Examples of multifunctional flood defences

working report

Mark Z. Voorendt

EXAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

- working report -

Mark Z. Voorendt

August 10, 2015

Picture on the cover page: Quay of Doesburg, Netherlands 2012 (picture by the author)

PREFACE

This working document is part of my research on the ’evaluation of multifunctional flood defences’. The research is part of the programme on ’integral and sustainable design of multifunctional flood de- fences’ which is subsidized by and being carried out in commission of the Dutch Technology Founda- tion STW. This programme is one of the ’perspectief’ programmes that have the character of consortia of research institutes and users. The research programme consists of several projects in which various aspects of multifunctional flood defences are dealt with. These include technical aspects (strengths and loads), safety philosophy, governance, architecture and financial aspects. For details of the programme, one is referred to the project proposal (see the information on www.flooddefences.nl). The current project on structural evaluation is being carried out under supervision of promoter prof.drs.ir. Han Vrijling and with help from ir. Wilfred Molenaar, dr.ir. Jarit de Gijt and dr.ir. Klaas Jan Bakker, all working at Delft University of Technology. The research project is externally supported by Wit- teveen+Bos (especially ir. Paul Ravenstijn and ir. Gerben Spaargaren), Arcadis (dr.ir. Marco Veendorp and dr.ir. Hessel Voortman), Deltares (dr.ir. Meindert Van, ir. Han Knoeff and ir. Harrie Schelfhout) and STOWA (ir. Henk van Hemert). I also got much support from many (other) employees of the Department of Hydraulic Engineering of Delft University of Technology, especially prof.dr.ir. Bas Jonkman, prof.dr.ir. Matthijs Kok, prof.dr.ir. Marcel Stive, ir. Ad van der Toorn, ir. Henk Jan Verha- gen, dr.ir. Paul Visser. All their support is highly appreciated! This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organisation for Scientific Research (NWO), and which is partly funded by the Ministry of Economic Affairs. Any comment on this work is most welcome!

Mark Voorendt Delft, August 10, 2015

i

CONTENTS

1 Introduction 1 1.1 Definition...... 1 1.2 A flood defence structure as part of a system...... 3 1.3 The difference between a flood defence structure and a water retaining wall...... 3 1.4 Multifunctionality: Integration of functions...... 3 1.4.1 Secondary functions...... 3 1.4.2 Spatial integration...... 6

2 Examples of multifunctional flood defences9 2.1 Arnhem...... 9 2.2 Deventer...... 11 2.3 Doesburg...... 13 2.4 Dordrecht...... 15 2.4.1 The Voorstraat...... 15 2.4.2 The Noordendijk...... 16 2.5 Düsseldorf...... 21 2.6 Emmerich am Rhein...... 22 2.7 Hamburg...... 27 2.8 Kampen...... 32 2.9 Katwijk aan Zee...... 36 2.9.1 The final design...... 36 2.9.2 The ’wall-in-dunes’ alternative design...... 39 2.10 Nijmegen...... 41 2.11 Rotterdam...... 45 2.12 Scheveningen...... 49 2.13 Sliedrecht...... 51 2.14 Tiel...... 58 2.15 Zaltbommel...... 60 2.16 Zutphen...... 61 2.17 Zwijndrecht...... 64

A Glossary 67

iii iv CONTENTS

References 71 1

INTRODUCTION

1.1. DEFINITION

A flood defence is a hydraulic structure intended to protect land from irregular covering by water1. This seems a correct and useful definition, and it comprises the four main categories of flood defences mentioned in (TAW, 1998):

1. dunes 2. soil structures (dikes, dams) 3. specific water retaining structures (cofferdams, gravity walls, sheet pile walls, etc.) 4. engineering works (sluices, locks, cut-offs, storm surge barriers, pumping stations, etc.)

Also high grounds protect against floods and can be part of dike rings, but these are generally not considered to be flood defences or hydraulic structures. It should be noticed that the covering by water is caused by exceedance of normal conditions. The Dutch Technical Advisory Committee on Flood Defences (TAW) distinguishes five types of flood defences, regards their role in the flood control system:

• primary flood defences • secondary flood defences • polder quays [boezemkaden] • quays in Limburg • small river quays

Within the class of primary flood defences, the difference between the delta area with tidal influences and the upper river areas plus the IJsselmeer has resulted in different legislative treatment. Secondary flood defences are chiefly situated in dike rings along the coast. Quays in Limburg haven been con- structed after the high water in the Maas river in 1995. Small river quays are mainly situated in the dike ring areas of the upper rivers. TAW/ENW made a classification, distinguishing function, location, type and threat per flood defence class, see table 1.1. This classification is relevant regarding the loads acting on the flood defence, and therefore has consequences for their shape.

1This definition is based on (Collins World English Dictionary, 2012), (European Commission, 2007) and (Website USACE, Coastal & Hydraulic Laboratory, 2012).

1 2 1.I NTRODUCTION

Table 1.1: Classification of flood defences based on their role in the flood control system 1.2.A FLOOD DEFENCE STRUCTURE AS PART OF A SYSTEM 3

1.2. A FLOOD DEFENCE STRUCTURE AS PART OF A SYSTEM It should be noticed that to provide actual protection against floods, a flood defence has to be part of a complete system. This system comprises an actual and an abstract part. The actual system consists of a continuous protective line around the area that has to be protected, like a dike ring, eventually combined with high grounds. The abstract system consists of the organisation of the operation and maintenance of the concrete part. Also the settling of safety levels and assessment methods belongs to the abstract system.

1.3. THE DIFFERENCE BETWEEN A FLOOD DEFENCE STRUCTURE AND A WATER RETAINING WALL

According to the definition given before, a flood defence protects land from flooding. According to (Collins World English Dictionary, 2012), ’land’ refers to the

solid part of the surface of the earth as distinct from seas, lakes, etc. and also to

ground, esp with reference to its use, quality, etc.

’Ground’ is defined as

the land surface; earth or soil.

This implies that, for example, an ordinary car park ’in the open air’ temporarily covered with water, is considered to be ’flooded’, but if only a structure is temporarily filled with water (say, the cellar of a house is filled with water due to an extremely high water level of an adjoining river), it is not ’flooded’ according to this definition. To formulate the difference in other words: a flood defence is part of the first layer of the Dutch multi-layered flood defence approach (Ministerie van Verkeer en Waterstaat, 2009), which is the flood prevention layer. If a house is made watertight only to protect the furniture and belongings of its inhabitants, but not to protect the hinterland, the water retaining walls of this house are not called ’flood defences’. This kind of measures belongs to the second layer of the multi-layered safety approach. The second layer is not intended to prevent floods, but aims to reduce damage and loss of life in case of an eventual flood. So only if water retaining walls are part of the first layer of the multi-layered safety approach, they can be described as flood defences.

1.4. MULTIFUNCTIONALITY:INTEGRATION OF FUNCTIONS

1.4.1. SECONDARYFUNCTIONS The most common reasons to combine functions with flood protection are summarized in the follow- ing list:

• necessary improvements of existing flood defences conflict with other functions (housing) • ongoing urbanisation requires additional space • public funding under pressure (economic crisis) • changed societal and political attitude

Improvement of existing flood defences (the first item of the list above) can be necessary because of:

• increased flood risk: 4 1.I NTRODUCTION

– expected increase of water levels / river discharges – increased economic activity – increased population – decreased risk acceptance

• scheduled maintenance • preventive maintenance (failed assessment round) • repair

A not exhaustive list of secondary functions is given in the following list

SECONDARY FUNCTIONS FULFILLED BY HYDRAULIC STRUCTURES • providing through-passage for shipping (navigation lock) • providing through-passage for pedestrians, motorised and non-motorised vehicles (cut-off, gate) • enabling berthing and (un)loading of ship (quay wall)

SECONDARY FUNCTIONS FULFILLED BY CIVIL STRUCTURES, NOTBEINGHYDRAULICSTRUCTURES • transport fresh or waste water (sewerage) • transport of vehicles (roadway, railway, tramway, cycle path or pedestrian path) • transport of natural liquid gas (through pipe) • transport of electricity for power supply (cable) • transport of data (copper or fibreglass cable) • provide parking space (parking garage)

SECONDARY FUNCTIONS FULFILLED BY NON-CIVILSTRUCTURES, OBJECTS • provide space for housing (house) • enable economic activity on the flood defence itself (office, workplace, factory) • provide founding for wind turbines • provide space for putting cattle to pasture • provide space for agriculture • cremate dead bodies of animals or human beings (crematory) • provide swimming facilities (pool) • improvement of spatial quality (w.t.m.b.) • enable recreation • providing rescue ways or shelter places • supply of drinking water (dune-water works)

It can thus be concluded that secondary functions can be served by hydraulic structures (other than the flood defence itself) and by other kinds of structures. Combining hydraulic structures in a flood defence is quite common in the hydraulic engineering practice and apparently causes no specific problems. The design and assessment of hydraulic structures are therefore not considered to be a big problem to be solved in the current research. The consideration of the combination of the ’other structures’ with the flood defence function, however, is rather new and it is the method of assessment of especially these structures that is studied in the current research. Some common examples of flood defences with additional functions are presented in figure 1.1. It could, by the way, be disputed if the grazing of sheep is a secondary function if their deliberate purpose is maintaining of the top grass layer of the dike. That directly contributes to the primary function. 1.4.M ULTIFUNCTIONALITY:INTEGRATION OF FUNCTIONS 5

(a) road and pedestrian path on a river dike (Tiel) (b) wind turbines founded in a dike around a chemical waste storage basin (Slufter, Maasvlakte)

(c) sheep grazing on a dike (Termunterzijl) (d) interference of a flood defence and a shipping way (Zevenhuizer Verlaat)

Figure 1.1: Examples of combined functions in flood defences 6 1.I NTRODUCTION

1.4.2. SPATIAL INTEGRATION Van Veelen, Voorendt and Van der Zwet studied the degree of spatial and structural integration of functions that are combined with flood defences (van Veelen et al., 2015). In this section only the degrees of spatial integration are explained. In the context of urban planning, concepts of multiple land-use refer to situations where the existing space is more intensively used (Habiforum, cited in Hooimeijer et al, 2001). This can be achieved by morphological integration of functions (stacking of multiple functions in one building or construc- tion), by mixed space use (multiple functions in a certain defined area) and by temporal shared-use of the same space. The degree of spatial integration used in this chapter is based upon a classifi- cation by Ellen (2011) and adapted by Van Veelen (2013), who distinguishes four spatial dimensions of multifunctionality. These dimensions are used for evaluating the degree of spatial and functional integration, with slightly adapted terminology (figure 1.2):

1. Shared use. A flood defence structure is (temporarily) used by another function, without any adjustments to its basic structure. It is, generally well possible to use the flood defence for in- frastructure, recreation and agricultural uses, as long as the functioning of the flood defence is not impeded. 2. Spatial optimisation. The basic shape of the flood defence is adapted to create space for other structures. These structures are technically spoken not part of flood defence structure. Spatial optimisation is found in many places in the highly urbanised areas of the Dutch delta. The most compact and spatially optimal shape is obtained if a vertical retaining wall is applied which replaces a dike slope or berm, leaving space for, e.g., housing. 3. Structural integration. An object is built on, in or under the flood defence structure, but does not directly retain water. The concept of structural integration is used in situations where the current dike is over dimensioned (super dike) or many times stronger than necessary (concept ’unbreachable’ dike). 4. Functional integration. The water-retaining element of the flood defence also functions as a part of the structure with another function (the ’object’). Although this concept is technically feasi- ble, it is hard to find realised examples of full integration. There are some historically evolved situations in which the dike is part of a medieval city wall (Kampen) or a row of old buildings (Dordrecht).

Figure 1.2: Degrees of spatial integration (van Veelen et al., 2015)

The determination of the degree of integration starts with identifying the composing elements of a 1.4.M ULTIFUNCTIONALITY:INTEGRATION OF FUNCTIONS 7

flood defence structure. As a first step it should be determined whether an element has a water- retaining function or influences the strength and stability of the flood defence structure as a whole. If this is not the case, the integration is categorised as ’shared use’, as long as the basic shape of the flood defence is not altered. If the flood defence shape is adapted to allow more spatial compactness, the situation is categorised as ’spatial optimisation’. If the object, or part of it, fulfils a structural role in the flood defence structure, it is evaluated as ‘structural integration’. If this structural role is retaining water, the category is called functional integration. The proposed assessment method is tested on a set of cases, of which three are presented in this chapter. In all cases it proved to be possible to distinguish the composing structural parts and to determine the integration category. It also appeared that the method is systematic and transparent and can be generally applied to a wide range of multifunctional flood defences. During testing it turned out that application of the method contributes to a better understanding of the structural composition of the sometimes inconsequently used spatial concepts like ‘super dikes’ and ‘broad dikes’. It also increases insight into the efficiency of the combination of functions: some of the selected examples look very innovative and multifunctional at first glance, while the level of spatial and structural integration is limited. Many examples are spatially optimised, but not structurally or functionally integrated. Other examples may not be very spectacular from a spatial designers point of view, but show that true structural integration of flood protection with multiple other functions is already feasible, depending on the local context. A better understanding of the integration of functions or structures could also contribute to a better allocation of responsibilities for inspection, maintenance and future investments. After all, a clear understanding of what structural element serves what purpose provides a common starting point for discussions. The main generic conclusion is that the method will help both urban planners and hydraulic engi- neers to develop a mutual understanding of the various interests from a flood management and spa- tial development perspective. Because of the design-based classification, the method can be applied to discuss spatial integration of multifunctional flood defence structures in different governance con- texts (van Veelen et al., 2015)2.

2This section is mainly copied from the indicated source and is considered as a self-quotation by the author.

2 EXAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

2.1. ARNHEM Arnhem is located at the bifurcation point of the Geldersche IJssel and the Nederrijn (Lower Rhine). Arnhem is presently protected by quay walls and high grounds along the Nederrijn, and by dikes in combination with high grounds along the river IJssel. The area adjoining the Nederrijn is not very attractive for leisure, especially the western end where the mooring places of river cruise ships are located. The quay consists of two levels: the lower level provides parking place for cars and mooring facilities for boats. The higher level is used as a street with pedestrian path and some outdoor cafés (figure 2.1). The restaurant shown in picture 2.2 does not retain water, but under it, integrated in the quay, there is a sheet pile wall that does have a water retaining function.

9 10 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.1: Arnhem: two-level quay wall

Figure 2.2: Arnhem: restaurant integrated in the flood defence 2.2.D EVENTER 11

2.2. DEVENTER Deventer is located on the eastern riverbank of the IJssel river. A quay and sand dunes provide some protection against floods, but recently some walls in combination with stop logs have been erected along the river to improve the safety level. The quay is now used for recreation, regarding the heavy timber beams to be used as benches, for mooring of ships and for preserving historic value by main- taining a former freight railway track (though not functional any more). The outer walls of some houses are integrated in the flood defence. See figure 2.3.

Figure 2.3: Deventer: renewed quay wall with extra retaining wall 12 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.4: Deventer: cut-off in the retaining wall for stop logs

Figure 2.5: Deventer: preservation of architecture 2.3.D OESBURG 13

Figure 2.6: Deventer: transition hard-soft flood defence

2.3. DOESBURG At the crossing of the IJssel and the Old IJssel, the city of Doesburg was founded. The old city was built on sand dunes, which provided some protection against floods. To raise the protection level, the water board had green dikes built around the city. Part of these dikes have been converted into a two-level quay wall in the beginning of the twenty-first century. The two levels were connected with a stairway that can be used to sit and relax. Dwellings and residential apartments were constructed along the upper quay, but are not part of the flood defence. The double quay combines urban functions and flood protection (Figures 2.7 and 2.8). 14 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.7: Doesburg: relax stairs in the retaining wall

Figure 2.8: Doesburg: two-level quay wall 2.4.D ORDRECHT 15

2.4. DORDRECHT The city of Dordrecht was founded along the creek Turedricht, or Turedriht, which was connected with the river Dubbel and the river Merwede. After the floods of 1150, the creek turned into an important stream and Dordrecht was founded on both sides of its riverbanks. Dordrecht aimed to become a suc- cessful trade city, which succeeded within a century. Dordrecht changed into an industrial city during the industrial revolution and in the twentieth century, the city centre developed into an important shopping area. Nowadays it fulfils a social economic function on a regional level.

2.4.1. THE VOORSTRAAT The initial river banks were raised and transformed into dikes, to form better protection against flu- vial floods. From the 15th century onwards, several city expansions have been carried out towards the river. Until the present day, these expansion areas are unprotected against floods. Moreover, houses were built on both sides of the dike, called the Voorstraat, which has been used as an important shop- ping street (Figure 2.9). This made the required heightening of the dike around 1917 problematic. Therefore, panels in doorways and bulkheads in alleys in between the houses were used for achieving a sufficient retaining height (Figure 2.10). The panels were placed in door openings at the street side of the houses of the Voorstraat, Prinsenstraat and Riedijk. In the Grote Kalkstraat, Houtsteiger and Boomstraat large bulkheads have been placed (Figure 2.11). The improved housing fronts could nevertheless not resist the storm surge of 1953. Sheet piles were then added and extra concrete walls reinforced the houses. During flood conditions, about 200 door- ways will have to be sealed with panels and six alleys will have to be closed with bulkheads. With this system the flood defence would be high enough, but the reliability of the system has not proven suf- ficiently. The panels, namely, were to be stored inside the houses, but some residents had used them for timber or for fire wood. Therefore, the water board presently presently organises a simulation of a flood event every year to stimulate the awareness of the residents. bulkheads, by the way, are stored in the unembanked area of the city. A study in 2013 proved that the bulkheads in the doorways of individual houses don’t have a positive contribution to the safety of the flood defence (Schelfhout and Slootjes, 2013). The probability of non-closure namely, appeared too high. The height of the bulkheads is therefore not included in the retaining height. The large bulkheads in the alleys, however, are sufficiently reliable. During the last decades, the Dordrecht flood defence needed further improvement because the river discharge has increased and the sea level has risen. A major problem is formed by the monumental status of the city centre, making it impossible to heighten and widen the existing dike. Also a part of the town centre is situated outside the flood defence, along the river the Oude Maas. Several solutions have been studied to solve this problem, like the study of the ’work group 1981/1982’, Heidemij Ad- viesbureau 1985 and Bouwdienst Rijkswaterstaat 1985. An alternative for the solution of Heidemij is depicted in Figure 2.13: a concrete retaining wall has been integrated in the houses at the waterside of the houses along the Voorstraat. This alternative solution was rejected because of the high realisation costs and negative opinion of the residents.

Graduate student Sjaak van ’t Verlaat made an inventory of structural solutions of previous studies. He divided the total alignment into sections and assigned the best solution to each section (Figure 2.14). For a representative section, Van ’t Verlaat made a design for a vertically sliding gate barrier, integrated in the quay wall (Van ’t Verlaat, 1998). This idea has been elaborated by MSc-student Milan Hinborgh, who studied on a new flood defence through the part of the city of Dordrecht outside the dike. The new flood defence could be constructed on the quays in the town centre. Various alignments are possible, which protect a smaller or larger part of the city. In his report one variant has been elaborated in detail. This design is based on the assump- tion that the flood defence has to be strengthened on the short term for the highest expected sea level rise and for a 1/10 000 safety level. The new flood defence would be able to retain a water level of NAP 16 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.9: Dordrecht: unprotected side of houses along the Voorstraat

+4,35 m, where in the current situation a level of NAP +3,00 m is prescribed.

Hinborgh’s flood defence has been designed as a floating barrier: Under normal circumstances a gate is immersed in a recess of the quay wall. During extreme high water, the recess is filled and the gate floats up because of the buoyant force and is kept in place by the water pressure. In this way the quay wall height is extended in height automatically when necessary. When the water level drops again, the recess is emptied and the gate returns to its resting position in the recess (Hinborgh, 2010).

Finally a storm surge barrier has been designed and constructed (completed in 1996). This surge bar- rier reduces the water levels during storm surge conditions (water entering from sea). A solution for the increasing flood discharge on the river Merwede - Old Meuse has not been found yet (Stalenberg, 2010).

2.4.2. THE NOORDENDIJK The Noordendijk, east of the city center of Dordrecht, has been improved too. Water board ’De Groote Waard’ initiated this project, called the ’Dordtse Wand’. In this project, the functions of flood defence, living and transport are combined. The reinforcement of the flood defence has been realised by ex- cavating the existing dike slope and constructing an L-shaped wall (figure 2.17). This wall is founded on piles and a cut-off wall prevents piping. The retaining wall reaches up to NAP + 4,30 m and has a design life span of 100 years. At the place of the excavated slope, there is space for cycling and pedes- trian paths and a green belt. The floor of the L-wall is at the same time the floor of the dwellings. The ground floor of these dwellings can be used for shops, offices or storeroom. At several places, the ground floor extends further into the dike, creating sufficient space for a car park. The involved parties have signed a covenant to ensure safety against floods and enable maintenance of the flood defence. The purchase contract of the houses contains requirements to guarantee the preservation of the water retaining function. House owners, for instance, are not allowed to bore holes 2.4.D ORDRECHT 17

Figure 2.10: Dordrecht: provisions for temporary sealing of door openings in houses in the retaining walls (van der Veen, 2003). 18 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.11: Dordrecht: gate along the Voorstraat at a road crossing (over a bridge)

Figure 2.12: Dordrecht: elevated ground level in between two houses along the Voorstraat 2.4.D ORDRECHT 19

Figure 2.13: Alternative design for Dordrecht: concrete retaining wall integrated in a house

Figure 2.14: Alternative designs for Dordrecht: best structural solution per flood defence section

Figure 2.15: Alternative design for Dordrecht: floating barrier integrated in a quay 20 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.16: Improved Noordendijk, Dordrecht: cross section Dordtse Wand (van den Merkenhof and Schipper, 1998)

Figure 2.17: Improved Noordendijk, Dordrecht, picture 2.5.D ÜSSELDORF 21

2.5. DÜSSELDORF The Rheinufertunnel was constructed from 1990 to 1993 to make the river bank of the Rhine better accessible to pedestrians and relieve the neighbouring areas from intensive traffic. The tunnel has a length of 1928 m and had to be constructed in two storeys near the old city centre. The construction pit reached a depth of 17 metres and the highest tunnel storey has been constructed with help of diaphragm walls. The lowest tunnel part has been constructed under high air pressure. Adjacent buildings have been underpinned using high-pressure injection to prevent their settlement. About 600 000 m3 of soil has been excavated for the construction of the tunnel, and 235 000 m3 concrete has been used, plus 22 000 t reinforcement steel. The capacity of the tunnel is 55 000 cars per day.

Figure 2.18: The Northern tunnel entrance (left) and the quay along the river (Rheinwerft, right)

(a) cross-section 1 (b) Cross-section at the ’Art-in-Tunnel’ museum location

Figure 2.19: Cross-sections through the Rheinufertunnel 22 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

2.6. EMMERICHAM RHEIN Emmerich am Rhein is a city located along the River Rhine (North bank) in the northwest of the Ger- man federal state of North Rhine-Westphalia. During its entire history Emmerich had to cope with floodings, bank slidings, island formation and erosion. The inner city is located at NN + 17,00 m, while its lowest point in the Rhine floodplane is at NN + 13,00 m1. Until the first part of the twentieth century, the lowest parts of Emmerich were not very well protected. The highest observed water level was NN + 17,80 m and the design level was fixed at 1 m higher (figure 2.20).

Figure 2.20: Rheinpromenade Emmerich, Germany: high water 1926

After the flood of 1995 the houses along the promenade were protected by bulkheads that can be installed in front of doors and windows to keep the water out of the houses and hinterlaying city. Roads could be closed-off with planks that had to be installed in grooves (figures 2.21 and 2.22.

Figure 2.21: Rheinpromenade Emmerich, Germany: high water 1995 with flood protection 1965

A few years later, these measures appeared not to be sufficient any more. The new design river dis- charge was estimated at 14 500 m3/s, corresponding to an exceedance frequency of 1/500 per year (Anonymous, 2004). It was therefore decided to more drastically upgrade the flood defence: along the Rhine promenade the permanent defence was raised up to NN + 17,50 m. On top of that wall mobile elements can be installed, temporarily raising the retaining height up to NN + 19,10 m to resist a wa- terlevel of maximum NN + 18,84 m, which is the design high water level of 1977. A diaphragm wall

1NN = Normalnull, an outdated German standard reference level. Since 1 January 2000 it has been replaced by Normalhöhen- null (NHN), which standard takes the gravitational field of the Earth into account. NHN is the equivalent of sea level and thus related to the Dutch reference level: NHN = NAP - 0,01m. 2.6.E MMERICHAM RHEIN 23

Figure 2.22: Old protective measures along the Rheinpromenade (grooves for the placement of bulkheads) with inserted sheet piles was constructed in the existing river slope to reduce the piping mechanism. The driving of sheet piles in the near vicinity of buildings was considered to be unacceptable. The wall is supported by Gewi-anchors (Bilfinger Spezialtiefbau GmbH, 2014). The mobile flood wall is 800 m long and consists of 204 poles and 1706 planks. Figure 2.23 shows a cross-section through the upgraded boulevard and figures 2.24 and 2.25 show pictures of a cut-off and the flood wall along the promenade. Part of the outer wall of the Saint Martin church (Martinikirche) is part of the flood protection. One of the windows in the wall facing the river appeared to be too low, but it is rather small and not really a threat for the city. Behind the window, however, there are some valuable properties of the church, so in that respect an open window could be undesirable (figures 2.26 and 2.27). Computer simulations have shown that a dike breach in Bislich, about 24 km upstream from Em- merich, would result in about 1000 casualties at the Dutch side of the border, and 35 billion euros of economic damage. That is why during several years preceding 2014 about half of the dikes of the Wa- ter Board Bislich-Landesgrenze were upgraded. It is hoped for that end 2015 a start can be made with the construction of a new dike that will connect the present dike with the B8 provincial road parallel to the Rhine. The flood protection measures in this area, to be carried out between 2015 and 2025, will cost about 450 million euros, which is about four million euro per km (Caroline Gustedt, 2014). 24 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.23: Rheinpromenade Emmerich, Germany: flood protection 2006 with design water level of 1977

Figure 2.24: A cut-off to be closed with temporary means 2.6.E MMERICHAM RHEIN 25

Figure 2.25: The flood wall can be elevated with a temporary extension wall

Figure 2.26: Part of the Sankt Martini church acts as flood defence 26 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.27: One of the windows of the Sankt Martini church is below the design retaining level 2.7.H AMBURG 27

2.7. HAMBURG Hamburg is a major trade and harbour city in the north of Germany, situated about 110 kilometres from the mouth of the river Elbe. The city was flooded in 1962, after which additional flood protection measures have been carried out. The North Sea flood of 1962 was a natural disaster affecting mainly the coastal regions of Germany and in particular the city of Hamburg in the night from 16 to 17 February 1962. In total, the homes of about 60 000 people were destroyed, and the death toll amounted to 315 in Hamburg. The flood was caused by a low-pressure system approaching the German Bight (Deutsche Bucht), coming from the southern Polar Sea. A storm with a wind force of 9 Beaufort and peak wind speeds of 200 km/h pushed water into the German Bight, leading to a water surge the dikes could not withstand. The wa- ter reached a level of NN + 5,70 m, which was 0,46 m higher than the highest water level up to then (registered in 1825). Breaches along the coast and the rivers Elbe and Weser led to widespread flood- ing of huge areas. Especially dikes that had not been heightened after the storm surge of 1952 were heavily damaged while most sea dikes withstood the surge (Wikipedia, 2012). More than 60 breaches occurred in the dikes with a total length of about 1.5 kilometres. The flooded area amounted 12 500 hectares, about 1/6th of the total area of Hamburg (Landesbetrieb SBG, 2012).

Emergency plans were implemented later and dikes were shortened and strengthened, leaving some river arms and bays detached from the sea. The design water retaining height was raised up to NN + 6,70 m and many dikes were reinforced, also in horizontal direction with more gentle slopes. In January 1976 a storm surge exceeded the one of 1962, leading to a water level of NN + 6,45 m. The re- inforced dikes, however, were sufficiently high and stable to withstand this water, but there was much damage in the less protected harbour area. The erection of a storm surge barrier in the Elbe mouth (near Brokdorf) was studied, but could not be agreed upon by the various Bundesländer. In the mid 90s, a flood protection construction programme was started to raise the retaining height with about one metre (to NN + 7,30 at St. Pauli, about 2 km West of Hamburg). The calculation method was more sophisticated now, taking local hydraulic conditions like wave run-up into account per dike section. This led to varying retaining heights of NN + 7,50 m up to NN + 9,25 m (Landesbetrieb SBG, 2012).

In 2000 a start was made with a project of the redevelopment of an old harbour area in between the Speicherstadt and the Elbe. This new area, the HafenCity, is intended for work, living, retail-trade, recreation, gastronomy and culture2. The HafenCity area, however, is located outside the area pro- tected by dikes (see figure 2.28). Proximity to large expanses of water, namely, is what gives the area much of its charm; dikes would have deprived it of the many exciting sight lines down to the water. It appeared also to be troublesome to start constructing the buildings before the 126 hectare area would have been surrounded by dikes (Website HafenCity, 2012). By elevating the buildings on plinths made of mounds, HafenCity is connected with the existing city. All new buildings stand on artificial bases eight meters above sea level - safe for the most extreme flooding. On the sides exposed to wind, such as the southern sides of Strandkai and Überseequartier, the external perimeter lies at NN + 8,03 to NN + 8,60 meters. It is the responsibility of the private developers of buildings to put these artificial compacted bases in place, so their number is growing as the number of buildings increases. This has dispensed with any need for premature financing of flood-protection measures years - or even decades - ahead of the sale and deployment of the sites concerned. The interior of flood-secure plinths provides ample space for underground car garages, which means that almost all stationary traffic can be accommodated. The mounds solution therefore also makes a significant contribution to reducing the volume of private transport in the new part of town. No additional sites for above-ground parking blocks will be needed as a result, which also contributes to the effective use of ground surfaces as a resource. Roads and bridges are also being built above the

2One of the most spectacular projects in this area is the Elbphilharmonie, an ultra modern concert hall constructed on top of old storehouses, see http://discover-elbphilharmonie-hamburg.com/en/ 28 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.28: HafenCity Hamburg, Germany

flood-line at least 7.5 meters above sea level. A broad strip up to 15 meters wide along the edges of the restored historic quays is down at the existing 4,00 to 5,50 meter level of the HafenCity area and provides 10,5 kilometers of waterside walks. This considerably adds up to public urban space right next to the water. In the western part of HafenCity many of these squares and promenades are already in constant use. Thus the mounds solution also has the side-effect of allowing a new topography to take shape - which affects the character and quality of the district (Website HafenCity, 2012). The HafenCity can continue to function virtually without restriction even during a flood and despite its ’island’ situation. In cases of high water, a few underground parking garage entrances along Am Sandtorkai and Brooktorkai (directly opposite the Speicherstadt) do have to close their flood gates. This is because, if the roadways passing directly adjacent to the historic warehouses had been retro- spectively elevated, the identity and function of the whole Speicherstadt ensemble would have been affected. Planners of the listed Speicherstadt had worked on the assumption that their area could be flooded in cases of extreme high water (Website HafenCity, 2012). Moreover, windows should be able to withstand high water pressures and steel bulkheads have to prevent eventual damage on the glass windows by floating debris. It is not allowed to live on these ground floors, so they are used for car parks, restaurants and offices. The apartment blocks have different access levels in order to cope with varying water levels around the blocks. There are also escape routes on different heights to guarantee a safe evacuation if needed (Stalenberg, 2010). The new multifunctional quay walls along the ’Baumwall’ and ’Vorsetzen’, just West of the Hafencity, contain a parking level, public toilets on street level and three places designated for building con- structions. These structures are planned to include a restaurant and a kiosk. Due to securing flood protection during the construction period, demolition and construction of the new flood protection barrier must only take place under cover of temporary flood protection. See figures 2.29 to 2.34 for some examples. 2.7.H AMBURG 29

Figure 2.29: Hamburg: stairs in the flood defence (Reesendamm)

Figure 2.30: Hamburg: multifunctional quay wall under construction (near the Baumwall) 30 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.31: Hamburg: apartment blocks in the HafenCity (Am Kaiserkai)

Figure 2.32: Hamburg: apartment blocks in the HafenCity (Am Sandtorkai) 2.7.H AMBURG 31

Figure 2.33: Hamburg: steel bulkheads can be closed to protect the windows of apartment blocks along the Sandtorkai

Figure 2.34: Hamburg: a cross-section of the apartment blocks along the Sandtorkai (Pols, Kronberger et al., 2007) 32 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

2.8. KAMPEN Kampen is located along the IJssel river. To protect the town of Kampen and meanwhile conserve the typical character of this old Hanseatic trading city (Hanzestad), a number of measures have been car- ried out, combining the flood defence with other functions. An existing quay wall has been upgraded and combined with stop logs to provide extra height. Also the historic city wall, in line with many private gardens and a few buildings, has been improved. This required the cooperation of the owners of the houses and buildings. The flood defence line crosses streets on some places, which required stop logs, or closable gates. A flood brigade (hoogwaterbrigade), consisting of many volunteers, has been formed by the water board to undertake safety measures when needed. This is simulated once per year. So, the flood defence of Kampen is combined with living, transport, parking, recreational and history preservation functions. Figures 2.36 to 2.41 show some examples of this multifunctional flood defence. Figure 2.35 shows a sketch of a flap gate, which has finally not been selected to build.

Figure 2.35: Design sketch of a flap gate in Kampen. Left: normal conditions, right: during high river discharge (TAW, druk op de dijken 1995) 2.8.K AMPEN 33

Figure 2.36: Kampen: during extremely high water, houses can be protected by stop logs

Figure 2.37: Kampen: attention has been paid to ’minor’ details 34 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.38: Kampen: submerged gate in a small street to be lifted vertically when necessary

Figure 2.39: Kampen: gate with hinge construction; the flood defence here switches from one side of the road to the other side 2.8.K AMPEN 35

Figure 2.40: Kampen: flood protecting city wall that can be heightened by adding separate elements

Figure 2.41: Kampen: the flood brigade is heigtening the flood wall with aluminium elements (source: IJsselTV, 5-1-2012) 36 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

2.9. KATWIJK AAN ZEE Katwijk aan Zee is located near the original mouth of the Rhine, which in early days formed the north- ern boundary of the Roman Empire. The original mound of this river, which was situated a bit more to the North than the present mouth, was blocked by siltation in 1163 after the Saint Thomas flood. After the damming of the Rhine near Wijk bij Duurstede, no water flowed through the old Rhine any more, which enabled siltation of the original river mouth. The natural river mouth near Katwijk was excavated again between 1804 and 1807 and meanwhile an inner and outer dewatering sluice was constructed. A steam-driven pumping station was added in 1881 to enable dewatering of the hinter- land even during high water levels at sea. In 1954 this pumping station and the old inner sluice were replaced by a modern, electrical pumping station, at present known as the Koning Willem Alexan- dergemaal, named after the king of the Netherlands. At the end of the twentieth century, part of the town of Katwijk, located along the coast, South of the dewatering canal, appeared to be not sufficiently protected against storm surges, threatening 3000 inhabitants who in fact lived in an unembanked area (Figure 2.42). It was the last weak link along the Dutch coast, as reported by Rijkswaterstaat in 2003.

Figure 2.42: Katwijk: the location of the original primary flood defence through the town in the original situation (Kustwerk Katwijk, 2012)

Several alternative designs were made to improve the flood protection of Katwijk, meanwhile dealing with growing parking problems along the boulevard. The final design, which was made by Arcadis, is described in the following section, followed by another section about the alternative design made by CURNET, the Municipality of Rotterdam and TU Delft.

2.9.1. THE FINAL DESIGN The weak part of the dunes has been reinforced from October 2013 to February 2015 with a dike em- bedded in the dunes. A sub-soil parking garage for 663 cars has been constructed between the dike and the boulevard. Meanwhile, the dune area was widened and newly arranged. The dike-in-dunes is constructed along the part of the boulevard that is too low to retain critical water levels that could occur on average once in 10 000 years, which is the norm for dike ring 14 (Figure 2.9.K ATWIJK AAN ZEE 37

Figure 2.43: Katwijk: overview of the area with location of the dike-in-dune and parking garage (Kustwerk Katwijk, 2012)

2.43). This is the part where the boulevard is lower than NAP + 10,00 m, a stretch of about 900 m. The total erosion volume of the dune and beach in cross-shore direction is leading for the evaluation of the flood-protectiveness of dunes. It is not really important whether this volume is present in the height or in the width, so for aesthetic reasons (view form the boulevard) it was decided to make the dunes lower and to put extra sand volume on the beach. To achieve an even lower dune, a ’hard structure’ was needed to prevent further erosion. The total width of the dunes over the dike, from boulevard to dune toe, is about 120 m. This is 90 m wider than in the original situation. The dike has a sand core and is covered by basalton blocks on top of a filter layer and geotextile (Figure 2.44). The crest level of the dike could be as low as NAP + 7,50 m, but for again for aesthetic reasons3 the dike is covered by sand, which brings the top of dunes to a level of about NAP + 8,00 m. At locations where dunes present before the start of the project were already higher than 7,50 to 8,0 m, the original dune top level was maintained4. The crest of the dike has a width of 5,0 m. The dike shall be exposed to wave attack when the sand on and in front of it would have eroded. The sand in front of the dike will then sufficiently reduce wave overtopping. It can relatively easily be adapted in future (Arcadis, 2013).

Figure 2.44: Katwijk: technical cross-sectional drawing of the dike-in-dune (Kustwerk Katwijk, 2012)

The design methodology of the ’hybrid’ dike-in-dune structure consists of the following main ele- ments:

• the erosion volume of the dune is calculated with help of a time dependent computational model that simulates the course of the governing storm conditions (changes in water level and wave heights) and the consequent erosion;

3The project plan gives the inaccessibility of the dike cover for disabled people as a reason for covering the dike with an extra, smooth layer, but this seems a bit odd, because most of the dune area over the dike is prohibited for pedestrians. 4It is remarkable that the effort and costs done to achieve this low dune level is partly made undone by the presence of en- trances/exits of the parking garage, that bulge out of the dunes with a height of about 4,00 metres above ground level. 38 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

• The eroded sand is deposited in front of the dike and will reduce the wave attack. In case of maximum erosion, the dike will be directly exposed to waves, but these will be relatively low due to damping by the amount of sand in front of the dike. A computational model can calculate the maximum wave height at the toe of the dike; • The cross-shore profile of the dune will always contain sufficient sand to reduce the overtopping discharge to 1 l/s/m at most; • The design and future assessment methods will comply with the Dutch Regulations Assessment of Flood Defences 2007 (VTV2007).

Methods to determine the crest level of the Katwijk hybrid structure are not prescribed, so a custom- made design had to be made. The starting point of the design was the prescription of the Dutch Regulations Assessment of Flood Defences 2007 (VTV2007), intended for the assessment of common dunes, that after the occurrence of a governing storm, a dune profile consisting of only sand should remain with a height of at least 1,00 m above storm surge level and a sand volume of at least 53 m3 /m1. In the case of Katwijk, this corresponds with a remaining crest level of NAP + 7,50 m. If the dike is considered as the required remaining dune profile, it could have the same crest level, because no arguments can be found to justify a lower level, regarding the retaining height. As far as the volume is concerned: the remaining profile of a sand dune should be sufficient to retain the water, but the dike slope is also exposed wave attack. The dike, however cannot erode or become unstable, so wave overtopping becomes a major design aspect for the dike. The freeboard is about 1,70 m, which is suf- ficient to reduce the wave overtopping discharge to acceptable amounts. Lowering the crest height of the dike would imply that more sand will have to be present on the beach, but in that case the flood defence would become too sensitive to relatively small deviations in the assumed hydraulic boundary conditions (Arcadis, 2013). To compensate settlements that will occur during the first few years after construction, the construc- tion height of the dike will be 0,10 m higher than the required crest level at the end of its design life time (50 years).

Figure 2.45: Katwijk: picture of the construction of the dike, February 2014

The parking garage is situated between the dike-in dune and the boulevard (Figures 2.46 and 2.47). It is not part of the flood defence, although it is covered by the same sand as the dike and therefore gives the impression that it is integrated. The main starting points for the design of the parking garage are:

• The design of the flood defence is leading. This restricts the dimensions of the parking garage; • The parking garage is entirely separated from the flood defence; • The parking garage shall not have a negative impact on the stability of the flood defence, nor result in unforeseen settlement of the flood defence; 2.9.K ATWIJK AAN ZEE 39

• The parking garage shall be situated outside the core zone and the protection zone as indicated in the ledger of the water board.

The development of the parking garage, therefore, does not resort under the Water Act and is therefore not included in the project plan for the reinforcement of the coastal defence. The new zoning plan (bestemmingsplan) ’Kustwerk Katwijk’ enables the construction of the parking garage. The reason- ing behind the design of the garage is therefore explained in the environmental effect report (milieu- effectrapportage, MER) and the zoning plan. The location of the garage is included in the integrated layout plan that is used as an underlay for the zoning plan and the project plan.

Figure 2.46: Katwijk: car entrance to the underground parking garage. The dike is embedded in the dunes (on left side of the picture under the sand, so not visible), May 2015

Figure 2.47: Katwijk: technical drawing of the parking garage, the most Southern part (final design Kustwerk Katwijk, 2014)

2.9.2. THE ’WALL-IN-DUNES’ ALTERNATIVE DESIGN In an early stage of concept development, several alternative designs have been made for the im- provement of the coastal defence of Katwijk. One of these designs has been made by Delft University of Technology, TNO, Rotterdam’s municipal engineering department, CUR building and infrastruc- ture, and other agencies. It comprised a parking garage in the dunes, but no dike. The seaward wall of the garage was a flood-retaining diaphragm flood wall with a depth of 15 to 20 m. (Figures 2.48 and 2.49). The idea was that the diaphragm wall would have to resist the waves after erosion of the 30 metres wide dune in front of it. The experience is hat dune erosion - if it occurs - can proceed quite rapidly: 40 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES about 80 to 100 metres in a few hours, so complete erosion of a 30 m wide dune can reasonably be expected. With help of a computer simulation it was calculated that these 30 m would be completely eroded after 15 h. Waves would than directly hit and overtop the wall. The amount of the wave overtopping volume that was still considered acceptable was determined by the storage capacity of the area behind the flood defence, rather than the structural integrity of the flood wall itself. This storage capacity was estimated at 50 000 m3. A 25 m wide bed protection should have prevented scour in front of the flood wall. A side-effect of this bed protection was that it would have acted as a shallow berm during a storm, thus reducing wave overtopping volumes. Three types of bed protection were considered: a flat layer of rubble, rubble on a slope and a break- water. The first solution appeared to result in too much overtopping volumes for the maximum crest level of NAP + 7,50 m. The second alternative was much too expensive (the costs of the rubble was estimated at 30 million euro), but the third alternative with the breakwater was the least expensive (about 10 to 15 million euro for the rubble). The breakwater crest was designed at NAP + 6,50 m with a width of 5,00 m and an outer slope of 1:3,5 (Duinmeijer, 2012).

Figure 2.48: Katwijk: sketch of the ’wall-in-dunes’ alternative, with a parking garage combined in the flood defence

The parking garage was designed at the land side of the flood wall. The flood wall had a double func- tion: next to retaining water, it provided stability to the garage structure. The flood wall was sufficiently strong and stable on its own, so a possible collapse of the parking garage would not affect the flood protection. The same applies to some restaurants adjacent to the flood wall, at the beach side. They are not needed for the flood defence function. This alternative design was finally rejected by the client for several reasons. 2.10.N IJMEGEN 41

Figure 2.49: Katwijk: technical drawing of one of ’wall-in-dunes’ alternative with combined parking garage

2.10. NIJMEGEN The urban river front of Nijmegen is much more attractive than the river front of Arnhem. Many restaurants and bars are located along the Waal river. As the city is built on hilly slopes, only the lower city has to be protected against river floods. Extra crest walls in the form of old fortifications are located on top of the quays. In order to not cause unnecessary visual hindrance, these crest walls walls can be temporarily heightened with poles and concrete stop logs. In front of the doors of the restaurants, the quay can be temporarily heightened with help of an aluminium wall. The measures for this extra retaining height have been taken in 2009. These walls will have to be installed when the river level exceeds NAP + 16,25 m.

Figure 2.50: Nijmegen: opening in the upper retaining wall, to be closed with stop logs 42 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.51: Nijmegen: opening in the crest wall with mitre gates

Figure 2.52: Nijmegen: outdoor café over water defence line - a temporary wall can be fixed to the pavement 2.10.N IJMEGEN 43

Figure 2.53: Nijmegen: the water defence line crosses the road

Figure 2.54: Nijmegen: the water retaining wall is embellished with art 44 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.55: Nijmegen: even more space on the quay for art expressions 2.11.R OTTERDAM 45

2.11. ROTTERDAM There are several examples of multifunctional flood defences in Rotterdam. Some of them are de- scribed in this section (see also figures 2.56 to 2.59).

The Maashaven is a inner harbour situated in between the Feijenoordse Brielselaan and Katendrecht. The ’Maashaven Oostzijde’ quay (Figure 2.56) also acts as flood defence. At street level, it contains a pedestrian path, a bicycle path, and a two-lane road.

Figure 2.56: Rotterdam: Maashaven Oostzijde: quay combined with road

The ’Maassilo’ (Figure 2.57) along the Brielse Laan is a former cereal storage building, nowadays in use as a place for business and dance events. The building itself is located outside the dike ring, but the wall at the Brielse Laan side has a flood defence function. In this case, it means that eventual high water is not allowed to come out of the building, which will protect the Brielse Laan and the area behind this road to become flooded. The Roof Park (dakpark) project is a redevelopment project on a former marshalling yard in the ’Vier- havengebied’,Delfshaven (Figures 2.58 and 2.59). A multifunctional building is combined with a shop- ping boulevard, a playground, a neighbourhood garden and a Mediterranean garden with orangery. There will be 25 000 m2 retail space under the city park. A car park for about 750 cars is also combined in the structure. The gardens bring more nature in the district and the project as a whole will also bring more employment. The Roof Park has a length of 800 metres, a width of 80 metres and its height is 9 metres. Involved parties are: the Municipality of Rotterdam, Hoogheemraadschap Delfland and DURA Vermeer (Website dakpark Rotterdam, 2012). The waterboard of Delfland initially strongly opposed this project, but under strong pressure of the Rotterdam Municipality, it has been realized after all. The water board is involved only as a licensing authority and the municipality has promised to pay the extra costs of the future strengthening of the flood defence (Siemerink, 2012). The shops and the park are integrated. The water retaining function, however, is and will be per- formed by only the dike core, which remains intact. The Roof Park therefore is not a fully integrated 46 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.57: Rotterdam: the ’Maassilo’ is is integrated in the flood defence multifunctional flood defence. 2.11.R OTTERDAM 47

Figure 2.58: Rotterdam: the ’Roof Park’ under construction (2012)

Figure 2.59: Rotterdam: cross section of the ’Roof Park’ (van Veelen, 2012) 48 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.60: Rotterdam: the wide ’Westzeedijk’, barely recognizable as a flood defence 2.12.S CHEVENINGEN 49

2.12. SCHEVENINGEN In a study of the provinces of North and South Holland, the coastal protection of Scheveningen was pointed out as a weak link in the Dutch coastal flood protection line (Visie Hollandse Kust 2050). As a consequence the boulevard of Scheveningen, between the Scheveningseslag and the terminus of tram line 11, was reinforced, in combination with upgrading the spatial quality of this coastal zone. The artistic design was made by the Spanish architect Morales. He tried to revitalise the vanished historical curves in the coast line. It appeared to be possible to incorporate a sturdy dike in these lines, camouflaged, and improve the relation between land, beach and sea. Morales created various levels in the boulevard, which come together at several places, like the Keizerstraat. At other locations, these levels are separated, like near the Scheveningseslag where the car traffic is separated from the strolling public. Figure 2.62 gives an impression of the construction of the dike in the boulevard and the curved line after completion of the work.

Figure 2.61: Scheveningen: construction of the dike in the boulevard (2011)

The technical design was made by Arcadis, a Dutch consulting company. The improved coast protec- tion was designed as a ’hybrid’ structure: a combination of a ’hard’ dike with a soft sandy beach and foreshore. The sand volume in front of the dike reduces the wave height and thus limits over-topping volumes to 1,0 l/s/m. Therefore, the crest height of the dike could be limited to NAP + 10,10 m, except for a small stretch near the Seinpostduin (NAP + 12,0 m) and the Schuitenweg (NAP + 8,60 m). The toe of the dike is situated below the level of eroded sand during a design storm. In this way collapse of the dike due to toe erosion is prevented. The revetment on the outer slope (1:3) was calculated to withstand immediate wave attack. The existing beach wall was removed because it was all covered by sand and its influence on the reliability of the flood defence was unknown. Removal resulted in more certainty about the erosion point. This point is now fixed by the dike. Figure 2.64 shows some technical details. The connection of the new structure with the existing flood defence consists of an extension of the dike into the dunes at the north side. These dunes sufficiently resist against erosion to protect the structural transition. At the south side, the dike is curved landward around the loop of the tramway and stretches beyond the erosion point. 50 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.62: Scheveningen: the new ’hybrid’ structure (2012)

Figure 2.63: Scheveningen: cross-section of the dike (without the dune)

Figure 2.64: Scheveningen: details of the crest and toe transition of the dike in the dune 2.13.S LIEDRECHT 51

2.13. SLIEDRECHT Dike improvement in Sliedrecht has for a long time been an object of study. Like in Zwijndrecht, it appeared that the dikes did not meet the standards of the Delta Committee and the demolition of many houses to enable dike improvement was a very likely prospect (figure 2.65). Because of devel- oping societal (democratic) awareness, inhabitants of dike villages were beginning to oppose against demolition plans ever more. The opinion was that especially in urban areas, ’green dikes’ interfere with housing, city shapes (stadsstructuren) and economical activities. Also characteristic and often unique landscape views can be completely and irreversibly destroyed by a green dike. Therefore, (re)construction of plain ’green’ dikes could not longer be considered as the only and best (because less expensive) solution.

Figure 2.65: Sliedrecht: the ’Rivierdijk’ with private houses on both sides

An integrated approach for solving the dike improvement of Sliedrecht (and other dike villages) was not included in the laws at that time (Delta Act and the Water Control Act). Detailed legal guidelines for solving these complex and diverse problems were not included in laws at that time, but had anyway not been thought of. Therefore, in the 1970s, the province of Gelderland appointed a committee, the Coördinatie Commissie Dijkverzwaring, CCD, to advise the Board of the Province (Provinciaal Bestuur, GS) on these problems. This committee concluded that it is not acceptable to disregard the secondary values on and around flood defences. On the other hand, it was recognised that the original inter- ests of water control should not become subordinate, for the protection of the polders against floods remained crucial. The CDD, however, did not lead to less discussions with stakeholders, so an Interdisciplinary Study Group Spatial Planning (Interdisciplinaire Studiegroep Planologie, ISP), a MSc-graduate group of Delft University of Technology, has been appointed to find a way to deal with the conflicts, by proposing smart, integral designs, taking into account the various interests (Baltissen et al., 1984). The minis- ter of Traffic and Water Control in 1986 commissioned the development and comparison of several alternatives for a special test project in Sliedrecht. Subsequently, a steering committee has been appointed by TAW to carry out the requested policy anal- ysis and a project team did the preliminary work of working out alternatives for the dike improvement 52 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.66: Sliedrecht: improved ’Rivierdijk’ of Sliedrecht. The project team consisted of five members of the Ministry of Public Works (Rijkswa- terstaat) with expertise on project management, hydraulic engineering, policy analysis, environment and planning, safety issues and dike design. This project group was supported by other groups and had to produce a report within three months (Huis in ’t Veld et al., 1986).

The project group then worked out several alternatives with variants for two test dike reaches, from which selections have been proposed. Criteria for selection of these representative dike sections are, amongst others: the height level of the road, the type of buildings (the distance between frontage or cellar wall and dike axis or the extent of insertion of the cellar in the dike), the geometry of the existing soil massive, the ground level outside the dike, and the location in the profile regards quantities in the dike section. Here below is a summary of the alternatives.

• Alternative I: Existing alignment and dike profile will be preserved; The dike is built-over on two sides. • Alternative II: See alternative I, but here a movable defence has been incorporated in the dike crest. • Alternative III: The dike will be reinforced on the river side and the buildings on the inner side will be preserved. • Alternative IV: The dike will be reinforced on the inner slope and the buildings on the riverside will be preserved. • Alternative V: A retaining wall on the river side with a movable or permanent part. • Alternative VI: An outward dike shift with a normal slope, a steep slope and a vertical wall. The existing dike profile and buildings remain preserved. • Alternative VII: An inward dike shift, with extreme possibility a rail-road dike or state road.

These alternatives with variants are presented in figures 2.69 through 2.69. Alternative II has not been selected for further elaboration because the combination of a movable defence in the crest with a road on the crest results in a too low performance reliability. Especially in the case of high waters, 2.13.S LIEDRECHT 53

Figure 2.67: Sliedrecht: the ’Kerkbuurt’ shopping street on the ’embedded’ dike many parked cars can be expected on the dike, which conflicts with the operation of the movable de- fence. Alternative VII has been disregarded for the further process because it could not provide ’delta safety’ for parts of Sliedrecht.

In general, the selection of the above alternatives highly depends on local circumstances. The criteria used for the selection of alternatives are:

• water retention – overtopping and overflow – heave [opdrukken] and sealing layers – seepage: permeability of the subsoil – seepage: permeability of the dike body – sliding circle on outer and inner slope; stability dike body – erosion inner and outer slope • spatial planning – urban aspects – traffic • social-economic aspects – enjoyment of residence [woonsatisfactie] – employment • urban landscape – relationship town - river – urban scenery form the river – culture-historical values • river technology 54 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.68: Sliedrecht: improved ’Rivierdijk’ with inner berm

– water quality – discharge – shipping • construction – construction safety – effects on the surroundings – construction period and phasing – technology • management and maintenance – possibilities of inspection and maintenance during high water – regular management and maintenance – damage by third parties – possibilities for future improvement (adaptability) • planning and procedures – duration of the total procedure – technical preparations – duration of the construction phase • finance – construction costs – purchase of soil and property, and indemnifications – present value of maintenance costs – present value of future dike improvements – revenues of becoming available of building lot – revenues for municipality and business 2.13.S LIEDRECHT 55

Figure 2.69: Alternatives I and II of the Sliedrecht study (from: Huis in ’t Veld et al., 1986) 56 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.70: Alternatives III, IV and V of the Sliedrecht study (from: Huis in ’t Veld et al., 1986) 2.13.S LIEDRECHT 57

Figure 2.71: Alternatives VI and VII of the Sliedrecht study (from: Huis in ’t Veld et al., 1986) 58 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

After completion of the report on the two test sections, the project group produced a policy analysis report for the entire river dike of Sliedrecht (Huis in ’t Veld et al., 1987). This report has been approved by the steering committee in 1987. A good evaluation of the interests of the various stakeholder was crucial for this case. The report, however, had to be completed within six months, so the form of a policy analysis was chosen for the study, to avoid making premature choices. Another reason for not making a final selection from the alternatives was the study on the effects of a storm surge barrier that had started to be carried out.

Finally, indeed the construction of a storm surge barrier in the Nieuwe Waterweg (the Maeslantkering) and a reduction of the safety level from 1/4000 to 1/2000 dwindled the necessity for complicated dike improvement measures. Some improvement works have been carried out, but to a less far extent than had been anticipated. Over 600 m a new dike has been constructed in front of the existing dike (completed in 2006). Not all of these measures appeared to be effective. According to the municipality of Sliedrecht, 6 m deep sheet-pile walls on the inner side of the dike near the Baanhoek appeared not to sufficiently stop the seepage. The subsoil was more permable than had been assumed. Therefore is was expected that during high water levels, the houses behind the dike would experience hindrance, but the safety of the hinterland was not threatened. The waterboard ’Rivierenland’ generated several alternatives and decided to just pump back the seepage water, when needed. The works to accomplish this were completed in 2007 (Website Municipality of Sliedrecht, 2012).

2.14. TIEL Parts of an old fortification today function as a flood defence against high waters of the Waal river. It appeared to be difficult to improve this structure, but the flood of 1995, which nearly inundated Tiel, made the national government decide to promptly improve the flood defence. It should be noticed that in Tiel as well as in other cities, cars have to be towed away by the municipality when the quay is about to be flooded. Apparently not all car owners are aware of the approaching high water. The municipality charges 75 euro for this service. 2.14.T IEL 59

Figure 2.72: Tiel: old fortification acting as flood defence

Figure 2.73: Tiel: cut-off in the flood defence 60 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

2.15. ZALTBOMMEL Zaltbommel, founded on a sand dune on the southern bank of the river Waal, is protected by dikes against fluvial floods. It used to be a fortified city and the fortification also functioned as protection against floods. At present, fortification walls still act as flood defence, but they were improved at the end of the twentieth century. The municipality also enhanced the visual and physical relation between the river and the city by constructing a promenade along the flood defence. The dike was improved with the construction of a short flood wall of 500 m length on top of the outer slope. This flood wall can be temporarily heightened by adding aluminium stop logs of 3,00 m length and 0,20 m height. The entire extension wall can be erected by six to seven persons within one day. These persons are not inhabitants of Zaltbommel, but professionally involved people who follow a training once per year (Stalenberg, 2010), (van der Veen, 2003).

Figure 2.74: Zaltbommel: dike with esplanade 2.16.Z UTPHEN 61

Figure 2.75: Zaltbommel: flood wall on the dike

2.16. ZUTPHEN The city of Zutphen is located at the concourse of the IJssel and Berkel river. The city was protected by a quay and sand dunes. To meet the present safety level, the retaining height has been improved by an extra wall made of sheet piles, about 10 metres behind the original wall. This gives space for cars to park when this area is not flooded (which is most of the time). The gaps that enable cars to reach this area can be closed with gates. The city side of this sheet-pile wall has quite successfully been embellished with granite stones, to preserve the authentic character of the city. Some pictures are presented in figures 2.76 through 2.77. 62 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

Figure 2.76: Zutphen: area for recreation and art exposure in between quay and extra wall

Figure 2.77: Zutphen: retaining wall made out of sheet piles and granite cobbles 2.16.Z UTPHEN 63

Figure 2.78: Zutphen: retaining wall with elevated pedestrian path

Figure 2.79: Zutphen: point of attention: parked cars in a cut-off of the primary water defence 64 2.E XAMPLES OF MULTIFUNCTIONAL FLOOD DEFENCES

2.17. ZWIJNDRECHT Zwijndrecht was founded on a sand dune on the northern bank of the current river Old Meuse. It has been protected by dikes from early days. Because of frequent failure of these dikes, the construction and maintenance of these dikes became regulated in the 14th century. This regulation stimulated the foundation of new urban areas, which became part of the city of Zwijndrecht in the second half of the nineteenth century. The crest of the dikes was used for transportation and dwellings were constructed on each side of the dike. Like in Dordrecht, the dikes of Zwijndrecht needed improvement after the storm surge of 1953. As a result, most dike houses were demolished (i.e. most of the town of Zwijndrecht, as this town was a typical ’dike village’). Only the road was rebuilt after the dike improvement. A large part of Zwijndrecht, where harbour and industrial activities took place, is located between the river and the green dike. Since the end of the twentiest century, the municipality is transforming this area into an area containing residential and office buildings. A quay wall protects the area to some extend against river floods wall. In addition, the interior of the ground floors of the houses has been made resilient to inundation. In the beginning of the twenty-first century, the ’Westkeetshaven’ of Zwijndrecht has been trans- formed into a living and working area, see figures 2.80 and 2.81. This area is located outside the primary flood defence, but the economic relation between the height of this area and the probabil- ity of a flood ahas been studied. An economic optimum was found for a height of the area of NAP + 3,10 m with a corresponding average exceedance frequency of 1/600 per year. The area has been extended into the river for thirteen metres. To accomplish this, a new sheet pile quay wall has been constructed. The old quay wall, also existing of sheet piles, is still part of the present water retaining structure. These sheet piles have been connected via anchors to new sheet piles. The area that is cre- ated between the two sheet piles serves as an underground car park. Each house has access to this car park. (Stalenberg, 2010).

Figure 2.80: Zwijndrecht: the Maasboulevard, part of the renewed ’Westkeetshaven’ 2.17.Z WIJNDRECHT 65

Figure 2.81: Zwijndrecht: schematic cross section of the parking garage under the Maasboulevard

A

GLOSSARY

67 68 A.G LOSSARY by-law / keur statute of a Water Board containing regulations for the administration of flood defences, water courses and accompanying engineering structures closure level / sluitpeil outer water level at which the closure of a gate should be started to prevent that the water level will exceed the open retaining level. For the estimation of the closure level, the raise speed of the outer water level and the closure time needs to be taken into account, as well as the circum- stances (currents) during which closure is still possible collapse / bezwijken (sudden) breakdown of a structure due to insufficient strength or stability construction height /aanleghoogte top of structure level at the beginning of the design life period needed to meet the criteria for maximum wave overtopping discharges at the end of the design life period crest freeboard / golfoverslaghoogte, retaining height needed to prevent overflow or overtopping discharges higher than allowed dike ring / dijkring continuous line of flood defences, possibly in combination with higher land areas, around an area to be protected against floods dike ring area / dijkringgebied part of land enclosed by a dike ring dike section / dijkvak part of a dike with the same geometrical, material and loading characteristics dike segment / dijksectie, dijksegment, dijktraject stretch of a dike with an equal required safety level dwelling mound, artificial dwelling hill / terp man-made soil body on which dwellings, or churches, were built to reduce the flood risk engineering structure / kunstwerk man-made civil structure as part of infrastructure. Most hydraulic structures are engineering structures. Exceptions are dunes and dikes. failure / falen inability of a structure or structural member to fulfil the specified functional requirements fault tree / foutenboom graphic presentation of the logical interconnection between various component failures and events within a system

flood / overstroming the temporary covering of land by water

flood defence / waterkering hydraulic structure intended to protect land from being covered by water freeboard / waakhoogte, kruinhoogtemarge retaining height needed to compensate for wave overtopping (= crest freeboard), local wave set- up, shower gusts and seiches higher land areas / hoge gronden areas of land that naturally have a ground level higher than the minimum required level regard- ing flood protection 69 hydraulic structure / waterbouwkundige constructie anything that is used to divert, restrict, stop or otherwise manage the natural flow of water human error a departure from acceptable or desired practice on part of an individual that can result in unac- ceptable or undesired results inundation / inundatie deliberate flooding of land (specifically for military purposes) ledger / legger legal document used by the Dutch Water Boards for official registration of the flood defences as regards their location, shape, dimensions and structural composition. Ledger zones indicate the area where structural modifications are restricted length effect / lengte-effect increase in failure probability with the length of a flood defence due to partial correlation or independence between different cross sections and / or elements multifunctional flood defence / multifunctionele waterkering structure that is intended to protect land from irregular covering by water, and also serving other purposes open retaining level / open keerpeil level of the outer water that would just not lead to an unallowable discharge through an opening with closure means in an engineering structure polder / polder low lying area, often below sea-level, protected against floods by a surrounding dike in combi- nation with drainage for rainfall and upcoming ground water probability / kans likelihood of an event (a flood in case of flood protection) reference crest level /dijktafelhoogte top of structure level at the end of the design life time, which is required to meet the criteria for maximum wave overtopping discharges reliability / betrouwbaarheid the ability of a structure or system to perform its required function adequately for a specified period of time under stated conditions risk / risico a function of the probabilities and the magnitude of specific consequences of undesired events. Flood risk is usually considered as the multiplication of the flood probability and consequences (= damage costs, or loss of lives) robustness / robuustheid the ability of a structure to survive after some initial damage seepage screen / kwelscherm wall to extend the percolation distance of water under or around a hydraulic structure in order to prevent failure of this structure due to extruding sand stability / stabiliteit resistance against moving (rotation of displacement) of a structure or structural member stiffness / stijfheid resistance against deflection of a structure or structural member 70 A.G LOSSARY storm surge / stormvloed high water with an average exceedance frequency of once per two year. This high water is usually caused by a storm, coinciding with astronomic high (spring) tides and an hour-averaged wind velocity of minimal 15 m/s. strength / sterkte resistance against internal stresses in a structure or structural member structural integrity / constructieve integriteit the state of a structure of being whole and fulfilling its function. In other words: the capacity of a structure to resist all actions, as well as specified accidental phenomena, it will have to withstand during construction work and anticipated use structural safety / constructieve veiligheid see ’structural integrity’ transitional berm / plasberm or kreukelberm (in Zeeland) revetment at the toe of a dike, with reed, brushwood, rubble (sometimes with stone), which protects a dike or dam soil against erosion by currents or waves. The slope of a transitional berm is often less steep than the outer slope. water board / waterschap, hoogheemraadschap regional authority that is administratively responsible for the quantitative and qualitative water management in an area. REFERENCES

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