 1. The closer the ecological impact score is to be given a score of around one. An individual with mini- 1, the greater the ecological impact (very valuable flora and mum exposure will have a score of approximately zero. not compatible with the type of flooding). An ecological impact score of 0 means that the nature target type will Ecological impact not experience any negative ecological impact from the floods (flooding offers opportunities). Ecological impact of floods In a number of ways a flood may have a direct or indirect For the overall ecological impact of an area, one has also effect on the natural environment (e.g. drowning, eutrophi- to take account of the flooded surface area. The ecologi- cation, alkalinisation, brackish- cal impact of a flood is obtained ness/desalinisation). The effect by multiplying the EIS per nature of floods is not the same for target type with the flooded every nature target type. Some surface area (in hectares). Subse- types are very compatible with quently these figures are added flooding and in this case floods Some types of together for all nature target can even offer opportunities, types present. This gives the while for other types the oppo- nature benefit overall ecological impact. site is true. from floods In the context of this project Input data we employed the method pro- In addition to the flooding pa- vided in the study ‘Waterberging rameters, various input data are en natuur – Kennisoverzicht ten required for the application of behoeve van regionale waterbe- this methodology. The types of heerders' [Water storage and nature – Knowledge overview flora present can be determined using the most recent Bio- for regional water managers] (Runhaar et al., 2004)’ of the logical Rating Chart (BRC). The BRC units have been con- Dutch Foundation for Applied Water Research (STOWA) verted to flora types and subsequently to the Dutch Na- and the associated web application1. Applying this method ture Target Types. We revert to the water quality measuring leads to a rating for the compatibility of floods with a given network of VMM for data on nutrient, sulphate, salt and nature target type. bicarbonate levels2. Substrate characteristics and seepage/ infiltration were determined on the basis of expert knowl- This rating of compatibility with floods is expressed as a edge and literature data. score of 0 (favourable) to 1 (not compatible).

1. http://www.synbiosys.alterra.nl/waterberging/ 2. http://www.vmm.be/geoview/

Damage and impact caused by flooding • 35 High water in the Doode Bemde ② Results

River Dijle

Flooding parameters In January 1891 Leuven experienced the worst flood in its history. At the time the authorities drew up a city map indicating the flooded area. There is also data available on the water level in a number of the flooded streets. The inundation depths in the flooded areas were assessed on the basis of these data.

Economic damage For the considered flood of 1891 in Leuven the overall economic damage is 395 million euros. This is the expected damage if the flood were to occur now.

City map drawn up by the authorities showing the consequences of the 1891 flood

36 Legend Flooded perimeter 1981 Streets with known inundation depth Watercourses

scale: 1:10.000

Digitisation of the flood contours and streets with known inundation depth during the 1891 flood

High water in the Doode Bemde Legend water depth (m) 0,001 - 0,5 0,501 - 1 1,001 - 1,5 1,501 - 2 2,001 - 2,5 2,501 - 3 3,001 - 3,5 3,501 - 4 4,001 - 4,5 4,501 - 5

scale: 1:12.500

Inundation depth in the flooded areas during the 1891 flood

Damage and impact caused by flooding • 37 Legend land use Houses Flats Industry Shops Supermarkets Car repair shops Gas stations Restaurants Bars Hotels Offices Theatres, cinemas Sport centres Educational institutes Hospitals Town halls Libraries Castles, historical buildings Religious buildings Recreational areas Other Flooded perimeter

scale: 1:13.840

Land use map of Leuven within the flood perimeter

Legend Economic damage buildings (€/m²) < 50.000 50.001 - 100.000 100.001 - 250.000 250.001 - 500.000 500.001 - 750.000 750.001 - 1000.000 1000.001 - 1500.000 1500.001 - 2500.000 2500.001 - 5000.000 > 5000.001

Economic damage roads (€/m) < 25.000 25.001 - 50.000 50.001 - 75.000 75.001 - 100.000 100.001 - 125.000 125.001 - 150.000 150.001 - 250.000 250.001 - 500.000 500.001 - 1000.000 > 1000.001 Flooded perimeter

scale: 1:12.851

Economic damage map within the flood contours in Leuven in the starting situation (damage in EUR per m²)

38 Legend Houses SFI per raster cell (50m x 50m) < 5.000.000 5.000.001 - 10.000.000 10.000.001 - 15.000.000 15.000.001 - 20.000.000 > 20.000.001 Flooded perimeter

scale: 1:12.820

Social impact of floods in Leuven expressed per grid cell of 50 by 50 metres. In the white patches in the flood contours there are officially no inhabitants and therefore no social impact can be calculated (schools, hospitals, etc.)

Social impact It could be postulated that the social impact score has an If the flood event of 1891 would occur today, the presented abstract significance and is therefore not so easy to inter- methodology would give a social impact of 3022 units for pret. Calculation of the score mainly allows mutual com- the city of Leuven. parison of various alternatives or scenarios of various protective measures. In theory a social impact score of 3022 means that 3022 people are maximally exposed to a flood, are maximally Ecological impact susceptible and have minimal ability to adapt. In practice The ecological impact of a flood in an extreme situation not all people affected are maximally exposed: certain was not determined for the city of Leuven as such, since no population groups are less susceptible and society has a large areas of nature are present there. However, the eco- certain ability to adapt. Therefore the social impact score logical impact for the 'Doode Bemde' was calculated. This is indicates an equivalent number of people who are affected a nature reserve upstream of Leuven where the Dijle floods to a maximum extent. in a natural way. Because there are no data available on the The maximum value of the social impact score is equal to situation in the 'Doode Bemde' during the extreme flooding the overall number of inhabitants of the flooded area. The event of 1891, we started from a modelled flooding event minimum value that the score may have is zero. This means with a return period of 100 years. For such an event we cal- that there is no flood and therefore not a single inhabitant culated an overall ecological impact score of 59.39 over the is affected. entire flooded area.

Damage and impact caused by flooding • 39 Legend Perimeter Doode Bembe Nature target types Lake Pool Reed and rush Quaking bog Sedge marsh Wet brushwood with Meadowsweet Marsh marigold meadow of river valleys Marsh marigold meadow on peat and clay soils Dog's tail meadow False oat-grass meadow Bent grass meadow on acidic soils Field Edge, mantle and dry scrub vegetation on acidic soils Edge, mantle and dry scrub vegetation on clay soils Willow scrub on moist, nutrient rich soil Meso-eutrophic swamp Alderwood Tall herb Ash-Alderwoods of slow rivers Ash-Alderwoods of slow rivers Oak-Hornbeam forest Acidophilous Oak forest with Beech Compatibility None Bad Moderate Good Favorable Ecological impact score 0 - 0.107 0.107 - 0.321 0.321 - 0.536 0.536 - 0.75 0.75 - 1 No data No data scale: 1:18.000

This would correspond to flooding of 59.39 hectares of nature which is biologically very valuable and not compatible with floods. But it can also correspond to a larger flooded surface that is either biologically less valuable or more compatible with floods, or a combination of the two.

The maximum overall ecological impact score that would be possible in a particular area is the overall surface of that area in hectares. This would mean that the entire area consists of very valuable nature and is not compatible with floods. The overall surface area of the 'Doode Bemde' nature reserve is 493 hectares. Therefore the theoretical maximum impact score is 493. The minimum ecological impact score is 0. This occurs when there is either no flooding or when the flooding -of fers opportunities for all types of nature present.

This impact score is also intended for the mutual compari- Nature target types, compatibility and ecological impact son of various scenarios. score in the event of a natural flood in the 'Doode Bemde' with a return period of 100 years

40 Legend Vlaamse Hydrografische Atlas - waterways Sub basin border Flood contours

scale: 1:16.000

Flood contours in the Woluwe river basin in the basic scenario

River Woluwe

Flooding parameters As already stated for the Woluwe river basin, the damage and impact of two flooding scenarios were determined.

Basic scenario Basic scenario +50% On the basis of the hydrological and hydraulic modelling To analyse the impact of an extreme event, a more ex- study of the Woluwe river basin, combined with the Digi- treme storm was also considered. No new modelling was tal Elevation Model, flood contours were modelled which performed for this purpose. The expected flood volume in would occur in a storm that on average only happens once a storm that occurs once every 100 years was increased by every 100 years. These were refined or extended on the 50% in the new, more extreme starting situation. basis of the contours of recently flooded areas. The flood contours and water levels corresponding to this larger flooded volume were determined using the Spatial Analyst GIS tool.

Damage and impact caused by flooding • 41 Legend Vlaamse Hydrografische Atlas - waterways Sub basin border Inundation depth (in m) 0,0001 - 0,5 0,5001 - 1 1,0001 - 1,5 1,5001 - 2 2,0001 - 2,5 2,5001 - 3 3,0001 - 3,5 3,5001 - 4 4,0001 - 4,5 4,5001 - 5

scale: 1:16.000

Inundation depth in flooded areas for the basic scenario

Legend Vlaamse Hydrografische Atlas - waterways Sub basin border Inundation depth (in m) 0,0001 - 0,5 0,5001 - 1 1,0001 - 1,5 1,5001 - 2 2,0001 - 2,5 2,5001 - 3 3,0001 - 3,5 3,5001 - 4 4,0001 - 4,5 4,5001 - 5

scale: 1:16.000

Inundation depth in flooded areas for the basic scenario + 50%

42 Legend land use Houses Flats Industry Shops Supermarkets Car repair shops Gas stations Restaurants Bars Hotels Offices Theatres, cinemas Sport centres Educational institutes Hospitals Town halls Libraries Castles, historical buildings Religious buildings Recreational areas Other Agriculture Vlaamse Hydrografische Land use map in the flood contours Atlas - waterways in the basic scenario +50% Sub basin border Flood contours

Damage and impact caused by flooding • 43 Legend Economic damage (€/m²) < 50.000 50.00001 - 100.00000 100.00001 - 250.00000 250.00001 - 500.00000 500.00001 - 750.00000 750.00001 - 1000.00000 1000.00001 - 1500.00000 1500.00001 - 2500.00000 2500.00001 - 5000.00000 > 5000.00001

Economic damage (€/m) < 25.00000 25.00001 - 50.00000 50.00001 - 75.00000 75.00001 - 100.00000 100.00001 - 125.00000 125.00001 - 150.00000 150.00001 - 250.00000 250.00001 - 500.00000 500.00001 - 1000.00000 > 1000.00001 Vlaamse Hydrografische Atlas - waterways Sub basin border

scale: 1:16.667

Economic damage If the flood in the basic scenario were to occur now, the overall economic damage would amount to 15.7 million euros. In the basic scenario +50% the expected damage is 22.4 million euros.

Economic damage of floods in the basic scenario

44 Legend Economic damage (€/m²) < 50.000 50.00001 - 100.00000 100.00001 - 250.00000 250.00001 - 500.00000 500.00001 - 750.00000 750.00001 - 1000.00000 1000.00001 - 1500.00000 1500.00001 - 2500.00000 2500.00001 - 5000.00000 > 5000.00001

scale: 1:16.698

Damage and impact caused by flooding • 45 Legend Houses Flood contours Sub basin border

SFI per raster cell (50m x 50m) < 5.0 5.001 - 10.0 10.001 - 15.0 15.001 - 20.0 > 20.001

scale: 1:16.677

Social impact If the flood in the basic scenario were to occur now, its social impact would be 450 units. In the basic scenario +50% the social impact is 527 units.

As for the Dijle river basin, here too the maximum value of this social impact score is equal to the total number of inhabitants in the flooded areas. The minimum value of this score is zero, when there is no flooding and therefore not a single inhabitant is affected. Here too it may be stated that the social impact score has an abstract significance and mainly allows for mutual comparison of various alternatives or scenarios of various protective measures.

Social impact of floods in the basic scenario expressed per grid cell of 50 by 50 metres

46 Legend Houses Flood contours Sub basin border

SFI per raster cell (50m x 50m) < 5.0 5.001 - 10.0 10.001 - 15.0 15.001 - 20.0 > 20.001

scale: 1:16.671

Social impact of floods in the basic scenario +50%' expressed per grid cell of 50 by 50 metres

Damage and impact caused by flooding • 47 ❹

Research on types of measures

48 Research on types of measures • 49 If a major flood like that of 1891 were to occur again in Leuven, or if floods occur in the Woluwe river basin, they would cause damage, especially on an economic and social level. This was already mentioned in Chapter 4. The next step is to search for and assess measures to avoid this damage or which limit the consequences of flooding. Below are the potential measures that were studied and subdivided according to the 4 As concept.

① Alleviation: protection against flooding

A first type of measure consists of protective measures. de' nature reserve in Neerijse. These two measures ensured They protect specific zones such as residential areas from that Leuven is ‘flood safe’ until a theoretical return period floods through the construction of hydraulic engineering of 100 years. infrastructure. Typical measures include the construction of (underground) buffer reservoirs, controlled flood plains In the context of this project, we wanted to investigate the (CFPs), buffer sewers and dikes. The water cannot reach the possibility of additional protection for the city of Leuven residential areas. from a more extreme event such as that of January 1891. The construction of a controlled flood plain (CFP) in Neeri- Various protective measures have already been taken in the jse in the 'Doode Bemde' nature reserve was studied. river basin of the Dijle as well as that of the Woluwe. Above-ground and underground buffer reservoirs and In the Dijle basin, the Flemish Environment Agency has al- buffer sewers were constructed at various places in the ready constructed a controlled flood plain in Egenhoven Woluwe basin. However, this does not completely elimi- and restored the natural valley storage of the 'Doode Bem- nate the flood risk. On the basis of the hydraulic model of

50 Flood reservoir Hoevekens

Air shafts of flood reservoir Charles Courdent

Research on types of measures • 51 Flooding of Woluwe river at Stockmans mill

the Woluwe, additional protective measures were present- Protective ed that may offer a solution for a number of the remaining bottlenecks. measures against

Alleviation measures as such, however, also have a certain floods as such impact. Their implementation takes up space, they have an also have an impact on nature and landscape, have a certain price, etc. Their assessment is not simple, and for that a methodology impact on was elaborated, viz. the 'extensive cost-benefit analysis’ landscape and (see below). nature and cost money

52 Flood reservoir at Moorsel

Research on types of measures • 53 High water in the Doode Bemde

Additional alleviation measures buffered at the level of Egenhoven and 506,000 m³ in the 'Doode Bemde'. Protection of Leuven by additional water The CFP in Egenhoven can now buffer a total of 800,000 m³ buffering in the 'Doode Bemde' of water. This means that already an additional 668,000 m³ The 'Doode Bemde' is a nature reserve upstream of is buffered in comparison with the past. It also means that Leuven. At high water levels the Dijle already floods there another 1,632,000 m³ still has to be buffered in the 'Doode in a natural way. In this study we investigated the advan- Bemde' to safeguard Leuven from the 2.3 million m³ of wa- tages and disadvantages of a second CFP near Neerijse. ter that stood in the city centre in 1891.

Dimensioning On the basis of the DEM and the placement of the shutter In an initial step it was determined how much water should weir and cross dikes we calculated that the water in the be stored in the 'Doode Bemde' on top of natural storage 'Doode Bemde' had to be headed up to 28.10 m TAW to be in order to fully safeguard Leuven from an extreme flood. able to buffer an overall volume of 2,165,000 m³ of water. On the basis of the DEM (digital elevation model), we calculated that there was around 2.3 million m³ of water in the The maximum area that will flood was delineated on the centre of Leuven in the 1891 flood. basis of the DEM and the upstream water level. We deter- An estimate was made of how much water was already mined the location, the height of the cross dike and the buffered in the upstream area at that time by combin- protective dikes and the dimensions of the weir construc- ing old flood maps and the DEM. In the case of a flood tion. We listed the other conditions such as protection of with a recurrence period of 100 years, 132,000 m³ could be the railway bank.

54 Legend Perimeter Doode Bemde < 5.000.000 5.000.001 - 10.000.000

Water depth (m) High: 3,17

Low: 0

scale: 1:14.000

Inundation depths when headed up to 28.10 m TAW in the Doode Bemde

Legend Perimeter Doode Bemde Flooded area at 28 m TAW Flooded area at 28.5 m TAW Weir Cross dikes Longitudinal dikes

scale: 1:14.000

Structural works proposal CFP Doode Bemde

Research on types of measures • 55 Maximum upstream water level 28,10 m TAW

Maximum floodable surface area 265 ha

Maximum volume to be buffered 2 165 000 m³

Maximum water depth 2,5 m

Crest level of cross dikes 28,60 m TAW

Length of cross dikes 1077 m

Maximum height of cross dikes 3 m CFP characteristics 'Doode Bemde'

Preliminary draft design and estimate Additional buffering in the Woluwe basin On the basis of these data (levels, dimensions, etc.) we In the event of violent summer storms, the capacity of made a preliminary draft design for the construction of this the present water system of the Woluwe at a number of CFP. The preliminary draft design comprises building the bottlenecks is not large enough, which results in flooding. weir construction on the Dijle and additional construction Various alleviation measures were elaborated on the basis on the Leigracht, the cross dikes and longitudinal dikes, and of the hydraulic model. These were grouped into three sce- the dike to protect the railway. The overall price is estimat- narios, besides the starting scenario ‘Doing nothing’. ed at 1.3 million euros. This is without any need for specific –– Starting situation: Doing nothing foundations (to be determined by geotechnical survey). –– Scenario ①: Full execution of measures that safeguard against floods downstream of Kraainem –– Scenario ②: Partial execution of measures that safeguard against floods downstream of Kraainem –– Scenario ③: Upstream municipalities master plan

Scenarios ① and ② address the flooding in low Kraainem that would occur after a similar downpour to that of 29 June 2005. In a few minutes, this cloudburst damaged homes and road foundations. These floods were recalculated using the hydraulic model, the bottlenecks were detected and a set of potential interventions was assessed for ef-

56 3.5 3.6

3.7

3.8

1.3 4.1 + 3.4 4.2 Dezangré

4.3 Dexia

2.4 1.1 3.2 1.2 2.7

3.1 2.2

2.1 2.6 2.5

Description of measures and indication of which scenario they fall under

Number Measures m3 Scenario 1.1 Ring collector – wooded area at the mouth of the Ring collector and the Vuilbeek collector 8,035 m³ ① & ② 1.2 Ring collector - flood reservoir to the east of the Ring and to the north of the Burburelaan 4,426 m³ ① & ② 1.3 Kleine Maalbeek collector - overflow spillway from the Kleine Maalbeek collector into the Kleine Maalbeek - ① & ② 2.1 Vuilbeek collector – storage at the intersection of the J.B. Overloopstraat and Kalestraat 2,948 m³ ① & ② 2.2 Vuilbeek collector – storage at the intersection of the Beekstraat and Bos Van Houthulstlaan 5,041 m³ ① & ② 2.3 Vuilbeek collector – winter bed in marsh area to the north of the roundabout, downstream of the Lange 9,008 m³ ① & ② Eikstraat 2.4 Vuilbeek collector – additional buffering in artificial pond downstream of the Lange Eikstraat 8,085 m³ ① & ② 2.5 Wezembeek-Oppem sewer system – storage at the intersection of the Dieweg and Verboomenstraat 1,248 m³ ③ 2.6 Wezembeek-Oppem sewer system – storage at the intersection of Leopold III-laan and Oudergemsesteenweg 2,995 m³ ③ 2.7 Wezembeek-Oppem sewer system – storage at the intersection of Hippodroomlaan and Sint-Hubertuslaan 3,977 m³ ③ 3.1 Wezembeek-Oppem sewer system – storage at the intersection of Hippodroomlaan - Ban Eiklaan 2,058 m³ ③ 3.2 Wezembeek-Oppem sewer system – storage at the intersection of Grote Geeststraat – Medekensstraat 7,771 m³ ③ 3.4 Discharge conduit Moorsel – storage at the intersection of Bosdellelaan –Tramlaan 4,440 m³ ③ 3.5 Kleine Beek – storage at the level of the 1st intersection of the Kleine Beek collector with the railway 7,000 m³ ③ 3.6 Kleine beek – storage at the intersection of Imbroekstraat – Werkmansstraat 545 m³ ③ 3.7.1 Kleine Beek – overflow spillway at the Henneaulaan – Stationstraat intersection to the reservoir in the 3,250 m³ ③ Devemincklaan – Grote Daalstraat 3.7.2 Sewer section – overflow spillway at the Henneaulaan – Stationsstraat intersection to the reservoir in Grote 2,109 m³ ③ Daalstraat – Devlemincklaan 3.8 Woluwe – winter bed along the football ground, between the Woluwedal and F. Smoldersstraat 10,000 m³ ① & ② 4.1 Discharge conduit Moorsel – enlarge existing flood reservoir by factor 2.2 8,000 m³ ③ 4.2 Discharge conduit Moorsel - improving inflow to the Moorsel attenuation reservoir - ③ 4.3 Discharge conduit Moorse - storage at the level of the sewer connection in the Boslaan 1,145 m³ ③ Dexia Flood reservoir 13,000 m³ ① & ② Dezangrélaan Flood reservoir 13,000 m³ ①

Research on types of measures • 57 Flood Zaventem fectiveness. The proposed interventions mainly consists of Assessment by means of extensive relieving the collectors and the temporary storage of that cost-benefit analysis water in the surroundings. Scenarios ① and ② are largely similar to each other. The only difference is that in scenario ② The alleviation measures elaborated for the Dijle river basin we do not execute the reservoir at the Dezangrélaan. and the Woluwe river basin reduce the economic damage and social impact that occur in the event of a flood. How- Scenario ③ is called the “Upstream Municipalities Master ever, each of these also has a certain price and possibly also Plan". The measures in this scenario are focused on the additional impact (landscape, taking up space, ecological upstream municipalities in the Woluwe river basin, in par- impact, etc.). The challenge is to compare these different ticular those that discharge into the Kleine Maalbeek col- elements with each other. lector and the Kleine Beek collector. These measures are intended to prevent the downstream municipalities con- A cost-benefit analysis provides a framework for mutual tinuously experiencing flooding as a result of unrestricted comparison of similar alternatives. The disadvantage is that water discharge in the event of severe storms. In addition many assumptions and basic data are required to enable these measures are also a solution for local flooding prob- the performance of such a cost-benefit analysis. In the lems that sometimes occur. context of the project we developed a methodology for performing an extensive cost-benefit analysis. This methodology was applied for the proposed protective measures for the Dijle river basin and the Woluwe river basin. We also performed a sensitivity and uncertainty analysis to estimate the effect of uncertainties in data and assumptions.

58 Methodology applied for the extensive cost- ❷ Subsequently we standardised the values from the deci- benefit analysis sion matrix. This is necessary to make the values from the matrix of the various scenarios mutually comparable. In the Extensive cost-benefit analysis context of this study we standardised the decision matrix The assessment criteria used for the extensive cost-benefit by means of a linear interpolation between the minimum analysis are the project costs, economic damage, social im- and maximum values per assessment criterion on the basis pact and ecological impact. The project costs of the vari- of the scenarios under consideration. ous scenarios were calculated on the basis of the preliminary draft designs that were drawn up for the alleviation To enable the scenarios to be classified we have to allocate measures in each scenario. The economic damage, social a certain weight to the assessment criteria from the de- impact and ecological impact were determined for the cision matrix. By weighting the assessment criteria we lay various scenarios according to the methods described in down the importance we attach to the corresponding ef- Chapter 3. fect. It goes without saying that this weighting has a major effect on the result of the analysis. It is important that the ❶ In an initial step we assembled the values of the assess- various stakeholders agree on the weight they allocate to ment criteria for the various scenarios in a matrix. In the each criterion. starting situation there are no project costs, since no protective work is executed. The combination of the standardised decision matrix and the weightings yields a score per scenario. With the aid of In performing the cost-benefit analysis, we compare the these scores we can classify the scenarios, including the costs with the benefits that a project entails. However, the starting situation. costs and benefits are spread over time. The costs are realised at the time the protective measures are constructed. Sensitivity analysis The benefits viz. the prevention of economic damage are Because of the computations performed, the results of realised at the time a flood is avoided. the cost-benefit analysis are not always easy to interpret. In order to compare costs with benefits, they should be It may be asked which parameter had the most effect on updated or discounted to a particular reference year. In the result. For this purpose a sensitivity analysis was per- other words, we have to calculate how much the damage formed. A sensitivity analysis serves to identify the critical that was prevented would mean today, i.e. the net current parameters (values and weightings for the assessment cri- value. This may be done on the basis of a discount rate. teria). We consider a parameter as critical when a relatively In this project we adhered to a discount rate of 4%. In lit- limited variation in the value and/or weight allocated to an erature, this value is pushed forward for Flanders, and the assessment criterion has a major impact on the result of a European Commission informally recommends it as well. scenario. In order to be able to perform the discounting we have to make a statement on the probability of a flood occur- Uncertainty analysis ring or the frequency at which it occurs. We performed the The input data contain some uncertainty. There are vari- cost-benefit analysis with three return periods: 100 years, ous types of uncertainty: uncertainties in the knowledge 200 years and 300 years (R100, R200 and R300). The fact that of economic, social, ecological and physical systems, short- we included more than one return period in the calcula- comings in the way in which the impact on these systems tion does not mean that we make any statement on the is modelled, and limitations concerning data availability. To frequency at which that flood may occur. However, it gives make it possible to make good decisions on the basis of us more insight into the evolution of the desirability of tak- a cost-benefit analysis it is necessary to take account of ing alleviation measures in accordance with the probability uncertainties as much as possible. of flooding. Here we used a Monte Carlo uncertainty analysis to assess The project horizon of the construction of the alleviation the uncertainty of the result of the cost-benefit analysis. measures also has to be taken into account. It corresponds The classification of the scenarios is recalculated 1,000 to the expected useful operational life of the investment. In times with different values and weightings. the context of this study we consider the period 2011-2100.

Research on types of measures • 59 Input data for the extensive cost-benefit analysis for the construction Starting situation: no protective measures, Scenario ①: of protective measures against floods in the city of Leuven. Construction of CFPs in Egenhoven and Neerijse

Starting situation Scenario ① Project costs 0 6,141,035 – Neerijse CFP 1,312,135 – Egenhoven CFP and associated works 4,828,900 Economic damage 394,885,751 0 Social impact 3,022 0 Ecological impact 59.39 164.45

Assessment of additional buffering of water in For the three selected return periods R100, R200 and R300, the 'Doode Bemde' scenario ① has a much higher score each time than the starting situation. At R300, scenario ① has a score of 0.77 Extensive cost-benefit analysis compared with a score of 0.16 for the starting situation. The The methodology for an extensive cost-benefit analy- shorter the return period, the greater the probability that sis was applied to the starting situation (a flood like that of severe flooding will occur, and the more desirable - itbe 1891) and scenario ① (construction of the CFP in Neerijse in comes to create storage upstream of Leuven. addition to the already existing CFP in Egenhoven). Sensitivity analysis As described, the first step is to assemble the values of the A sensitivity analysis of the weight we allocated to the assessment criteria for the various scenarios in a matrix various assessment criteria indicates that only adjusting In the starting situation there are the weight allocated to the cri- no project costs, since no pro- terion of ecological impact has tective work was realised. This relevant impact on the result. If means that a large part of the A cost-benefit the ecological impact is given a city centre of Leuven will flood. analysis creates much greater weight, scenario ① This would entail economic dam- will become proportionally less age of approximately 395 million a context for positive. euros and a social impact of 3022. In the 'Doode Bemde', nat- comparing similar Uncertainty analysis ural flooding will occur with an alternatives with We performed this uncertainty ecological impact of 59.39. analysis for the situation in which However, in scenario ① there are each other it is assumed that the flood un- project costs, a total of around 6 der consideration has a return million euros for the construc- period of 300 years. Scenario ① tion of the CFP in Neerijse and the CFP in Egenhoven. In has a 100% probability of turning out to be the best sce- Leuven proper no more floods will occur and therefore the nario. Even in the event of longer return periods, creating economic damage and social impact are equal to zero. In additional storage continues to have most preference. the 'Doode Bemde' a much larger surface area will flood with a longer duration and greater water depth. This entails Conclusion a much higher ecological impact score (164.45). The results of the cost-benefit analysis of the two scenarios, including the sensitivity and uncertainty analyses, make In this project we allocated the following weight to the it clear that the construction of the CFP in Neerijse entails various assessment criteria for the Dijle: economic flood a major absolute benefit for society. risk 0.4158; social flood risk 0.3534; project costs 0.0308, and impact on nature values 0.2000. The way in which the impact of an extreme flood on the

60 Input data for the extensive cost-benefit analysis for the Starting situation: no protective measures, Scenarios ①, ② & ③: construction of protective measures against floods in the Woluwe various combinations of alleviation measures) river basin.

Starting situation Scenario ① Scenario ② Scenario ③ Basic Basic +50% Basic Basic +50% Basic Basic +50% Basic Basic +50% Project costs 0 0 8,203,943 8,203,943 5,703,943 5,703,943 10,427,604 10,427,604 Economic 15,718,954 22,413,808 12,941,841 19,077,633 12,942,783 19,105,741 12,997,301 19,491,026 damage Social impact 450.28 526.63 351.24 415.25 351.24 415.25 269.61 409.39

existing nature and landscape values is assessed has the the various bottlenecks. This will result in overall economic greatest effect on the result of the cost-benefit analysis. damage of 15.7 million euros in the basic scenario and 22.4 million euros in the basic scenario +50%. Moreover, it also Alternative protective measures for the Dijle River basin entails a social impact of 450 in the basic scenario and 527 In the context of this project we only assessed one possi- in the basic scenario +50%. ble alleviation measure to avoid extreme floods in Leuven. It appears from the cost-benefit In the three scenarios there are analysis that creating additional however project costs of 8.2, 5.7 buffering upstream of Leuven is and 10.4 million euros for scenarios certainly positive. Various more ①, ② and ③ respectively. None small-scale buffer zones that According of these scenarios can complete- are closer to natural flooding to the cost- ly reduce the flood risk to zero, or buffering by 'roughening' the and therefore in the event of waterway whereby the natural benefit analysis, heavy rain there will still be eco- buffer capacity of the valley is nomic damage and social impact. used in a better way are some of construction of For each of these three scenarios the alternatives that have to be an additional the economic damage is around investigated further. 12.9 million in the basic scenario CFP upstream of and around 19 million in the ba- Assessment of additional sic scenario +50%. The values are buffering in the Woluwe Leuven is clearly different per scenario. The social river basin positive because impact score is 351 in the basic scenario and 415 in the basic sce- Extensive cost-benefit analysis of the low price nario +50% for measure scenarios We applied the methodol- ① and ②. For measure scenario ogy for extensive cost-benefit and the major ③ the social impact score is analysis to the starting situation damage thereby 270 in the basic scenario and (‘Doing nothing’) and the three 409 in the basic scenario +50%. scenarios. prevented In the context of this project we As already described, the first allocated the following weights step is to assemble the values of to the various assessment criteria the assessment criteria for the for the Woluwe: Economic flood various scenarios in a matrix. No ecological impact was cal- risk 0.3581, social flood risk 0.3044 and project costs 0.3375. culated for the Woluwe river basin. In the starting situation there are no project costs since no protective works were By comparing the scenarios in the different floods (basic realised. This means that there will be floods at the level of and basic +50%) with each other we can draw the follow-

Research on types of measures • 61 'Basic' flood 0.50 Score 0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.5

T25 T50 T100 T200 Considered flood probability

Starting situation Scenario ① Scenario ② Scenario ③

ing conclusions. If the floods (basic and basic +50%) occur the 'Basic' flood at R100 the following conclusions are valid. more frequently (R25 and R50), measure scenario ② is the In view of the given uncertainty of the values and weights, most advantageous. If these floods occur less frequently ‘Doing nothing’ will be the best scenario in almost 88% of (R100 and R200) the starting situation is the best option. the cases. Scenarios ①, ② and ③ present a probability of The option to take measures therefore depends on wheth- around 2%, 12% and 0% respectively to emerge as the best er we believe that (extreme) floods will occur increasingly scenario. The starting situation and scenario ② will virtually more frequently or not. Scenario ③ is the least attractive in never be the least attractive scenario. the event of more extreme floods (basic +50%). However, if this flood occurs more frequently, for example on average once every 25 years, the situation looks com- Sensitivity analysis pletely different. In this case all scenarios have a realistic A sensitivity analysis of the weight we allocated indicated chance of emerging as the best scenario, but scenario ② that adjustment of the weight allocated to ‘social flood (55%) and ③ (27.5%) clearly come out on top. risk’ has the greatest potential to affect the classification of the scenarios. Modification of the weight allocated to Conclusion 'project costs' has the greatest effect on the relative differ- Depending on the probability (R25, R50, R100 or R200) at ence between the score for the various scenarios, but the which the floods under consideration (‘Basic’ of ‘Basic classification is retained. +50%’) occur, ‘Doing nothing’ or Scenario ② ‘partial execution of measures that safeguard downstream Kraainem Uncertainty analysis from floods’ will tend to emerge as the most desirable op- The uncertainty analysis yielded the following results. For tion. In view of the basic values, weights and assumptions,

62 'Basic + 50%' flood 0.50 Score 0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.5

T25 T50 T100 T200 T25 T50 T100 T200 Considered flood probability

Starting situation Scenario ① Scenario ② Scenario ③

Classification of the various measure scenarios for various floods (basic and basic +50%) and flood probabilities (T25, T50, T100 and T200) in the Woluwe river basin. The higher the score, the higher the scenario is valued. For example, for the basic flood with a flood probability of every 100 years (R100) the starting situation gets the highest score, and is therefore the scenario with the highest value. Scenario ② has the second highest score, followed by scenario ① and scenario ③. So in this case, scenario 3 has the lowest value.

Scenario ② is the most desirable option if the floods under consideration (‘Basic’ and ‘Basic +50%’) occur relatively frequently (every 25 or 50 years). In the other cases 'Doing nothing' is the best option if the floods under consideration occur relatively less frequently. However, it is not pos- There is an sible to make a statement on the probability that can be obvious need for ascribed to a flood. supplementary The three scenarios consist of groups of measures which each have their own effect and impact. The result of the prevention, cost-benefit analysis is obviously highly dependent on the measures that are grouped within a particular scenario. awareness If the measures were to be grouped in a different way, it and/or assistance could lead to a different result. measures None of the proposed scenarios ensures that damage resulting from floods will be completely reduced to zero. For this reason other types of measures will definitely also have to be deployed.

Research on types of measures • 63 ②

Avoidance: prevention of Planning regulations are legal stipulations valid for a par- flooding and damage ticular territory (municipality, province, region); they contain regulations for destination, composition and management. An important regulation in the context of this study A second type of measure consists of avoidance meas- is the regional rainwater regulation. This applies to the en- ures. These measures are intended to mitigate the damage tire Flemish Region and has to limit the consequences of caused by an unavoidable flood. additional surface hardening by requiring rainwater drains, infiltration and buffer provisions, and the construction of a Although floods are a natural phenomenon, the causes of segregated water system. flood risk point more and more in the direction of mankind. Two major reasons are increasing activity (living, working, If a zone is indicated in the SIP where the pre-emptive right etc.) in flood risk areas and the impact of human beings on is valid, the favoured bodies can request the Flemish land the natural water system. The first objective of flood risk bank to exercise the pre-emptive right in the sale of real prevention is to put a stop to these unwanted develop- estate in that zone, on their behalf and for their account ments. and under the conditions they lay down. In this way, for example, a flood-susceptible area can be cleared of buildings Furthermore, flood risk prevention is also concerned with again, without the need for compulsory purchase. driving back the existing risk by mitigating possible damage. People can protect and equip their homes better in order The permit-issuing authority checks the application of the to reduce or even minimise flood damage. various tools and laws. Therefore an allotment permit has to be applied for in order to divide a piece of land into dif- In this study we first listed the tools that are currently ferent parcels that are sold as building plots. This allotment available to the authorities to fill in flood risk prevention. has to comply, among other things, with the conditions of Subsequently we formulated a number of objectives which the water assessment. Additional measures can also be im- were then translated into spe- posed in the permit. cific policy recommendations. A building permit is also required In a final step we performed an for each building project. If the area-focused analysis of the Di- Avoidance can programme or building plan is in jle and Woluwe river basins and conflict with the spatial imple- drew up a wish list. This wish list mitigate damage mentation plans or the applica- states where we can take which resulting from ble planning regulations, no per- avoidance measures. mit can be issued and the project floods cannot be executed. With the Management tools application for a permit a 'checklist for verifying the regional Tools of the Flemish Spatial Planning codex rainwater regulation' is also required. For every individual Within spatial planning there are various tools that can be building project, this form enables simple verification of deployed to implement flood risk prevention in practice. compliance with the regulation.

The pre-eminent management tool in spatial planning is the Sectoral legislation: integration of water spatial structure plan. This type of plan outlines the desired management and spatial planning policy future development of a particular area. Spatial structure There are several laws that help to realize the integration of plans are converted to spatial implementation plans (SIPs) water management and spatial planning policy. and regulations. These tools constitute the legal anchorage of the policy. They determine which functions, activities The decree Integrated Water Policy of 18 July 2003 imposes and interventions are or are not permissible in a particular a water assessment for every spatial plan. The water as- area. There are various ways to include water management sessment investigates whether the intended plan may have measures in a SIP. negative consequences for or cause damage to the water

64 Water as an organising principle in a Spatial Implementation Plan A Spatial implementation plan (SIP) can: –– Change the land use allocation: thus a flood plain or area for water buffering can be indicated. Water is rarely the main land use allocation of an area and is generally included as a secondary function in addition to another land use allocation. –– Establish conditions for structural work to the area such as: •• the use of certain materials (water-permeable hard surfaces, applying pile foundations, etc.); •• limiting the dimensions of (underground) constructions; •• prohibiting constructions; •• imposing protective measures against flooding (additional buffering, core dikes, embankments, excavations, pile dwellings, etc.). –– Determine the plan borders so that in the planning area there is room for measures for integrated water management. –– Include management measures such as maintenance of waterway-bank zones. –– Include compensation measures such as the construction of a common buffer reservoir or infiltration provisions. The plan has to provide the latter within the planning area. Moreover, it is important to state the type, dimensions or space required and the most suitable location. –– Determine the staging of the execution of the plan. Therefore the plan can foresee the condition that a certain development can only take place when sufficient water storage space has been provided elsewhere. ––

system. If this is the case, measures have to be included to Flanking tools prevent, limit, repair or compensate potential damage. In addition to the plans from the current spatial planning procedures, master plans, vision memoranda and struc- Every plan or programme that is the framework for granting tural plans are regularly drawn up. Here too an integrated a permit for a project, and therefore every SIP, falls under approach to spatial planning and water policy is of crucial the EIA [Environmental Impact Assessment] plan decree. importance. According to the Integrated Water Policy decree, the elements to enable the water test to be performed also have There are several subsidy possibilities to support projects to be included in the screening report or in the EIA plan. for flood risk prevention. Assessing whether or not a plan may have severe effects on The Rubicon Fund of the Flemish Region supports local au- the environment also means that potential effects on the thorities in preventive actions that prevent future damage water system are studied. from new floods. In the context of the 2008-2013 cooperation agreement, subsidies are available for integrated water There are some other laws that affect water. For exam- management projects realised by municipalities, such as ple, the groundwater decree, Vlarem I and II [Flemish Envi- ecological structural work on waterways, the construction ronmental Permits Regulation] and environmental quality of flood plains, infiltration provisions and interventions standards, the decree on soil remediation and soil protec- to increase the infiltration and buffer capacity of a canal tion, the manure decree and implementing orders, water system. The Integrated Water Policy decree has also made quality objectives, the law on unnavigable waterways, the available a number of financial tools, including the pre- water policy memorandum, priorities for integrated sew- emptive right and purchase obligation. erage policy in Flanders and the elucidation on the good practice code and catchment area, basin and sub basin Various European projects or programmes also grant subsi- management plans. This legislation stands alone, but should dies for flood prevention projects. be integrated if it has spatial planning consequences. There- fore spatial planners have to ensure that they do not make A municipality as such also has the possibility to give its in- sectoral legislation impracticable. habitants financial support for the execution of preventive measures such as installing a rainwater well. Many Flemish municipalities make use of this possibility.

Research on types of measures • 65 Objectives of flood prevention Converting objectives into measures

If we want to limit the impact of floods effectively, we The three core objectives of flood risk prevention can be have to opt for solutions that link up with the water sys- defined in a number of measures that are not specific to tem. This is necessary to prevent new problems surfacing. a particular area. We can often deploy these measures in Furthermore, the baseline of a more integrated strategy spatial planning policy. should ensure that incompatible building in flood risk areas is no longer allowed. Infiltration and water storage capacity of the soil A preventive approach to floods starts from respect for the In principle the objective, to safeguard and improve the natural water system. Using this approach we pursue the infiltration and water storage capacity of the soil, applies objectives below: to the entire territory. However, not all measures can be –– To safeguard and improve the (natural) infiltration and deployed at all sites, since not every type of soil has suf- water storage capacity of the soil. ficient infiltration capacity. The measures comprise the first –– To safeguard and increase the water storage capacity three steps in the good practice code for rainwater: re-use, of waterways and neighbouring valley regions. infiltration, storage and delayed discharge. Therefore it is –– To limit non-adapted building in flood-susceptible important to inform cities and municipalities, architects areas. and private individuals regarding the good practice code.

66 ◀ ▲ ▼ Water squares: depending on the severity of the shower, the water storage takes up more or less space on the square Source: De URBANISTEN, www.urbanisten.nl

Research on types of measures • 67 The first measure is retaining and extending infiltration and be combined with the water storage function of the area. buffer zones by means of zoning. However, if that is not the case and the zone has not yet been built on, a SIP can give that zone a new land use allo- Infiltration zones and natural retention areas should be cation which safeguards the water storage function. clearly visible in the spatial structure plans and correspond In various plans and SIPs we have to use the water network to the river basin management plans. Therefore they can be as a carrier for urban ecology and other functions such as taken into account when recreation, living, etc. By planning the various func- linking various functions tions. The physical system 3 ways to safeguard and improve we can optimise the use is the basis for good spa- the infiltration and buffer zones = of space. By ensuring ac- tial planning in which the ➞ cessibility in the right water storage function zoning places we acquire a versa- and the infiltration capac- ➞ equipping districts tile, flexible and high quality of the area should re- ➞ preserve roughness of the landscape ity network with great so- main at least equivalent. cial support capacity. This should be included in Moreover, we have to subsequent planning pro- safeguard space for future cesses and in development plans. measures by indicating them on the structure plans and In addition, land use allocations can be attuned to flood taking them into account when drawing up SIPs. In this way susceptibility. There is no problem if the intended use can we can 'reserve' space for water storage.

68 Water buffering in the green-blue public space in the 'De Vloei' sustainable district in Ypres ARCADIS commissioned by the West-Vlaamse Intercommunale (West Flemish Intercommunity)

A second measure is preservation and extension of infil- A third practical point is the construction of common and tration and buffer zones when equipping and renovating individual buffer and infiltration provisions. We can deploy districts. green areas in districts to function as buffer and infiltration zones, and there are various concepts for this purpose. A first practical point here is the concept of sewerage. The choice depends largely on the soil and subsoil and the Waste water and rainwater have to be optimally separated. expected degree of water pollution. It should be examined In existing mixed sewer systems, rainwater has to be dis- on a case-by-case basis. The obligation to incorporate this connected as much as possible. Rainwater should be em- in the draft can be imposed by means of structure planning ployed to a maximum for re-use, or be infiltrated or buff- and in the SIP zoning and equipment regulations. Green ered. A municipality may make this a priority by including it roofs, water roofs or storage cellars can also function as in its planning and when implementing the plans. buffer capacity.

A second practical point is hard surfaces. The use of imper- If there is a need for additional water storage space, it is meable hard surfaces has to be optimally restricted or even recommended to consider taking additional measures such prohibited. This can be incorporated in spatial structure as the construction of retention ponds and water squares. plans as a principle, applied in an SIP and checked with the This should certainly be combined with information to the permission policies. Urban regulations can also make the public because their construction has a major impact on use of permeable hard surfaces mandatory. The pollution people living in the neighbourhood. level of the run-off water is a point for attention here.

Research on types of measures • 69 Example of flood-resistant building without reducing storage capacity The garages underneath this apartment building in Frankfurt are floodable

A third measure is the retention and extension of infil- Space for waterways can be created by re-meandering wa- tration and buffer zones by retaining or increasing the terways. In addition the existing waterways have to be re- hydraulic roughness of the landscape. tained. Vaulting or filling in waterways or pools should be avoided. The 5 m land servitude zones and bank zones have The water storage capacity of an area is retained or in- to be complied with or be restored. creased by protecting and restoring vegetation, woods and marshes. This should be taken into account when an area is For creating space around waterways it is important to at- being planned. Delaying and reducing the run-off from agri- tune spatial structure plans and basin management plans to cultural and wooded areas mitigates problems downstream each other. In the spatial structure plan, zones should be and loss of fertile soil. An example is erosion-controlling sought with opportunities for opening up waterways or for measures. re-meandering. This is preferably combined with the devel- By dealing with these measures creatively, they can also be opment of nature and recreation areas or with upgrading a applied in residential, industrial and recreational areas. residential zone or industrial area. This results in zones with opportunities for temporary flood plains and zones where Water storage capacity of waterways and building is best avoided. adjoining valley areas The surrounding spatial usage has to be attuned to this. Safeguarding and increasing the water storage capacity Green zones, slow road networks and recreational areas can of waterways and valley areas can be achieved by taking be combined with the water network. This has the advan- measures that help to retain and create this space for wa- tage that the space around the waterway acquires a num- terways and space around waterways. ber of functions and a greater social supporting capacity is generated.

70 In the case of larger waterways or rivers, zones for flood- There are also possibilities for flood-resistant building with- ing during peak flow rates can be made available again by out reducing the storage capacity. This is possible for ex- means of dike relocation. The use of the soil then has to be ample by constructing a floodable crawl space, building on attuned to the flood risk. platforms or piles or by providing a floating house.

Restricting (non-adapted) building in flood- In areas with frequent floods, the demolition of houses susceptible areas may be considered in the case of low building and low hab- Non-adapted building in flood-susceptible areas can be itation density. The purchase obligation according to the avoided by no longer building there, building in an adapted Integrated Water Policy decree can be called in or compul- way or by demolishing existing buildings. sory purchase takes place.

Alluvial areas can be safeguarded by including them in the Area-focused analysis: wish lists for spatial structure planning and SIPs. In spatial structure plans the Dijle and Woluwe river basins the functions homes and industry are combined with areas to be developed or zones to be redeveloped. It is impor- We have already demonstrated how the known tools of tant that alluvial areas or areas with a high flood risk are not spatial planning can be deployed to achieve the objectives used for this purpose. If they are still opted for, it should to prevent floods. That analysis was not area focused. be clearly indicated that building can only take place on In the context of the project we went through the exer- certain conditions. In that case only flood-resistant building cise of performing an area-focused analysis for the Dijle can be carried out. and Woluwe river basins on the basis of existing maps on In an SIP a building prohibition can be imposed in particular the one hand and the specific planning situation in the area zones. In addition, zones can also be given a different land studied on the other. The results of this analysis are rep- use allocation so that their original function (home, indus- resented in a wish list. This list divides the study area into try, etc.) can no longer develop. various zones. We assigned a task to each zone, depending The pre-emptive right can be applied in zones where com- on the present land use allocation and the risk of floods. Example of flood-resistant building without reducing storage capacity pulsory purchase is not desirable, but which are important These task allocations can be reduced to one or more ob- The garages underneath this apartment building in Frankfurt are floodable as flood plains or where there is a high flood risk. jectives for the preventive way to deal with the floods, as Building land where no building should actually occur be- already identified. cause of flood susceptibility can be exchanged for other equivalent plots of land outside flood-susceptible zones. On the basis of this division we developed a standardised GIS procedure with the aid of the available GIS material According to the principles of spatial planning, no building (Cadmap 2008, regional plan, land use map, water catch- permits should be delivered for building projects in actual ment areas for drinking water, naturally flooded plains, re- flood-susceptible zones. However, legally and socially this cently flooded plains, historical flood maps, topographical remains difficult to realise if the land use allocation of the map). Every task allocation was given a colour code. This area allows building. In that case, informing future inhabit- colour code returns in the area-covering wish list and indi- ants and architects is an appropriate strategy. cates the various task allocations.

Adapted building can also be performed in flood-suscep- The wish list offers an overview of where and which ac- tible areas. Here an important step is informing planners cents can be placed concerning flood and damage preven- and architects. If they have better knowledge of the tech- tion. niques and become familiar with them, they will also apply them more often and correctly. In the urban context it seems rather irrelevant to impose Guidelines are needed for reinforcing the flood resistance building prohibitions. However, the public domain can ob- of buildings, for example on the construction of storage tain a major water storage function for excess rainwater. cellars, waterproof protection, and higher siting of fuse This more or less theoretical exercise can be further fine- boxes and sockets. These guidelines have to be part of the tuned in cooperation with the competent authorities for urban development regulations for floodable areas. spatial planning.

Research on types of measures • 71 Wish list of task allocations in flood prevention in the Dijle river basin

72 Wish list of task allocations in flood prevention in the Woluwe river basin

Definition of zones where a particular task allocation has priority on the basis of the risk of a particular type of flooding and the type of land use Flood Land use status Task allocation

Floods from the river or sewerage Built-on Zone for risk management II: increase protection and ability to cope

Floods from the river or sewerage Not built-on, housing extension area/ Prohibit building and safeguard and/or increase water storage capacity industry extension area in the valley (attune current land use to water storage)

Floods from the river or sewerage Not built-on or suitable for building, no Safeguard and/or increase water storage capacity in valley I (attune cur- meadowland, nature, woods, water, green rent land use to increasing the water storage) zone etc. (agriculture or recreation)

Floods from the river or sewerage Meadowland, nature, woods, green zone, Safeguard and/or increase water storage capacity in valley II etc.

Floods through surface run-off Built-on Zone for risk management II: increase protection and ability to cope and only build in a flood-resistant way

Floods through surface run-off Not built-on, housing extension area/ Resistant building mandatory, avoid building where possible, complying industry extension area with the task allocations in connection with local storage and infiltration of rainwater

Floods through surface run-off Not built-on or suitable for building, no Comply with the task allocation in connection with local storage and meadowland, nature, woods, water, green infiltration of rainwater zone etc. (agriculture or recreation)

Floods through surface run-off Meadowland, nature, woods, green zone, Comply with the task allocation in connection with local storage and etc. infiltration of rainwater

No floods All zones Comply with the task allocation in connection with local storage and infiltration of rainwater

Research on types of measures • 73 Online flood maps Flood maps for the whole of Flanders can be viewed on the AGIV website. These are maps showing recently flooded areas, naturally flooded areas and flood risk zones. A search function zooms to a street, municipality or a location with known coor- dinates. Other kinds of maps can also be viewed on this website. (http://www.agiv.be/gis/diensten/geo-vlaanderen)

③ Awareness

In spite of all alleviation and avoidance measures, floods cannot achieve the capacity to respond to a flood risk. Be- cannot be avoided at all times and in all places. Therefore ing capable to respond indicates the degree to which peo- citizens have to be aware and have to know what has to be ple are personally capable of mitigating the consequences done to protect themselves before and during an emer- of floods because they are prepared and know exactly gency situation and to know where any help is given. This what they can undertake before, during and after a flood. is called flood risk awareness and the capacity to respond to a flood risk. In the context of this project we checked what knowledge is already present on awareness and the capacity to re- We define flood risk awareness as knowing, recognising and spond and the communication on the subject in Flanders understanding the possibility of floods in one’s surround- as well as in other countries. We made a list of the existing ings, as well as the risk they entail. Without awareness, initiatives and propose a number of new initiatives to rein- measures will be less effective or less easily implemented. force awareness and the capacity to respond with respect Being aware makes people understand the usefulness of to floods. the other measures. Without awareness, the population

74 Safety advice on the Internet There is specific safety advice with regard to flooding on the portal of the Belgian Government and on the Civil Defence site. Tips are given on the measures citizens can take personally before, during and after floods, not just for their own safety but also to limit damage. On the Assuralia (the professional association of insurance companies) website there is a checklist for what you should do when you are affected by a flood and you are insured.

Portal of the Belgian Government: http://www.belgium.be/nl/ > huisvesting’ > ‘huisvestingsproblemen’ > ‘natuurrampen’ > ‘overstromingen’ (‘housing’ > ‘housing problems’ > ‘natural disasters’ > ‘floods’)

Civil protection: http://www.civieleveiligheid.be/ > ‘je veiligheid’ > ‘veiligheidstips’ > ‘overstromingen’ (‘your safety’ > ‘safety tips’ > ‘floods’)

Assuralia: http://www.assuralia.be/ index.php?id=206&L=0&tx_ttnews%5btt_news%5d=1805

Safety advice brochures In the framework of the EU project on high water management in border areas (FLAPP - Flood Awareness & Pre- vention Policy Border Areas), the Province of East Flanders developed the brochure ‘Bent u voorbereid op een over- stroming? Voor-tijdens-na’ [Are you prepared for a flood? Before-during-after]. This brochure includes a checklist for an emergency package, what you should do when there is a threat of flooding, what you have to do in the case of evacuation, and what to do if evacuation is not possible. In addition a more concise folder was made with the most necessary points for attention. These folders are available on the website of the Province of East Flanders.

Research on types of measures • 75 Dutch communication campaigns A large part of The Netherlands lies well below sea level. Therefore in many places there is a high risk of floods. For this reason, awareness of the risk of flooding and the capacity to respond are addressed on many fronts. On the one hand there are the national campaigns such as ‘Denk vooruit’ [Think ahead]. This campaign focuses mainly on being prepared for 11 types of disaster, including floods. The slogan is: disasters cannot be planned, but preparations can. The campaign ‘Nederland leeft met water’ [The Neth- erlands live with water] is also well known. This is intended to make the Dutch aware of their relationship with water. These campaigns include TV and radio commercials and a website, and targeted use is made of education. In addition there are also more local initiatives.

Knowledge of awareness, capacity to teresting insights. Not everybody has a risk perception of respond and communication potential floods and the associated damage is often not estimated as high. So there is clearly a need for informa- Knowledge tion. Merely providing information on the flood risk does Little is known about flood risk awareness and the capac- not suffice to increase the capacity to respond. Most peo- ity to respond to a flood risk in Flanders. In many places ple regard the authorities as responsible for avoiding flood the flood risk is not clearly visible. The various alleviation damage. Therefore the authorities have to provide specific measures taken enhance this phenomenon. The same goes information on the possibilities for personal protection. for the river basins of the Dijle and the Woluwe, where long sections of the waterways and tributaries were often Communication vaulted and therefore only partly visible. In both river ba- Through regular communication people can get to know sins there are a number of several hazard areas where flood and be reminded of the flood risk and the possibilities of damage may occur. Various alleviation measures were al- preparing and protecting themselves. This is known as risk ready taken, which does not always make it clear to citizens communication. how great the risk is at various locations. For this reason we may assume that the population generally does not have Risk communication means communicating about hazards, adequate knowledge of the flood risk and neither does it i.e. the probability of a flood occurring and its consequenc- know how to deal with it. es. The aim is to increase knowledge of the flood hazard and of the behavioural options in the event of an imminent Recently some studies on the subject were performed in flood. The effectiveness of all communication largely de- a number of European countries. They provide some in- pends on the factor 'receiver of the communication'. This

76 Building precautions in flood-susceptible areas in Germany In the German Federal State of North Rhine-Westphalia the authorities have distributed a special information brochure on precautionary measures for buildings situated in flood risk areas. It discusses issues such as potential stability problems, preventing water ingress, and possibilities of damage reduction.

should be taken into account in drawing up a communica- Existing initiatives tion strategy. In Flanders there is no targeted strategy for reinforcing From the literature we can identify a number of impor- flood risk awareness and the capacity to respond. There are tant points for attention with regard to risk communica- however a number of initiatives which make a contribution: tion about floods. Generally people are not interested in the online flood maps of the AGIV (Flanders Geographical the precise probability of the risk occurring, and a more Information Agency), the water assessment, the inclusion vague indication (high or low risk) is often sufficient. The of flooding as a risk in fire insurance, the National Disaster use of extreme images of floods may have a negative ef- Relief Fund, information evenings on the occasion of spe- fect. They lead to resignation because people think that cific projects for water management, safety advice on the taking measures is useless anyway. Trust in the source of website of the Belgian authorities or the Civil Defence, the information is very important. If something does not come insurance checklist on the Assuralia (the professional as- across as credible, people will not comply. The publisher of sociation of insurance companies) website, etc. the communication always has to be presented clearly and Most of these initiatives were not set up with a view to a contact address has to be provided. these objectives (only), and their effectiveness is not veri- fied. Neither are they actively announced to the general Risk communication is related to crisis communication, but public. it is not the same. In the safety chain, risk communication has to come before crisis communication. In other countries there are also bodies which are taking initiatives to reinforce awareness and the capacity to re-

Research on types of measures • 77 spond, e.g. drawing up brochures and information booklets Assistance before, during and about floods and potential measures. There is also infor- after a flood ④ mation on the websites of the authorities and emergency services. A fourth type of measures comprises assistance measures. Reinforcing awareness and the These measures have to support the community before, capacity to respond during and after a flood.

From the above study we may conclude that awareness In the context of this project we performed a study to gain of flood risks and knowledge insight into risk and crisis man- of the capacity to respond are agement and communication in rather limited in Flanders. Several the event of flooding. First we initiatives were set up for this investigated the current state of purpose, but they are not well affairs in Belgium, with the focus known by the public at large. Citizens have on Flanders. We had conversa- to be aware that tions with safety and communi- The population needs to be bet- cation officials at the federal and ter informed about the risks, the floods cannot provincial authorities. In this way available sources of information we gained better insight into the and potential measures. This can be avoided at all way in which emergency plan- be done, among other things, times and in all ning currently operates and what by combining a communication might be improved. We also campaign at a Flemish level with places sounded out practical experi- a campaign at a local level. The ence in the field and the role wa- campaign at a Flemish level will ter managers could have in the preferably deal with risks in gen- event of flooding. eral (so not just flood risks). The local campaign will specifically highlight the bottlenecks of We also carried out a survey in a number of European the river basin in question. This has far more appeal. countries and performed a limited international literature study. We focused on risk and crisis communication in the A local communication campaign can be supplemented event of flooding. with specific actions such as putting up information pan- els near protective infrastructure or displaying high water State of affairs in Belgium marks on historical buildings. Crisis management A specific point for attention for the whole of Flanders In Belgium, various bodies organise intervention and assis- is the divided competence for water management. The tance, depending on the severity of the emergency situa- municipality, the province or the Flemish Government is tion. The mayor is competent for managing an emergency competent, depending on the category of the waterway situation in his/her municipality, the governor in his/her in question. This does not make it very easy for people to province and the Minister of the Interior. Announcing the know whom to address for questions or how they have to emergency situation is possible on three levels. interpret particular information. On this issue too, further coordinated action is required. Municipalities and provinces have to set up an emergency and intervention plan. It comprises a General Emergency Specifically for the Woluwe river basin, there is also the im- and Intervention Plan (ANIP) and possibly one or more Spe- portant interrelationship between the waterways and main cial Emergency and Intervention Plan(s) (BNIP). The ANIP sewers. This also has to be explained to the public. contains the general guidelines and the required information to ensure management of an emergency situation. A

78 Measuring points and status of navigable waterways in the Dijle and Zenne river basin on 23/05/2011 represented on the website www.waterstanden.be

Measuring points and status of unnavigable waterways on 12/11/2010 represented on the website www.overstromingsvoorspeller.be

possible BNIP supplements the ANIP with specific guide- or the governor or the Minister of the Interior to provide lines for a particular risk (e.g. flooding). the population and the media with information. For this purpose, he/she appoints an information manager and The safety division is charged with drawing up and up- spokesperson. dating the emergency plans. The following disciplines are represented: the emergency services (principally the fire The Federal Crisis Centre assists the Federal Government brigade), medical, sanitary and psycho-social emergency in the emergency planning and interdepartmental manage- services, the police of the municipality of the emergency ment of crisis situations and major events. It sees to the situation, logistic support (civil protection, the army) and national coordination of crisis management and provides information (communication with the population and the support at regional and local level. press). Experts in a particular subject may supplement the safety division to integrate their experience in the planning Over the last few years, the idea is gaining ever more work. ground that risk communication to citizens should have a place in emergency planning. In July 2007 a guide for crisis During an emergency situation, the population has to be communication was created for the provinces and munici- alerted and informed as soon as possible about the situa- palities. This guide comprised a theoretical context as well tion and the precautionary measures people have to take. as practical checklists. After the emergency situation has been called off, there should still be information about the measures enabling a In order to alert the population as well as possible and pro- return to the normal situation. It is the task of the mayor vide information in the event of an emergency situation,

Research on types of measures • 79 the Crisis Centre signed an 'Agreement for the communi- www.waterstanden.be historical data of the past 10 years cation of urgent messages to the public by means of the can be found, as well as high water reports. These high wa- media' with various Belgian audiovisual media. ter reports comprise information on the present and expected weather situation and the hydrological situation up In contrast to other countries, to 48 hours ahead. however, there is no ongoing general risk communication cam- The website www.overstro- paign for all kinds of disasters. Communication mingsvoorspeller.be provides But since 2009, the Department similar reports for unnavigable of the Interior has acquired more is an important waterways. In addition, maps can competences for prevention discipline in be consulted with information campaigns. Among other things, on the flood risk at street level. the Department executed the emergency and The VMM manages this website. Seveso campaign. The Crisis Centre intends to work further intervention As regards the Flemish Region, on risk communication and the planning the Integrated Water Manage- capacity to respond, including ment Coordination Committee flood-related situations. (CIW) ensures the preparation, planning, control and follow-up Recently the Federal Crisis Centre acquired the 'Federal of the integrated water policy. The Water Quantity work High Water and Flood Plan'. The plan provides for setting up group deals with follow-up and steering for the project separate procedures that specifically apply to flooding. The ‘Crisis communication in the event of imminent floods Hydrological Information Centre of the Mobility and Pub- through flood water discharge’. lic Works Department collected and recorded the existing action undertaken during floods in this plan. At the mo- Comments from provinces, cities and ment the plan is a confirmation of a practice that has been municipalities working well for years. It is now the intention that the plan, We held interviews with the individuals involved in the with the input of all partners involved, should receive con- emergency planning departments of the five Flemish prov- crete implementation. Then the plan will be applied when inces and the various cities and municipalities. We sounded there is imminent flooding of some waterways and rivers out the state of affairs in their particular province or mu- as a result of extreme or exceptional weather conditions. nicipality as regards flood management and the opportuni- These may be heavy rain, steady rainfall for a long period, ties and gaps still present. rapid thawing of a mass of snow, etc. The fear that major floods will occur in the short term may arise from the sud- Not all provinces have drawn up a Special Emergency and den increase in the water level as a result of an emergency Intervention Plan (BNIP) for floods yet. They are being cre- situation. This may be sudden heavy rain, a breach in a dike, ated or are still to be planned. There are only a few munici- an earthquake or a storm tide on the River Scheldt. palities that have drawn up a flood BNIP.

Monitoring and forecasting high water An important comment is the imbalance between the In Flanders a great deal has been achieved in the field of Emergency Planning Royal Decree (RD) and competence monitoring water levels and forecasting floods. There are allocation in Belgium. In the Emergency Planning RD the two bodies that are concerned with forecasting high wa- Flemish level was not mentioned. But in the event of a ter in Flanders. They are the Flemish Environment Agency crisis, elements are often involved that fall under Flemish (VMM) and the Hydrological Information Centre (HIC) of competence, e.g. waterways management. According to the Mobility and Public Works Department of the Flemish the Emergency Planning RD, the Flemish Region does not Government. need to have a crisis division. However it would be better The HIC collects and manages the relevant data for the if one were established, so that there could be a point of management of navigable waterways. On the website contact in the event of a crisis.

80 Due to the allocation of water management competenc- In general, the federal authorities are responsible for the es in Flanders it is often difficult to ascertain the point of pro-active and preventive phase in European countries. Re- contact for an imminent flood. Most provinces and mu- sponsibility shifts to the local authorities in the ‘prepara- nicipalities indicate the need for a point of contact with tion & response’ phase. At that moment the national au- expertise, decision-making pow- thorities play a subordinate role er and recent and correct infor- and assist by providing equip- mation on the state of affairs in ment and expertise. Their role the event of (imminent) flooding. comes to the fore again in the This point of contact should be The role of ‘recovery’ phase. If there is less staffed and accessible 24/7. of a transition between the vari- water managers ous phases, it is between the pre- In certain problem areas, the in- vention and preparedness phase. tervention services (e.g. the fire during flooding in Proper transition depends on the brigade) regularly hold internal various European fine-tuning and communication exercises. It would be recom- between the various authorities. mendable to hold such exercises countries is on a wider scale and not just in A comparison based on the one particular service. clearer at the ‘Safety Chain Approach’ shows operational that the different countries are Survey on flood-related focused on diverse steps in the suffering than at the safety chain. Various European In 2000 a survey was performed countries accentuate different among the inhabitants of Halen communication aspects in their flood risk man- (Limburg) and Bassenge (Liege) – level agement as a result of geographi- two municipalities that were se- cal, demographical and political verely afflicted by floods in 1998. structures, policy options and The intention was to make an other factors. However, they inventory of the reality of flood may learn from each other in or- damage. The survey clearly demonstrated that the pub- der to reinforce some phases in their safety chain. lic thought that the financially intangible consequences of flooding (having to be evacuated, loss of emotionally Risk and crisis communication valuable objects and stress during and after a flood) were In many countries there is an ongoing large-scale general more serious than the direct material losses. So it is not and national risk communication campaign aimed at get- just a question of repairing the tangible damage, but also ting people to think about risks in their surroundings and of providing psychological assistance or at least taking into to personally make preparations for all kinds of emergen- account the public's suffering. cy situations. These general national campaigns focus on a number of general disaster types such as fire, terrorism, International state of affairs major power failure, a nuclear disaster, and floods. Floods are invariably included. Risk and crisis management in the event of flooding In other countries too, risk and crisis management are prac- The various authorities obviously opt for attributing part tised in the event of floods. Analysis is performed with the of the responsibility during disasters to the public. The rea- aid of the ’Safety Chain Approach’, which is employed in son is that in critical events, such as floods, the emergency the United States. It is divided into the sections: ‘mitiga- services cannot help everyone immediately, and a number tion, preparedness, response & recovery’. This approach of authorities also communicate this clearly to the public. was implemented in The Netherlands in 1993 and slightly There is great emphasis on the concept of the capacity to modified, in the sense that the ‘mitigation’ phase was fur- respond. ther divided into ‘pro-action and prevention’.

Research on types of measures • 81 Furthermore, communication campaigns in many countries From a Dutch study it appears that the different phases are specifically focused on the subject of flooding as well. in (imminent) flooding require a different communication Generally speaking, they deal with risk communication rath- strategy. er than crisis communication.

Risk communication in the preparedness phase The press is the most effec- ❶ tive way to communicate risks. All utterances should carry the same message and confirm each other as much as possible.

Communication in the warning phase Verbal communication is the most appropriate in this phase. Studies show that when people do ❷ not get a verbal warning, they do not identify the events around them as dangerous.

Crisis communication in the response phase The message has to be spread by a person who is respected and trusted in the community. Ensure that the message is consistent, clear and transparent. Make it advisory and direc- ❸ tional. Explain how great the danger is and where it is occurring. Repeat the message again and again. See that the information is complete and is also diffused via unofficial channels. In case of evacuation: communication has to address the concerns of the evacuees. They want to know how much time they have to leave, how the district is being protected from looting, which precautions they can take, and how reception accommodation has been arranged. In this phase, account should also be taken of resistance to evacuation.

Communication in the post-phase Maintain the information flow to those affected, e.g. ❹ with respect to damage settlement.

82 The following conclusions can be drawn from the survey planning and crisis communication at the various authori- performed in a number of European countries. ties, as well as with the various disciplines within emer- –– The role of water managers in the event of floods gency planning (e.g. fire brigade and civil protection). Water is clearer at the operational than at the communica- managers can conclude cooperation agreements with gen- tion level. Improved agreements on communication eral safety and crisis communication officials. are required. –– Only a few surveys have been performed among the A plan is only as good as the people who execute it. There- public afflicted by flooding. Most water managers fore training sessions and exercises have to be provided, therefore have little insight into the public's percep- focused on risk and crisis management in the event of tion on the subject. flooding. In this way, gaps in the plan can be identified, -co –– The majority of responders say that they have a clear operation with other parties can be tested and the team operational emergency plan for floods. Moreover, this learns to cooperate. The general public can also be involved plan has been elaborated from a practical viewpoint in order to enhance flood awareness. and is integrated in day-to-day operations. Such an operational emergency plan has not often been prac- In Belgium there is little communication regarding floods tised or not at all. and certainly not in quiet periods. What does exist is not –– The majority also say that they have a risk commu- communicated in an integrated way at the present time. nication plan and a crisis communication plan. The Certain parties intend to work on a communication cam- participants in the survey are less positive about paign on floods and the capacity to respond. Concur- the practical nature and integration of the plans in rently with this general risk communication campaign there day-to-day operations than about the operational should be a portal that brings together all risk and crisis emergency plan. The crisis communication plan is not information on the subject of floods. practised in any country at all. –– There is obviously room for improvement in the field The study of risk communication and its effects is still in its of follow-up: not one responder had a positive opin- infancy. It is still not clear which are the 'proper solutions'. In ion regarding the operational follow-up of his/her any case we should not expect miracles: people do not eas- organisation. Communication follow-up is considered ily modify their behaviour. Campaigns are mainly successful as even less positive. when they are closely linked with people’s perceptions. To –– Most organisations consider their risk and crisis man- this end a target group study should be performed. On the agement in the event of floods as good. But in the other hand, national campaigns can create general aware- communication field the various responders think ness on the subject. that they can still improve matters. In the post-phase, authorities are confronted with enor- Recommendations mous logistic challenges: major pressure on emergency services resources and people, food provision for the affected On the basis of the study performed we can formulate the public, offering alternative accommodation etc. This has to following recommendations to improve assistance before, be planned. during and after a flood in Flanders. The follow-up phase is very important as regards floods. There should be a central crisis contact point, which in the For this purpose long-term planning has to be drawn up. event of flooding can rapidly deliver technical expertise to Communication should be as close to the people as possi- the crisis team and the crisis communication team in the ble. Proximity and availability are important for the people municipality, province or federal authorities. In the event affected. In this phase, government services should help of a crisis the water managers should delegate one or two in clean-up operations, drawing up damage claim files, etc. individuals with decision-making competence. The reason is that floods entail a large amount of financial damage. However, people are most perturbed by intangi- A ‘Federal High Water and Flood Plan’ was drawn up. The ble losses. Therefore it is of the utmost importance that Federal Crisis Centre explicitly invites water managers to the various services that have contact with the victims in outline their part of the plan. In this way they can develop the first place show understanding and empathy, and offer good contacts with the people in charge of emergency psychological support wherever possible.

Research on types of measures • 83 ❺

Consultation with stakeholders

84 Consultation with stakeholders

Consultation with stakeholders • 85 Floods affect many people and the measures that are taken to mitigate floods or the damage have an impact in various fields. It is therefore important to involve different players and stakeholders in the process of defining measures. All these stakeholders consider the issues from their own particular point of view and they all In these workshops we discussed the river basins of the have their own wishes and concerns. Dijle and the Woluwe. These are two river basins with dif- fering characteristics and their assessment methodologies In this project, participative consulta- furnished partly different results. It was interesting to make tion was achieved in a series of work- the comparison and to assess the measures in these differ- shops. The municipalities in question, ent basins. Six workshops were organised. province, crisis managers, the Farm- It was not the intention to decide during these workshops ers' Association and other Flemish which methodologies were to be used further or which authorities such as the Agentschap measures should be implemented or not. The main inten- voor Natuur en Bos [Nature and For- tion was to have the various parties test the approach and est Agency] and the Vlaamse Land- results obtained and to hear their ideas and elaborate a fur- maatschappij [Flemish Land Agency] ther strategy for the future. were invited to these workshops. The During the workshops there were discussions regarding aim of the workshops was not only to methodologies on the one hand and, on the other, also on discuss the proposed measures but potential measures that can be applied. The most relevant also to evaluate the starting point and results of the discussions are presented below. methodologies used.

86 Workshops programme Workshop 1 - 16 September 2010 Workshop 4 - 25 November 2010 –– Proceedings of the workshops and positioning within –– Presentation of the first version of the Woluwe ac- the grander project tion plan (drawn up on the basis of previous studies –– Flood impact in the present situation and how it was and results of discussion during the first workshops) calculated (see Chapter 4 Damage and impact caused –– Evaluation and discussion of the proposed measures by flooding) –– Extensive cost-benefit analysis as a framework for the Workshop 5 - 7 December 2010 assessment of protective measures –– Presentation of the first version of the Dijle action plan (drawn up on the basis of previous studies and Workshop 2 - 28 September 2010 results of discussion during the first workshops) –– Assessment of the alleviation measures with the aid –– Evaluation and discussion of the proposed measures of an extensive cost-benefit analysis (explained in this brochure in Chapter 5.1 ‘Alleviation’) Workshop 6 - 25 January 2011 –– Discussion on the method applied for the cost-ben- –– Elucidation of the results of discussions in the entire efit analysis series of workshops –– Discussion on the specific relevance to the river basin –– Evaluation among participants as to how they experi- of the Dijle and subsequently to the Woluwe (specific enced the approach and the further course assumptions, appreciation of nature values, what strategy in the event of a negative cost-benefit ratio, etc.) Tijdens de workshops werd enerzijds gediscussieerd over methodieken en anderzijds ook over de mogelijke Workshop 3 - 21 October 2010 maatregelen die kunnen toegepast worden. De meest rel- –– Elucidation of the study work performed on avoid- evante resultaten van de discussies worden hier weerge- ance of damage and floods, awareness and capacity geven. to respond, and assistance before, during and after floods (see Chapters 5.1, 5.2 and 5.3). –– Debate on the proposed measures

Extensive cost-benefit analysis

In general the participants thought that the cost-benefit Apart from the results of the extensive cost-benefit analy- analysis was a good method for comparing the various sis, some risks are no longer acceptable. It would be good if scenarios to each other. However, there could be greater clarity a number of questions still arose in regarding which risks are ac- connection with its specific applica- ceptable or not. tion. The added value of the workshops The flood risk in Leuven A more extensive sensitivity analysis was estimated pragmatically enables greater insight to be gained is that all parties on the basis of the event in into the significance of assump- 1891. There was no consen- tions, parameters and weights. The were brought sus among the participants concept of discount rate is not easy together on whether this risk was es- to interpret and assess. It would be timated as being too high or good to retain it for future projects too low. There is a need for in the interests of comparability. Ad- a (uniform) methodology to ditional criteria might also be included in the analysis, such estimate the risk. This is currently being elaborated in the as impact on cultural heritage, drinking water provision, etc. context of drawing up the flood risk management plans.

Consultation with stakeholders • 87 0 5 10 15 20 25 30

Alleviation 9 7 4 6

Avoidance 7 11 5 3

Awareness 6 5 8 6

Assistance 4 3 8 11

highest priority lowest priority

Priorities that the participants in the workshops attach to the different types of measures for the Dijle river basin

The proposed alleviation measure for the Dijle impacts Prioritising different types of markedly on the nature values of the 'Doode Bemde'. We measures should elaborate the evaluation of the nature values in more depth in consultation with the nature sector. We are The participants were asked to say how much importance considering including the maintenance objectives and/or they attached to the application of the different types of integration of ecological system services. measures in the river basin of the Dijle and the river basin of the Woluwe: viz. alleviation, avoidance, awareness or as- In the cost-benefit analysis that was performed for the sistance measures. Woluwe river basin, the impact of floods and of the protective measures on the existing nature values was not taken into account. This aspect should also be integrated. Although most participants thought the cost-benefit There are few analysis was a good tool, opinions were divided regarding people who end up what should happen in the event of a negative cost-benefit analysis. About 50% of the participants thought it not self- with wet feet, but evident that certain protective measures should not be implemented if the costs were to be higher than the ben- there are many who efits. In this respect they stated that the authorities have cause it the obligation and responsibility to solve the flooding issue as far as possible and to protect people from flood-related damage and suffering.

88 0 5 10 15 20 25 30

Alleviation 11 4 7 5

Avoidance 12 12 2 1

Awareness 3 7 14 2

Assistance 1 4 4 18

highest priority lowest priority

Priorities that the participants in the workshops attach to the different types of measures for the Woluwe river basin

When we examine the measures that were given a For the Woluwe river basin, the participants gave higher priority score for the Dijle river basin, we see that avoidance a higher priority score. The Woluwe river basin is about the same importance is attached to alleviation and very densely populated. For this reason the general opinion avoidance. It clearly emerged from the discussion that is that implementing avoidance measures can have a great most participants opt for additional protection by means impact. “Many a little makes a mickle”. of buffering. The participants attach great importance to Alleviation measures emerged as the second most highly avoidance measures, but do not believe that the latter can rated priority. However, not everyone sees an added value provide a substantial contribution to reducing the flood here, and certainly not with a view to the high cost and risk for the river basin of the Dijle, only that they can re- limited benefits for society. duce the damage. Assistance was also found to be the lowest priority, also They thought assistance to be the lowest of the priorities because assistance is already well organised in Flanders and for the Dijle river basin, mainly because assistance is already should only be a last resort. But it was indicated that it is well organised in Flanders and should only be a last resort necessary. when the other measures are exhausted. However, they do agree that assistance is necessary.

Consultation with stakeholders • 89 Alleviation measures The cost-benefit analysis was performed for three measure scenarios. Each scenario comprised various partial meas- As regards to alleviation measures, opinions greatly differed ures. This made it difficult to judge the opportunity of the for the river basins of the Woluwe and the Dijle. construction of one of the partial measures. The cost-benefit analysis should be repeated for each partial measure or Dijle river basin for each sub-area. To protect Leuven from floods we presented and- as Meanwhile, it also appeared that sessed two scenarios: the con- It is important there have been a number of de- struction of the CFP in Neerijse velopments and projects started and no additional construction to formulate in this river basin, from which op- of protective measures (starting specific proposals portunities may emanate. An in- situation, ‘Doing nothing’). ventory of the former should be now and to made. Any promising new meas- It clearly emerged from the de- ures should also be included in bate that the participants opt for translate them the assessment. additional buffering upstream of into practice Leuven. But they would prefer The impact of floods and the not to see that storage concen- construction of alleviation meas- trated in the 'Doode Bemde' na- ures on nature values were not ture reserve. It would be better to spread the additional incorporated in the cost-benefit analysis. These values storage over the valley. More investigation into alternatives should be integrated for the future. is required. Avoidance measures The impact on nature values and the way in which they should be assessed has not yet been sufficiently investi- We presented six specific avoidance measures and asked gated. The nature in the 'Doode Bemde' has great value and the participants to indicate two measures in each case as cannot be replaced without more ado. It is difficult to as- the most important and the least important. This exercise sess its value and compare it with other criteria. This re- was performed for the two river basins separately, and the quires more in-depth discussion. results are partly similar.

Woluwe river basin ❶ Prohibit rainwater run-off in case of new builds and In order to mitigate floods in the Woluwe river basin, major renovations. four scenarios were presented and assessed: three measure ❷ Reconstruct the public domain in accordance with scenarios and the starting situation, ‘Doing nothing’. reduced run-off of rainwater. ❸ Prohibit new builds in a residential area or residen- From the debate it appeared that not everyone was an ad- tial expansion area if they are located in a flood risk vocate of the construction of additional alleviation meas- zone. ures. There was reference to the fact that this pillar should ❹ Impose obligations in case of new builds and major certainly not be the only one to be implemented. The renovations so that there is flood-resistant building other As should be deployed too, in particular avoidance in a residential area or residential expansion area if it measures. However, the participants commented that it is is located in a flood risk zone. important not to eliminate measures from a possible pro- ❺ Impose obligations on building so that there is no gramme of measures for this river basin. Measures that do loss of water storage capacity in a residential area or not currently emerge as positive owing to high cost or oth- residential expansion area if it is located in a flood er negative preconditions can still become positive if there risk zone. is an opportunity (possible purchase of plots of land, or ❻ Right of pre-emption in a residential area or residen- through a combination with other infrastructure work, etc.). tial expansion area if it is located in a flood risk zone.

90 highest priority lowest priority

0 2 4 6 8 10 12 14 16

Prohibit rainwater run-off in case of new builds and major renovations. 4 7

Reconstruct the public domain in accordance with reduced run-off of rainwater. 15

Prohibit new builds in a residential area or residential expansion area if it is located in a flood risk zone 12 2 (frz).

Impose obligations in case of new builds and major renovations so that there is flood-resistant building 10 3 in a residential area or residential expansion area if it is located in a frz.

Impose obligations on building so that there is no loss of water storage capacity in a residential area or 3 4 residential expansion area if it is located in a frz.

Right of pre-emption in a residential area or 4 8 residential expansion area if it is located in a frz.

Indication of the importance of various avoidance measures by the participants in the workshops for the Dijle river basin

highest priority lowest priority

0 2 4 6 8 10 12 14 16

Prohibit rainwater run-off in case of new builds and major renovations. 13 2

Reconstruct the public domain in accordance with reduced run-off of rainwater. 12

Prohibit new builds in a residential area or residential expansion area if it is located in a flood risk zone 8 3 (frz).

Impose obligations in case of new builds and major renovations so that there is flood-resistant building 6 6 in a residential area or residential expansion area if it is located in a frz.

Impose obligations on building so that there is no loss of water storage capacity in a residential area or 3 4 residential expansion area if it is located in a frz.

Right of pre-emption in a residential area or residential expansion area if it is located in a frz. 5 10

Indication of the importance of various avoidance measures by the participants in the workshops for the Woluwe river basin

Consultation with stakeholders • 91 In general the participants considered avoidance measures made to implement the two tools correctly and to check to be useful, but did not think much of their effectiveness this before stricter action can be considered. on the flood risk for Leuven. In the closely built-up centre of Leuven, many measures seem less applicable. The next measure is reconstruction of the public domain in accordance with reduced run-off. This entails, for ex- For the Woluwe river basin, avoidance measures are gener- ample, laying grass verges and open road ditches (possi- ally considered as useful measures that may have a major bly with partitions and flow restrictors, and possibly with impact on the flood risk. infiltration boxes) and more infiltrating road covering (e.g. cobblestones). This also includes the construction of water The first measure, ‘prohibiting run-off of rainwater for new squares and buffer zones in park areas. Almost all partici- builds and major renovations' renders the water assessment pants gave high priority to this measure. It seems feasible and rainwater regulation more strict. The general reaction and efficient, creates awareness and fits into the exemplary was that firstly correct application of the two tools has to nature of public administrations. This could for example be be ensured and that this has to be checked before stricter combined with a kind of rainwater regulation for the public action can be considered. domain.

During the discussion on the Woluwe river basin, it was said The following three measures concern conversion and that application of this measure seems to be feasible and building in flood risk areas. Measure three prohibits build- may be an added value. The problems are tackled at source. ing in such areas. Measure four only imposes flood-resistant However, it was also remarked that first efforts have to be building (limiting damage to the home by means of higher

92 thresholds, sturdier materials, no cellar openings, etc.), and The last measure, exercising the right of pre-emption in measure five prohibits taking up space for water (building flood risk zones, was not experienced as positive by the on piles, bases, floating homes, etc.). participants. It is an expensive measure, difficult to achieve To prohibit building altogether seems a good measure and and the question arose of what should be done with the most participants were in favour. However, the drawback is separate plots that the authorities acquire in these cases. that such a prohibition prevents owners from cashing in on their property. On the one hand this means financial loss, but on the other it exacerbates the shortage of building land. So it entails a burden for society. There are Measures four and five are alternatives. Converting or splendid examples building in a flood-resistant way seems a minimum and certainly the most applicable approach in existing districts of living with and urban centres. Building without losing storage space is not yet established in Flanders and for this reason does not water, in which seem very realistic. We should follow the example of our water is optimally neighbouring countries where this option has been developed. This not very popular obligation is difficult to impose integrated in on a municipal level, and should therefore take place at a urban conditions Flemish level.

Consultation with stakeholders • 93 highest priority lowest priority

0 1 2 3 4 5 6 7 8 9

Survey on flood risk awareness and capacity to respond 5

Communication campaign at a Flemish 2 3 level

Communication campaign Dijle/ 5 Woluwe river basin

Supplementary online tool ‘floods in 5 3 your street?’

One single contact/information point 5 for water and water management

Extension of the water assessment 64

Flood risk analysis and possible measures for businesses 1

Indication of the importance of various measures for awareness and capacity to respond by participants in the workshops for the Dijle river basin

Awareness measures The first measure is to perform a survey, since we do not yet know much about flood risk awareness and capacity to Reinforcing citizens' flood risk awareness and capacity to respond in Flanders. The participants in the workshop on respond is not the group of measures with the highest pri- the Dijle did not think this was a good measure. They did ority. This is endorsed by the great extent to which both not see it as being useful. the river basins of the Dijle and the Woluwe are already protected: these measures therefore seem less urgent. Two participants in the workshop on the Woluwe considered this to be a good measure, since not much is known We presented seven measures in accordance with aware- about it yet in Flanders. During the discussion the question ness and capacity to respond. was asked what this would yield specifically, and it was said that this measure entails the risk that it can be said that ❶ Survey on flood risk awareness and capacity to re- measures are being taken, although in fact nothing specific spond is being done. ❷ Communication campaign at a Flemish level ❸ Communication campaign Dijle/Woluwe river basin The following two measures are a communication cam- ❹ Supplementary online tool ‘floods in your street?’ paign at Flemish level and one at the level of the river basin ❺ One single contact/information point for water and of the Dijle or Woluwe. Almost all participants were posi- water management tive about a campaign at local level. Here clear specific ex- ❻ Extension of the water assessment amples can be given of the situation in the Dijle river basin. ❼ Flood risk analysis and possible measures for busi- A campaign at Flemish level is more abstract and people will nesses

94 highest priority lowest priority

0 1 2 3 4 5 6 7 8 9

Survey on flood risk awareness and capacity to respond 2 1

Communication campaign at a Flemish 6 1 level

Communication campaign Dijle/ 2 3 Woluwe river basin

Supplementary online tool ‘floods in 1 3 your street?’

One single contact/information point 5 for water and water management

Extension of the water assessment 1 2

Flood risk analysis and possible measures for businesses 5 2

Indication of the importance of various measures for awareness and capacity to respond for participants in the workshops for the Woluwe river basin

therefore not easily accept it. A campaign at a Flemish level should organise it. Conversely, other participants proposed in a broader context, with subsequently a local campaign an inter-communal organisation. that is more specific, is a possibility. However, it was also remarked that communication campaigns are often inef- The sixth measure is the proposal to extend the water as- fective. sessment with an obligation to also state the following when submitting an application for a building permit: am Starting an additional online tool to request the flood sus- I in a risk zone? Did I take this into account when draw- ceptibility of a plot of land by entering an address was not ing up the plans? Will my project withstand possible flood welcomed altogether positively. On the one hand it can be damage, etc. This obliges the property developer to think useful since information can be given in a simple way. But about the issue. This measure is connected with avoidance on the other hand, it was said, there is a great chance that measures, but as such is more focused on awareness. Most the user would interpret it incorrectly, meaning that the participants did not consider this measure as a priority. tool would miss its mark. From the discussion afterwards it appeared that they still found it more important to first maximally deploy correct Setting up a single contact point for all questions on water execution and checking of the water assessment in its pre- and water management was generally received positively. In sent form. view of the competences for water, it may be a convenient portal for citizens to obtain an answer to their questions. The last measure was offering assistance to businesses to Opinions were divided on the specific organisation of such analyse their situation concerning floods: flood risk and a portal. Some participants thought that the municipality possible measures to restrict damage. The participants in

Consultation with stakeholders • 95 the workshop on the Dijle did not consider this as a pri- Assistance measures ority. In contrast, the participants in the workshop on the Woluwe did consider this measure as a priority. It may have We also presented a number of measures for assistance be- considerable impact since a great deal is possible on busi- fore, during and after a flood. The discussions on this sub- ness terrains. But the remark was made that this also should ject were about the same for both river basin workshops. be opened up towards private individuals. ❶ Setting up a central crisis point for technical expertise on floods ❷ A consultation platform for emergency plans Increasing ❸ Training and exercises in crisis management safeguards is ❹ Study of crisis communication necessary, but it is ❺ Aftercare after floods Most participants were positive towards the proposed certainly positive measures, but thought that they had too little practical to make people knowledge on crisis management to be able to give input. It also does not seem to be a great priority to start new aware of the initiatives for assistance, since this is already very well or- problems ganised in Flanders. A number of officials, however, admit to not knowing personally who to address in an emergency situation.

96 Assistance during floods is already well organised, but there After every flood a public report should be made. Among is clearly a need for more communication on the subject. other things, it could describe how the emergency services Within the water sector too, clear agreements are need- were organised and which decisions were taken. On the ed concerning who is competent to take decisions in the basis of this report, crisis management of floods and the event of actual or imminent floods, and who is responsible assistance for people could improve in the future. for communication with crisis managers.

All participants agreed that too little assistance is provided to the inhabitants before, during and also after a flood. For example, aid should be offered to move furniture to higher ground beforehand and put it back again afterwards. Citizens can already be helped with simple measures. The It is worth municipality should also have an overview of where the applying this elderly, the sick, families with small children and socially weaker people live who need more assistance. Then spe- exercise to other cific assistance can be organised for these people in the event of an imminent flood. river basins in the A coordination point can be set up on a local basis for vol- future unteers who are willing to help victims. From that coordination point, the focus can be on the places where there is the greatest need.

Consultation with stakeholders • 97 ❻

The future, how will we continue this work?

98 The future, how will we continue this work • 99 During this project we went through a study pathway. In this we determined the consequences of extreme floods at an economic and social level, and studied and assessed various types of measures. In a series of workshops we extensively discussed the method used and the results as well as the types of measures with various stakeholders.

On the basis of the results of the study and the consultation we defined a set of measures which together counteract extreme floods and the resulting damage. We classified these measures according to the 4 As. In the future we will further elaborate that set of measures for the flood risk management plans. Every measure is accompa- nied by a number of action points for further fine-tuning of the measure. Some measures may be axed or adjusted.

Certain measures are not location-specific and may be use- The Dijle upstream of Leuven ful at other sites. These measures fall under the general measures. In addition, measures are also defined that are specifically valid for one of the two river basins. These spe- ciety. During the workshops too it appeared that the par- cific measures also include a number of action points that ticipants were positive about creating additional buffering. have to be elaborated at a higher level than the river basin of the Dijle or the Woluwe. They are indicated with ‘+’. Measure All1 is intended to realise additional water storage capacity upstream of Leuven, spread along the Dijle and its tributaries. The starting point here is to store water over a surface area that is as large as possible. On the one hand, Protection from we achieve this by reusing natural flood plains (removing floods can never dikes, roughening waterways, etc.) and, on the other hand, with additional plots of land (constructions for retaining be absolute run-off water). In order to realise this measure various actions are required: ① –– Feasibility study into possible locations for water storage. Alleviation: protection from –– Calculation of the effect on the flood risk per loca- flooding tion. –– Creating clarity about the possibility of combining The alleviation measures that were formulated are all basin- water storage with other land use (agriculture, nature, specific. etc.). Here we are looking for win-win situations. –– Adjusting the methodology for determining the im- Alleviation measures for the Dijle pact and cost-benefit analysis: taking into account river basin conservation objectives and preferably including ecological system services as well, refining the meth- MEASURE DIJLE ALL1: odology for determining social impact, integrating Creating additional buffering upstream of several types of impact such as cultural heritage or Leuven landscape, determining the impact of the combina- From the cost-benefit analysis it appears that creating tion of buffering and drinking water catchment area, additional buffering upstream of Leuven is positive for so- etc.

100 The Dijle is closed in or vaulted in many places in Leuven

–– Applying refined extensive cost-benefit analysis to To achieve this, the following action points have to be ex- the various defined buffer measures or in combined ecuted: scenarios. –– Making an inventory of the possible locations to create space for the Dijle and its tributaries. On the basis of the results of the above-mentioned ac- –– Drawing up a feasibility study per location: list the tions, it can be decided which locations are desirable for (technical) bottlenecks and possibilities. water storage. This should take place in cooperation with –– Elaborating agreements between the partners in- various players and stakeholders. volved for financing and maintenance: VMM, City of Leuven, private project developers, etc. MEASURE DIJLE ALL2: –– Communicating with the inhabitants. Creating space for the Dijle and its tributaries in Leuven MEASURE DIJLE ALL3: The Dijle and its tributaries are largely vaulted or lie Working out modalities to keep the grounds deeply and shielded in between the houses in Leuven. By of the KUL [Catholic University Leuven] laying them in an open bed again or by widening their bed, available as an emergency area in the event of additional buffer capacity can be created to a limited ex- imminent floods tent. In addition this measure increases the visibility of the When flooding is imminent in the centre of Leuven water in the city, which is an added value for awareness as and buffering upstream can no longer be used, there is the well as for the urban climate. historical possibility to have the grounds of the campus of the KULeuven in Heverlee along the Dijle and the Voer

The future, how will we continue this work • 101 Construction of the Dijle terraces in Leuven. An exemplary project which creates space for water in the city and enhances perception of the value of water

(Arenberg campus, Arenbergpark, sport fields, etc.) flooded. These grounds are the former natural flood plain that is deployed by closing the sluices at the Vollemolen near the Ring. To achieve this we have to execute the following action points: In the city too –– Consultation between the water manager, KULeuven and the City of Leuven regarding possible application: we have to create modalities for mitigating damage, evacuation timing, space for water etc. –– Investigation of the effect of higher water levels: it is possible that a larger area would be inundated than in natural floods and specific protection infrastructure is required. –– Ascertaining which (temporary) measures are required if we use this land (closing cellar openings etc.).

102 Construction of the Dijle terraces in Leuven. An exemplary project which creates space for water in the city and enhances perception of the value of water Marshy area along Vuilbeek

Alleviation measures for the Woluwe Measure Woluwe All1 proposes additional research and river basin involving the relevant partners as well. This comprises the following actions: MEASURE WOLUWE ALL1: –– Performance of an extensive cost-benefit analysis per Further investigating and weighing up whether measure or group of measures (sub-area): or not additional buffering along waterways •• recalculate the cost-benefit analysis; should be realised •• include ’ecological impact’ as well; On the basis of the hydraulic model, various measures •• consultation with the municipalities, the Inter- were elaborated to counteract flooding in the Woluwe Community Association of the Woluwe, prov- river basin. The cost-benefit analysis did not give anun- ince and other parties involved; equivocal answer to the question of whether a particular •• consultation with the VLM [Flemish Land Agency] measure scenario should or should not be executed. The about re-equipping the Woluwe valley (e.g. the partial measures were grouped in scenarios, which makes it plans to open up the Vuilbeek again); difficult to assess a particular partial measure. That partial •• list opportunities such as execution together measure may however be positive. with other planned work, parcel exchange, etc. The participants thought that on the basis of the present –– Disconnection of the discharge points for waste wa- data, no decision could be taken about which partial meas- ter on the Woluwe and its tributaries. This creates a ures should be executed. To this end the costs, benefits bearing support to realise open buffering with co-use. and practical possibilities for the execution of each partial –– Defining the limit of the maximum permissible flood measure have to be determined. risk. As long as the risk is higher than this limit, pro-

The future, how will we continue this work • 103 The fishing pond of Dexia Bank at Dezangrélaan

tective measures MUST be taken. If the risk is lower, heritage, landscape, etc.; weighing up should be done case by case. This is a •• refine the ‘extensive cost-benefit analysis’: ap- very difficult and theoretical exercise.+ ply refined methods for determination of the –– Creating clarity on the modalities of the combination impact, monetisation. of water storage with a different use of the land, e.g. •• The above-mentioned points require maximum agricultural or recreational. Also in the event of dam- pursuit of practical and pragmatic approaches. age resulting from the additional floods. Endless calculation exercises should be avoided. –– Adjustment of the 'impact determination and cost- The different parties have to be involved here. benefit analysis’ method:+ –– Per selected partial measure: start drawing up an ex- •• refine the method to determine the ecological ecution dossier, permits, compulsory purchases, etc. impact during floods, in cooperation with the nature sector; In addition there should be consultation with the various •• work out a method for determining the im- partners regarding who has to be financially responsible for pact of the construction of a flood plain and designing and realising water storage. the change in the type of land use: ecological system services; MEASURE WOLUWE ALL2: •• fine-tune the ‘social impact determination’ Using the Dexia pond for buffering method; The Dexia pond in Kraainem, acquired by the VMM, •• analyse which types of impact can/should be could serve for buffering. The purchase of this pond was an integrated additionally and how. E.g. cultural opportunity that emerged during the bank crisis. Dexia was

104 Kleine Beek

The future, how will we continue this work • 105 compelled to sell part of its estate, including this pond. This Avoidance: prevention of measure comprises the following actions: flooding and damage ② –– Listing the preconditions for buffering (filling, steering, water levels, etc.) from the model of the Woluwe –– Organising consultation between the various water General measures managers in the area –– Consulting the parties involved on the secondary MEASURE AV1: functions Strictly applying the water assessment and –– Starting the drawing up of the execution dossier and rainwater regulation and checking compliance the permits pathway. The water assessment and rainwater regulation are two existing tools that contribute to the avoidance of floods. For this measure it should be defined who is responsible for However, they are not always strictly applied. the financing. The following actions should change this: –– Performance of a study into the state of affairs con- MEASURE WOLUWE ALL3: cerning compliance with the standards and laws: is Investigating buffering in agricultural areas account taken of the advice on granting the building The Woluwe river basin is highly urbanised. Yet there permit and does the property developer meet the are still a number of agricultural areas. They have steep restrictions in permits? (bottleneck analysis). slopes and contribute enormously to rainwater run-off –– On the basis of the knowledge acquired from the during severe storms. Erosion in the fields leads to the pres- previous action: possibly amend the legislation for ence of sludge in the run-off water. easier application. Small-scale interventions in these agricultural areas can cre- –– Establishment of a body for checking application of ate buffering and keep a great deal of sediment out of the the legislation. water. This measure corresponds to a number of measures –– Offering of training to the officials responsible for taken to prevent erosion. They involve small-scale, source- granting permits. targeted measures that cannot provide complete protection from floods during heavy downpours. Further elaboration of this measure requires close coopera- The following actions have to be undertaken for imple- tion with the public services that are competent for town menting this measure: and country planning. This measure may also be applied to –– Consultation with the municipalities and the VLM on other relevant (new) legislation. already existing measures to prevent erosion. –– Drawing up an inventory of the terrain to indicate the MEASURE AV2: possibilities. Mandatory flood-resistant building and –– Consultation with the land owners. renovations –– Drawing up the execution dossier and permits path- In case of new builds and renovations, precautions have to way. be taken to limit damage from floods. The type of precau- tion depends on the location of the plot of land. In sloping areas protection from run-off of rainwater is needed (ori- entation of doors, cellar openings). In flood-susceptible val- Account should ley areas that are highly urbanised there should be flood- resistant building, so that damage to the home is limited be taken of or avoided (thresholds and ground-level floors should be opportunities to sufficiently high, public utilities above any water line, sturdy materials). In flood-susceptible valley areas where there has realise protective not been any building yet, e.g. a new housing estate, there measures should be flood-resistant building (building on piles). In the other areas only source-targeted measures have to be taken, as prescribed in the water assessment and rainwater regulation.

106 A waterproof entrance gate improves resistance to floods

The following action points have to be elaborated for im- The elaboration of the measure also has to take place in plementing this measure: close consultation with the services responsible for spatial –– Spatial analysis and zoning: where does which obliga- planning. tion apply? –– Making a list of minimum obligations, applicable techniques, examples of best practices, etc. per zone and per type of flood resistance. –– Performance of a study into gaps in knowledge of techniques for flood-resistant building. Measures to –– Creation of a brochure with examples and exemplary make homes projects of flood-resistant building. –– Ascertaining whether it is possible to integrate flood- resistant to floods resistant building in the legislation and the permits pathway (practical and legal aspects). can prevent a –– Training the officials responsible for granting permits great deal of and providing advice. –– Linking the insurance premium with whether or not damage these measures are applied.

The future, how will we continue this work • 107 Restored Woluwe in the new office park along the eastern Brussels ring road

MEASURE AV3: MEASURE AV4: Reconstruction of public domain in Creating opportunities for waterways in accordance with reduced run-off of rainwater infrastructure works When the public domain is constructed or reconstructed, Planned infrastructure works, such as construction or re- various interventions can be applied to help reduce the construction of a road or industrial site, often come into run-off of rainwater. Examples include grass verges, open contact with a waterway. When the design is being made road ditches (possibly with partitions and flow constrictors) the initiator has to take the waterway into account. For and a more infiltrating road surface when re-laying roads. example, a waterway which was previously channelled in This measure may also include the construction of water pipes can be restored to an open bed, or a waterway can squares or buffer zones in park areas. be remodelled with more natural banks. By providing de- fragmentation measures, migration along a waterway can The following actions are required to implement this measure: be restored when it crosses a road or another obstacle. –– Dissemination of knowledge on possible measures: The possibilities largely depend on the situation. The wa- study days for municipalities, a brochure with exam- ter manager can impose the obligation to do this via per- ples of application and advantages that mitigate the mits. This measure has to be applied everywhere, not just flood risk. in flood plains. –– Optimising the legal context. –– Investigating existing and new subsidy mechanisms The following actions are required: for municipalities to bridge additional costs. –– Training the bodies that grant permits (recognise op- –– Performance of a spatial analysis of the possibilities in portunities, know when to contact the waterway the Woluwe river basin. managers).

108 Campus Arenberg of the KULeuven is situated in the flood plain of the Dijle Restored Woluwe in the new office park along the eastern Brussels ring road New buildings are still being constructed here without measures being taken in relation to flood resistance

–– Ascertaining whether this can be legally implemented Avoidance measures for the Dijle in the building permit. Are additional instructions re- river basin quired? –– Ascertaining what is the desired effect. MEASURE DIJLE AV1: Obligations in connection with flood resistance and space for water in reconversion areas in the centre of Leuven Infrastructure Flood resistance obligations for areas accessible to the works may create public have to be imposed on sites where urban expansion opportunities for or reconversion is planned. Examples are: buffering water from the Dijle and tributar- more space for ies in squares and parks, optimising provisions for limiting waterways flood damage (e.g. material used for street furniture, possible drainage after a flood, facilities for cleaning up after a flood, etc.), restricting surface hardening in a public area, delayed discharge of rainwater (e.g. installing water squares, buffer zones in parks), and giving maximum space to waterways.

The future, how will we continue this work • 109 Campus Arenberg of the KULeuven is situated in the flood plain of the Dijle New buildings are still being constructed here without measures being taken in relation to flood resistance

This concerns additional obligations on the water assess- It may be interesting to implement such a measure at Flem- ment and rainwater regulation (e.g. buffering in relation to ish level. It may also be useful in other urban centres, thus the number of square metres of roof surface area; measure ensuring uniform application. Av1) and damage to buildings in these reconversion areas (measure Av2). MEASURE DIJLE AV2: Plan flood-resistant grounds of the KULeuven A municipal regulation is needed to make the above manda- upstream of Leuven along the Dijle and the tory. This includes, among other things, the following items: Voer –– Listing the requirements with which a new develop- A large part of the terrain of the KULeuven upstream of ment has to comply and the necessary measures, de- Leuven along the Dijle and the Voer are situated in a natural pending on the zone. flood plain. In the past there have already been flooding –– Zoning of Leuven based on where which measure is problems. mandatory. For example, buffering Dijle water is only relevant for urban expansions situated along the Dijle. In the regional development plan, the campus is largely –– Determination of the minimum surface area of an indicated as an area for community provisions and public urban expansion or reconversion and indication of amenity. The university is allowed to further develop its which projects fall under the regulation and which do activities there. Recently a number of buildings were added not. and even now a number of buildings are under construc- –– Definition of the legal conditions and the permits tion. In the further development of this terrain the univer- pathway. sity has to take into account the flood risk and the fact that the area at risk will have to be used more as flood plain.

110 ③

This measure is related to measure Dijle All3: it is necessary Awareness to make this terrain flood-resistant. General measures This requires consultation between the university and the city of Leuven. They have to find out whether the aspect of MEASURE AW1: floods was taken into account in designing the new build- Supportive communication campaign at ings. Is account taken of the flooding problems in the plan Flemish level for campus development? Are there specific statements in In addition to a local campaign, a supportive campaign at the Leuven structure plan? Flemish level can be elaborated. A Flemish campaign creates the broader context and can only serve as an exten- It is also necessary to define possible measures for flood sion to the local campaign. resistance of the existing buildings and infrastructure. On this basis, a plan for further development of the campus This Flemish campaign would then mainly focus on aware- can then be realised, which includes the flooding issues. ness. Flanders could provide elucidation of the risk of floods (from waterways and rainwater) and state that in Avoidance measures for the Woluwe spite of the measures there is still a risk. Examples of ex- river basin isting protective measures could be shown. The division of water management competences in Flanders could be MEASURE WOLUWE AV1: explained. Existing and any new initiatives for awareness Mandatory flood resistance and maximum could be announced in the campaign. space for water in reconversion areas Similar to the river basin of the Dijle, in the Woluwe The campaign could also respond on the capacity to re- basin flood resistance obligations have to be imposed for spond. It might give hints on the way to protect a home areas open to the public near sites where urban expansion from floods or what to do in an actual flood. The existence or reconversion has been planned. of risk plans can also be presented.

The former industrial zone of Machelen-Vilvoorde is an ex- As in the local campaign, a Flemish campaign has to be ample of a site where this measure can be applied. A master worked out in consultation with the parties involved. plan was already drawn up for this site. Parts of the site are situated in a flood-susceptible area. The measures for flood MEASURE AW2: resistance have to be integrated in the further elaboration Establishing one single contact and of the master plan. The opportunity should be seized to information point for water and water upgrade the natural structure along the Woluwe and to management disconnect any discharge points for waste water. This is Water and water management competences are widely closely linked with measure Av4. dispersed in Flanders. The measure proposes the establishment of a single contact and information point where As also indicated for the Dijle, it may be worthwhile to im- citizens can go for all their questions on water (water man- plement such a measure at the Flemish level. agement, water quality, drinking water, water treatment, planned work on waterways, flooding, etc.). Information on the ongoing communication campaign can also be found there. Interested parties may request campaign material (folders, brochures). Educational material for schools and groups is also available. The information point has to be accessible by means of different channels (website, telephone number, e-mail, and post). Use might be made of the infrastructure of the Flem-

The future, how will we continue this work • 111 ish information line for setting up the information point. This communication campaign for the Dijle river basin This measure could be publicised by local and Flemish in- might touch on the following subjects: formation campaigns. –– Explanation of the hydraulic system, where are the For very specific questions, the information point could re- risks. fer to the water manager or body in question. –– Which measures have already been taken upstream? ('Doode Bemde' natural valley system, Egenhoven The parties involved (water managers, Aquafin, sewage CFP). managers, drinking water companies) have to elaborate the –– Which measures are going to be taken or have al- modalities for establishing such an information point, e.g. ready been taken in the city? (Dijle terraces, opening specific competences and procedures. up the Dijle, restoring quay walls). –– The role of water in the city. MEASURE AW3: –– What an individual can do personally to reduce floods Simplifying online information on flood risk or to mitigate damage (preventive measures). for the general public –– Provide information on crisis management in the From studies performed in oth- event of a severe flood. er countries it appears that the public at large has difficulty inter- It is difficult In the campaign, specific com- preting thematic flood suscepti- munication actions to munici- bility maps or websites giving in- to provide palities upstream of Leuven can formation on water levels (flood information on be held on the risk of run-off of warning sites). rainwater and source-targeted the flood risk measures to mitigate problems There should be a simplified on- downstream. line source of information. How- in a simple and When working on waterways, ever, the problem is that provid- unambiguous way the water manager makes his role ing information on flood risks clear by publishing articles and cannot always be put across in brochures, and through an infor- a simple and yet correct way. Data such as return periods mation stand or information board. cannot be presented in a simple way. Its application requires cooperation with the various par- Therefore an initial investigation is needed into the pos- ties involved. The various partners together work out the sibilities of providing simple and unambiguous online infor- modalities to set up the campaign. The elaboration of the mation on floods. If it appears to be feasible, a portal site campaign as such is a task for communication specialists. could be created or the existing online sources of information could be expanded. If it appears not to be feasible, it MEASURE DIJLE AW2: would be best to stop altogether. Installing plaques commemorating historical floods in various places in the city Awareness measures for the Dijle At various places in the city plaques can be installed to river basin indicate how high the water rose during various floods in the past. This measure is a “soft” way of making inhabitants MEASURE DIJLE AW1: aware of the flood risk. Communication campaign for the Dijle river basin upstream of and in Leuven In the first stage it should be investigated where they can The measure comprises a communication campaign spe- be installed. It is also necessary to elaborate an appropriate cific to the Dijle river basin. A local communication cam- information board to accompany these plaques (informa- paign is clear and appealing. To support the local campaign, tive, clear and unambiguous). A specific communication a Flemish campaign might be associated with it (measure campaign accompanies installation of the plaques (measure Aw1). Dijle Aw1).

112 A plaque on a public building indicates a high water level of the Loire in France (source: Conseil Général du Loiret)

Awareness measures for the Woluwe –– Indicate remaining flood bottlenecks with specific basin explanation of measures already taken or any planned measures. MEASURE WOLUWE AW1: –– What an individual can do personally to mitigate Elaborate a communication campaign for the floods or limit the damage (avoidance measures). Woluwe river basin –– Information on crisis management if a severe flood The measure comprises a communication campaign was to occur. specifically for the river basin of the Woluwe. A local communication campaign is clear and appealing. A Flemish cam- During the campaign, specific communication actions to paign may support the local campaign (measure Aw1). upstream municipalities are possible. They can deal with the risk of run-off of rainwater and source-targeted meas- This communication campaign for the river basin of the ures to mitigate problems downstream. Woluwe may include the following subjects among others: When working on waterways, the water manager makes his –– Explain the hydraulic system, including the risk. role clear by means of articles and brochures, an informa- –– Pay specific attention to the link with Brussels (inter- tion stand or an information board. action, consultation between water managers, agreements, etc.). This measure requires cooperation between the various –– The measures to be taken or that have already been parties involved. The partners establish the modalities for taken (buffer reservoirs, buffer conduits). the campaign. Elaborating the campaign as such is a task for communication specialists.

The future, how will we continue this work • 113 In a flood, the emergency services provide assistance ④

Assistance before, during and after a flood

The measures formulated on assistance before, during and after a flood are all general measures that can be applied anywhere in Flanders.

MEASURE ASS1: Ensuring unambiguous agreements between water managers on communication during floods The decision-making competence in emergency situations depends on the scale of a flood. The municipalities decide at municipal level, the governor decides at provincial level, and the minister of the interior at national level. Since the water competences are dispersed in Flanders, it is

114 In a flood, the emergency services provide assistance not always clear which water manager should be addressed. –– Develop a watch-keeping system for crisis situations. Clear agreements between water managers are required, so –– Elaborate an information plan so that water managers that they can advise the crisis divisions as best as possible can exchange with and transfer information to crisis (e.g. on the options for using flood reservoirs, what should managers. happen if a dike breaks). The responsibilities of every water –– Make a portal site available, so that the affected or manager have to be clear. It should also be investigated in at-risk inhabitants can readily find the information which way water managers can exchange information as they need (risk, possible evacuation, temporary ac- quickly as possible, with each other as well as with the of- commodation, assistance offered). ficials of the municipality in question. MEASURE ASS2: Delegates of the water managers have to be involved in Offering crisis management training and preparing emergency and intervention plans. In addition exercises emergency planning has to be developed further at nation- A plan is only as good as the people who execute it. There- al level. This requires consultation between the Walloon fore training sessions and exercises have to be organised. and the Flemish bodies. The emphasis has to be on risk and crisis management, and on risk and crisis communication in floods. In this way, gaps The following actions can outline the development: in the plan can be detected, and cooperation with other –– Organising consultation between the water managers parties can be tested. The team also learns to work to- concerning optimal and smooth contact in the event gether and develop crisis reflexes. Involve the inhabitants of floods, also at national level. so that flood awareness is increased.

The future, how will we continue this work • 115 MEASURE ASS4: MEASURE ASS3: Organising aftercare after floods Organising manual assistance before, during Aftercare is very important. Floods entail tangible damage, and after floods but the intangible losses are also important. For many people, it is difficult to get prepared when a flood The authorities can assist the population more effectively is imminent. For elderly people, families with small children, by organising aftercare. For example, helping to complete sick people, etc. it may be difficult to put down sand bags, claims forms, offering psychological support, etc. raise furniture, clean and dry their homes, etc. These people need assistance and this assistance can be The municipality can work out a plan with guidelines for organised at municipal level. organising aftercare: –– Indicating who is responsible for organising psycho- To this end, municipalities have to undertake the following logical support. actions: –– Organising help in completing claims forms for insur- –– Questioning the recent victims of flooding about ance companies. how they experienced the assistance and which –– Organising district meetings after a flood to explain needs they continue to experience. what actually happened. –– Making an inventory of the homes of people who are –– Providing practical help (e.g. by placing containers in more vulnerable to damage and distress. the affected areas in which inhabitants can easily de- –– Organising (municipal) services to lend assistance in posit faulty electrical appliances free of charge). case of danger. –– Organising an on-site visit to the victims, in which –– Setting up a reporting point for volunteers who want simple measures are presented to mitigate the dam- to help. age in the future. –– Finding out if assistance is possible by means of –– Indicating where these services can be offered (at the framework agreements with contractors and service town hall, in district houses, etc.). providers. –– Defining and releasing budgets. –– Setting up contracts with possible help services (e.g. psychologists). –– Agreeing which administrations can contribute. ––

116 Kleine Beek just before culvert under Imbroekstraat (Zaventem)

The future, how will we continue this work • 117 Epilogue The European Flood Risk Directive obliges Flanders to draw up flood risk management plans (FRMPs) for all flood-sensitive areas. The emphasis is on protection, prevention and preparedness (forecasts). In a first step modelling work is done to create flood risk maps. In this project we wanted to find out which measures can be taken to address flooding issues in the Dijle and Woluwe valleys. We did not only consider classic protective measures, but also found inspiration in the Scottish concept of the ‘4 As’. This doesn’t only take into account alleviation but also measures for avoidance, awareness and assistance. We gained insights into the conditions, sensitivities and possibilities of the various measures. We also learned a great deal about the usefulness and importance of consultation with all stakeholders. We can draw lessons from this for other river basins in Flanders. For these elements, this project may be considered as good training for drawing up FRMPs.

In addition we have a specific set of measures that can contribute to more flood-resistant Dijle and Woluwe river basins. This set of measures can be found in Chapter 6. In order to realise these measures, a number of actions still have to be undertaken. This has to take place in cooperation with the various parties involved. We hope that together with them we can specifically elaborate the set of measures, so that we achieve a plan of approach to better protect the river basin of the Dijle as well as that of the Woluwe from extreme floods in the future.

118 Woluwe River

Epilogue • 119 This brochure was drawn up with the support of the European Union.