Flood-resilient urbanity along the Meuse
Safe-fail design suggestions
Johnny Boers & Simon Pille - Thesis landscape Architecture
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Flood-resilient urbanity along the Meuse June 2009
Wageningen University and Research Centre Master Landscape Architecture & Spatial Planning Major Thesis Landscape Architecture (lar 80436)
Signature Date Author: J. (Johnny) Boers Bsc
Signature Date Author: S.C. (Simon) Pille Bsc
Signature Date Examiner Wageningen University: Prof.Dr. J. (Jusuck) Koh
Signature Date Supervisor and examiner Wageningen University: Dr.Ir. I. (Ingrid) Duchhart
Co-supervisor Deltares: Ir. M.Q. (Maaike) Bos
© Johnny Boers & Simon Pille, Wageningen University, 2009 All rights reserved. No parts of this report may be reproduced in any form without permission from one of the authors. [email protected] - [email protected] Flood-resilient urbanity along the Meuse
Safe-fail design suggestions
Johnny Boers & Simon Pille - Thesis landscape Architecture 6 Preface
For eight long years, we have studied landscape architecture at the will actually work. Disappointed, but not defeated, we went on in Wageningen University and Research Centre. During this period, our search for a safe urban environment. With a lot of effort and we were educated in designing new functioning and attractive regained positive energy, we were able to do so. In this thesis, you landscapes by using the existing landscape and its processes. Now, will find the result. we are able to end our study with this thesis, which will show what we have learned in this phase of our lifetime. We would never have been able to finish this thesis without some people though. Foremost we would like to thank Ingrid Duchhart, We have chosen for a thesis that focuses on water and urban our supervisor. Without her assistance and positive attitude, it would landscapes. Living in a densely populated delta country facing a have been a lot harder to finish this thesis. We thank her for the time changing climate does give some incentives to do so. But the fact that she spent on us, especially since it might have exceeded the that we both have affinity with water might also have been a reason. time that is granted by university rules. We also thank Roel Dijksma We both believe that the old method of flood-protection is not the for the hydrological input during this thesis. We thank Maaike Bos best way to cope with the changing climate. During our study, we for her matter-of-fact approach and structural advice on the subject. have become aware that working with the natural processes instead We would like to thank the people of Rijkswaterstaat, which we of working against them will have far better result. Therefore, this could always contact for hydrological questions and data. They study presents an example of how the Dutch people can work with have been so fast with replying that we were forced to change our water, not fighting against it. This might ask for a complete change idea of public servants. We thank our family for their comforting and in culture, but it might be worth it. financial support. We thank our friends for their critical advice and positive support during this thesis. And last but not least we thank We started this thesis with a positive attitude, but halfway through our girlfriends. They always took care of us and they have been an it became very grim. We became aware that our goal could not anchor of rest and hope during this hectic period, even tough they be reached in the way we had envisioned it. Our plans of making had to put up with grumpy, absent-minded and tired boyfriends. beautiful streets and parks that at the same time could protect the people against floods could not be realised. It simply would not solve In return, we hope we can all impress and inspire you with this the problem. This has been a real eye-opener for us. For the first thesis! time we became aware that just because it is possible to envision a solution to a problem, this does not mean that such a solution Johnny Boers & Simon Pille
7 8 Abstract
In the future the Meuse valley in Limburg will face higher water levels because of climate change. The dikereefs of Limburg have stated that the current dike system has reached its limit and the safety of the inhabitants of urban landscapes in the floodplain of the Meuse cannot be guaranteed during an expected river discharge of 4600 m3/s. Other approaches of dealing with the predicted amount of water have to be investigated. Dikes cannot be heightened endlessly and they only reduce the chance of flooding, instead of the risk of flooding. We envision that the flood risk of the urban landscapes has to be reduced and flood-resilience was expected to do so. We researched by designing whether it was possible to replace the current dike system by an ultimate flood-resilient system. These designs were assessed with calculations, thereby giving the potentials of: • Parks and streets as storage basins and bypasses respectively. • Large scale interventions in the urban landscape like large basins and bypasses. • Flood-resilient adaptations of buildings in the floodplain. However, the space that is required to construct basins and bypasses with the required capacity exceeds the area of the urban landscape. In case of the building adaptations, the flow speeds and water levels in case of flooding were too high and the constructions would be damaged. Furthermore, the surrounding urban space would become a dangerous area in case of flooding. So the conclusion had to be that ultimate flood-resilience in the valley of the Meuse cannot be a good replacement of the current chance-reducing interventions. Next, we investigated if flood-resilience could enhance the current chance-reducing approach. This also proved to be impossible, because the expected water levels and flow speeds remained too high. Therefore, the conclusion had to be that flood-resilience can not cope with the expected discharges in the current landscape of the Meuse valley. We then searched possible other approaches that could guarantee a safe living environment in the Meuse floodplain. The only option that remained after this search is raising the urban landscapes, with as result several mounds in the floodplain of the Meuse. By law, the height of the mounds is limited to the height of the current dikes, because they would raise water levels further upstream otherwise. Consequently, the mounds can still flood when the middle scenario of the KNMI becomes reality. Therefore, flood-resilient interventions need to be applied on top of the mound, which can now be done because of the lower water levels and flow speeds. Several design suggestions for such urban landscapes are presented in this thesis.
Keywords: flood-resilience, Meuse, flood-risk, flood-chance, mound, Limburg, urban landscapes, dikes, landscape architecture, safety, river, climate change, safe-fail, floods
9 Table of contents
1. Introduction 13 7.3 Different categories of flood-resilience 73 1.1 The main problem, goal and hypothesis 14 7.3.1 Area-adapt 74 1.2 Research process and methods in retrospect 15 7.3.2 Point-adapt 75 1.3 Reading this thesis 19 7.4 Technical analysis of the different categories 76 7.4.1 Store (Basin) 76 2. Landscape of the Meuse basin 21 7.4.2 Channel (Bypass) 77 2.1 Description of the Meuse basin 22 7.4.3 Evade (Floating, amphibious, on poles and 79 2.2 Historical development of the landscape along the 24 mounds) Meuse in the Netherlands 7.4.4 Resist (Water-resistant house) 83 2.3 Division of landscapes along the Meuse 27 7.4.5 Endure (Wet-proof house) 84 2.3.1 Division based on surrounding landscape 27 7.5 Conclusion 85 2.3.1 The undiked and diked Meuse in the 30 Netherlands 8. Asses flood-resilience in the Meuse valley 87 2.4 Conclusion 30 8.1 Area-adapt 88 8.1.1 Storage 88 3. Aspects and history of floods in the Netherlands 31 8.1.2 Channel 90 3.1 Effects of flooding 32 8.1.3 Conclusion concerning area-adapt 92 3.2 History of floods and flood protection in the 32 8.2 Point-adapt 93 Netherlands 8.2.1 Assessment of the evade, resist and 93 3.3 Floods of 1993 and 1995 36 endure methods 3.4 Conclusion 37 8.2.2 Conclusion concerning point-adapt 95 8.3 Conclusion area-adapt and point-adapt 95 4. Climate change 39 4.1 The process of climate change 40 9. Flood-resilience supplementing current approach 97 4.2 Global climate changes in the future 41 9.1 Combination of approaches 98 4.3 Expected effects of global warming in Europe 42 9.2 Technical possibilities of the combination 99 4.4 Climate change in the Netherlands 42 9.3 Safety and liveability aspects 100 4.4.1 Predictions for the Netherlands 42 9.4 Conclusion 100 4.5 Conclusion 44 10. Remaining choices for the Meuse floodplain 101 5. Flooding problem of the Meuse valley 45 10.1 Using the upstream area in Belgium 102 5.1 Water level prediction projected on the landscape 46 10.2 Using the floodplain in southern Limburg 102 5.2 Categorization of the urban landscapes 48 10.3 Leaving the floodplain 103 5.3 Conclusion 51 10.4 Continuing on the current path 104 10.5 Raising the urban landscapes 104 6. Current approach 53 6.1 Policy and future policy explorations 54 11. Analysis of Arcen 105 6.1.1 De Maaswerken 54 11.1 Choice for Arcen 106 6.1.2 Integrale Verkenning Maas 54 11.2 Description of Arcen 106 6.1.3 Integrale Verkenning Maas 2 55 11.3 IVM around Arcen 109 6.1.4 Beleidslijn Grote Rivieren 57 11.3.1 The IVM measures around Arcen 109 6.2 Safety 57 11.3.2 Effects of the IVM measures 111 6.2.1 Policy of safety 57 11.4 Conclusion 111 6.2.2 Safety in daily life 58 6.3 Flood chance and flood risk 59 12. The concept of raising Arcen 113 6.4 Conclusion & discussion of the approach of 63 12.1 The height of the mound 114 12.2 The shape of the mound 115 nowadays 12.3 Location of the mound 116 6.5 Hypothesis and research question 65 12.4 Concept of appearance of the mound 121 12.4.1 Is there space and necessity for areas that 121 7. Flood-resilience 67 need extra protection on the mound? 7.1 The origins of the resilience concept 68 12.4.2 Which measures can lower potentially 123 7.2 Flood-resilience 70 dangerous currents in the urban landscape?
10 12.4.3 What design will allow a safe flooding of 124 the mound? 12.4.4 How is the water guided inside the urban 126 landscape? 12.4.5 How will the connectivity of the mound be 127 maintained during a flood? 12.4 The process of raising an urban landscape 128
13. Design principles for a flood-resilient urban landscape on 129 a mound 13.1 Design principles of a flood-resilient urban space 130 13.1.1 Urban green 130 13.1.2 Infrastructure 132 13.1.3 Public utilities 133 13.2 The private spaces in a flood-resilient urban 135 landscape 13.3 The design principles of several crucial parts of 136 the mound 13.3.1 The head of the mound 137 13.3.2 Internal measures that improve safety 146 13.3.3 Sub-mound and tail of the mound 151 13.3.4 The floodplain surrounding the mound 156 13.4 Exporting the design principles to other areas 157 13.5 Conclusions regarding the design principles 159
14. Conclusions, discussion and recommendations 161 14.1 The conclusions 162 14.2 Discussion 164 14.3 Recommendations 165
References 167
11 12 Introduction
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13 1. Introduction
This thesis discusses the practical possibilities of a new theory in the Limburg is a province in the Netherlands that is different from the field of flood protection. This new theory is called flood-resilience and other provinces in terms of gradient and landscape. Most of the it focuses on “living with floods” instead of preventing them. Since Netherlands is relatively flat and most of the rivers are situated on flood-resilience is a new theory, there is a lack of knowledge on how a higher level in the landscape than their surrounding areas. This is it will work in practice. Nevertheless, we assumed that this theory caused by the intensive drainage of the peatlands, which caused could be translated in a set of designs for small-scale interventions in them to consolidate. There is however one river in the Netherlands the urban landscape. When implemented, these interventions would which is different from the others and that is the river Meuse. The create flood-resilient and safer urban landscapes in the floodplain of reason why the Meuse is different from the other rivers in the the Meuse in the province of Limburg, which are currently threatened Netherlands is that the Limburgian part of this river is situated in a by floods because of the changing climate. valley. Internationally, this is a normal situation for a river, but in the Halfway through the thesis, it became apparent that this goal was Netherlands, it is an exception. Because the Meuse is situated in too ambitious however. Our assessments showed that the proposed a valley, climate change will have different effects on this river and interventions would not solve the problems that we identified. Even its floodplain compared to the lower situated polders in the other a completely adaption of the urban landscape would not suffice. It parts of the Netherlands. Many of the solutions that have protected seemed that flood-resilience would not be the solution for the flood- the lower parts of the Netherlands do not work in Limburg, or at related problems in the Meuse floodplain. least not in the same way. Yet, most research on flood-protection Therefore, we looked for other approaches that could create safe focuses on the other rivers and polders in the western part of the urban landscapes. We found a solution in the creation of a mound Netherlands. This apparent neglect is the reason why we will discuss (artificial hill) on which an urban landscape could be situated. From the Limburgian part of the Meuse in this thesis. there on, we concentrated on the appearance and technical aspects of such a mound and the urban landscape on top of it. In the end, During the preliminary studies, it became apparent that the old flood- it proved that the mound could only be realised if a flood-resilient protection method would not suffice for the future climate. Therefore urban landscape was placed on top. a new look on the problem was needed. It became apparent that This thesis therefore differs from other ones. We could not reach our especially the urban landscapes are vulnerable for flooding. To goal in the way we had first envisioned. Instead of quitting the thesis reduce this vulnerability and thereby the flood risk, flood-resilience at this point, we made a new beginning and tried to reach the goal in was presumed to be the solution. The main problem and goal of this a different manner. This thesis shows the complete process though, thesis are therefore: because the data that was gathered in the first part is essential for the second part. We will begin with a description of the original goals Main problem: and hypotheses. The urban landscape along the river Meuse in Limburg faces a higher flood risk in the future while contemporary flood protection techniques are not appropriate to reduce this flood risk.
1.1 The main problem, goal and hypothesis Goal: To show how urban landscapes along the river Meuse in Limburg The first ideas for this thesis started when the dikereefs of Limburg could become more flood-resilient, while keeping them functioning published an article in the local newspaper. They stated that parts of and attractive. the Province of Limburg in the Netherlands could still be flooded by the river Meuse after the finishing of the Maaswerken project in 2017 In our architectonic vision, we imagined that the use of innovative and that these people should get used to “wet feet”. (De Limburger, techniques could lower the vulnerability of the urban landscape. 2007) This is an unusual statement to be made by dikereefs, whose Important objects could be adapted and streets and parks could be task it is to guarantee the safety of people in flood-prone areas. used to lower the water levels. Therefore, we stated our hypothesis An increase in precipitation caused by climate change will cause like this: higher potential water levels in the Meuse in the future. The statement of the dikereefs was an open invitation to designers and planners Hypothesis: to produce an alternative look on the flood protection of Limburg, The vulnerability of urban landscapes along the Meuse in Limburg because they believe that the current system will not be sufficient to can be lowered by making them more flood-resilient with the use of cope with the higher potential discharges of the river. Therefore, we innovative techniques, thereby reducing flood risk. started a study on the problems in the province of Limburg.
14 This research thesis focuses at the search for these innovative water. We would translate these visions to a landscape level and techniques or the innovative use of existing techniques. Since the solve the flooding problem in Limburg by adapting the public space. work field of the landscape architect is mainly situated in the public Imagine no more need for dikes and people would truly live in the domain of the landscape, this thesis tries to find the answers for the floodplain of the river. flooding problem right there. We tried to verify our hypothesis by answering the following main question and sub-questions: With this knowledge, we stated our goals and hypothesis and began our thesis. The research began with a study on the specific landscape Main question: of Limburg and the future water levels. From literature, we got the What are appropriate techniques that can contribute to scenarios for the next 100 years representing the discharges in the more flood resilient urban landscapes along the Meuse in river Meuse. The middle scenario is the most likely to become reality Limburg, taking the predicted raise of potential water levels and many policy documents take that one as starting point, so we into account? chose this middle scenario to work with during the thesis, which predicts a rise in potential discharges of 800m3/s in 2100. Sub-questions: With the use of an elevation map and the water levels per river -Which innovative techniques can be used in the specific kilometre, it was possible to create a map that shows the current landscape of Limburg? and future floodplain. From this map, we could deduce that there -How can these measures be implemented while keeping the are three different types of urban landscape. Both, a large and small urban landscape liveable, or even improving it? type of urban landscape that are already protected by quays, but -How could this transformation be realized in time? would nevertheless need better protection. In addition, there is a third one that has no flood protection at all and is situated at the edge of the floodplain. Next, we looked further into the subject of flood-resilience and tried to 1.2 Research process and method in retrospect find techniques that could make an urban landscape flood-resilient. In literature, we found many techniques, which we categorized into two Here, we will discuss the process of this thesis. For every step, different groups, based on their functioning. The first group is called we will also give the methods that were used during that phase, area-adapt. This method converts a part of the urban landscape to integrated in the description of the step. This is the process as it protect other important parts by lowering the water levels. Examples actually happened during this thesis, which, as noted before, differs are bypasses and storage basins within the urban landscape. The from what we original intended. second group is call point-adapt. This method focuses at adapting individual objects. The objects are constructed in such a manner that The starting point for this thesis was a statement of the dikereefs they are placed above the water or are not damaged by it because that Limburg should get used to wet feet, which is a very peculiar of their construction. We then looked at the possibilities and limits of statement, especially when it comes from professionals who are the individual techniques that could be called flood-resilient. supposed to protect the people against floods. Such a statement To test the hypothesis, it was investigated if ultimate flood-resilience tells that something is truly wrong in Limburg and thus we started a would be possible by completely replacing the current dike system. small study to find out what was wrong. First area-adapt was investigated, because it is cheaper and safer to After a preliminary research on the foundations of this statement, use some areas to protect other areas than adapting the complete it was clear that the urban landscapes in the valley of the Meuse in urban landscape with point-adapt. We expected that flood-resilience Limburg will face substantial higher water levels in the future because could be applied on a more detailed level of scale by using the public of changing climate. The dikereefs’ opinion was that the current spaces, like streets to channel water and parks to store the water. system of dikes has reached its limit and that another solution has We assessed this idea by designing imaginary urban landscapes to be found. and used the data from literature and our own calculations to see if Challenged by this statement we looked for other solutions in literature the water levels went down far enough. This was not the case. and talked with experts on this subject, including the dikereefs When this conclusion was made, a research by design study was themselves. We found a possible solution on the basic premises of made to find solutions on the larger level of scale of the complete flood-resilience. This theory is based on coping with floods instead urban landscape like using a highway as a bypass and whole of resisting them. Rather than reducing the flood chance, it reduces neighbourhoods as storage basins. We made designs of the urban the vulnerability of the urban landscape against a flood. We found landscape, using the techniques we researched. We then assessed visions of parks and streets that were adapted to transport or store the effectiveness of these designs with simple calculations and by
15 Figure 1.1 Scheme of the process of the research.
16 1) Dikes cannot be heightened endlessly. Beside of that, the current approach with dikes as flood defence creates a pseudo-safety, as it only reduces the chance of flooding and not the vulnerability. As a result, the risk of flooding may actually rise. Therefore, this approach is not the solution to deal with the predicted water levels. 2) Applying measures to retain water in Belgium is hardy possible because of the rocky and urbanized landscape along the river Meuse. Besides that, the political situation in Belgium makes it very hard to cooperate with the Belgians. 3) In our opinion the flood risk and thus the vulnerability of the urban landscapes has to be reduced. This is what flood-resilience does and therefore it has to be investigated if the resilience-approach can replace the current chance- reducing dike system. 4) We expected that flood-resilience could be applied on a detailed scale by using the public spaces like streets to channel water and parks to store the water. This proved to be impossible because of the amount of water, which is simply too much. 5) After the conclusion of point 4, we look at solutions on a larger scale, like using a highway as bypass. Assessments on this scale showed that the amount of water is still too substantial to solve with area-adapt solutions, so area-adapt cannot be applied to replace the current dike system. 6) When urban areas cannot be protected by using parts of it (area-adapt), it has to be investigated if it is possible to protect only the most important objects, like buildings and infrastructure. This proved to be impossible because the height of the water levels and the speed of the currents exceed the technical limits. 7) If flood-resilience cannot be used as replacement of the current system, is it possible to use it as supplement to the approach of nowadays? This also proved to be impossible because water levels and flow speeds are still the same during a flood. 8) We had to admit: we were too ambitious to think that flood-resilience can contribute to a solution for the predicted high water problems in the valley of the Meuse. The question is what can be done to improve the safety in this area in that case. This will be investigated in the next part of the research. The gathered knowledge of the first part will be used as much as possible. 9) People have to get used to wet feet and accept that the urban area is flooded sometimes. Money can be reserved to pay the victims. A problem with this way of reasoning is that human casualties are not included and these are really possible to happen and in our opinion unacceptable. Since this thesis focuses on improving the safety of the inhabitants, this option will not be worked out further. 10) Leaving the floodplain and relocating all the settlements to the higher parts is an option that creates ultimate safety against flooding. Nevertheless, this option lies far behind the original goal of this thesis and needs a different research. 11) The only option that remains to really increase the safety of the inhabitants without pseudo-safety is raising the urban settlement to diminish the flood- risk. This will result in urban settlements on mounds in the floodplain. 12) In an ideal situation, the ground level is raised far above the potential water levels. This will create an ultimate level of safety, but at the same time it creates higher water levels upstream. Since it isn’t allowed by law to shift problems to other areas, the height of mounds is restricted to the current level of the quays. 13) Because of the reason mentioned in point 12, the highest possible height is that of the current quays. This means that the mound still can flood in case of water levels that exceed this height, which is the case when the middle scenario of the KNMI becomes reality. To deal with this flooding of the mound, flood-resilience can be applied to the buildings and public space. The result is a range of flood-resilient mounds in the valley of the Meuse.
17 comparing them with examples in the field. option creates ultimate safety against flooding. Nevertheless, this Testing showed that solutions on the larger scale would also not work, option lays far from the original goal of this thesis and needs a because the surplus of water was still too large. So the conclusion different research, so we did not follow this path. had to be that area-adapt cannot be applied to replace the current The only option that remained that was within the context of this dike system. thesis is increasing the safety of the inhabitants by raising the urban When it became clear that area-adapt could not be the solution to the settlement on a mound. A higher ground level will automatically mean flooding problem, we looked at the possibilities of the point-adapt lower water levels, which will decrease the flood-risk. Law forbids techniques. This proved to be impossible too, because of the very however that the mound will be higher than the current quays. As high water levels and the speed of the currents. Therefore, point- a result, the mound can still be flooded. To deal with this flooding adapt could also not be used to deal with the predicted amount of the mound, flood-resilience can be used to adapt the buildings of water. This was tested by comparing the water levels and flow and public space. The result is a rigid hydrodynamic mound, with a speeds with the limits of the point-adapt techniques that we found flood-resilient urban landscape on top of it. in literature. Therefore, the conclusion had to be that flood-resilience To find design principles for such a mound, we chose the floodplain could not be used as replacement of the current system, because the village of Arcen. This landscape of this flood-prone town was the amounts of water that have to be dealt with are simply too large. basis of a situation, height and shape of a mound, which would have the least effect of the river. To find the best shape and location Slightly disappointed with these results we looked at whether the of the mound itself we used translational design. This means that we flood-resilience method could complement the current system; the looked for examples in nature. We then copied the principles behind system that has reached its limit, according to the dikereefs. We these examples and applied them on the scale of the mound. looked at the current system and the plans for the Meuse floodplain. Once the location, height and shape of the mound were known, we Afterwards, we looked where the flood-resilient measures are still could try to find design principles for the flood-resilient techniques on useful. This was only behind the dikes, in the urban landscape. We top of the mound. These techniques need to protect the inhabitants compared the new data with the technical limits of the flood-resilient of Arcen during a flood. We made some conceptual designs for the techniques. The water levels were still the same though during a flood complete urban landscape but this proved to be impossible, as and the flow speeds also did not change much. Therefore, the use of there were too many uncertainties. A design of a complete urban flood-resilient techniques was still impossible. Therefore, we had to landscape that incorporates all the factors that will influence it during admit that we have been too ambitious to think that flood-resilience the next 100 years is simply unrealistic. Therefore, we decided to can contribute to a solution for the predicted flood problems in the show the design principles of the most important parts of the mound valley of the Meuse. We still wanted safe urban landscapes however that were needed for the safety. For most of these we made two and finishing our thesis with such an unsatisfying conclusion extreme options, a smooth and rigid alternative. From the examples was simply not an option. The goal was to show what innovative that we found in nature, we learned that it was important to “think techniques could be used to create safe urban landscapes in the like water”. Water always obeys some simple rules. With these rules Meuse floodplain. The question became what could be done to in mind, it was possible to create design principles that enable a improve the safety in the floodplain. This was investigated in the flood-resilient urban landscape on top of the flood-prone mound. next part of the research. The gathered knowledge of the first part We applied techniques on top of the mound and then assessed was not thrown away, but used. their effects. The techniques were then adapted and assessed again. This process was repeated until the assessment showed To reach a safe urban landscape, there are still several options that the urban landscape would be safe when the design principles available that increase the safety of the urban areas along the are applied. The design principles showed that it was possible to Meuse. These options were found in literature. The first one is that implement these techniques in the urban landscape, while keeping people have to get used to wet feet and accept that the urban area is it functioning and attractive. The design principles that are found flooded sometimes. Money that is saved by not adapting the current on the location of Arcen can also be projected on the other urban system can be reserved to pay for damage. landscapes in the valley of the Meuse. The problem with this method it that it only repays victims or their At the end of the thesis, we tested the design principles. We did this relatives; it does nothing to protect them. In addition, this option left in cooperation with Rijkswaterstaat Limburg. They put our designs nothing to actually design because it is a policy question and not a in a computer program and calculated their effects. Here, it was design question. concluded again that the design principles would result in a safe Another option is leaving the floodplain and relocating all the living environment in the floodplain of the Meuse. settlements to the higher parts of the landscape of Limburg. This
18 1.3 Reading this thesis
The structure of the book shows more or less the process of the research chronologically. In this chapter this process is already described, together with the applied methods. The next chapters contain the analyses that are necessary to understand the problem of flooding within the landscape of Limburg. In chapter 5 these analyses are combined and the impact of the predicted amount of water on the landscape is derived. Chapter 6 gives insight in how the government deals with this predicted increase in water levels and discusses this approach. In chapter 7 flood- resilience as alternative for this current approach is described. The testing of flood-resilience as alternative and thereby the test of the hypothesis can be found in chapter 8. The conclusion of this chapter made it necessary to look if flood-resilience could be a supplement of the current approach instead of a replacement, which is investigated in chapter 9. The conclusions of the chapters 8 and 9 made us explore what other solutions could be to deal with the predicted amount of water. The result was that the urban landscapes should be raised to increase sufficient safety. Chapters 11, 12 and 13 show how this could be done by conceptual and design principles for the village of Arcen. Chapter 14 contains all main conclusions of this research and shows whether the hypothesis is true or not.
19 20 Landscape of the Meuse basin
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21 2. Landscape of the Meuse basin
2.1 Description of the Meuse basin
The Meuse is a rainwater transporting river that has a length of nearly 1000 km. It starts flowing 200 km northeast of Dijon in France, at a height of 409 meter above sea level. From there the Meuse flows through France, Luxembourg and Belgium before it enters the Netherlands at the village of Eijsden. In the Netherlands the Meuse crosses the provinces Limburg, Brabant and Gelderland, before ending up in the Haringvliet in Zuid-Holland. The total river basin is approximately as big as the Netherlands and with that known fact it’s small, compared to the basins of other rivers. This relative small basin causes that intensive rainfall in Luxembourg causes a high water level in the Netherlands within a day. The Meuse is a river with an average water discharge of 230 m3/s. (Ministerie van Verkeer & Waterstaat, 2003a) (Middelkoop, 1998)
Figure 2.1 River basin of the Meuse.
22 Upper reaches The upper reaches of the Meuse, also known as the Lotharingian Meuse, streams in France from the source until the point where it meets the river Chiers near Bazeilles. The river basin is elongated and narrow and the winter bed is wide. The French part of the river basin has a sloping landscape with wide valleys and long stretched ridges. The slopes contain often forests and the valleys are used for agriculture and cattle-breeding. The area along this part of the river basin is relatively thinly populated, with the exception of some bigger cities like Charlevile-Mézières.
Figure 2.2 Upper reaches (Bazoilles-sur-Meuse) Middle reaches (Jcube52, 2007) The narrow middle reaches, the Ardennes Meuse, streams until the Dutch border. Important tributaries like the Viroin, the Semois, the Lesse, the Sambre and the Ourthe enter the Meuse in these middle reaches. Because the river cuts through the hard rock of the Ardennes, the Meuse has a narrow winter bed with a steep gradient at the edges. Many parts of the Ardennes consist of forest for wood production. Also, agricultural areas can be found on the higher parts, especially extensive cattle-breeding. In addition, this zone is relatively thinly populated, except the industry-axis along the line Charleroi-Namur- Liège. The rain water which falls in the Ardennes flows directly into the Figure 2.3 Rocky landscape of the middle reaches Meuse because of the rocky soil. This, in combination with the (Waulsort) (Dr.Bob, 2007) fact that mankind has reduced the flooding areas of the Meuse by canalizing, damming and urbanising, makes that the Belgium part has an important contribution in the high water levels of the Meuse.
Lower reaches; Dutch Meuse The Dutch part of the Meuse is about 250 km long and enters the Netherlands at the village of Eijsden. From here on, it flows through four different landscapes. In the south of Limburg, the Meuse flows through a hilly landscape. Then it enters the sand landscape before it enters the river landscape in the middle of the Netherlands. Eventually it reaches the sea clay landscape before entering the Figure 2.4 Canalised and urbanised landscape of North Sea. the middle reaches (Namur) (Uyttebroeck, 2007) Geo-morphological, geological en hydrodynamic processes have had a great impact on the landscape, the ontogenesis and the current appearance of the Meuse. Within the Netherlands, we can make a differentiation between the diked Meuse and the undiked Meuse, which will be discussed in chapter 2.3.2. (Ministerie Van Verkeer & Waterstaat, 2003a)
Figure 2.5 Lower reaches (Venlo) 23 2.2 Historical development of the landscape along the Meuse in the Netherlands
Geology Geology has played a big role in the formation of the valley of the Meuse in the Netherlands. The formation of the valleys, the height where you can find different shingle-, sand-, and clay-layers, the position of the meanders and the places where high water levels flood the river forelands are all influenced by geological processes. The most important geological force is the formation of the highlands. The earth in the south of Limburg rises slightly and the fastest of the Netherlands (approximately 2 cm per century). Rivers like the Meuse and the Geul have cut themselves through the landscape, as fast as the earth was rising, leaving deep gullies in the highlands. More to the north of Limburg the ground level is rising, which it has been doing since the ice retreated after the ice age so there was less weight pushing the land down. This rising of the land, the erosion and meandering of the river have produced a very distinct landscape of terraces, plateaus and floodplains. This process is shown in figure 2.7. Besides the influence of the river, the wind also played an important role in the formation of the landscape of Limburg. In cold or dry periods, the vegetation disappeared and the sea retreated, which gave the wind the chance to move the sand that remained after the ice retreated. Especially between the ice ages, the area west from the Meuse was covered by a thick layer of sand of 2 to 3 meter, with excesses of nearly 20 meter.
Figure 2.6 Relief map of the meuse river basin in meters above N.A.P.
Figure 2.7 The meandering and erosion of the Meuse carved terraces in the rising landscape.
24 Development of settlements The resulting landscape has been the basis for the settlements along the Meuse. Roughly, three kinds of areas can be categorized, (figure 2.8). The first place where settlements started are the terraces. These areas are situated higher than the river water rose during flood events and were still relatively close to the fertile floodplains. The second place where settlements started was on small islands in 1 2 the floodplain. These areas did not flood during times of high water. These areas were small though. They were big enough to place castles and other defences, which later evolved into villages, like Borgharen. (Hupperetz, 1996) The third location where settlements started was on places where the floodplain was wide. As a result the flow speed of the river was low and the river could be crossed, a so-called ford. These were ideal places for markets and the largest cities along the Meuse started this way. All the settlements began on relatively high places in the landscape, since there was enough space and flood protection was still a personal matter. In the past, the floodplains of Limburg flooded 3 frequently and the people who lived close to the river adapted their houses to these floods by e.g. raising the entrance, adapting their furniture and by systems that allowed them to lift their furniture out of the reach of the floodwater quickly. This situation remained the same 1. Village on terrace 2. Fortress for many centuries until the industrial revolution. Because of better 3. Village near fords living standards, the population grew and cities began to expand rapidly with it. For the Meuse valley, this meant that settlements Figure 2.8 Settlements started on high places near the river spread out into the lower part of the floodplain, where the houses could be flooded. After the Second World War, this process speeded up even further. Figure 2.9 shows this process as it has happened with the village of Borgharen.
Compared to the western part of the Netherlands this was a relatively slow process though. In the western part of the Netherlands the lands were drained and as a result, the peat oxidized. This process made the land to descend and dikes were built to protect the invested capital. The labor and organization needed for this were the reason that the first waterboards were formed. The dikes cut of the river from the rest of the floodplain. Sedimentation of the river heightened the summer bed of the rivers while the lands around the rivers went down because of drainage. Eventually the typical Dutch landscape of polders and higher situated rivers evolved. Meanwhile, Limburg remained a province with relatively few inhabitants and the ground level of the landscape did not change like in the west of the Netherlands. The need for dikes and quays was less because there was less to protect and water levels during floods were low. As a result, there were just a few dikes in Limburg. (Ven, Van de, 1993)
25 Figure 2.9 Development of Borgharen over time.
Consolidation in the west of the Netherlands
Starting situation
Figure 2.10 Consolidation resulted in large height differences in the west of the Netherlands, while Limburg remained the same. Limburg
26 2.3 Division of landscapes along the Meuse resulting in deep lakes around the streambed of the river. Currently most of these lakes are used for leisure and tourism. Most urban This chapter will discuss the different landscapes that are present in areas a located at the borders of the floodplain on the terraces, safe Limburg in the Meuse valley. These will follow below in a sequence for current flooding. from the Dutch-Belgian border until the mouth of the Meuse in the Hollands Diep. The Peelhorstmaas (Peelhorst Meuse) starts at the point where the Meuse enters the Peelhorst and ends at the village of Arcen. The Peelhorst is tectonic active area and rises slightly each year. This 2.3.1 Division based on surrounding landscape has caused the river to carve itself into the landscape and has left a comparatively deep and narrow valley. This part has a low gradient. The Bovenmaas (Upper Meuse) begins at the border of Belgium Sand is the most found material in this part of the river course, since and ends at the village of Borgharen, 15 river-kilometres to the north. it lost mostly the heavier material. Because this part of the Meuse is Here, the Meuse meanders a little and is situated in a narrow valley. barraged, there is not that much dynamic present, except just after The river is mostly bound to its current stream bed by artificial banks. the barrages or when the barrages are lowered or overflowed. This part of the Meuse is barraged, which makes it navigable by big ships. Most of the Meuse is situated within urban areas. Compared The Noord-venloslenk and the Zuid-venloslenk run from Arcen to the to the rest of the river trajectory, the Bovenmaas holds relatively much Village of Mook. The Meuse has carved a broad and shallow valley water. It has a deep summer bed with a narrow winter bed. There in the sandy sediments of this track. The river meanders a little here, are some parallel tributaries, but they only consist of a small portion but there are no complete meanders like before. The relative large of the total water surface. On both sides of the river the landscape area the river can use expresses itself in old streambed systems and quickly transcends into the plateaus through which the Meuse valley terraces. Because of barraging of the river, this stretch of the river has eroded. Urban areas are mainly situated on the lower plateaus has little dynamics. Most urban areas are located on the edges of or terraces, close to the water, but safe from flooding. the floodplain on the terraces. Some are however located on higher areas within the floodplain on old flood banks. These areas have The Grensmaas (Border Meuse) begins at the village of Borgharen the same problems of potential flooding as the urban areas in the and ends at the village of Maaseik. The floodplain of the river is floodplain in the Grensmaas stretch. wider in this part and meanders strongly. The gradient of the river is however lower, the water flows freely within the streambed and is The Benedenmaas (Lower Meuse) begins at the village of Mook and not barraged. The river here holds just a small portion of water since stretches until the village of Lith. The character of the Meuse here is most water is directed to the Juliana canal east of the river. Because mainly based on the strong meandering and riverbank systems. This of this, this part of the river cannot be navigated by ships and can part of the Meuse has dikes and bank protection, controlling most of even dry up completely during times of drought. On the other hand, its course. This stretch of the Meuse has relatively little space within during times of a high river flow rate, the landscape can change its winter bed, and most of the winter bed is agricultural area. Most drastically because the banks and riverbed are not confined by urban areas here are located on old flood banks, parallel to the river. any artificial means. Within the floodplain of the river, several small Yet, because of sedimentation of the floodplain and consolidation of villages can be found, like Borgharen and Itteren. Because of their the peat lands, the villages are situated lower than the water level of location within the floodplain, they are likely to flood during a high the river during high water levels. river discharge. The Getijdenmaas (Tidal Meuse) starts at Lith and runs until Hedel. The Plassenmaas (Lakes Meuse) starts at the village of Maaseik and The Meuse again gets a meandering character here and the effects runs until Neer at river-kilometer 87. After Maaseik the river enters the of the tides can be noticed. Clay is the most dominant material to Roerdalslenk (Ruhrvalley graben). At this point, the river changes be found here although the floodplain mostly consists of sandy from a sediment carrying system to a sediment depositing system, materials. The course of the Meuse is mostly bound to the artificial because of the changes in the gradient of the river. Complete banks. Because of this, there is almost no hydrodynamics even meanders in the river are typical for this part of the Meuse, and the though there are no barrages. Most urban areas here are located on floodplain has about the same width as at the Grensmaas stretch. old flood banks, parallel to the river. Yet, because of sedimentation When a river starts depositing sediments it deposits the heaviest of the floodplain and consolidation of the peat lands, the villages particles first. This has resulted in large layers of pebbles in this part are situated lower then the water level of the river during high water of the Meuse. The layers have been excavated in the past decennia, levels. (Ministerie van Verkeer en Waterstaat, 2003b)
27 Figure 2.11 Division of landscapes along the Meuse.
28 Figure 2.12 Bovenmaas Figure 2.16 Zuid-venloslenk
Figure 2.13 Grensmaas Figure 2.17 Noord-venloslenk
Figure 2.14 Plassenmaas Figure 2.18 Benedenmaas
Figure 2.15 Peelhorstmaas Figure 2.19 Getijdenmaas
29 2.3.2 The undiked and diked Meuse in the Netherlands behind the dikes could flood and merge again with the river, further downstream. In the winter bed, the sedimentation still continued The Meuse flows in a valley until the town of Cuijk. The valley has been and raised the winter bed higher then the surrounding landscape. eroded out of the Pleistocene sand layers. During the ice ages, the The consolidation of the komgronden increased with the use of Meuse carved itself deeper and deeper into these layers. Because better drainage systems, making the difference between water level of the differences in climate over time and the accompanying river and surface level even bigger. Although the river-morphological flow rate, this has resulted in terraces, where the upper terraces are processes have become more and more human-controlled there is the oldest valley bottoms. still some dynamics left within the floodplain. These dynamics are the The transitions of the Meuse valley to the higher sandy areas are foundation of the characteristic difference between the areas within mostly not a clear boundary but a slow transition. The presence of and outside the dikes. Although the dikes have altered the influence the relatively big gradient makes that the landscape-pattern of the of the river on the landscape in a significant way, the Meuse and Meuse valley is unique in the Netherlands. The abiotic underground Rhine still are, until this day, the carriers of the river landscape in the of the valley has been a large driving force for the occupation process Netherlands. (Ministerie van V & W, 2003b) (Ministerie van Verkeer and accordingly the spatial built-up of the landscape in Limburg. en Waterstaat, 2004b) The different land uses are related to the different gradients and position of the terraces. For example, the old villages are situated on the transition of the lower terraces to the middle terraces. The “napoleon roads” (roads build by napoleon for military use) were 2.4 Conclusion built parallel to the Meuse. Even today, the shape of the valley is a driving force for the spatial development of the landscape. The Meuse is a rainwater river with large differences between The Meuse is a very unpredictable river, related to the fact that it is high and low discharges. Since the main part of the river basin a rain-river. During times of flooding, large parts of the surrounding is situated outside the Netherlands, a large portion of the river landscape were submerged, while during times of drought the discharge is caused by foreign precipitation. The rocky soil and Meuse became unnavigable. With time, the capricious nature of the high urbanisation in the upstream parts of the Meuse makes river was decreased by technical measures. Vulnerable areas along retention of precipitation nearly impossible. As a result, much of the the Meuse were protected by quays and eventually the river was precipitation flows directly to the Netherlands and our neighbouring dammed, making it navigable during the whole year. countries are unable to stop this. (Ministerie van Verkeer en Waterstaat, 2001) Downstream form Cuijk the Meuse enters the central river plains Many settlements were originally started at the safe higher places, where the rivers Waal en Rhine also flow. Here the rivers deposit outside the floodplain, but through time they were expanded and their sediments, which they have transported there from the houses were built in flood-prone areas. Much of this has happened mountains and the hills. The influence of the dynamic regime of the after the Second World War when the river had a relatively calm Meuse used to reach a large part of the river plains. During times period. Dikes and quays seemed unnecessary since the last of flood, larger layers of sand where deposited right next to the flood was in 1926 and the danger of flooding was forgotten. The river, eventually forming the flood banks. Behind these flood banks consequence is that nowadays much of the buildings are situated heavy clay was deposited. This has resulted in a meandering ribbon in flood-prone areas. of higher flood banks and low-lying “komgronden”. These abiotic circumstances were the starting point of the human occupation. The new settlements were built on the higher flood banks, which are dryer than their surroundings. The transition zone to the higher sandy areas of Brabant is the foundation of the urban zone of Oss, ‘s-Hertogenbosch, Waalwijk, Oosterhout, Breda, Roosendaal en Bergen op Zoom. With the use of dikes humans tried to protect the settlements against flooding from the 10th century onward. The influence of the Meuse was reduced from a zone of tens of kilometers to just one or two kilometer. Still, during times of extreme high water levels, dikes were likely to break or overflowed. Sometimes, this was anticipated and some dikes were built lower than others. In this way the areas
30 Aspects and history of floods in the Netherlands
3
31 3. Aspects and history of floods in the Netherlands
Floods are among the most common and dangerous natural disasters on planet earth. They kill a large amount of people every year. More and more floods occur every year with the most recent climate changes. (IPCC, 2007) A flood is the rising of a body of water and its overflowing onto normally dry land. (Princeton University, 2008) This can happen in a multitude of manners with many causes, ranging from hurricanes to tidal influences. The Meuse has only one reason though. The water level in the river rises as a result of much precipitation in the river basin. The water can’t be contained by the summer bed and flows into the floodplain.
3.1 Effects of flooding
The effects of flooding on the landscape depend on multiple factors. These factors include flooding from a salt- or freshwater source, duration of the flood, the flow rate of the flood, etc. Since we discuss the river Meuse in this thesis we will only discuss the effects of a freshwater flood from a river. The effects encompass a wide range of harmful effects on humans, their health and their belongings, on public infrastructure, cultural heritage, ecological systems, industrial production and the competitive strength of the affected economy. Some of these damages can be specified in monetary terms, others – the so called intangibles – are usually recorded by non-monetary measures like number of lives lost or square meters of ecosystems affected by pollution. Flood damage effects can be further categorized into direct and indirect effects. Direct flood damage covers all varieties of harm which relate to the immediate physical contact of flood water to humans, property and the environment. This includes, Figure 3.1 Degree of loss related to depth of inundation (Messner & Meyer, for example, damage to buildings, economic goods and dikes, 2005) loss of standing crops and livestock in agriculture, loss of human life, immediate health impacts, and contamination of ecological 3.2 History of floods and flood protection in the systems. Indirect or consequential effects comprise damage, which Netherlands occurs as a further consequence of the flood and the disruptions of economic and social activities. This damage can affect areas quite Humans need water for their survival. Because of this, most human a bit larger than those actually inundated. One prominent example settlements are situated near a source of water. Before the middle is the loss of economic production due to destroyed facilities, lack ages humans tended to build their settlements in places where of energy and telecommunication supplies, and the interruption of there was water within walking distance, but where the water could supply with intermediary goods. Other examples are the loss of time not reach the settlement itself. Usually, for the Netherlands, this and profits due to traffic disruptions, disturbance of markets after meant building at the higher parts of the landscape, on the sandy floods to, reduced productivity with the consequence of decreased grounds in the eastern part of the Netherlands. When the population competitiveness of selected economic sectors or regions and the increased, humans were forced to live also in the wetter areas of the disadvantages connected with reduced market and public services Netherlands, near the big rivers and in the peaty areas. In these parts, (Messner and Meyer, 2005) the human settlers were still forced to seek the higher grounds, in this case: sand dunes and river embankments. Human technology was still not advanced enough to withstand the forces of nature, especially the water.
32 This all changed during the middle ages. As technology advanced period). Moreover, much of the forests in the upper regions of the and human population pressure increased, humans were able Meuse were cut down. This resulted in a more irregular runoff from to move into the wettest areas and exploit them. For the areas the Meuse, increasing the floods. This in turn made the necessity of surrounding the rivers in the Netherlands this meant that the flood- new flood defences even bigger. prone areas were exploited. Settlements expanded outside their safe high grounds into the flood-prone areas. First, they used flood- From 1600 onwards, there was a huge acquisition of new land in the resilient measures like mounds (artificial high grounds) and resilient Netherlands. With the use of the improved windmills, many of the housing (on mounds, on poles). But eventually the investments lakes and floodplains along the coast could be drained and used for in the flood-prone areas became too high to be protected by agriculture. Around 60.000 ha. was reclaimed in this way. Although individual means. As a result humans began to cooperate and the 23.000 ha. of this figure was made out of lakes that had been created first collective flood defences were created. Together the human by humans by extracting peat from the underground for the use of settlers were able to build better and larger flood defences. For fuel. Another great breakthrough during this time was the ingenious financial and technological reasons these mostly took the form of way in which people were able to regulate the amount of water dikes and quays. This started around the year 800. Eventually, the between the Rhine and the Waal. This greatly reduced the amount waterboards were established that managed whole regions. This of floodings in the river area of the Netherlands. Yet, most of these resulted in the construction and maintenance of complete “dike measures were aimed at the protection of the province of Holland, rings”, incorporating more settlements than before. These were the where most of the economy and population was concentrated. first flood resistant measures that were built in the Netherlands and For Limburg this was a turbulent time, with several wars and began to control the run of the rivers effectively. Along the Meuse conquests from different countries. Because of this and the focus on people had started to build small settlements on the higher grounds the province of Holland, Limburg was a bit neglected on a national along the valley. On some locations where important roads crossed scale. Private enterprises went on however. Yet, around the Meuse the river, small villages were built. These were situated on higher there were no lakes that could be drained. Limburg also counted less parts where the road and the houses were safe for flooding. wealthy investors than Holland. The deforestation went on however. Also, more of the floodplains were drained. This way they could be In the late Middle Ages, around 1250, the structures of water control used for the grazing of bigger livestock like cows. became mature. With the invention of the pumping mill, which can pump the water in and out of the areas, many of the human imposed After 1800 the Netherlands transformed into a modern democracy. negative conditions, like the consolidation of the peaty areas, were This had its effects on both politics as on the waterboards. They both diminished. In the surrounding areas of the rivers new canals became better organised. Further advancement in technology and and ditches were dug. This improved the drainage of the higher the invention of the steam engine made it possible to reclaim the grounds. The mouths of the new drainage system were situated larger lakes in the west of the Netherlands. This could only be done as far downstream as possible. This improved the speed at which with the support of the whole nation, since the required finances were the excess water could be transported to the river because of the too large to be granted by private financiers. About 100.000 ha. of difference in height. During the winter seasons however, many of new land was reclaimed from the lakes. The reasons for reclamation the drainage systems were unable to get rid of the excess water were different than before however. In contrast to the need for new because of the high water levels in the rivers. Besides that, there was agricultural land, the new reason was to protect the bigger cities in the extra precipitation that fell during the winter period. As a result the lower parts of the Netherlands. During storms, the erosion on much of the lower areas were still flooded during the winter period. the shores of these lakes was so substantial that the lakes were Sometimes this situation lasted until springtime, severely hampering growing very fast. Eventually this would threaten the large economic the planting of new crops and the grazing of livestock. hubs and therefore, they were drained. The new land was of course Along the Meuse, villages were still situated on the higher grounds. gratefully used for agriculture. The valley of the Meuse is relatively small compared to the floodplains Apart from the newly reclaimed land from lakes and sedimentation of the Waal and the Rhine. Also the differences between the water along the shore, the biggest part of the newly reclaimed land was level and the height of the surrounding landscape are bigger than from moors. In the past many of these moors were forests, but along the Rhine and Waal. Nevertheless, people started to exploit overgrazing and clearcutting had reduced it to moor land, sometimes the wetlands around the river Meuse and turned them into meadows even sand landscapes. The moors were far from dry and therefore for livestock. On the higher grounds of Limburg, many of the small needed a good drainage system to be reclaimed, so brooks were streams were straightened. The same happened in Belgium and straightened and transformed to canals. They were also broadened France (Which was controlled by different factions during this to use them as transportation routes for the acquired peat.
33 In Limburg, the floodplains of the smaller brooks leading to the Meuse mostly consisted of “woeste grond” (land that nobody owned and was used for the grazing of livestock). During this period much of this land’s drainage was improved and the brooks were straightened and quayed even more. This resulted in a faster drainage of the higher grounds, which made it more suitable for agriculture. A disadvantage was that this also resulted in higher water levels in the Meuse, which also occurred faster than before. The fact that this process was also going on in countries like France and Belgium only made matters worse. Much of the attention on flood defences was given to rivers during this time. In 1809, 1820, 1855 and 1861 the rivers had flooded large parts of the river area in the Netherlands. Partly this was caused by the lack of river-mouths. But much of the floods can be contributed to the lack of hydrodynamics of the river. In the past much of the dikes had breached. The force of the burst created holes, which filled up with water and were called “wielen”. These wielen had to be bypassed when the dike was rebuilt. This had happened so often that the dike had become very irregular. Moreover, the dikes had large and sharp corners that sometimes went deep into the floodplain itself. Humans had also created many obstacles in the floodplain by planting forests and reed for timber and roofing respectively. Even in the summerbed of the river there were many islands and other obstacles. This lack of hydrodynamics resulted in frequent piling of ice and resulted in large floods. The industrialisation solved this problem by adding lots of cooling water to the Meuse and Rhine, making them warmer during the winter period. The further warming because of the climate change will make this scenario even more unlikely in the future. During the 19th century, the problem of navigability was also tackled. Under pressure from more industrial developed countries like Germany, the rivers were transformed for shipping and new canals were dug to improve shipping further. When most of the problems along the Rhine were solved the attention turned to the Meuse. Around 1875 the riverbed was normalized by fixing, deepening and narrowing the main channel. In the 1930’s Figure 3.2 Map of canals related to the Meuse in Limburg. some bends were cut off and sand banks and islands were removed. In addition, some stretches were canalised and new dams were built to control the water levels in the Meuse and make it navigable during the summer. To improve the accessibility of towns in Belgium and Limburg further, new canals were dug, like the Juliana canal in 1935, which was constructed for navigation. Figure 3.2 shows where and when these canals were dug. With these canals it was easier to control the water levels in the Meuse and they still have a large effect on the water levels today.
34 Flood disaster of 1953 casualties that fell during this night (including two babies who were The year 1953 was a year of great disaster for the Netherlands. On born that very night). Furthermore, 33 people died on ships at sea, the 1st of February a high tide of the North Sea coincided with a storm 4 soldiers died while rescuing people the next days and 1 person surge. The resulting high water levels proved too much for the flood died of a heart attack. This resulted in a total of 1835 casualties. It is defences in the south of the Netherlands and they broke through at likely that more people have died after they were evacuated, but no several places. Some villages had 3 meters of water in their streets numbers do exist about this. This number of casualties was huge for within half an hour. This surprise effect was the cause of the 1797 the Netherlands and still captures people’s imagination.
Figure 3.3 A breached dike during the flood of 1953. (KNMI,2008)
35 The dikes that should have protected the people who died that night were already considered insufficient in 1942. But the rebuilding of the country after the war was a process which required hard choices. The chances that a storm surge would occur at the same time that there was a high tide were very small and thus, the limited funds were directed to the rebuilding of houses, infrastructure and the economy. The great flood of 1953 had a great impact on the inhabitants of the Netherlands. The government wasn’t blamed for the disaster. People felt that they had been overwhelmed by the forces of nature, guided by a higher force. Of course the people demanded a quick repair of the dikes, but this would take some time because these repairs tend to be time consuming. Yet, by May 1953 ninety percent of the inundated land was dry again. Then the attention of the people and their representative government turned to the prevention of such disasters. Engineers were called upon to come up with a plan to protect the Netherlands against future floodings. They came up with the “deltaplan” which incorporated new dikes and dams in the delta area in the estuary of the south- western part of the Netherlands. The “deltawerken” were finished when queen Beatrix opened the Maeslandkering on the 10th of may 1997. The Netherlands were safe against floods from the sea. (Ven, Van de, 1993)
3.3 Floods of 1993 and 1995
Like said in chapter 2, settlements originally started at higher safe places. But because of population growth, people have been building in the lower situated flood-prone areas during the last century. And Figure 3.4 A boy in the flooded streets of Venlo in 1993. (Green- peace,2008) so it was a matter of time until the first flood. This happened in 1993. After long periods of rainfall in the Ardennes, peak discharges showed up in the river Meuse in the Netherlands. In December 1993 a peak discharge of 3,120 m3/s passed the Belgium-Dutch border. An area of about 8% of the province of Limburg was flooded. Around 8.000 people were evacuated, because their houses were flooded or the power supply and other services had stopped functioning. A little bit more than one year later, another flood appeared. In January-February 1995 a peak discharge of 2,861 m3/s reached the Netherlands. The total damage in 1993 was 115 million euro and in 1995 75 million euro.
The flood of 1993 was the first river flood since 1926. People have a very short-term memory when it comes to disasters and this was no exception. Many people didn’t remember the flood of 1926, just the big one caused by the sea in 1953. In other words: people didn’t expect a flood from the rivers. Because of this, the government Figure 3.5 Borgharen totally flooded in 1995. (Kennislink, 2006) was also mainly focussed on sea defences and tended to neglect
36 the rivers. The river floodings were quite a surprise for the Dutch that has to resist the water and reduce the chance of flooding. government and came as a shock for the people. Fortunately, there The appearance of two floods within two years was totally not were no casualties, nor were there any heavy injuries, because of expected. Statistically and therefore theoretically, such a high the quick reaction of the government and the firm grip of its leaders discharge would happen again at least 50 years later. However, the on the situation. (Ven, Van de, 2007) But the economical damage problem of statistics is that it calculates with chances, which means was severe, although comparatively small to the flood of 1953. that in reality an event could reappear the next year already, or even The damage to the feeling of security was much worse however. the next month. And that’s what the floods of 1993 and 1995 and The people felt threatened by the rivers and demanded that the also the high water of 2003 underline. It is impossible to predict government would do something about their lack of safety. when a high water event will appear. After the floods, the government ordered the construction of Until the floods of 1993 and 1995 embankments were considered quays and dikes around the flood-prone urban landscapes. These to be senseless, because people thought that the floods in this embankments still protect the current urban landscapes. area were not life threatening and would not affect large areas. They believed that the gradient of the Meuse valley would give enough protection against flooding. Furthermore, because of gravel in the subsoil, seepage below the embankments is very likely. Building embankments and preventing this seepage is expensive and has disadvantages in situations with low discharges. However, after the floods of 1993 and 1995 there was reason to change this attitude. Rivers were reasoned to be safe, but this was not reality anymore. The people involved, like the water boards, realized that just the valley of the Meuse with its geomorphology wouldn’t guarantee the required safety anymore. So during the following years, dikes and quays were realized quickly, to prevent that this kind of floods would happen again. Embankments of about 75 cm to 1 m height were constructed around urban areas. They are designed to withstand discharges with a probability larger than 1/50 a year. (Bruijn, De, 2005)
3.4 Conclusion
A flood is one of the most dangerous disasters that could happen with a wide range of harmful effects on civilization and ecology. The higher the water levels of the flood, the higher the potential degree of loss. In Limburg the gradient of the Meuse valley was reasoned to give enough protection against flooding. Besides that, the last flood happened decades ago (1926), so many people didn’t remember that one, so they didn’t expect a flood at all. People believed they were safe, so the floods of 1993 and 1995 came quite as a shock for them. As an emergency response after these floods dikes and quays were constructed very quickly around the settlements in the floodplain, to prevent this to happen again. Figure 3.6 Appeared maximum discharges (m3/s) Borgharen-dorp. In the ninth century, people started to build dikes and quays as flood- Homogenized values show the discharges that would have caused comparable defense. So many centuries ago, people changed the approach from water levels in the current situation. reducing the risk into reducing the chance by building a dike-system (Schrojenstein Lantman, 2004)
37 38 Climate change
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39 4. Climate change
Besides a higher chance of floods because of building in flood- Causes of climate change prone areas in the last century, another process is going on, namely The climate changes because of changes in the different climate climate change. In addition, climate change will have its impact on factors. They can be divided in factors that change the climate over how the rivers will influence the urban landscapes in the future. a long term and over a short time. Examples are the fluctuation in solar radiation and volcanic activity respectively. Neither of these factors can explain why the temperature has risen so much for the 4.1 The process of climate change last 100 years. So another factor was introduced, called humanity.
Since the beginning of the industrial revolution the amount of CO2 The climate is described as the earth’s long term weather patterns. has increased with 35%. This gas is a big contributor to the natural It is an interaction between the earth’s atmosphere (troposphere greenhouse effect. The natural greenhouse effect is caused by gas- and stratosphere), the ocean, the polar ice caps, the land masses ses and clouds that keep solar radiation from leaving the earth’s and the biosphere. Climate change is the process of change in the atmosphere. This keeps the average temperature over the world on weather patterns, caused by a change in the interaction between the mentioned 15oC. Without the natural greenhouse effect, the tem- these factors. The changes of these patterns have always existed perature would be 33oC lower than the current temperature, a very and are part of the natural system of planet earth. For example, cold -18oC. Without the greenhouse effect, life on earth would get in o during the time of the dinosaurs, it was much warmer than the current trouble. CO2 is responsible for 12 C (66%) of the natural greenhouse temperature. The earth has been cooling down since then. effect. An increase in this gas could therefore have a large influence
140.000 years ago a big part of the world was covered under ice on the temperature. CO2 is mainly produced when fossil fuels are and snow. The sea-level was 120 meter lower than the current level. burned, which has seen an increase since the invention of the steam After this ice age the temperature rose again until the last ice age, engine and, later, the combustion engine. (Crutzen et al., 2004)
125.000 years ago, which lasted for 100.000 years. About 12.000 CO2 is not the only reason that the temperature is rising. Because of years ago, the current average temperature of 15oC was reached. the use of a variety of machinery, spray cans, chemical processes Since then this temperature has been relatively constant, apart from and intensive land use all kinds of gasses have entered the atmo- small changes like the warm middle ages and the small ice-age sphere for the last 250 years. The main greenhouse contributors are around the year 1600. (KNMI, 2007b) N2O, NH4 and O3 (Nitrous Oxide, Methane and Ozone). Above these Since the year 1900 there has been a clear increase in the tempera- came the chlorofluorocarbons, which caused the ozone layer to di- ture however. The last 100 years the average change of temperature minish. This caused more radiation to enter the earth’s atmosphere, was 0.6oC across the world (see figure 4.1). The sea level has risen which in turn raised the temperature even more. (KNMI, 2007c) 10 cm to 20 cm and ice caps and glaciers have melted. Moreover, the growing season has increased all over the world. This is going faster than we would expect from historical evidence.
Figure 4.1 Reconstruction of the average temperature on the Northern Hemisphere for the last 1000 years. (Crutzen et al., 2004)
40 Figure 4.2 Global processes and effects of climate change. (UNEP, 2008)
4.2 Global climate changes in the future be kept at the level of the year 2000, the temperature would still rise for 0.1oC per decade. This is a lot faster than the rise of the tempera- When we take the above into account we can ask ourselves two ture in the last 100 years, even when we focus on stopping the rise main questions. How will the climate change in the future? And of GHG emissions. (IPCC, 2007) The rise of temperature has a large when we know that, how will it affect us? First the future scenarios effect on the weather patterns of the world and thus, the climate. It is for the global warming will be described. Later we will discuss the uncertain what the exact effects of global warming are. The system effects of the climate change on the world, Western Europe and the is too complex to forecast this. There are instead different scenarios Netherlands. which give a possible picture of the future climate. All these sce- Since the climate change is mostly caused by the emission of green- narios have many things in common, which we will describe below. house gasses (GHG’s), the future climate is largely dependent on The world will have to face more extreme climate conditions. Parts the scenarios of emissions of these gasses in the future. On top of of the world that are already dry will get drier and wet areas will get that are the “slow effects” of the climate change that will happen be- wetter. As a result of higher temperatures, the sea water will expand, cause of the emission of greenhouse gasses in the past. The emis- causing a rise of the sea level. Melting of the ice caps and glaciers sions of the greenhouse gasses aren’t likely to slow down. In fact, will increase this even more. Weather extremes will also increase in a rise of 25-90 percent is expected. This range is largely dependant frequency. Heat waves and tropical storms are expected to appear on the political course of large countries like China and the USA. more frequent in the areas where they were already present. But it As a result, the global temperature is likely to rise with 0.2oC per de- is very likely that this will also happen in the areas were they weren’t cade. Even when the greenhouse gas and aerosol emissions would seen before.
41 The effects on the ecosystem and humanity are numerous. 4.4 Climate change in the Netherlands • Ecosystems are likely to decrease in biodiversity, as much as 60% in arctic areas for some scenarios. In the Netherlands, climate change is also perceptible. The devel- • Plagues will be more common and disease-spreading opment of temperature is comparable to the rest of the global de- animals will expand their habitats. velopment of climate change. During the 20th century, temperature • Crops will face more difficulties to grow, leading to more has increased with 1oC and the top 10 list of warmest years consists malnutrition and competition over food-sources. complete of years after 1989. The growing season is extended with • The spread of social diseases like HIV are more likely be- one month because of the warming-up. Concluding from the com- cause of increased poverty. position of the Dutch lichens (see figure 4.3), there is a shift from • Higher chance of forest fires, heavy wind, extreme precipita- northern species to tropical species. Also the precipitation in the tion and other dangerous events. Netherlands has been increasing. (Crutzen et al., 2004)
For this thesis the main focus will be on the effects of increased precipitation and sea level rise. Research on poverty and diseases belong to other specialisms.
4.3 Expected effects of global warming in Europe
Like stated before, the effects of climate change are visible in the weather. Europe will have to endure more extreme weather in the future. There is a clear division in the north and south of Europe however. The south of Europe will mostly have to cope with a drier climate. The warm summers will get longer and warmer, with more heat waves. This will result in more problems with the supply of wa- ter and the growing of crops. For the north, a large problem for the winter periods can be expected. The summer periods will get warm- er, but this won’t be a very large problem for most countries. Some people just can’t wait to go to the beach in their own country during the summer, though this shouldn’t be generalized. Warmer periods Figure 4.3 Recent shift of Dutch species of lichens. (Crutzen et al., 2004) in summer, but also winter, cause also for example longer periods of pollinosis (hay-fever). The largest problem for the north of Europe will be the increase of 4.4.1 Predictions for the Netherlands precipitation during the winter however. The effects of the climate change on precipitation will result in longer periods of precipitation With the change of the climate, the chances of having longer peri- with heavier rainstorms. (KNMI, 2007a) Even in the warmer southern ods of precipitation will increase. Also the chances of extreme pre- parts there will be a clear increase in heavy precipitation, causing cipitation will increase. These events both have different effects on problems. the landscape. Extreme precipitation is very local and causes problems for local drainage. Especially urban areas are vulnerable. Streets and cellars are likely to flood when the drainage of an urban area doesn’t have enough capacity to deal with the amount of water.
Effects on the rivers in the Netherlands Longer periods of precipitation cause the biggest problems along rivers. The rivers collect water within their water basin. This causes that the water level of the river rises during these periods of precipi- tation. When amount of water is larger than the run-off of the river, 42 the water will expand beyond its summer bed. In extreme cases it the climate models these have been divided into different scenarios, will even expand beyond its winter bed, which is called flooding. a minimum, middle and maximum scenario. As shown in this table, This is a relatively slow process. First the soil will get saturated with all scenarios predict a higher water level for the Meuse. This means water. Only then, the precipitation will directly flow to the river, which that the current water defenses will not be able to deal with this pre- causes that the river to be filled with water. After the period of precip- dicted amount of water and will be overflowed. The middle scenario itation, the water levels will slowly diminish again as the soil looses is used by the government as the standard for future developments the stored water. and it will be the basis for this thesis. (KNMI, 2006, Ministerie van The primary defenses along rivers protect the landscape against Verkeer en Waterstaat, 2003a) flooding. These primary defenses are calculated for a certain river discharge and the related water level. An increase in precipitation The problems with high water levels can even be larger than a slow in the future will increase these river discharges and water levels. In rise of water levels. When there is a long period of precipitation, many cases this exceeds the design level of the primary water de- followed by an extreme event with extreme precipitation, water lev- fenses, so the chance of flooding will increase in the future. els will rise very fast. During the period of precipitation the soil gets Different institutes have calculated the future river discharges the saturated with water. When an extreme event happens at such a rivers in the Netherlands. In figure 4.4 the predictions can be found moment, the soil can’t slow down the water on its way to the river. for the rivers Meuse and Rhine. Because of the uncertainties within This causes a rapid rise in the river flow rate and water levels. When
Figure 4.4 Future scenarios for the rivers in 2050 and 2100. (Commissie Waterbeheer 21e eeuw, 2000a)
43 this exceeds the maximum capacity of the primary defenses, there is almost no time to evacuate or otherwise prepare for the coming water. A multitude of the floods along the river Meuse was caused by such events for example. (Ven, Van de, 2007)
4.5 Conclusion
The main conclusion of this chapter is that the climate has been changing the last 100 years and will change even faster the next 100 years. The largest problem as result of the climate change in Western Europe is the increase of precipitation during winter. Also in the Netherlands the chance of longer periods of precipitation and more extreme precipitation will increase. Extreme precipitation causes problems for local drainage, particularly in urban areas. Longer periods of precipitation cause the biggest problems along the rivers by higher discharges and higher water levels. When the water levels rise higher than the flood defenses can deal with, floods are the consequence. So because of the climate change, in the future the chance and impact of a flood will increase.
44 Flooding problem of the Meuse valley
5
45 5. Flooding problem of the Meuse valley
We now know the effects that the changing climate will have on designed for and has the current return rate of 1/1250 (Ministerie van the future discharges of the river. In addition, we have data on the Verkeer en Waterstaat, 2005). The water levels are given in meters landscape of Limburg. We will combine this data and extrapolate above N.A.P. for every river-kilometre-point of the Meuse. Since the actual problems that will occur in the floodplain of the Meuse. the water level is given in N.A.P., for the Meuse the water levels are approximately 50 m N.A.P. near Maastricht and 0 m near the mouth of the river. Therefore it’s necessary to deduct the elevation map from the water levels. The points are extrapolated to a grid and the 5.1 Water level prediction projected on the landscape elevation map is then deducted from this grid. This gives the actual water levels at every location along the river. To make sure that this The change of the climate will have an impact on the water levels model is correct, it is compared to the official map of the floodplain in the river Meuse. They are likely to rise because of an increase in of the Meuse. Both maps are comparable, except for the areas that precipitation. (KNMI, 2006) Since the Meuse is situated in a valley, the are protected by dikes, which are left out of the map that is obtained floodplain is likely to expand, compared to the current floodplain. from the government. Areas behind dikes are only flooded on this map when the dikes are not high enough to withstand the water Since the goal of this thesis is to design a more flexible flood levels. protection system, it’s necessary to research the actual floodplain Like already said in chapter 4, the middle scenario of the KNMI will 3 of the river Meuse. The floodplain is the total area that is inundated be the starting point. In this scenario a discharge of 4600 m /s is during the highest possible water level. This area includes the areas predicted. The water levels that are connected to this discharge are that are protected by dikes and other primary water defences, since not available. Therefore, an estimation is made according to the rules 3 these areas are still part of the river system. In case of the predicted of the RIZA, which states that every 100 m /s increase in discharge 3 water levels, the dike will be overtopped and besides that it can fail above the 3800 m /s means 10 cm increase in water level. (RIZA, 3 in many other ways. So by showing how far the water will reach in its 2005) Applying this rule of thumb to the discharge of 4600 m /s, natural way, the actual floodplain will become clear. there is an increase of 80 cm in water levels compared to the 3800 m3/s discharge. Combining this 80 cm with the map of 3800 m3/s in GIS gives the map with the future floodplain of the Meuse for 3 Method of creating high water level map in GIS the discharge of 4600 m /s. Figure 5.2 shows the produced map of To decide what the actual floodplain of the Meuse is, the water levels Limburg with the current and future floodplain. Figure 5.3 is a part of during a 3800 m3/s discharge are put in a GIS program. This 3800 this map and shows the floodplain around the city of Maastricht. m3/s is discharge, which the Maaswerken (see chapter 6.1.1) are
Figure 5.1 Creation of the water level map in GIS.
46 Figure 5.2 High water level map for the valley of the Meuse in Limburg. Figure 5.3 High water level map for the valley of the Meuse around Maastricht.
47 Interpretation of the map 5.2 Categorization of the urban landscapes From these maps, it can be concluded that the floodplain that corresponds to a discharge of 3800 m3/s already contains large On the scale of urban landscapes it possible to make some other parts of the urban landscapes. In case of the 4600 m3/s discharge, conclusions. Not every urban landscape is affected in the same way. even more urban areas are threatened by water of the river Meuse This is largely dependant on the situation of the urban landscape and the areas that will face already water in case of the 3800 m3/s within the valley and the size of the urban landscape. It’s possible to will face higher water levels. divide the urban landscapes into different categories, each with their own set of problems and possible solutions. The figures 5.6 and 5.7 Some other aspects of the river floodplain can be seen within these show these categories for a river discharge of 3800 m3/s and 4600 maps, which will be explained below. Unfortunately, the elevation m3/s. map of Limburg includes the height of buildings. These heights are higher than the water levels and therefore leave holes in the It is rather difficult to give all of these urban landscape categories inundation map where these buildings are located. As a result, it’s names that completely describe the situation and problems impossible to calculate the current and future amount of buildings concerned. This is because they are categorised according to that are threatened by high water levels. at least 4 different criteria; size, water levels, flood defences and Within the urban landscapes some small holes can be seen in the geomorphic composition. To avoid using whole sentences as a inundation maps. These are the houses which show up on the map name for the separate categories smaller less descriptive names because of the way elevation maps are generated. There are also will be used. These names are. some larger holes within the urban landscapes however. These are the higher areas within the floodplain. These locations are mostly Category 1: terrace village - a small town far from used as building grounds for older buildings, like churches, castles river, relatively high situated and old inns. An example is the village of Borgharen. Here, a small Category 2: valley town - a larger town situated tower was built to defend the lords of Venlo against the Vikings. This throughout the valley tower was built on a higher, strategically important point. Eventually Category 3: floodplain village - a small town near river, this tower became a castle and a village evolved around it. The relatively low situated village is lower situated, while the castle still stands higher in the landscape (see figure 5.4). Also these higher situated locations are not high enough to withstand the new water levels however. This is Category 1 – terrace-village troubling, because these old buildings have a high cultural value Urban landscape 1 is situated outside the current floodplain. These and are difficult to adapt. urban landscapes are situated on the higher grounds, outside the reach of any known high water level recorded in history. Because these areas have never been threatened by high water, they were the first areas that were occupied in the past, close to the water, but still safe. This can still be seen from the old houses, fortified farms, churches and castles. The gradient of the landscape was enough to protect against high water levels and therefore no existing flood defenses are present. The gradient won’t be enough to protect these urban landscapes in the future though. The discharge of 4600 m3/s can produce water levels that will reach these places. Fortunately, this will only happen during extreme cases and even then the water levels will be relatively low. Water levels of maximum 80 cm can be expected. Figure 5.4 The castle of Borgharen is higher situated in the landscape than the Nevertheless, this can cause heavy damage to the old houses, surrounding village which have no protection against water. Sometimes these buildings are made of materials like marl, an easy to obtain building material, which will dissolve in water. (Wikipedia, 2008) Therefore these urban landscapes need to be protected and adapted to be prepared for the possible floods in the future.
48 Figure 5.5 Three categories for a river discharge of 3800 m3/s (current situation)
Figure 5.6 Three categories for a river discharge of 4600 m3/s (future situation)
49 Category 2 – valley-town These had some supporting farms and other buildings, but the Urban landscape 2 is rarer in Limburg but has a large influence on floodplain was largely uninhabited. This changed when the human the floodplain and other urban landscapes. It consists of a large control over the Meuse grew. Floods became less common and town which is situated on both sides of the river, running from higher people moved into the floodplain. Little villages developed around grounds, through the floodplain, to the higher grounds on the other the old centres, but they remained relatively small. side of the river. As a result they are a mix of landscape types 1 and 3. This type of urban landscape is completely surrounded by water and Yet, they deserve their own category, simply for their enormous size, cut of from the rest of the world during a flood. Urban landscapes compared to most of the other urban landscapes in the Meuse valley. of this category are the villages that were flooded by the floods of It is assumed that the size of this landscape needs more space and ’93 and ’95. Examples are Itteren en Borgharen. They had a small therefore other measures than in the other two landscapes. Some quay around the village to protect them against floods, but these examples of this category are Maastricht and Venlo. These urban proved to be too low. Since then the quays have been heightened landscapes are among the oldest cities in Limburg, already existing to their current height. These are supposed to withhold the water during Roman times. They are situated in a broader part of the levels until the year 2017. But projecting the water levels for the year valley, where the river floodplain is wider. As a result, the water levels 2100 on this landscape, the possible water levels will be higher than and flow speed diminish, which makes the river traversable. Bridges the height of the quays and the villages will be flooded completely. were built here and cities evolved around these bridges. The cities (Ministerie van Verkeer en Waterstaat, 2005) Since these urban were originally situated on the higher places within the landscape, landscapes lie in the floodplain near the river, the water levels during but eventually grew into the floodplain itself. Nowadays these cities extreme floods can become high enough to reach the second floor completely fill up the floodplain, creating a bottleneck in the river. of the buildings. This creates higher water levels near these urban landscapes and in upstream areas. Category 3B is also located within the floodplain, but further The above mentioned urban landscape is mostly protected by dikes. away from the riverbed. Nevertheless they are largely the same in Where there is not enough space available for the construction of topography as category 3A. What makes a huge difference is that dikes or where they are unwanted because of aesthetic values, they are protected from floods by a single large dike, which also removable quays are used. This urban landscape type has areas functions as a canal for large transport ships. This canal, called that are currently threatened by floods and areas that will be the Juliana canal was built in the beginning of the 20th century. Its threatened in the future. Therefore there will be a large difference function was to make it possible that larger ships could navigate in water levels within this urban landscape during a flood, ranging to Belgium. The Grensmaas can have a very low water level during from mere centimetres to 4 meters. This range in water levels and summer periods. This made shipping to Belgium impossible for a the amount of people living in these cities makes that these urban part of the year. When it was built, the engineers saw an opportunity landscapes are the most threatened areas within Limburg. and constructed the canal higher than the floodplain. In this way, it would function as a dike and would protect several villages behind Category 3 – floodplain-village the canal. Urban landscape 3 is situated in the floodplain of the river. This These settlements of category 3B are thus situated behind a large category is divided into two subcategories. The most common dike, which is unsafe from a flood-risk point of view. But this dike/ category 3A is a single urban landscape, protected by a dike or canal is needed for the transportation of goods to Belgium. This quay. Category 3B consists of urban landscapes that are protected adds a completely different question to the list of questions that by dikes which also have a function as a canal. This is the case involve a more flexible flood protection. This landscape type won’t with the Juliana canal in Limburg. The canal is higher situated in the be addressed any further during this thesis. The geomorphology is landscape and protects several villages against flooding. This is a mainly the same as landscape 3A, therefore the result of 3A can be separate category, because this is a combination the flood defence copied to 3B. The Juliana canal can make some of these solutions and shipping issue. superfluous, but the question of how the Juliana canal needs to work has little to do with the goal of this thesis. Urban landscapes of category 3A consist mostly of a very small old core, maybe with a castle or old inn, and an amount of houses from after the Second World War. The areas of these urban landscapes were hard to live in during the ages. Only a small amount of higher places were available in the floodplain. These were mostly used for their strategic value by the lords, who built castles and towers there.
50 5.3 Conclusion
Like shown in figures 5.1 and 5.2, the floodplain that belongs to a discharge of 3800 m3/s contains already large parts of the urban landscapes that could be flooded. Looking at the floodplain of the 4600 m3/s discharge, even more urban areas are threatened with flooding, because no flood defence is prepared for this discharge. The areas that already could flood in case of a 3800 m3/s discharge will face higher water levels when the 4600 m3/s event happens. Projecting this on the three distinguished landscapes, they al will face more water in the future. The terrace-villages will have to deal with floods for the first time. The valley-towns will face more water in a larger part of the town and the floodplain-villages will face higher water levels; even the highest places like the castles and churches will get in trouble.
After this projection of data on the floodplain of Limburg, we now know the water levels accompanying the future discharges. With this knowledge it is possible to asses flood-resilient techniques. First, these flood-resilient techniques have to be found. This will be discussed in the next chapter.
51 52 Current approach
6
53 6. Current approach
This thesis focuses on the water problem in the valley of the Meuse. the floodplain of the river. The costs of the measures that need to be The large amount of water that is predicted by the KNMI can flood taken to accomplish this are diminished by extracting pebbles and many urban areas in the future and can be life-threatening. So what sand from the undergrounds and selling this as building material. are solutions that can be applied to deal with these predicted high The Zandmaas is the part of the Meuse where the river enters water levels? the lowland of the Netherlands. Here the water stagnates and has deposited sand in the past (hence the name). Because of a geomorphology that is different from the Grensmaas, the measures that can be taken to protect the villages against flooding are also 6.1 Policy and future policy explorations different. The goals are the same however. The focus is at protection of the villages, while incorporating the development of new nature. The waterboards and governments know the predictions of the The last part of the Maaswerken, the Maastraject, involves the whole KNMI and thereby the potential threat. Therefore, they have started Meuse and focuses on the shipping on the Meuse. The Meuse is a different projects and explorations to prevent this life-threatening small river compared to the river Rhine. Big ships like 2-container tow situation from happening. In the next chapters these projects of the barges cannot reach the Belgian city of Liege and other industrial government will be described and discussed. cities along the Meuse. This needs to be changed to satisfy the economical needs of the future. The Maastraject mainly focuses on the improvement of the river and the canals that connect the big industrial cities with Rotterdam and the sea. 6.1.1 De Maaswerken All the different sub-projects of the Maaswerken need to be finished After the floods of 1993, quays and dikes were hastily constructed by the year 2015/2017. After completion in 2017, the urban areas around the floodplain villages in Limburg to prevent this kind of floods should be protected against discharges with a probability larger from happening again. The flood of 1995 hastened this process. In than 1/250 a year, which corresponds with a maximum discharge of 3 1995, it was not only the Meuse that confronted the inhabitants of the 3250 m /s. For the safety of the flood-prone areas along the Meuse 3 river areas with high water levels; the Rhine also caused threatening the rive flow rate has been set at 3800 m /s, which is a discharge situations. After 1995 the government investigated the strength of with a chance of appearance of 1/1250 a year. the dikes and quays along all the rivers in the Netherlands. When (Ministerie van Verkeer & Waterstaat, 2003c) this investigation was finished and new figures of possible water levels were known, the government ordered a new set of measures that should guarantee the safety of the flood-prone areas. For the Meuse in Limburg this set of solutions was called the 6.1.2 Integrale Verkenning Maas “Maaswerken” (Meuseworks). This project focuses on the safety of the urban areas that could be flooded during high water levels of Looking at the climate predictions mentioned before in chapter 4, it the Meuse. The Maaswerken is a package of measures that lowers can be concluded that these predictions show larger discharges than the water level and also compensates negative effects of the dikes the number of 3800 m3/s where the Maaswerken are constructed for. that were hastily constructed after 1993. Besides safety, the project A river flow rate of 4600 m3/s is feasible in the year 2100 and even focuses on the development of nature and the improvement of larger numbers like 5300 m3/s are modelled in an extreme scenario. shipping on the Meuse. (KNMI, 2006) In the Maaswerken project, the river is divided into three different In an effort to deal with this amount of water, the government parts or projects in Limburg: the Grensmaas (Bordermeuse), the has started a new project to investigate the climate change and Zandmaas (Sandmeuse) and the Maastraject (Meusetrack).The its effects on the Meuse. This examination is called the Integrale Grensmaas is the part of the Meuse in the south of Limburg. Here Verkenning Maas (Integral Examination Meuse) and was finished the river is located in a valley and is situated at the border of Belgium and published in 2003. During the search for possible solutions and the Netherlands (hence the name). The river is quite shallow to deal with the predicted amount of water, also the possibilities to here and shipping goes through the Juliana canal. During very hot improve the spatial quality of the valley of the Meuse are examined. summers it’s sometimes possible to cross the river by foot in this Including the national policy to give space for water, in first instance stretch of the Meuse. The Maaswerken project focuses mainly on it’s supposed that dikes and quays won’t be heightened anymore. the development of new nature in this part of the Meuse. Another Integrale Verkenning Maas (IVM) focuses mainly on the answering focus is the protection of some small villages which are situated in of five key questions:
54 1. Is a river flow rate of 4600 m3/s realistic? 6.1.3 Integrale Verkenning Maas 2 2. What are the possibilities of retaining water in France and Belgium? Integrale Verkenning Maas 2 started in 2006 and is the successor of 3. What are the possible river-expanding measures in the the IVM project. Its goal is to, in deliberation with the municipalities, Netherlands and where can they be located? provinces, ministries and stakeholders concerned, come to: 4. How and in which perspective can safety and spatial • A proposal for a multitude of measures that guarantee the developments be integrated? legal flood protection along the Meuse on a long term and 5. What does the content, the procedures and the communication which improves the spatial quality at the same time. following the IVM look like? • An overview of the areas that are needed for the protection against flooding and areas that are not needed for the In short these questions are answered as follows : protection against flooding from the Meuse, in the long Ad 1. If a river flow rate of 4000 m3/s occurs, the flood defences term. in Belgium will be unable to hold back the water, resulting in • A vision on the sequence in which the measures should be an inundation and a lower water level in the Netherlands. It’s taken if the need arises. expected that Belgium will try to prepare the flood defences • A vision on how the areas that are needed for the long term for a discharge of 4600 m3/s, but will be unable to slow down protection against flooding can be kept clear of developments the water or retain it. Therefore the water will flow directly to the that would obstruct this future protection. Netherlands and a river flow rate of 4600 m3/s is realistic. Ad 2. As explained in the answer of question one, the possibilities The measures of retaining water in France and Belgium are quite small and For the measures along the Meuse, that need to be taken in the long will need big measures. This is caused by the high degree of term for flood protection, the following advise was given: ‘The IVM 2 urbanisation along the river and the geomorphologic built-up project supports the findings of the IVM project and advises to reserve of the landscape along the Meuse, which is quite rocky. areas that could be needed for the protection against flooding in the Ad 3. River-expanding measures can be taken upstream and future.‘ In this case, the findings were that the measures against downstream from where the highest water peaks are high water levels should be taken in the winter and summer bed expected. This is why a cohesive national and international of the river. Measures in areas that are situated on the landside of plan for protection against high water levels is needed. the dike should only be taken when floodplain-measures are not Some possible river amplifying measures that are proposed sufficient in the long term. River-widening measures, like lowering in IVM are creating retention areas along the river, removing the river foreland, creating a side channel or high-water trench and obstacles, deepening the summer bed, creating bypasses expanding the summer bed locally, are the main measures that IVM and lowering the river foreland. Some locations have been 2 proposes. Measures along the undiked Meuse have hardly effect suggested, but to make decisions it’s necessary to attune along the diked Meuse. this with the local governments. Green rivers situated on the landside of the dike aren’t proposed, Ad 4. Spatial developments and safety can be integrated. The because they have some significant drawbacks, according to the strategies of the IVM show that a sustainable protection, IVM 2. They cut strongly through the landscape, create isolated without further heightening of dikes and quays, is possible islands in case of high water levels, require adaptation of existing in the Netherlands. Space for the river Meuse will be an infrastructure, require a long track of new dikes (expensive in important aspect in this. More space for the river should be construction and maintenance), are unattractive for the landscape the catalyst for the development of spatial quality. The focus because of high dikes and are not cost effective. should be on the addition of safety aspects in regular spatial Retention areas are only possible in the winter bed of the undiked developments and the other way around. A safe discharge Meuse. Retention areas outside the winter bed aren’t possible, will be the basis in searching for this kind of solutions. because these areas are situated too high. Disadvantages of Ad 5. Shared responsibility of the countries where the Meuse flows retention areas are that these areas claim space of the winter bed, through requires a transgressing approach, which has to which causes higher water levels in case of a discharge with an be given shape, for example within the European Union. appearance chance of 1/250 a year. The subsoil around Roermond Also communication with the region and getting support is consists of gravel, which lets the water through via the under layer important. The project succeeding the IVM is called the IVM2, into the retention area. Retention areas are only effective for the which we will be explained in the next sub-chapter. (Ministerie diked Meuse in case of a discharge with an appearance chance van Verkeer en Waterstaat, 2003b) of 1/1250 a year. This means that they may not be used when the
55 quayed areas along the undiked Meuse will flood, which is difficult as places that could potentially be used for the protection to explain to the affected people. It’s also difficult to use the retention against flooding. The current land use of these areas should areas just at the right moment, because the prediction time is very be maintained and new, large scale developments in these short. areas should be discouraged or forbidden. Deepening of the summer bed is one of the last options, because • The space within the winter bed of the river should be kept this measure generates higher water levels downstream, may lead clear of objects. The Beleidslijn grote rivieren (Line of policy to desiccation, and requires much maintenance. main rivers) could and should be used for this as it is a good Using and heightening dikes and quays should be avoided as much benchmark for new developments in the winter bed. In areas as possible, because they will cause higher water levels when the where no IVM measures are planned, more space should be discharge increases. In addition, the measures that are taken in one used for durable developments. place are not allowed to put pressure on other places along the • The protection level of 1/250 a year near the cities of Maastricht, river. Venlo and Roermond should be re-evaluated. Also measures that are taken along one track to solve problems • A phased approach is advised, incorporating intervals along other tracks, up-stream or down-stream are not wanted. Most between 4200 m3/s to 4600 m3/s. of the parties concerned don’t want measures that aren’t necessary • It’s advised to monitor all developments that could influence for their own protection in their ‘backyard’, the Not In My Backyard the needed space for the flood protection and evaluate them principle. Measures where only the neighbours profit from aren’t that regularly. popular. So every track should solve its own problems. International perspective IVM2 tries to keep the water levels at current dike level. The quays Retention areas only function for areas that are downstream. In of the undiked Meuse should be able to deal with a discharge that case of the Netherlands, these areas should be situated along the appears 1/250 a year, which is 3950 m3/s in the year 2100. The Belgium part of the Meuse. Retention areas are only effective for the protection level of the quays is lower than that of the dikes along Netherlands if they are used in case of a discharge that could lead the diked Meuse (1/1250), because the consequences of a flood of to threatening situations in the Netherlands. Before that moment the low situated polders are much bigger. Nevertheless, in case of a is reached, there will already be floods in France, Wallonia and flood in the quayed areas, the water can still reach the level of some Flanders. It doesn’t seem socially acceptable to ask these countries meters, which can lead to life-threatening situations. IVM 2 already to abstain from using the retention areas for their own safety. indicates that in case of higher discharges, it won’t be possible at IVM 2 concludes its research with a list of advises to the Secretaris some locations along the Meuse to reach the protection level of van Verkeer en Waterstaat (Secretary of state for traffic and water 1/250 behind the quays with river-widening measures only. This will affairs). For the international tuning and possible measures across happen especially near the valley-towns Maastricht, Roermond and the border the following advises are given: Venlo. • It’s necessary for the Netherlands to do research concerning the extreme river discharges of the river Meuse, together with Financial aspect the effects of such flow rates and the possibilities of retaining IVM 2 is about retaining space for future measures, not about the water and where this could be done. For the work that needs realisation of measures that will cost money in the short term. The to be done afterwards there is a need for an enthusiasm on a IVM 2 project concludes that no financial means are needed for the political-governmental level. IVM measures since they involve a long term reconnaissance of • The group of governmental officials currently working on the the possible measures. Therefore it’s not needed to reserve extra tasks at hand should also include servants from the local and finances for possible IVM measures along the Meuse. An estimation provincial governments. It should also include servants from of the costs for the total package of measures in case of a discharge the waterboards. of 4600 m3/s is in the range of 3,6 billion euro, plus or minus 50%. • The minister and secretary of state should support the plan The costs of the IVM 2 measures are four times larger than the “Actionplan High water” from the European Union. This could prevented damage. ensure a better corporation on an international scale. • The river discharge of 4600 m3/s for the year 2100 should Retention of space be maintained as the assumption for the increase in the For the space that needs to be retained for future use against possible extreme river discharges in the Meuse, unless a flooding, the following advises are given: collective, international research can give more insight in the • The IVM project assigned areas on the landside of the dikes effects and achievability of retaining the water in the upper
56 reaches of the Meuse during extreme weather conditions. In storage capacity of the riverbed and to oppose developments that addition, the continuous research concerning the effects of make the creating of space for the river by widening and deepening the climate could give reason to change the given number of impossible now and in the future. 4600 m3/s. The line of policy presumes a responsibility and personal risk • The Dutch government should collaborate with the German for damage caused by high water. Initiators in the riverbed are government to diminish the river flow rate of the small rivers accountable to take measures against potential damage. Users that pour in the Meuse. This could be done by retaining water of the riverbed won’t be able to claim an indemnity from the Wet in the upstream areas of these streams. Tegemoetkoming Schade (WTS) (Calamities Compensation Act). • The corporation between Belgium and the Netherlands (Ministerie van Verkeer en Waterstaat en Ministerie van should be continued with the Vlaams-Nederlandse bilaterale Volkshuisvesting, 2006) maascommisie for the long and short term. The findings from the IVM 2 should be marked as long term plans. • The corporation with Belgium should be improved by copying the bilateral approach with Flanders to the Wallonian part of 6.2 Safety Belgium. (Ministerie van Verkeer & Waterstaat, Rijkswaterstaat Dienst Flood safety has always been important in the Netherlands and Limburg, 2006) plays an important role concerning flood risk management and confrontation with floods. People want to live safe and care-free, The IVM2 project can thus be considered as an number of without any threat from any source. But what is safety? proposals that could improve the safety of the flood-prone areas In case of safety against flooding, safety is about protecting along the Meuse. They are however not obligatory for the province inhabitants and invested capital against flooding and protecting or municipalities. If the need arise, other measures that protect the the community against disruption. In recent decades, the threat inhabitants against flooding could be implemented. of river flooding and damage has made clear that it’s a fact that complete security against floods does not exist and that it is not possible for the government to guarantee complete safety. Absolute safety doesn’t exist, because safety is related to a certain possibility. 6.1.4 Beleidslijn Grote Rivieren This possibility describes the chance that a certain phenomenon will manifest itself. This chance will never become 0%, there will always The threat of floods from the main rivers in 1993 and 1995 have made be some left-over risk. The same applies for the protection against clear that another approach of the space for discharges and storage floodings in the Netherlands. An infrastructure of primary flood of river water is necessary. The river needs more space by widening defences offers an agreed amount of safety against floodings from the riverbed. Only heightening the dikes will not give a sustainable the North Sea, estuaries, the lakes and the rivers until the agreed solution for the future, considering the climate change which will chances of reoccurrence, the normative conditions where the flood bring more wet winters. A new kind of measures is needed: the river defences are designed for. There will always be a chance that an has to get more space, for example by shifting dikes or lowering the extraordinary event will occur. (RIVM, 2004) floodplain. It is also necessary to make policy for spatial interventions in the riverbed, like building, living and recreation. These activities have to be judged if they lead to higher water levels. Because of this new approach, the line of policy Ruimte voor de rivier 6.2.1 Policy of safety (Space for the river) has come into being in 1996. In principle only river restricted activities are allowed in the riverbed; other activities Flood risk management is an important issue for the Netherlands. are only allowed in case of strong social interest. One third of the country needs artificial protection against floods from the sea or the major rivers. In the past few hundred years, we In 2005 this line of policy is evaluated and after that a succeeding have learned to protect ourselves effectively with dikes against high line of policy is made, called the Beleidslijn grote rivieren (Line of water. Dikes are our basic safety system against flooding. Around policy main rivers), which replaces the line of policy Ruimte voor de 1000 AD people started building dikes around their belongings and rivier. Starting point of the Beleidslijn grote rivieren is guaranteeing in 1400 an almost completely closed dike system existed along the a safe discharge of river water by normal and high water levels. The rivers. goals of this line of policy are to keep the available transport and In the past, after a flooding, dikes were heightened a little bit above
57 the latest known water level. Structural measures were only taken to offer up their land for the sake of the community. And since, they after a big disaster. In 1953 a major flood from the North Sea killed already felt safe, they don’t see the need of these space demanding 1835 people. This flood forced the government to generate new measures. regulations for safety for the coast, but also for the river areas. The trust of the Dutch people in the water managers is of such an Until that flood, dike heights were based on the maximal recorded extent, that they have the idea that management of safety can be water level. But after 1953, a more scientific approach was used. left completely to these water managers. People think that it’s well The optimal level of safety was defined as the accepted probability organised and so they don’t know much about water management. of flooding for the different areas in the Netherlands. To make this The average Dutch person isn’t well-known with the organisation norm usable, it was simplified to the demand that dike levels should behind the water management. They often don’t know what exceed water levels related to a discharge with a chosen return time. waterboards are, or what their tasks and competences are. Dutch In the 70s the river commissions Becht (1977) and Boertien (1992) people incline towards a government that organises everything defined norms for the flood defences along the rivers. One safety concerning water policy and do hardly anything with protective level was chosen for the whole diked area that was threatened by measures that can be taken by themselves. river floods: the discharge with a probability of once in the 1250 year. Nevertheless, inhabitants of the Netherlands think that it’s important This norm is based on the fact that sweet water gives less damage that sea defences and dikes along rivers are safe. More than 75% than salt water. In 1996 the government fixed these norms in the law of the inhabitants of the river areas expect that the problems with on the flood defences. Flooding by other causes than overtopping high water in the future will increase if measures will not be taken of dikes and uncertainties in nature and in the calculations were and 92% of these inhabitants think that big measures have to be considered by adding 0,5 meter to the required height and some taken instantly. People believe that the protection against the sea regulations for the design of the dikes. by the government is better organised then the protection against Every five years the design discharge is recalculated, based on floodings of rivers. the recorded discharges. In addition, every five years it is checked The experience of safety against flooding by inhabitants of whether the dikes meet requirements, because of possible changes the Netherlands differs strongly per region. People have more in hydraulic conditions, like possible discharges, height of waves, consciousness about risks when they have experienced a flood or etc. If they do not meet the certain requirements, measures will be evacuation. Before the water problems of 1993 there was a feeling taken like the Deltaplan grote rivieren and the plan Ruimte voor de of safety. Ninety percent of the inhabitants felt safe behind the dikes rivier. After finishing the measures, the flood defences should be in the river areas. In general inhabitants were not really familiar with tested with the hydraulic preconditions of that moment. It could the height of the real chances of flooding of 1/50 or 1/100. be possible that these preconditions have to be changed during In the whole river area, people who live in the winter bed are better the realisation of the measures. Therefore it is impossible to state known with high water levels than people who live behind the dikes. that the flood defences along the main rivers will meet the certain In 1995 that threat of a higher water level made more impression requirements after finishing the measures and plans like mentioned on inhabitants who hadn’t been living there for several generations. before. Inhabitants that had been living there for their whole life and whose (Bruijn, De & Klijn, 2001) parents lived there, had a strong connection with the area, and had learned to live with the risks so they could take the right measures. Inhabitants along the main rivers feel less safe than inhabitants along the coast, the IJsselmeer or even in the down stream areas. But even 6.2.2 Safety in daily life between the different rivers there is a difference in experience of safety. Nevertheless they think that risks of flooding are smaller risks than Experience of safety risks in traffic, by criminality, health, unemployment and the weather. Apart from the cold and hard numbers of safety, which are used by In their opinion, it is also more important that the government invests the government, there is the actual feeling of safety, experienced in social certainty, health care and fighting crime. (RIVM, 2004) by the people. Experience of safety and the risk of flooding differ strongly per country. In countries like the Netherlands, where risk Insurance management clearly is institutionalised, inhabitants don’t care One of the ways to increase the feeling of safety is by granting about it. An average Dutch person feels safe and has big faith in the insurance for certain disasters, in this case: floodings. Of all natural water manager. He understands that water resistant measures are hazards encountered in the world, floods are the most frequent, necessary, but measures that give the water more space, will not cause the largest number of deaths and generate the largest automatically get support, because land owners, often farmers, have economic losses. That’s why the insurance industry has great
58 reserve and caution when granting insurances for flood damage or 6.3 Flood chance and flood risk has refrained from offering insurances altogether. But, people living in regions affected by floods may acquire financial security against After the flood disaster of 1953, the government realised that floods risks, and ask for compensation in case of a flood. heightening dikes after a flood occurred was dangerous and that another approach was necessary. The approach became more This is a case of both the government and the insurance industry. focused on the future by starting to work with probabilities and For the state because the demand for compensation in case of a chances. Like mentioned before, the dimensions of safety are disaster is always high and cost sharing by the total society could expressed by the chances of a threat. Nowadays policymakers work be the solution. Yet, the loss potential can be very high and the state mainly with chance to define the criteria for protection against floods. does not wish to provide full coverage for potential losses. Moreover, This is the chance that during a certain year the dikes will not be high repetition of a disaster can lower the willingness of the society to enough and water will flow over them and flood the areas behind compensate. the dikes. The waterboards, and other governmental institutions The insurance companies are also not in a position to provide that are concerned with flood defence, also use flood chances and coverage for this problem. In the Netherlands, it is not possible 94% of the Dutch safety is defined in this way. But there are some anymore to take an insurance against the consequences of flooding consequences of using flood chance. since the flood of 1953, because after the event it was realized that insurance companies can become bankrupt if they continue to cover While flood chance gives a workable prediction of how often an area the flood damage. At this moment, no insurance company offers will flood, it doesn’t incorporate the actual risk of flooding. Flood risk standard compensation of flood damage. Only flood damage of works as an equation between flood chance and vulnerability of an content and dwellings, caused by local heavy rainfall, not by failure area during a flood: Risk =Chance x Vulnerability. Vulnerability is of flood defences, can be insured. how much an area can potentially be affected by a flood in the sense Other ways in which flood coverage could be granted include of economic damage and damage to human lives (lethal and non- international insurance companies and reinsurance companies. lethal). Many factors affect this vulnerability, for example the value of These work over a very large area with more insured people. Therefore the area, the amount of people, the resistance of the houses but also they have more money available and they are able to spread their the time the area is flooded and the amount of evacuation routes. chances over a large area. It should be noted however that these The result of the equation is a number and the higher the number, solutions only minimize the negative effects of flooding; they don’t the higher the risk of flooding. Actual numbers of the flood risk of an take the actual threat away. area are hard to get and time consuming to calculate, because of the many factors involved and their interactions. Nevertheless, such All losses caused by the river floods in the Netherlands are therefore calculations do give a better view on the measures that are needed uninsured. Especially the high water levels in the Meuse in 1993 to protect the inhabitants of a threatened area. and 1995 inflicted considerable damage on the properties in the When the flood chance for an area protected by dikes is calculated, lower parts of the valley. These properties were not insured against the chance is the same for the whole area. An urban area has the floods, because the Dutch insurance industry excludes flooding same chance of flooding as a meadow or a nature park when they from rivers or the sea. In the end the government decided to cover are protected by the same flood defence. When we look at the flood the losses fully. So in fact the owners were compensated by the risk of an area, there is a clear difference however. Since the risk of Dutch taxpayers. an area also incorporates the value of an area and the people that In 1998, the Dutch government has chosen to create compensation live there, the urban area has more risk of flooding than the meadow rules by law. In January 1998, the Wet Tegemoetkoming Schade or the nature park. For example, the EU states that a human live (WTS) (Calamities Compensation Act) came into existence. In this is worth one million Euro for the sake of calculations. The village act it’s stipulated that under certain circumstances the state pays may hold 500 humans while the agricultural area may only hold 20. compensation for loss or damage, caused by natural catastrophes, This raises the flood risk of an urban area drastically compared to which cannot to be insured. But floods from the sea are explicitly the agricultural area, even though they have the same chance of excluded because of extremely high potential losses. flooding (Raad van de Eurpese Unie, 2003) (Duin, Van & Mesu, 1995) (Kok et al., 2003) Another consequence of using flood chance is that it creates a paradox. When an area has gained a higher chance of flooding, the measures will be aimed at lowering the flood chance to an acceptable level. On first sight, everything is safe enough then. The
59 chance that an area could be flooded will be the same again and the people behind the dikes should be safe. There is however a paradox in this. When the area is reasoned to be safe for living, more people will build their houses and companies there, followed by all kinds of other valuable developments and visa versa. Looking at the risk of this area, it’s clear that the actual risk of flooding has increased, because the vulnerability has increased. More people and houses mean more value. (Neuvel, 2007) And If the value behind the dike is increased, the height of the dike should be recalculated and heightened until a level that the area is reasoned to be safe again. In this way the circle goes round and round (see figure 6.1). This is what happened the last decades. The areas behind the dikes and quays have been used more and more intensive and more houses and companies have been built. The population need more Figure 6.2 Risk increases with a higher dike houses and large investments are made. Because of this, the flood risks are increasing and the effects of an eventual flood will be large. heightened. When this dike is heightened to e.g. 9 meter, the chance If a dike would breach, the economic damage will be immense. will be again 1/1250, so the area behind the dike is reasoned to be safe again. In this way the chance is the same after adaption of A third consequence of using flood chance is that using flood chance the dike. From a risk point of view, there is a difference however. focuses on flood prevention. Flood prevention can however raise In comparison, the overflow of a 5 meter high dike will cause less the risk of an area. An example will explain this. When a dike along damage than a 9 meter high dike. Because of this, it is actually a river of 5 m high and designed for a 1/1250 chance is threatened possible that the flood risk of an area increases when a dike is by overflowing because of higher water levels, it is adapted and heightened.
Figure 6.1 Paradox of heightening dikes
60 Last, flood chances automatically assume that all dikes and quays groundwater is the eroding of materials from the core of the dike. are in optimal condition and won’t have any problems in resisting Another manifestation of micro-instability is instability of the top layer the water, so failures aren’t incorporated. During the last centuries, because of a high phreatic line in the dike. dikes have been the main tool to protect the land against floodings Micro-instability and instability because of infiltration and erosion by reducing the chance of it. And if they would not have been there, seem more or less the same, because they both appear on the many floods would have plagued the land and large parts of the inside slope. The difference is that in case of micro-instability the Netherlands would have looked a lot different from their current water has streamed through the dike and that it seeps from inside appearance. But there are also examples from the past, where it went to outside and that in case of infiltration after overtopping, the water wrong and great damage was the result. When a dike breaches, an infiltrates from outside to inside. area can fill up very fast because of the pressure of the water held 8. Instability of covering. The covering of the outside slope gives back by the dike. These forces are also capable of causing great protection against erosion of the dike body. The covering can give damage to buildings and infrastructure. way by wave attacks, after which the waves can attack the core of Dikes can fail because of several reasons. Nine mechanisms of the dike directly. failure of dikes and dams are explained in figure 6.3. 9. Instability of the foreland (gliding and liquification). When a 1. Overflow and overtopping. The failure mechanism of overflow forebank is constructed of weak clay- and peet layers, or sand that appears when the calm water level is higher than the top of the is soak-sensitive, big shifts could happen and liquification of the fore dike. Overtopping is the mechanism where the water defence fails bank, with possible influence on the safety of the water defence. In because waves reach over the top of the dike, even though the case of liquification, the mass of saturated sand is shifted because water level is lower than the height of the dike. When designing and of soaking. testing, overtopping will be the normative demand. This overtopping (Ministerie van Verkeer en Waterstaat, 2004a) can make the water defence fail in two ways. First the covering of the top and inside slope can fail; second the situation will get out of control by high water. 2. Instability caused by infiltration and overtopping. In case of overtopping, the water will infiltrate in the top layer of the inside slope of the dike. Because of this, a full infiltration zone will be created, in which tensions of granules are low and because of that also the resistance against shifting. At the same moment, the weight and volume remain the same, causing the driving force to be high. Both effects have a negative influence on the stability of the top layer. Instability will appear by transformations and the appearance of cracks parallel to the top of the dike. Cracks as a consequence of infiltration will stimulate the process of erosion. 3. Piping. A seepage stream in case of (longer periods of) high water levels takes too much soil elements from the underlying soil layers, which causes loss of stability. 4. Heave. This can appear in situations in which a concentrated vertical seepage stream appears. Heave is the forming of quicksand in case of outgoing vertical groundwater, for example, behind a seepage screen on the inwards side of a dike. 5/6. Macro-instability inwards and outwards. Macro-instability inwards is the shifting of big parts of the earthen body. This shifting happens along curved and straight slide-surfaces or plastic zones, in which no equilibrium of forces exists anymore, because of overburdening. 7. Micro-instability. This is the loss of stability of soil layers with a very small thickness at the surface of the inside slope, influenced by groundwater that streams through the earthen body. One of the manifestations of micro-instability caused by streaming
61 Figure 6.3 Failure mechanisms of dikes (Ministerie van Verkeer en Waterstaat, 2004)
62 6.4 Conclusion & discussion of the approach of situation. Besides that, dikes can fail in many other ways than just nowadays overflowing.
The water problem in the valley of the Meuse has mainly to do When an area has got a higher chance of flooding, for example with safety levels. Like already said, absolute safety does not because of the climate predictions of the KNMI, measures are taken exist, because it is related to a certain possibility; in this case the to lower the chance. Often these measures mean heightening the possibility of a higher river discharge than the water defences are dike, which in our opinion does not create more safety. Heightening designed for and thereby the possibility of failing of the dike system. the dikes raises the risk and thereby increases the pseudo-safety. A more scientific approach has been added to this system after the People think they are safe again after a heightening and strengthening major flood of 1953, which introduced the chance of appearance of of the dike, but if it goes wrong, they are eventually more vulnerable a flood-event as safety-norm. than before. Like said in chapter 6.3, using flood chance has some consequences. Heightening the dikes to reduce the flood chance also creates an By using chance as starting point, risk is left out of account. From undesirable paradox. When dikes are heightened, people start our point of view, this is a wrong presentation of reality. Flood to build new buildings, because the area is reasoned to be safe. chance only shows how often a flood could happen statistically and But when the amount of capital increases (new buildings and their the possible consequences of a flood are left out of account. Also content plus more human lives), the height of the dikes have to be vulnerability should be incorporated in the considerations of how recalculated and so the circle goes round and round. This cannot be should be dealt with the threat of a flood, so the real risk for an area done endlessly, because dikes will get such a size that is not practical is known. Focussing on the risk that an area has to deal with should anymore, but also aesthetical not acceptable. By heightening the be the starting point. dikes, the paradox process is kept running and even enhanced. Therefore, from this point of view dikes should not be heightened. Besides the fact that possible consequences of a flood are not considered, the current dike-system, which is based on the chance- Therefore, the use of the current dike-system does create pseudo- reducing principle, does create a pseudo-safety in different ways. safety, which is really undesirable in our vision. The use of flood In the experience of safety of inhabitants it must be said that small chance focuses on flood prevention, which can raise the risk. We chances for disasters don’t say anything. When chances exceed the think the focus should be on reducing the vulnerability and thereby reoccurrence-rate of 1/100 years it will be seen as “this will not happen the risk. In that way the focus should not anyhow be on protection in my life, even not in that of my children”. It is difficult to explain that against a flood, but more on ‘enduring a flood’. this is the reoccurrence rate of a normative event. The chance that this event will occur is 1% every year. This event gives a certain water Preventing floods in the valley of the Meuse level, for which the dikes and quays are constructed. The problem In Limburg, many dikes and quays were constructed to reduce the with this way of reasoning is that people don’t realise enough that chance of flooding after the floods of 1993 and 1995.These dikes 3 it is about a chance. This means that theoretically and statistically are designed for a volume flow rate of 3950 m /s, calculated to speaking, a flood could happen once in a certain time period, for appear once in the 250 years. But looking at the predicted climate 3 example 1/1250 years. This doesn’t mean that once an event has change for the year 2050 and later, a discharge of 4600 m /s or even occurred, it won’t reoccur for 1249 years. Although the chances are more can be expected (see chapter 4 for the KNMI predictions). low it might happen next year again. It could even happen for 4 Consequently, the question rises: How should safety be guaranteed or 5 years in a row. It is like throwing a dice. The chance that you when taking these predictions into account? throw a four is 1/6. Let’s say the first time you throw that number four, then the next 5 throws won’t automatically be something else. The Dutch government is trying to get insight in how can be dealt with The second throw could also be a four and the third one too. But the predicted amount of water in the Netherlands. After the floods theoretically it’s also possible that you will not throw a four for weeks. of 1993 and 1995 the Maaswerken project is started, which has to So, event chances are merely a norm for the height of dikes, they be finished in the year 2017. This project is already a contribution don’t say everything about when the dike will be overflowed. This is to lower the water levels to deal with a higher discharge of the already shown in the past by the floods of 1993, 1995 and the high Meuse. But the focus of the project is on the near future, to make water of 2003. Statistically these events would appear 1/50 until 1/75 the valley of the Meuse prepared for discharges that can appear a year, but in reality it happened three times within 10 years. already nowadays. So it’s a project that is necessary for the safety Another aspect that creates pseudo-safety is that the dikes are of nowadays, but it doesn’t incorporate the predictions of the KNMI reasoned to be in optimal condition. But this is not always the real for the year 2050 and 2100. Besides that, the Maaswerken project is
63 based on the current dike-system, which is a system that is already could turn into a WIMBY (Welcome In My Backyard) or even PIMBY discussed above. The Maaswerken project even raises the risk and effect (Please In My Backyard). pseudo-safety by heightening and strengthening the quays and dikes along the floodplain villages. It’s understandable that the application of a measure in the urban landscape, in the way it’s applied outside the urban landscape, Integrale Verkenning Maas would give problems. But this should not be a reason to state that Because the government realised that the Maaswerken won’t be this measure should not be used in the urban landscape, give up sufficient to deal with the predicted discharges in the future, they the idea and state that the people of Limburg should get used to wet started a reconnaissance to investigate the possibilities to deal with feet. It is a reason to state that these measures have to be adapted these predicted discharges. This resulted in the IVM, later followed to the urban landscape and visa versa. There are many aspects of by the IVM 2. measures that deal with floods, which could be used to enhance IVM 2 strongly recommends cooperation with the countries that are the urban landscape. For example people like to live near water situated upstream. We subscribe to this cooperation with Belgium or (urban) green. The implication of flood resilient measures gives and France, which is difficult but necessary, but it’s not possible to the opportunity to redesign large parts of the urban landscape to assume that everything will be solved upstream. So we must take produce an improved one, thereby reducing the NIMBY effect and our own measures in the Netherlands, in a way that it functions. guaranteeing the safety of the inhabitants, or at least reducing the life-threatening situations that could appear. It’s also good to realize The IVM 2 project tries to solve the high-water problem by applying that there is a lot of time to implement the measures. many measures with relatively little effects. It does not want to solve it on the landside of the dike. As a result the whole floodplain is divided Another aspect of the IVM is that it tries to lower the chances of into smaller parts by the presence of cities and dikes. Therefore less flooding. Actually, it tries to maintain the 1/250 chance per year of space is available for measures that could be taken in the floodplain. flooding in case of higher discharges. This chance is set at 1/250 When urban landscapes are also added to the space that could be per year, unlike the other parts of the river areas of the Netherlands, used for solving the high-water problem, larger and more efficient where it’s set at least at 1/1250 per year. In the IVM is already written solutions will become a possibility. IVM 2 already states that it will that when the 1/250 chance is exceeded, life-threatening situations be impossible to solve the problems around the cities of Maastricht, may arise. Besides that, the Deltacommissie states in their advice Roermond and Venlo within the summer and winter bed only. This that these chances should be multiplied by 10 to create a realistic shows that urban landscapes might actually be needed to solve the safety level. (Deltacommissie, 2008) Like already stated before, high-water problem. it’s not just the chance that should be lowered, but the risk. In that perspective, the IVM project doesn’t have the right focus. It works Some solutions that are mentioned in the IVM 2 project are already with the chance-reducing dike-system and therefore continues the rejected by IVM 2 because of the drawbacks. The mentioned pseudo-safety. In our vision there should be much more attention for drawbacks for retention areas concern the technical aspects of lowering the risk and therefore the vulnerability, instead of chance constructing retaining areas. Many preconditions for the construction only. of retaining areas aren’t present in the valley of the Meuse, because of the geomorphologic build-up, so it will indeed be hardly possible Another approach to retain water along the undiked Meuse. Like explained before, using the traditional approach of heightening But the mentioned drawbacks for other measures outside the the dikes would type to a further increase of the risks. Dikes cannot be floodplain, for example the green river, are of a different nature. heightened endlessly. Therefore we plead for a different approach. Instead of technical drawbacks, they are more concerned with the Dikes should no longer be seen as the most important and only resulting landscape after a green river has been realized in an urban option for gaining security against flooding. There are already some landscape, for example the appearance of isolated islands in case examples where people started to change their thoughts. of high water levels. Instead of a new round of heightening the dikes, the RiversandLand Another, more general, drawback is the appearance of the NIMBY concept is chooses to realise safety against floods by giving the effect, resulting in a large public resistance against measures that river more space. The concept RiversandLand strengthens the could be taken in or by urban landscapes, because nobody wants to population’s awareness of the value and dangers of water. Water take measures for the profit of neighbour settlements only. However, becomes once more an accepted part of the inhabitable environment. many of these drawbacks could be neutralized or even turned into The direct proximity of water at the same time heightens alertness advantages for the urban landscape. In that light the NIMBY effect for its power and dynamic nature and this alertness will lead to a
64 robust flood safety consciousness. (Road and Hydraulic Engineering 6.5 Hypothesis and research question Institute, 2001) In addition, the waterboards that are responsible for the construction The previous sections sufficiently asserted why the current chance- and maintenance of the dikes that currently protect the inhabitants reducing system is not properly capable to guarantee the safety of of the areas near the Meuse from potential floods, are widening their the inhabitants of the Meuse floodplain. focus. The dikereefs of Limburg have stated that Limburg should get At this point we would like to repeat the goal of this thesis: exploring accustomed to wet feet (De Limburger, 2007). They do not think that other ways of dealing with floods within the urban landscape than heightening the dikes is the solution for the coming water problem just heightening dikes. Base for this exploration will be the concept because of, for instance, aesthetic and historic-cultural reasons. of resilience. The essence of the concept is that the water will not They base their beliefs on the fact that many people object to the be kept behind dikes, but that it will react in a more natural way and heightening of dikes. People object to the destruction of old houses return to an equilibrium by itself. Not fighting against the water by for new dikes and seem to think that high dikes are a sort of visual heightening dikes, and by that reducing the chance of flooding and pollution of the landscape. The main reason of the dikereefs is increasing the vulnerability and the risk, but by living with the water. however, the fact that heightening the dikes creates a false sense of The goal of this thesis is therefore to show how urban landscapes security, because a flood is always possible and the results only get along the river Meuse in Limburg could become more flood-resilient, worse when you heighten the dikes. Their message is clear: explore while keeping them functioning and attractive. We think that this is the range of other solutions for the water problem in Limburg. possible by using techniques that lower the vulnerability of important objects or that guide the river through the urban landscape. Therefore the hypothesis of this thesis has become:
The vulnerability of urban landscapes along the Meuse in Limburg can be lowered by making them more flood-resilient with the use of innovative techniques, thereby reducing flood risk.
The research question for this thesis runs as follows: What are appropriate techniques that can contribute to more flood resilient urban landscapes along the Meuse in Limburg, taking the predicted raise of potential water levels into account?
Sub-questions that will be used during the research are: • Which innovative techniques can be used in the specific landscape of Limburg? • How can these measures be implemented while keeping the urban landscape liveable, or even improving it? • How could this transformation be realized in time?
In our search for how urban landscapes can be made more flood- resilient, we expect that it is possible to use the public realm for the implementation of innovative techniques. For example parks and squares are expected to function as retaining areas and streets as bypasses.
65 66 Flood-resilience
7
67 7. Flood-resilience
This chapter will discuss the theories and techniques behind the flood- resilience concept. It is a new way of looking at the flood problem, but it has its roots in very old techniques. Instead of focussing on the prevention of floods, it focuses on enduring the flood itself. The flood-resilience concept will be explained further below.
7.1 The origins of the resilience concept
Since flood-resilience is a new concept, there is not much literature on this subject. It is therefore necessary to study the origins and of the resilience concept to create a good definition of flood-resilience. Afterwards we can link the concept to the flooding problem.
The areas that are part of the floodplain of rivers are considered to be dynamic systems in ecological terms (Environmental Data Compendium, 2006). Within these systems the rivers cause a lot of periodic disturbances during river floods. These floods kill many of the plants and animals. Furthermore, they change the landscape, sometimes quite drastically. Nevertheless, the ecology within these dynamic river systems seems to be quite stable. Plant and animal populations are almost never wiped out by floods; they only suffer Figure 7.1 Returning of a system to its equilibrium after a disturbance. some minor regression on population scale. This amazed many of the ecological researchers in the 70’s and 80’s. It eventually became The normal state of a system is at the bottom of a ‘valley’. A one of the main questions during this period. How can it be that disturbance gives the system a push, increasing the instability and these complex ecological systems are so stable and persistent? the state of the system, moving it sideward in the graph. Eventually Holling introduced the concept of ‘resilient systems’. He states that this process slows down and stops. Then it slowly goes back to the the most essential feature of ecosystems is that they recover from original state. disturbances. This recovery means that the principal characteristics This brings us to the third way a system can react to a disturbance. of the system are restored, not that the exact same situation returns When the disturbance is big enough to push the system over a certain again. (Holling, 1973) threshold (the tops of the valley in the figure), the system moves into the next ‘valley’. This means a total change of the system. An In current ecological research there are two different definitions of example would be the addition of a large dose of nutrients to a pond. resilience. We will explain them by looking at the ways a system can One of the effects will be the expansive growth of algae. Most of the react to disturbances. There are four different ways a system can fish and plants will be killed by the effects of this growth, effectively react to any disturbance it encounters: destroying the existing system of grazing fish and food-producing plants. Yet, a new stable system may eventually come into being, 1. The system does not react in any way. with many algal blooms and some algae eaters. Another example of 2. The systems reacts but returns to the equilibrium state where this could happen would be a very fragile system, with only a 3. The system reacts and returns to another equilibrium state very shallow ‘valley’. In such a case only a small disturbance would 4. The system does not return to any equilibrium state. be required to move the whole system into a new equilibrium in the next ‘valley’. There are even some cases known where the equilibrium In the first case there is no apparent reaction to the disturbance. An is situated at the top of the figure, just between two “valleys”. Such a example is the tidal effect on the coast. Many plants and animals system would be very fragile and just a small disturbance is required endure the changes in water levels and the impact of the waves is to send it off into the next valley. Such cases are mostly very short- like we would endure a sunny day in June. lived and are mainly the result of a previous disturbance that has In the second case the system endures the disturbance and takes sent a system out of its equilibrium. After this disturbance it came to some damage, but eventually returns to the equilibrium state. This a rest at the relatively flat top of the figure. process of returning to an equilibrium is illustrated by figure. 7.1 The fourth way of reaction is when, after a disturbance, no equilibrium
68 arises again. This is mainly the case where a rare and highly destructive Dynamic flood plains event takes place. An example would be the eruption of a volcano. As stated before, river landscapes are dynamic in nature. Resilience The magna would eradicate all life from the surrounding landscape, is the way nature tries to survive in these landscapes and therefore completely destroying the existing ecological system. Some plants it might be useful to look into this strategy. The floodplain and its and animals may survive, but they will be greatly hampered by the systems will be explained more extensive below. event, resulting in plagues or shortages. Eventually the landscape The earth functions as one big ecological system, but within this may be repopulated by different plants and animals from other system, smaller systems can be categorized. One of the most systems, but it is highly unlikely that the original system affected by basic categories is the division between stable (low dynamic) and the volcano will be able to get back into equilibrium. It is more likely dynamic (high dynamic) systems. Stable systems tend to have little that a new system comes into being. (Bruijn, De , 2005) influences from the external sources (weather, floods, landslides, etc.). Dynamic systems however are situated in areas where there is These four cases involve a static starting situation or equilibrium. In much influence from external sources, like steep mountain ranges real live however, systems are rarely static. They change constantly (landslides) and floodplains (floods). (Holling, 1973) due to influences from both outside and inside the system. The floodplains near rivers are categorised as dynamic systems. Therefore, systems won’t have an exact equilibrium state to return The yearly return of the floods drastically affects the surrounding to after a disturbance. A natural system needs to have some kind of landscape. It changes the position of the river bed, it covers large stability or stabilizing process to recover from disturbances and to areas with sediment and it kills many plants and animals. Yet, most persist. (Holling, 2000) But it is important to remember that resilient animal and plant communities are adapted to this dynamic nature systems don’t return to a pre-disturbance static equilibrium but to a of the landscape. This can clearly be seen in the way plants grow pre-disturbance pattern of development. A system might look very and reproduce. They show the characteristics of so called “pioneer- different after a reaction to a disturbance, but the system would also species”. Examples of these characteristics are the fast grow rate look different from the original because of its internal processes. For and the area that their seeds cover. Figure 7.1 Returning of a system to its equilibrium after a disturbance. example, when a flood occurs at the end of the summer it would be Originally most of the areas along the rivers in the Netherlands strange to expect it to return to its summer state, since it would be in could have been categorised as high-dynamic river landscapes. an autumn state during normal times. The landscapes are characterised by their marshes, swamps, wet grasslands and wet forests. The influence from the river was clearly Taking the above into account, resilience can be defined in two noticeable in these parts. The water from the river could reach the different ways. complete floodplain and many parts were completely flooded for at 1. Resilience is the ability of a system to maintain its most least 20 days every year. (Bal et al., 2001) important processes and characteristics when subjected to This changed when the industrial revolution began. Since 1850 the disturbances. (Holling, 1973) high-dynamic ecological systems along the rivers in the Netherlands 2. Resilience is the ability of a system to return to its equilibrium have declined drastically. With the building of dikes and other flood after a reaction to a disturbance. (Begon et al., 1996) defences the floodplain was effectively cut off from the river. This has resulted in a slow transition from high to low-dynamic ecosystems In the first definition, resilience is measured as the magnitude of the along the rivers. (Environmental Data Compendium, 2006) These disturbances a system can absorb before it changes its characteristics low-dynamic river landscapes are characterised by their stagnant and processes. In the before mentioned cases, numbers 1 and 2 water, dry grasslands and semi-wet forests. If the area is flooded, it’s would be resilient. Case 3, where another equilibrium than the one only for less than 20 days every year. (Bal et al., 2001) before is achieved wouldn’t be resilient by this definition. Case 4 will never become resilient, whatever definition is used. This recent transition to a low-dynamic river landscape is not The second definition mainly focuses on the ability of a system to irreversible however. As soon as the influence from the river is return to a previous equilibrium. By this definition only case 2 could reinstated, the river landscape will return to a high-dynamic river be called resilient. Case 1 doesn’t react to the disturbance and thus landscape. Although this may take some time, depending on many is not resilient but resistant. Most researchers who use this definition factors like the size of the river and how long the landscape has been measure the resilience of a system by the time it needs to return to low dynamic. Depending on the starting state of the river landscape, its equilibrium. For the research of this thesis it is needed to make it may take between 300-1000 years to recreate the high-dynamic a decision about what our definition of resilience will be. But first it landscape. With the use of technical measures this time can be will be explained why the resilience concept is legible to use in the reduced to 25- 100 years. Meuse valley.
69 Humans in a dynamic flood plain 7.2 Flood-resilience Humans have been living in the vicinity of rivers for a long time. When we look at the measures that haven been taken to prevent Flood-resilience is just one of several ways people can cope with flooding of their investments we can see a clear tendency in the way floods. First a division can be made between pre-flood measures people set up their prevention. In the beginning, when investments and event measures. Event measures are taken during or after a were low and technology was crude and primitive, people tried to flood such as evacuation and the placement of sandbags. Since this protect their investments with small scale interventions, focussed on thesis focuses on preventing the need of these measures, they are the survival of floods. not discussed any further. Pre-flood measures can be divided into Later, when technology advanced and more people occupied the physical measures and policy measures. Physical measures focus same region, it became logic to work together and create bigger and on changing the landscape in such a way that a flood is prevented better flood defences. Interestingly, this is the point where the focus or controlled. Policy measures focus on planning, financial and changed from the survival of floods to the prevention of floods. More communicative aspects of flood protection. As landscape architects, and more the rivers were forced into more narrow floodplains. This we will mainly focus on the physical part of flood protection. We will, has taken hundreds of years, since technology advanced steadily however, still refer to the policy aspects when needed. but slowly. During the industrial revolution the population rose enormously and with it, the investments in the flood-prone areas. The physical measures can be divided into three separate classes. The pressure to protect the investment rose equally and thus the 1. Retreat measures, which focuses on the evacuation of further constraining of the river continued ever faster than before. humans, livestock and assets. This evacuation can be By this time most of the rivers in the Netherlands became guided by temporary or lasting. For the Meuse this would mean that dikes and groynes (rigid structures that interrupt the flow of water flood-prone areas would be abandoned and humans need to and sediment). Furthermore, the rivers were deepened for better settle in the higher and dryer parts of Limburg. Although this shipping and islands and sandbanks were removed to reduce the would be interesting and legitimate, it’s not what this thesis danger of ice accumulation in winter. focuses on, so this option won’t be elaborated any further. These measures all try to prevent flooding. They lower water levels 2. Control measures, which include another division. and prevent water from reaching parts of the regular floodplain. a. Flood preventing measures. An example would be the Compared to nature this would mean that humans are trying to use dikes and quays that protect the urban landscapes resistance methods in a dynamic environment. All species that live along the Meuse. in the flood-prone areas of the river can be called resilient. Instead b. Flood mitigating measures. An example would be the of trying to resist flooding they try to live with it. For example, a willow water storage along rivers that keep the water levels tree grows very quickly and spreads its seeds far by wind. This way it down by storing it. can regenerate quickly from inflicted damage and if the flood is very c. Flood-resilient measures. An example would be large and destructive, its seeds will have reached safer places. If a floating houses that react to the water level while they more resistant oak would be in the same place, it would withstand keep on functioning. most of the smaller floods, with only minor damage. If a particularly 3. Adaptation measures, which focus on adapting to the large flood would damage the tree it would likely die, with no offspring reoccurring floodings. An example of adaptation would be to to take its place because they would have been washed away. In a live in the higher parts of the landscape while using the lower more stable system the resistance theory would work better. The parts for grazing. more resilient oak would keep upright during a small storm and take all light from the fallen willow, eventually killing it. Before flood-resilience can be used in this thesis, a good definition Nature always chooses for the resilient solution in dynamic of flood-resilience is needed. Like mentioned before there are two landscapes. (Bal et al., 2001) But the Dutch people have chosen different definitions of resilience, originating form ecological studies, for a resistant approach, with dikes and quays. As with the oak, this namely: causes little problems when the floods are small, maybe it’s even better. But when a large flood will hit the Meuse valley, the damage 1. Resilience is the ability of a system to maintain its most will be a lot higher, maybe even higher than if no preventive measures important processes and characteristics when subjected to would have been used. Therefore we have chosen to examine disturbances. (Holling, 1973) the effects of resilient flood protection in the urban landscapes of 2. Resilience is the ability of a system to return to its equilibrium Limburg. after a reaction to a disturbance. (Begon et al., 1996)
70 If these definitions are taken and integrated with the protection on. People are willing to help flood-struck areas with financial aid against flooding of urban landscapes, the following definitions are a couple of times but after a few times they get weary. Thoughts the result: of potential donors will change from “poor people, I’ll send some money to this disaster stricken region” to “again? Are those people 1. Flood-resilience is the ability of an urban landscape to still living there and doing nothing?” (Duin, Van and Mesu, 1995) maintain its most important processes and characteristics Outside help is therefore unable to be a constant part of the process when subjected to a flooding from the river. of returning to equilibrium and should be excluded from the flood- 2. Flood-resilience is the ability of an urban landscape to return resilience definition. Although the former definition already suggested to equilibrium after a reaction to a flooding from the river. that the urban landscape should be able to return to equilibrium by itself, we want to make it absolutely clear. The new definition will For an urban landscape the first definition would mean that this urban therefore be: landscape would keep on functioning during a flood, with respect • Flood-resilience is the ability of an urban landscape to return, to the most important processes of this urban area. For example, by itself, to equilibrium after a reaction to a flooding from the people can still live in their houses and go to work/school while there river. are high water levels. This doesn’t imply in any way how this is done however. Therefore this is not a clear definition of resilience, since it Secondly, it’s not clear from the definition of which equilibrium the could just as easy incorporate resistance. Instead, this is a definition system should return to. Like mentioned before, an equilibrium of a of ‘persistence”, the ability to cope with disturbances. This can system lies in a ‘valley’ when the state of the system is drawn against include both resilient and resistant strategies as long as the system the stability of the system. The higher the instability of the system, keeps on functioning during a disturbance. the quicker it will change in the direction of more stability. External The second definition of resilience would imply that an urban factors can change the stability of a system in such a way that the landscape should be able to become a functioning urban landscape state of the system moves over the ‘peak’ and moves into the next again. This definition doesn’t imply whether it returns to the original valley, giving a totally different system. It will then never return to the equilibrium or to some other equilibrium. It also doesn’t say anything old state without another external cause. (see figure 7.2) about the severity of the reaction to the flood. For instance, an urban This would mean that an urban landscape could change in such landscape could loose a large part of its population and still function a way by a flooding that it could never return to the old state. An like an urban landscape should. This was the case with New Orleans example would be when a flooding would wash away a park, leaving where, after the hurricane Katrina, a large part of the population a big lake. The system would not be able to regenerate that park, not decided not to return or was killed. (Knabb et al., 2006) Moreover, the even in a very long period. The definition should therefore include damage of this hurricane was very extensive. So extensive actually, that the system does not move into another equilibrium as before. An that only a great financial contribution of the US government could equilibrium is also never an exact point. It is always a range of states restore the city to its former shape. This could however still be called through which it moves through time because of natural processes resilient since outside help is not expelled from the definition. So, the second definition of flood-resilience, although more precise, still doesn’t cover the flood-resilience concept in a useable way for landscape architecture. Therefore it will be further improved in the following paragraphs.
Since it’s already established that the first definition is too wide, from now on the second definition will be used when it’s about flood-resilience. This second definition does need some additions however to make it useable for the following research in this thesis and to become a realistic alternative for the current approach of flood protection. First it’s necessary to determine if an urban landscape should be able to recover from a flood by itself or that it is allowed to receive help from outside the urban landscape (i.e. financial support from charity). Outside help would be great for returning to equilibrium of the urban landscape, but since it’s irregular there can’t be counted Figure 7.2 A system moves into another equilibrium after a disturbance.
71 like seasons and predator-prey relations. Therefore the definition will become: • Flood-resilience is the ability of an urban landscape to return, by itself, to a similar equilibrium after a reaction to a flooding from the river.
This definition mentions a reaction to a flooding. After this reaction, the system should return to a similar equilibrium. The state of the system during this reaction is never mentioned in the definition. For the definition itself this is not important. For the landscape enduring the flooding and the people living there it is very important however. If a new way of flood protection is to be introduced, then the people involved should benefit from it. Otherwise they won’t accept it as a better solution and democracy will work its way around it. Therefore, Figure 7.3 Reaction of a system to a disturbance. the people should see a clear benefit in the new approach. In the therefore undesirable. For example a sudden drop in amplitude could current definition it’s still possible that a house will be completely mean that a preventive measure could not withstand the magnitude flooded but can return to the previous situation. This could be done of the disturbance, like a dike that is too low for the water levels when all the furniture and construction material is made waterproof. at that moment. (Bruijn, De , 2005) Furthermore a reaction should However, since for most people the ground floor is the most important be appropriate for the humans who live in the urban landscape. A of the whole house, the house will be practically unliveable. The reaction could improve the process of recovery but be harmful for the people won’t see why this is better for them since the new method people involved. For example, the quick drainage of a street could forces them to evacuate, just like the old one. Therefore the reaction improve the recovery but the quick currents could pose a threat for needs to be limited to the flooding; otherwise the new approach has the people who need to use that street. no realistic value for the flood-prone areas. The reactions of urban landscapes to disturbances reflect the Since the definition of flood-resilience is focussed on the urban landscape’s resilience and resistance. (Bruijn, De, 2005) By landscape, it is possible to add this limitation of the reaction to the studying the reactions, the landscape’s resilience and resistance definition. The definition should therefore be: can be determined. Figure 7.3 shows a hypothetical system whose appearance (or state) reacts to disturbances. The left two graphs • Flood-resilience is the ability of an urban landscape to return, show how the system reacts to a disturbance with a negligible by itself, to a similar equilibrium after a reasonable reaction to duration during a certain time. The reaction amplitude (A) and the a flooding from the river. recovery rate (the indicated angle) together describe the reaction to the disturbance. The amplitude is a measure for the magnitude The term ‘reasonable’ needs some further explanation. ‘Reasonable’ of the reaction while the recovery rate shows the speed at which means that the reaction is proportionate both to the disturbance and the system recovers from a disturbance. As can be seen in the to the affected people. This means, big enough to cope with the graph, smaller disturbances have no effect on the system since it disturbance and soft enough to let people live in the affected area. has the ability to cope with these. When the disturbance reaches the disturbance threshold, the system begins to react, which can be Lastly, it will be discussed in what way flood-resilience works in actual seen in the top graph. real-life. As can be seen in figure 7.3, resilience immediately reacts The right graph shows the amplitude of three hypothetical systems to a disturbance, contrary to the resistant method, which begins to and how they react to a whole range of disturbances with different work at a certain threshold. This means that a resilient system needs magnitudes. From this graph, a third reaction aspect can be to work from the point that a river exceeds its flow bed. It also means derived. The graduality of a reaction, which increases when the that the higher the disturbance in this case, the higher the water level magnitude of the disturbance increases. The steeper the slope of and the more the system needs to react to the disturbance. This is the line that represents the relationship between the disturbance important to remember since the water level that corresponds with magnitude and the corresponding amplitude is, the less gradual a discharge of 4600 m3/s is the highest possible water level in the the reaction. Instinctively, a gradual response that is proportionate Meuse following the predictions of the middle scenario of the KNMI. to the disturbance is to be expected. A sudden discontinuity in (see chapter 4) Most of the time the water level will be a lot lower the disturbance-response relationship is usually unexpected and however. 72 7.3 Different categories of flood-resilience Categorisation The problem is the potential flooding of urban landscapes. It is In the previous chapters the theoretical background of flood- expected that flood-resilience can be an answer to this problem. resilience has been addressed. Flood-resilience is the ability of an The problem can be solved in two separate ways. urban landscape to cope with flooding without any help from outside The first approach is lowering the water levels. This will reduce the or any large damage as a result of the flood. amount of damage that a flooding can potentially induce to the whole The question is how these urban landscapes can become flood- urban landscape. Since only some parts of the urban landscape are resilient. used to protect the remaining parts, this category is called Area- During this thesis a multitude of examples have been found that adapt. could help in making the urban landscape more flood-resilient. They The second approach is only protecting the most important objects range from simple adaptations of buildings to complete channels in within the urban landscape, which are buildings and important the public space. What lacks however is a clear categorisation, what infrastructure. The rest of the urban landscape will be flooded during makes use of them in the design process more difficult. Therefore high water levels. This category is called Point-adapt. Figure 7.3 Reaction of a system to a disturbance. we have made the following categorization.
Figure 7.4 Categorization of flood-resilience
73 7.3.1 Area-adapt
Within the category of area-adapt two sub-divisions are made, namely Store and Channel.
Store Store focuses on the construction of large basins in the urban landscape that don’t hold water during normal conditions. When the water level rises, all the excess water is stored in basins until the water levels start to go down again, at which point the water is released back in the river. The water levels will stay at a level that is low enough to protect most of the urban landscapes in this way. An example of this would be the large polders that are used in the river landscape of the Netherlands for retaining water when the water level of the Rhine exceeds the capacity of the regulated floodplain. Large quantities of water are released in specially prepared polders then, where it is kept until the water levels are at a level that is low enough again. The pressure on the dikes is lowered in this manner, which prevents dikes of breaching and overtopping. An example of a storage basin is shown in figure 7.5. It is a design for a storage basin near the village of Berkel. Since it will be used quite regularly it is designed as a nature reserve.
Figure 7.5 Basin near the village of Berkel. (Hoogheemraadschap Delft, 2008) Channel Channel focuses on the increased discharge of excess water in the river. It tries to lower water levels with the construction of extra arms of the river that only function when the water levels reach a certain level, and thereby effectively increasing the size of the river. Because the excess water is discharged as soon as it reaches the area, the water levels won’t rise too high and thereby won’t damage the urban landscape. Without the side-arms, the water would be unable to flow away and heap up against the dikes, potentially damaging or, even worse, breaching the dike. An example of a bypass is the construction of an extra river-arm near the city of Deventer. The extra river-arm diverts the excess water around the city, effectively protecting the city against high water levels.
Figure 7.6 Bypass Deventer. (Visser, De)
74 7.3.2 Point-adapt
The point-adapt category has three sub-divisions, namely Evade, Resist and Endure.
Evade Evade focuses on the evasion of high water. The most important objects are constructed outside the reach of high water levels by raising them, moving them to higher grounds or building them Figure 7.10 The highest mound in the Netherlands of underground. This can either be done in a permanent or temporary Hegebeintem (VVV Hegebeintum, 2007) state (static or flexible). This approach is very common when it comes to the protection of individual objects so there are different well- Resist known examples like a floating building and buildings on a mound. Resist is the protection of individual objects by making them more Other examples are buildings on poles and buildings underground. resistant against the forces of high water levels. Water is kept outside the object by strengthening the exterior. Good examples of resist are the many castles with thick walls along the river Rhine. The function of fortress was effectively combined with the goal of keeping water outside the building.
Figure 7.7 Floating house (Aquacasa, 2008)
Figure 7.11 Fortress in the Rhine near Kaub, Germany (Mtanasuica, 2007)
Figure 7.8 House on poles (Constructionjobsarticles, 2008)
Figure 7.9 Amphibious house (Ecoboot, 2008)
75 Endure 7.4 Technical analyses of the different categories The last category within area-adapt is the endurance of a flood. The object is constructed in such a way that water is allowed to flood Before it is possible to asses whether these methods can be used to the first floor of the building. Because the layout of the building is create a more flood-resilient urban landscape it’s necessary to take a prepared for this, the damage is a lot less than with normal buildings. better look at the technical qualifications of the different approaches. Good examples are the old houses along the Rhine. The first floor of In the next chapters it will be investigated how and where they can these houses only has floors of stone and the stairs are extra broad be used and what their effects are. to make it possible to transport the furniture to the second floor.
7.4.1 Store (Basin)
A storage basin is effectively a large bathtub in which excess water can be stored temporarily. The goal is to “decapitate” the high-water wave. When water levels reach a certain point, the basin is opened and the water flows from the river into the basin. The moment of opening the basin is put off as long as possible, because the goal is to store the highest peak. If a higher peak appears after the basin is filled, it could be possible that this peak overflows the dikes. The effects of storing are noticeable immediately: the water level stops Figure 7.12 Stone floors and movable furniture. to rise and if the basin has a large opening, the water level will even (Eco stone floors, 2008) drop. Taking the water from the river has an effect far beyond the location of the basin and many areas downstream will benefit from it. The basin is a fairly simple method when it comes to the storage of water. The only thing that is needed is a large, dry piece of land where water can be stored. There are some requirements however: 1. The basin should be situated on a lower level than the water level of the river, otherwise water needs to be pumped in. Existing pumps are mostly too small to pump the amounts of water that are needed to lower the water level and they also require costly maintenance. 2. Basins should be located close to the river. When the basin is of long distance from the river, the amount of water that can be transferred to the river is dependant on the size of the channel that connects both. This is likely to limit the amount of water that can be transferred per second. 3. Basins should be located outside the floodplain. When a basin is located in the floodplain it isn’t able to store extra water, because it is part of the river. Besides that, the dikes that are needed around a basin in the floodplain are likely to influence the water-levels. 4. Basins should be dry. When water (e.g. rain water) can heap up in the basin it may already be filled when it’s needed mostly. For the same reasons the level of the ground-water should be kept low. (Folkertsma, 2008)
76 Basins have some strong and weak points. The strong points include: • Effect on large area, especially downstream. • Can be used during dry times for nature or agriculture.
The weak points are however: • When the basin is filled, it losses it’s function, which is dangerous during long periods of high water levels. • Humans have to decide when the basin should flood and this difficult to do exactly at the right moment. • Since basins are used mostly to protect areas downstream, they are unwanted by locals who have little benefit from them. • Basins usually require a large area to be constructed.
7.4.2 Channel (Bypass)
The goal of channeling is to discharge the excess water as fast as possible and thereby reducing the water level. In a way, channeling is like having an extra river to discharge the water. The effects of channeling mainly manifest themselves upstream from the bypass. Near the end of the bypass, the water level returns to the normal level, with a small peak where the two currents meet each other.
Figure 7.14 Effect of a bypass. (Projectorganisatie De Maaswerken, 2001)
Figure 7.13 Requirements of storing water in a basin.
77 The technical requirements of channeling are largely focused on the hydrodynamics of the bypass. There are some fairly simple rules that improve the functioning of a bypass. 1. Bypasses should have as little intersections as possible; this reduces the amount of conflicting currents. 2. When an intersection is needed it shouldn’t be a direct crossing but an irregular crossing. Again, this reduces the amount of conflicting currents. 3. A bypass should be as straight as possible, because bends in the bypass slow down the water. These bends may be useful in small tributaries where water needs to be stored before it enters the river, but the goal here is to discharge water as fast as possible. 4. One large bypass is better than several smaller ones. This reduces again the amount of interfering currents. Furthermore, a bypass with a larger surface can flow faster than smaller ones, which increases the amount of water that can be discharged. 5. Reduce the amount of friction in the bypass. The smoother the surface of the bypass, the faster it will flow. Irregularities will cause small turbulences in the currents which slow them down. 6. Optimize the volume/circumference ratio. The larger the volume of water the bypass can hold compared to the circumference, the less contact with the sides of the bypass. Because of this, the bypass is able to discharge more water and faster. (Brink, Van den, 2007)
The bypass has some strong points: • Bypasses never stop working. When water levels rise, the bypass transports more water. Even though this amount of water might not be the same as the rise in river flow rate, it’s not as limited as a basin. • The main effects are near the location where the bypass is situated. This makes it a politically interesting option since the locals benefit from the effects. • A bypass can start to function at a certain water level, which can be done automatically.
There are however some weak points: • The current in the bypass during high water makes many other land-uses impossible or very difficult to maintain.
Figure 7.15 Technical requirements of a bypass.
78 Next are the subdivisions of the point-adapt category. For these categories house are used as an example since these are the most common buildings where it is used for. Nevertheless the methods could be used for other buildings or infrastructure.
7.4.3 Evade (Floating, amphibious, on poles and mounds)
Floating houses The goal of floating houses is to keep the houses out of the reach of dangerous currents by floating on top of the water. When the water levels rise, the object rises with it. The floating object is always positioned on a body of water. The currents will safely flow under the houses, without damaging it. Effectively it can be compared to a boat or pontoon. There are some technical requirements to a floating house, which are: 1. At least one meter of water is required beneath the houses to safeguard the quality of the water. 2. A base of expanded poly-styrene and concrete is needed. This is both durable and can float. 3. The base is never allowed to touch the ground, because it’s not built for this and will break. 4. A connection with the mainland that can adjust to the variations in water levels. 5. A flexible connection for electricity and drinking water with the mainland. This can be replaced with an individual source of electricity and drinking water for every house or several houses. Although this might prove difficult for waste water disposal.
The strong points of floating buildings are: Figure 7.16 Floating house. • Unrestricted water levels • No basement or foundation is needed • Little impact on water levels in the river • Can be built in the current of a river • No limit to the duration of a flood • No limit to the frequency of a flood
The weak points are however: • Vulnerable to ice and floating debris • Vulnerable to waves • Vulnerable to wind • Needs a flexible electricity/water connection • Needs a flexible waste disposal system (Dura Vermeer Business Development, 2008)
79 Amphibious houses Amphibious houses resemble floating houses in many aspects with one major exception. The houses are situated on dry land during normal water levels. They start too float as soon as the water levels start to rise and the water reaches the houses. The technical requirements are therefore largely the same:
1. A base of expanded poly-styrene and concrete is needed, which can float and is durable. Besides that a static base is needed where the house is situated on during dry periods. 2. A connection with the mainland that can adjust to the variations in water levels. 3. A flexible connection for electricity and drinking water with the main land. This can be replaced with an individual source of electricity and drinking water for every house or several houses. Although this might prove difficult for waste water disposal. 4. A strong anchorage with the base is required to prevent the house from floating to far from the base.
The strong points of the amphibious building are: • Unrestricted water levels • Little impact on water levels in the river • Can be built in the current of a river • No limit to the duration of an flood • No limit to the frequency of a flood • Normal urban planning can be applied during normal water levels
The weak points are however: • Vulnerable to ice and floating debris • Vulnerable to waves Figure 7.17 Amphibious house. • Vulnerable to wind • Needs a flexible electricity/water connection • Needs a flexible waste disposal system (Dura Vermeer Business Development, 2008)
80 House on poles The goal of a house on poles is keeping the water out of reach of the house, by building large pillars under the house that are higher than the highest potential water level. During normal water levels the space under the house will be dry, although it is possible to build this type of houses in a wet area. The technical requirements for this type of house are: 1. Strong pillars under the house with a maximum length of 3 meters. When the pillars get longer the effects of currents will too strong and the pillars will break.
This type of house has some strong points: • Little impact on the river • Static construction, no flexible parts are needed like flexible waste disposal and electricity • Space under house is still useable as a garden or parking space • Can be built in the current of a river • No limit to the duration of a flood • No limit to the frequency of a flood
The weak points are however: • Limited to a variation in water level of 3 meter • Vulnerable to floating debris • Large difference between street level and level of houses when potential water levels are high (Dura Vermeer Business Development, 2008)
Figure 7.18 House on poles.
81 House on a mound A mound is an artificial hill made of sand, clay etc. Mounds are one of the oldest methods to protect buildings against high water levels and they are very common in the areas near the sea in the Netherlands, especially in the north. A large heap of sand is placed in an area where high water levels occur and all the houses are built on top of it. The effects of a mound are straightforward. Water can’t reach the house and will flow around the mound. There are some technical requirements for this: 1. If currents are present, hard materials are needed to prevent erosion. 2. Stability of the mound requires a large base on top, which increases if the height of the mound increases.
The strong points of this method are: • Very safe, almost no risk of failure of the protecting construction • Static construction and therefore no flexible parts are needed • No limit to frequency of floods • No limit to duration of floods • Very robust, no vulnerabilities • Can be built in currents of river • There is room for basements • Always dry, therefore normal urban layout can be applied to the area
Weak points are however: • Requires relatively more space than other methods • Height of the mound is not unlimited, but likely to be higher than the potential water levels • Large effect on water levels in the river since the flow of water Figure 7.19 House on a mound. is blocked
82 7.4.4 Resist (Water-resistant house)
The resist method is based on the theory of fortification. A thin wall is more likely to succumb to the force of flowing water than a thick wall. The house has therefore thick walls and removable plates that can protect doors and windows. When water levels rise, the plates are placed and the house is protected against the water. The surroundings of the house are still flooded and the entrance to the house is blocked. The technical requirements for the water-resistant house are:
1. Thick walls made of hard material which can resist water. 2. No basement to prevent an extra entry for water. 3. Water resistant floors to prevent water to enter the house from beneath. 4. Electricity needs to be transported above ground level to prevent short circuitry. 5. An extra entrance to the building above the highest potential water level.
The strong points of this category are: • Normal layout of the urban landscape can be used, no extra space is required • Relatively easy to adapt houses, no reconstruction needed
The weak points are however: Figure 7.20 Water-resistant house. • Houses are isolated during high water levels • Humans need to place some barriers, which can fail if high water levels occur suddenly • Can deal with a maximum water level of 1 meter, otherwise the difference of pressure between the outside and inside of the house will collapse the walls, which means destruction of the house • Can only be flooded for 2 weeks, after this time damage occurs • Can only be flooded once per year • Vulnerable to currents • Vulnerable to floating debris and sludge (Dura Vermeer Business Development, 2008)
83 7.4.5 Endure (Wet-proof house)
Wet proofing is the pinnacle of the flood-resilient concept. The house is completely adapted to the presence of water within the house itself and no action is taken to keep it outside. The technical requirements for this method are:
1. Different layout of the house than a common house. Important living functions need to move outside the reach of the water. Important and vulnerable objects like the meter closet and central heating system need to be transferred to the top floors. The ground floor can be used for less vulnerable usage, like a garage. 2. Water-resistant material is used on the ground floor until a height of 1.5 meter. 3. Electrical sockets are placed outside the reach of the water. 4. Enough openings in the walls to let the water in. If there aren’t enough openings the difference in pressure will increase and the walls will collapse. 5. Possibility to move large pieces of furniture around with ease (wide stairs).
Strong points of the wet-proof house are: • Low costs, houses don’t have to be built once again Figure 7.21 Wet-proof house. • Normal layout of the urban landscape can be used • A basement is possible
Weak points are however: • Very low frequency of floods is allowed, only once every ten years • Duration of a flood has to be less than two weeks • Water levels should be lower than 1.5 meter • Vulnerable to currents • Vulnerable to sludge • Vulnerable to floating debris • Entrance of the building is flooded and therefore the building might be unreachable (Dura Vermeer Business Development, 2008)
84 7.5 Conclusion
Flood-resilience is based on the resilience concept, which describes how a system reacts to a disturbance. Resilience is the ability of a system to return to its equilibrium after a reaction to a disturbance. Floodplains are dynamic systems, but in the last century, humans have started to use resistance methods like dikes in these dynamic systems to prevent floods. In a more stable system, resistance would function better, but in a dynamic system like a floodplain it would be better to choose for a resilient approach, like nature does. Therefore flood-resilience could be applied to urban landscapes and be an alternative for the current resistant dike-system. Flood-resilience is defined as the ability of an urban landscape to return, by itself, to a similar equilibrium after a reasonable reaction to a flooding from the river.
The flood-resilient solutions can be divided into different categories and subdivisions. Area-adapt is preferred above point-adapt, because in case of area-adapt one area is needed to protect several other areas. In case of point adapt, the whole area is flooded with water and only the most important objects like buildings and infrastructure are adapted and protected. Flood-resilience can only be measured at the scale of the whole urban landscape, not just its individual components. Some measures could be resistant by themselves instead of flood-resilient, but still make the urban landscape more flood-resilient. For example, when a house is adapted to become a resist house by strengthened walls, the adaptation is not flood-resilient by itself. But this adaptation makes it possible to allow the water in the street and neighbourhood and so the urban area reacts in a flood-resilient way to that flood. All categories of flood-resilience have different strong and weak points. In case of area-adapt, store has more limitations than channelling. When a basin is filled, retaining is stopped, while a channel always keeps on discharging water. In case of point-adapt, only the amphibious house doesn’t have limitations because of currents and water levels. The floating building cannot be used in case of building along a river, because a permanent presence of water is needed.
85 86 Assessment of flood-resilience in the Meuse valley
8
87 8. Assessment of flood-resilience in the Meuse valley
To find an answer to the question of how urban landscapes can become more flood-resilient, the techniques and principles of resilience mentioned in chapter 7 have to be tested. The optimal situation would be a valley of the Meuse that contains complete flood-resilient urban landscapes, without the current dike system. Therefore this optimal situation is the starting point for this test. Is it possible to replace the century-old tradition of using and heightening dikes by applying the resilience-concept? And in what way is this possible? To test this for the optimum situation, the dikes are considered absent. The area-adapt method is preferable above point-adapt, because it is cheaper and safer to use some areas to protect other areas than adapting the complete urban landscape. Therefore we will start to test whether area-adapt measures can cope with the predicted discharges in the Meuse.
8.1 Area-adapt Figure 8.1 There is only a limited amount of public spaces in Maastricht. Like mentioned in chapter 1, landscape architects extract solutions from the landscape. We stated that we want to use the public space to realize solutions to lower the flood risk in the urban landscape. Therefore, the described area-adapt solutions from chapter 7 are projected on the urban landscape. But before that can be done, it’s necessary to know what kind of public space is present in the urban landscapes of the valley of the Meuse. To gain insight in this, all three urban landscapes (see chapter 5), we will examine them and check the total area of free public space. We will discuss one settlement for every urban landscape category.
Looking at the terrace village of Oost-Maarland, there is hardly any public space besides the presence of streets. This is also the case in other terrace villages. This is to be expected, since most of the terrace village are small, mostly between 2,000 and 3,000 inhabitants. In many cases, these settlements have a low grade of Figure 8.2 Flood-resilient Park Corbière, designed to store water from the urbanity with many gardens and low-rise buildings. In addition, they Seine. are situated in rural environments. These factors decrease the need for parks and other green urban spaces. 8.1.1 Storage
Similar to the terrace villages, the floodplain villages also does not Here, we will discuss the possibilities of areas that can store water have much urban space, apart from the streets. Again, this is because during a flood. We were inspired by some examples that show how these villages are small and surrounded by rural landscapes. the public space is used to create some area-adapt solutions. In the case of storage, the use of parks and squares to store water are Analyzing the public space in valley town Maastricht (see figure interesting examples of how solutions can be created by using the 8.1), a couple of public areas (especially parks) can be found. It is public space. This is for example done in Le Pecq in France where already clear that they are small, scattered and seldom connected parts of Park Corbière are used to store water during high water to another one. levels of the Seine (figure 8.2). (H+N+S landschapsarchitecten, 2006)
88 The search for public space in the three mentioned landscapes, to check if solutions like this are also possible in Limburg, gave us some conclusions already. It can be concluded that the floodplain villages and terrace villages hardly contain any public spaces like parks and squares. The small parks and squares that are present in some of these villages are that small, that they really won’t have any influence in lowering the water level of the river when using them for storing water. In the valley town more and bigger parks and squares can be found. So at first sight the valley town has more potential to let its public areas function as storage areas during high water levels of the river Meuse. But before we can conclude more, some simple calculations have to be made.
Taking the 4600 m3/s of the middle KNMI scenario for the Meuse, it can globally be calculated how many water has to be stored. Looking at figure 8.3, it can be concluded that a peak discharge is present for at least 5 days. Let’s assume that the river can handle 2000 m3/s by itself. This is already much water, because in case of a peak discharge of 2000 m3/s, the waterboards start monitoring the water defences permanently with dike-watches. This assumption means that still 2600 m3/s: 2 = 1300 m3/s has to be stored somewhere (half of the surface of the graphic is taken). 1300 m3/s means 561.600.000 m3 during those five days of the peak discharge. When you have for example a basin of 5 m deep, a basin of 112.320.000 m2 is needed to store the water, which is 112 km2. Figure 8.4 shows this difference.
2 Maastricht itself is approximately 26 km , so an area of more than Figure 8.3 Duration of river discharges. (Rijkswaterstaat, 2001) four times Maastricht is needed to solve the water problem with the method of water storage. This is clearly impossible. Even if we take the discharge accompanying a 1/10 chance of appearance in the graph, an area of 5 km2 is needed. (40 hours * 3600 s * 200 m3/s : 2 = 14.400.000 m3). Using a basin of 5 m deep again, a basin of 2880000 m2 is needed, which is 2.88 km2, which is still impossible to find or create within the urban landscape.
Conclusion concerning store To conclude from the above showed calculation, it’s really impossible to lower the water level sufficiently by using the storage method. Storing on a detailed scale by using some parks is impossible, looking at the amount of water that has to be dealt with. In addition, any other scale will not give the solution, because it really needs a disproportional amount of space. Moreover, the problem is that there is hardly any space in the urban landscape in the valley of Figure 8.4 Even if Maastricht is completely used as a basin (left reservoir) the Meuse. The amount of space that is needed even exceeds the there won’t be enough space, because the amount of water is much larger amount of space that is available outside the urban landscape. (richt reservoir).
89 8.1.2 Channel
In case of channelling we expect that streets can be used like small bypasses to transport water in periods of high water levels.
The main question for this method is what the effect will be on the water levels when they are implemented. To find an answer, we investigate some examples of small bypasses that are proposed for the Zandmaas project, a part of the Maaswerken project. Looking at the high water trench Vierlingsbeek, the maximum effect of this trench is lowering the water level with 2.0 cm. The bypass Stadsweide Roermond even shows a negative effect, with an effect on the water level of +2.0 cm, which is also with bypass Baarlo (Belfeld-West). (Dienst Landelijk Gebied, 2008) Above mentioned bypasses are already larger than most streets in size, so it can be expected that the effect of streets that function like a bypass will be less or even negative. Streets also have many crossings, which will obstruct the discharge, because different currents will clash. Besides that, there is a bad relation between volume and circumference, which causes a street to have more friction, slowing down the water. Figure 8.5 Section of a street that can channel water, as we imagined it. A 2-meter deep trench in the street functions as a parking lot during low water Concluding from this, the effect of streets that function like a bypass levels. is very little, or even negative. Only centimeters per bypass can be gained. In villages like Arcen and Oost-Maarland, there is just enough space for some of these streets that can function like a bypass. Considering that, it will be hard to realise a sufficient lowering of the water level. For example, if three of these streets could be realised, a lowering of the water level of maximum 6 cm (3 x 2.0 cm) can be
Figure 8.6 A large bypass as we imagined it. During low water levels it can be used as a park and living area.
90 realised. Such an amount is neglectable, compared to the water Bigger scale levels during a flood. Since the amount of water is too much to solve the problem with Taking the 4600 m3/s of the middle KNMI scenario for the Meuse, it streets functioning as bypass, a look is taken at the options of a can be calculated globally how many m3/s has to be channelled by larger scaled bypass. Because of the scale, solutions can only be the bypasses. applied to one of the three urban landscapes, namely the valley- Let’s assume again that the river can handle 2000 m3/s by itself, town. The terrace village and floodplain village are simply too small even though this does include the existence of dikes. In such a case and don’t have enough space. there is 2600 m3/s left for the streets to be channelled. Using the rule An example of using urban infrastructure as a bypass on the larger of thumb that a discharge of 100 m3/s matches with a water level of scale can be the highway of Maastricht. What will be the effect of 10 cm, 2600 m3/s matches with a water level of 2.6 m. (RIZA, 2005) using a highway to channel the water? A rough calculation can show Therefore the conclusion has to be that lowering the water level with this. Taking a highway of 60 m wide and 2 m deep gives 120 m2. some centimetres at most really won’t work, when a lowering of 2.6 Multiplying this with a rate of flow of 1.5 m/s, which is already fast, m is needed! So making the valley of the Meuse more flood-resilient gives a discharge of 180 m3/s. This corresponds with a lowering with the use of streets within the urban areas to channel water isn’t of the water level of 18 cm. It is already a better result than using an option. The amount of water is really of another scale.
Figure 8.7 A highway that can function as a bypass as we imagined it.
91 the streets, but it’s clear that it’s not nearly enough. So it has to be 8.1.3 Conclusion concerning area-adapt concluded that making use of the public realm even on the bigger scale won’t give the right solution to create a safe flood-resilient The analysis in the above chapters shows that the channel method valley of the Meuse. and the store method both cannot be used within the urban landscape to deal with the predicted amount of water. The amount of The question rises then what the effect will be when solutions on water that flows through the river during high discharges is too large the largest scale are used, like big bypasses through the urban and water levels will not be lowered enough that a flood-resilient landscape. We imagine a bypass that is several hundred meters urban landscape is feasible. Therefore, the area-adapt method is wide and that incorporates parts of the city. To find an answer on unsuitable for a flood-resilient protection of the settlements in the the effect of such a bypass, we look again at the bypasses of the valley of the Meuse. Zandmaas. The largest bypass, the old arm of the Meuse Ooijen- Wanssum of 390 ha. has a maximum effect of lowering the water level with 22 cm, which corresponds with a discharge of 220 m3/s. This is a bypass that starts flowing only from a certain water level; it is dry during normal water levels and is therefore called a green river. Blue Rivers, bypasses that always contain water, are also possible. But in this case it doesn’t matter if it’s a green or a blue one. The conclusion is still that lowering the water level with just 22 cm is not enough. This would mean that at least 12 of these bypasses should be realised and this is really impossible. Even in a large valley town, it is not possible to find this amount of space.
Conclusion concerning channelling From this assessment, it can be concluded that it will not be possible to make an urban area fully flood resilient by using bypasses. Using the streets as small bypasses does not have enough effect or does even have negative effects. Also the bypasses on the bigger scale don’t have the required effects to create a fully resilient urban landscape. An additional problem with the solutions on the bigger scales is that they cannot be applied in two of the three distinguished landscapes. They are really too big to implement in the floodplain village and the terrace village. Only in the valley town they can be applied on locations of, for example, highways and railways. However, even if only bypasses of the largest scale, the urban blue and green rivers, are used in the urban landscape of a valley town, many of them are needed. This requires a lot more space than is actually available in the urban landscape.
92 8.2 Point-adapt Water levels 4600m3/s (cm) If the water problem cannot be solved by using a part of the urban
8.2.1 Assessment of the evade, resist and endure methods
To get insight in which point-adapt solutions are usable on which locations, they will be analysed below, projecting them on the three distinguished urban landscapes categories. The terrace village has never faced a flood, but this will change in the future when the predictions of the middle scenario of the KNMI are taken into account. In that case, a maximum water level of 80 cm can be expected. The floodplain villages are situated a lot closer to the river. The ground height is also a lot lower and therefore it is not impossible that water levels of more than 4 meters will occur in these urban landscapes. The valley town holds both of these water levels and a range between these, because this kind of urban area is situated through the whole Text valley. Taking these water levels into account, it will become clear which point-adapt solutions are suitable for which locations.
The Evade method
The amphibious building method is a method that can be used everywhere. It is not limited by water levels, since the building can float and therefore can handle even the highest water levels in the Meuse floodplain. It is however very susceptible to floating debris that can seriously damage the building during floods. It is impossible to prevent floating debris during a flood. This is a reason to state that amphibious buildings might not work in a flood-resilient urban landscape. There is a better reason to state that amphibious buildings cannot contribute to a flood-resilient urban landscape however. Even though the building itself is safe during a flood, the surrounding landscape is not. Amphibious buildings don’t have any effect on the flow speed of water. Therefore, water will flow through the streets with speeds of 1.5 m/s, which is potentially lethal. In addition, water levels will remain 3 meters or more during a flood. Such water levels contribute to a very unsafe public space. An urban landscape with only amphibious might have safe areas in the form of floating buildings, but the surrounding areas are too dangerous to consider this method as a Figure 8.8 Water levels during a flood accompanying a discharge of 4600m3/s 93 good replacement of the current system. The last argument of high flow speeds and water levels is not true for terrace villages, where water levels are only 80 cm. Here, the amphibious building method will solve the flooding problem. Measures have to be taken to reduce the amount of floating debris tough.
The building on poles method can technically be used in all of the three landscapes. It is limited by a water level of 3 meter though, so it can not be used in some areas. It has however the same problems as the amphibious building method. High water levels and high flow speeds create a very unsafe public space during floods. Since our goal is to create a good alternative for the risky system of dikes, this method cannot be used to create a flood-resilient urban landscape. Moreover, buildings on poles have a fixed position, unlike the flexible amphibious buildings. This means that there will be large, dark empty spaces under the buildings that will not have a function, except for maybe a parking spot. Moreover, the difference in height has to be traversed over very short distances. Every building needs stairs and ramps to be connected with the lower urban space. If an urban landscape is protected against flooding by using buildings on poles, a landscape will be created with large dark spaces and a disorderly amount of stairs. In addition, there will be many electrical cables and other infrastructure that is needed for every building. This landscape is not liveable, nor will it function well. We cannot Figure 8.9 The problems that occur around the “safe” amphibious building. imagine such a landscape as a good replacement of the current, see figure 8.10.
The building on a mound can be used in all of the three landscapes. In theory a mound can be built as high as is needed, considering the water levels. A weak point of this method is however, that mounds have a negative effect on the water levels, because the flow of water is blocked. Therefore, it is undesirable to use mounds in the floodplain of the Meuse. In addition, the higher a mound is, the more space is needed. Therefore, a lot or space is needed in locations where the potential water levels are high.
Figure 8.10 Urban landscape on poles of 3m will result in an unliveable landscape with unwanted spaces under the houses and a lot of big stairs.
94 The resist method 8.3 Conclusion area-adapt and point-adapt
The water-resistant building has restrictions to water levels and can Like mentioned before, we expected that the public realm in the deal with a maximal water level of 1 meter. Considering that, this urban landscapes could be used to store and channel water to type of building can only be used in the terrace village and on some make the urban landscapes in the valley of the Meuse more flood- higher situated locations of the valley town and floodplain village. resilient. But the amount of water that is predicted during future Besides that, a water-resistant building is vulnerable to currents. flood is larger than these methods can handle. The effects that the This makes it impossible to use this type of building in areas that area-adapt methods have on the water levels are neglectable and are under the influence of the current from the river, because in case can therefore not contribute to a flood-resilient urban landscape. of high water levels the river has a high speed of flow. This means The point-adapt methods are also unable to cope with the amount that it can’t be used in the lower lying valley towns and floodplain of water. The water levels and flow speeds will be larger than the villages. techniques allow. Therefore, it has to be concluded that the urban areas in the valley of the Meuse cannot be made fully flood-resilient as an alternative for the current system. The endure method
The Wet-proof building can be used in the terrace village and on the higher situated locations of the floodplain village and valley town, because this type of building has restrictions to water levels and can deal with a maximum water level of 1.5 meter. Besides that, a wet- proof building is vulnerable to currents, which makes it impossible to use this type of building in areas that face currents from the river. It can therefore not contribute to a flood-resilient urban landscape, since the water levels exceed the 1.5-meter limit on most locations.
8.2.2 Conclusion concerning point-adapt
We have assessed the possibilities of the different point-adapt methods for a flood-resilient urban landscape. Most of the methods are limited by their technical aspects. Most methods cannot cope with the water levels or with the flow speeds in the floodplain in the Meuse. The ones that can cope with such an amount of water have as a result such a dysfunctional and or unliveable urban landscape, that they are deemed to be inappropriate for the realisation of a flood-resilient urban landscape.
95 96 flood-resilience supplementing current approach
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97 9. flood-resilience supplementing current approach
Flood resilience cannot be used as a complete replacement of the current approach, which has been concluded during the assessments in the previous chapter. Large parts of the Meuse floodplain in Limburg have potential water levels that cannot be handled with the use of flood-resilient techniques. Still, a solution for the unsafe situation in de floodplain of the Meuse has to be found. Therefore, we look at whether a combination of all kinds of different approaches can be used.
9.1 Combination of approaches Figure 9.1 In the current situation the dikes can deal with a discharge of 3150m3/s. In chapter 6, some of the current approaches that are used to create safer urban landscapes in the floodplain of the Meuse are described. Interventions in the upstream area of the Meuse were discarded because they either lacked effect or are impossible to realize (see chapter 10). Other interventions like the IVM project together with the dike system were also discarded because they focus on the chances of flooding instead of the risk (see chapter 6.4). Since it is already established that the flood problem could not be solved by only lowering the vulnerability, a combination has to be made of these chance-reducing and vulnerability-reducing interventions. Simply said: What can flood-resilience contribute to the current approach? Figure 9.2 After the application of the IVM measures a discharge of 3950m3/s can be handled. Chance of flooding The current dike system in the valley of the Meuse is aimed at a return rate of 1/250 a year. The IVM project tries to reduce the new water levels, caused by climate change, to a height where this chance remains the same, while the discharge increases with 800 m3/s from 3150 m3/s currently to 3950 m3/s. The chance of flooding of 1/250 a year is a very high chance compared to the rest of the Netherlands. In our opinion, this is unfair and the chance of flooding should be lowered. In addition, the Delta commission 2008 stated that the current safety levels should be multiplied by ten. (Deltacommisie 21e eeuw, 2008) This would reduce the flood-chance to 1/2500 a year. There is no data for water levels Figure 9.3 The middle scenario of the KNMI predicts a discharge of 4600m3/s, corresponding to such a chance however. Therefore the highest which still will overflow the dikes and thereby the urban landscapes. water levels that can be calculated are taken, which corresponds to a flood-chance of 1/1250 a year and a river discharge of 4600 m3/s.
The discharge that can currently be retained by the dikes is 3150 m3/s (figure 9.1). (Ministerie van Verkeer en Waterstaat, 2005) With the implementation of the interventions that are proposed in the IVM project, the discharge that can be retained will become 3950 m3/s (figure 9.2). Using the rule of thumb found in the IVM project (Ministerie van Verkeer en Waterstaat, 2001), it can be calculated
98 that a discharge of 4600m3/s will produce water levels that are 65 It is also important to remember that when the water levels overflow cm higher than the current dike levels. Therefore the dikes can still the dikes, the water levels on the landside of the dike will rise until be overflowed, see figure 9.3. they equal the water levels on the waterside of the dikes. Therefore, the water levels will become at least as high as the dikes are and When the dikes are overflowed with water, the water levels on not lower. the landside of the dike will rise fast. In the current situation of vulnerable housing, the houses are likely to receive a lot of damage. Furthermore, there is a large risk of personal injuries and casualties. In the previous chapter, it is concluded that flood-resilience could 9.2 Technical possibilities of the combination not be used as replacement for the current dike system, because the water levels are too high. With the use of the IVM interventions With the new maximum water level of 3 meter, it is possible to look and the dike system, the potential water levels in the urban areas at the possibilities of the point-adapt measures. For the technical should be lower. As a result, it is possible to look at whether flood- aspects of the buildings see chapter 7. resilience can be applied to protect the buildings behind the dikes or not, see figure 9.4 1. Buildings on poles. Buildings on poles have a maximum distance of 3 meter between ground and buildings. Therefore it is now possible to use this option in the floodplain of Limburg.
2. Amphibious buildings. Amphibious buildings have no restrictions and are therefore a viable option behind the dikes.
3. Endure buildings The endure option works only with water levels that do not exceed 1 meter. Therefore Figure 9.4 Flood-resilience behind the dikes. endure is still not a possible option to make the urban landscapes more flood-resilient
Flood-resilience 4. Resistant buildings Flood-resilience can be divided in area-adapt and point-adapt Resistant buildings can only handle water measures. Area-adapt measures will be impossible behind dikes, levels of maximum 1.5 meters. Therefore, the because a direct link with the river is needed to either store or channel water levels that could occur behind dikes the water. Furthermore, the required space is still too large. For will damage these buildings and this option instance, if all the water that could overflow the dike near Maastricht cannot be used. is collected in a large basin of 5 meter deep, a 112 km2 large basin is needed. This is much larger than the area of Maastricht itself. (see 5. Buildings on mounds also chapter 8) Buildings on mounds is always a viable option Point-adapt is therefore the only viable option that could be used since technically every height is possible. behind the dikes. Since the water levels are 80 cm lower than they would have been without the IVM, the number of building types Technically the list of viable options has now been extended to three that can be used should increase. The water levels without IVM options, namely: amphibious, mound and poles. However, other interventions could rise to a maximum of 4.0 – 4.5 meter at some aspects of a flood-resilient urban landscape have to be also included locations in the urban landscapes along the Meuse, but there are into this analysis. Therefore, we look at the safety and livability of the not so many places where these water levels are possible. When the urban landscape IVM is applied, the water levels in most of the urban areas can reach a maximum height of approximately 3 meter.
99 9.3 Safety and liveability aspects 9.4 Conclusion
Flood-resilience originally states that people should be aware of the The water levels in the Meuse floodplain will become lower when approaching water. When people see that water is slowly progressing the IVM measures are implemented. The lower water levels create a towards their houses, they can take measures, like moving their cars possibility for point-adapt techniques to be used in the flood-prone and furniture. With the use of dikes, people will lack this form of urban landscapes. . warning and will become completely dependent on the forecasts of However, during a flood the water levels behind the dike are still the government. very high and can rise to approximately 3 meters. This water level is When the dikes are overflowed, the water levels will start rising unsafe for the urban realm and people might drown. Furthermore, relatively quickly. Especially since the water will erode the dike away. the speed at which the urban landscape will flood when dikes fail will After just 3 hours, the water levels can already be at knee height. cause very dangerous situations. Besides the impact on the current (Smit, 2007)This will seriously hamper the inhabitants of the urban urban landscapes is considered too high for the implementation of areas to prepare their property for the coming water or evacuate. the flood-resilient techniques. Cars already begin to float with such a water level. (SEMO, 2006) When the dikes start to overflow, the speed at which the water will In the context of the safety of the urban landscapes in the floodplain flow over the dikes is slow. When the water levels rise further, more of the Meuse in Limburg, some larger conclusions can be drawn water can flow over the dike and the speed with which the area now. To recapitulate: behind the dike fills up increases. As a result, the water levels can 1. Current methods, aimed at lowering the chance of flooding be equal to the water levels outside the dike after 6-8 hours, even should not be used because they create a false sense of though it is at knee height within 3 hours. This is very little time for security, which can increase the flood risk even further. people to prepare. The amount of danger that is caused by this is a 2. Flood-resilience cannot be used as a complete replacement reason to say that flood-resilience should not be used behind dikes, of the current system. since the flood will happen too fast. After this chapter, a 3th conclusion can be added: In addition, even though the buildings are outside the reach of water, 3. Flood-resilience cannot be used to complement the current the water levels outside the buildings can become 3 meters high. system to guarantee the safety of the inhabitants of the urban This is still a water level that can potentially kill people if they fall into areas. the water, especially children and old people. Lastly, we have ignored the possibility of a possible breakthrough of At this point, we can state that the safety of the urban landscapes is the dikes. Although the potential water levels will be lower, the rate very difficult to maintain and improve with the proposed measures. at which the urban landscape is flooded will be higher. Furthermore, Therefore, the question is what the other possibilities are for a safe the people will be even less warned before the dike breaches. floodplain of the Meuse. This causes very unsafe situations and is already a large point of discussion when it’s about the current method of using dikes to protect urban landscapes. (Neuvel, 2007)
Also from a livability point-of-view, the usage of the three possible types of buildings causes problems. Amphibious buildings will cause no problems, since they resemble “normal” buildings. However, buildings on mounds or poles will cause large differences between street and building levels. These height differences will occur between very short distances, which are difficult to overcome with people, cars and other vehicles. Large constructions need to be built to overcome these height differences, which require a large amount of space. The impact of these constructions on the livability and quality of the living environment is unknown, but a negative effect is expected, which is undesirable.
100 Remaining choices for the Meuse floodplain
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101 10. Remaining choices for the Meuse floodplain
None of the measures that have been proposed in the previous the Dutch urban landscapes. (Ministerie van Verkeer en Waterstaat, chapters of this thesis can completely guarantee the safety of the 2006) inhabitants of the Meuse floodplain in Limburg. The amount of water All these reasons make it impossible to find a solution for the Dutch that can flow through the Meuse in the future causes water levels flood problem in Belgium. that cannot be handled with the current methods, even with the use of flood-resilience. The big question that remains now is how the safety of the inhabitants of the Meuse floodplain can be guaranteed. This chapter will discuss five options that could improve the safety of the inhabitants of the floodplain. The first two options aren’t useful to be implemented in the Meuse valley, but they need to be mentioned in this thesis because they seem to be quite obvious solutions to the flood problem at first glace.
10.1 Using the upstream area in Belgium
Currently the Dutch government is making agreements with Germany to create flood-basins in the upstream area of the Rhine. These areas can retain water even before it reaches the low-lying diked areas of the Netherlands. It is logical to investigate if this approach also could work for the Meuse. The answer to this question is quite likely to be ‘no’. There are three important reasons for this. The first one is the geography of Belgium (see figure 10.1) In Belgium the Meuse is also situated in a valley, but it has eroded the valley out of the rocky Ardennes. The higher situated areas were difficult to farm on, while the floodplain had some sediment and good trade connections. As a result, the floodplain of the Meuse in Belgium has a large grade of urbanization. Apart from large urbanized areas, there are also many cliffs, situated right next to the river. This begins roughly at the border of France and Belgium and continues until just before the border of Belgium and the Netherlands. It would be quite difficult to find space for the construction of water retaining areas in Belgium within this densely populated and rocky floodplain. Figure 10.1 The floodplain of the Meuse in Belgium is very urbanised and rocky. (Ministerie van Verkeer en Waterstaat, 2001) The second reason is the political situation in Belgium. Belgium is divided into two large parts, Flanders and Wallonia. These areas are cultural very different, which has resulted in a complex governmental situation with two independently acting sub-governments. For the 10.2 Using the floodplain in southern Limburg Belgians it is already difficult to come to agreements between the two different parts, let alone for another country to make agreements Since the floodplain in Belgium cannot be used, the focus with both parts. (Rijkswaterstaat Dienst Limburg, 2009) automatically shifts to the Netherlands. Is there enough space in Lastly it’s a fact that Belgium will flood before the Netherlands. Before the Dutch floodplain to implement large-scale flood-preventing the water-retaining areas are needed to guarantee low water levels measures? The answer to question is also a clear ’no’. in the Netherlands, large parts of the Belgian floodplain and urban The space that is available in the Dutch floodplain is limited by the landscapes will already be flooded. If the water-retaining areas are city where a large drop in potential water levels is first necessary. used for the protection of these urban landscapes, they cannot be Just eight kilometer after the Meuse has entered the Netherlands, used for the protection of the Netherlands. It will be impossible to it reaches the large town of Maastricht. Since it is unthinkable that demand of the Belgians to sacrifice their own urban landscapes for the largest urban landscape is sacrificed for the remaining part of
102 the Meuse valley, only the area south of Maastricht can be used for 10.3 Leaving the floodplain large-scale measures. The area south of Maastricht is limited in size. It is situated in a narrow valley, with steep rocky cliffs on the western side. The eastern side of the valley has a more gradual gradient, but is still steep for Dutch standards. Since 112 km2 is needed for a basin (see chapter 8) and the area of the floodplain itself is roughly 9 km2, flood-preventing basins are not feasible. Water retaining basins cannot be used then, but what are the possibilities of a bypass around Maastricht? The only area that could be used for a bypass is situated on the eastern side of Maastricht. The western side is Belgium territory or has a rocky soil. The area east of Maastricht has a more suitable soil. The problem here is that since Maastricht is situated in a valley, the eastern edge of the Figure 10.3 Stop living in the floodplain and relocate to the higher parts. urban landscape is situated 25 meter above the level of the Meuse. Therefore the bypass should be at least 25 meter deep before it This option always lingers in the back of the minds who think about can function. The effect that such a bypass would have on the the flooding problem. Why do people even live in areas where a flood landscape leads to the conclusion that a bypass around Maastricht can occur? It is much safer to live in areas that are situated higher is also unfeasible. than any known potential water level. This is legitimate reasoning and it has some advantages, but also some disadvantages. The most obvious advantage of leaving the floodplain is the absolute guarantee that people will be safe from flooding. When all people and buildings are relocated to the higher grounds of Limburg the water will never be able to threaten them. Another advantage is the amount of land made available by leaving the floodplain. This land can be used for the development of nature or agriculture. However, in the sense of safety, this land could also be used to protect the urban landscapes in the lower situated diked river-landscape in the centre and West of the Netherlands. Large basins could be built to keep the water from reaching these areas. If the complete floodplain of the Meuse in Limburg is used, then the possibility of a large dam is also possible. This should be built at the place where the Meuse valley transitions into the diked river landscape of the west of the Netherlands. This dam would allow normal discharges to flow directly to the north sea but when the water levels reach levels above 1500m3/s it could keep the water in the Meuse valley. In this way, the entire Meuse valley in Limburg can fill up with water and be used as one large storage basin. This would keep a large population in the lower situated Netherlands safe from flooding. Other possibilities could also be imagined. The disadvantage of leaving the floodplain is the enormous cost of relocating all buildings and inhabitants outside the floodplain. Besides that, if the government accepts that the Meuse valley is a dangerous place to live and that the safety of the inhabitants Figure 10.2 Impact of a bypass around Maastricht. cannot be guaranteed, then all the capital in the floodplain will lose its value. All insurances, mortgages and other investments will lose their coverage. This is the main reason why the Dutch government will never admit that the polders in the west are a dangerous place to live, even though scientists claim otherwise. (Neuvel, 2007) 103 The option of leaving the floodplain lies far from the original goal victims are to be expected during a flood. This could be accepted of this thesis and requires much more research. This is the reason as a risk that the inhabitants of the Meuse floodplain are willing to why it will not be further discussed in this thesis. From a safety point take, but this seems unlikely. Since the safety of the inhabitants of view, this might still prove the best option though and this option of the floodplain is important for this thesis, this option will not be should be further investigated by others. discussed any further.
10.4 Continuing on the current path 10.5 Raising the urban landscapes
The main problem for urban landscapes in the floodplain of the Meuse is the high potential water levels. This problem can be solved by creating higher areas within the floodplain and start building on top of these so-called mounds. This method has been practiced all over the world, especially along the coasts of north-west Europe. A mound will create a safe place where urban landscapes can be built, which are never flooded or only flooded with low, acceptable water levels. This will lower the vulnerability of these urban landscapes considerably and consequently will have a low flood-risk. It does raise some large questions though. What should the shape be like? What height should such a mound have? How can an existing urban Figure 10.4 Maintain the current system, accept the risk of flooding and landscape be raised with several meters? These questions will be reserve a bag of money to compensate victims after a flood. answered in the next chapters.
Continuing on the current path means that the current dike system is maintained in its current shape and that the risk of flooding is accepted. The adaptations that should be made to cope with the climate change are not implemented. The money that is normally put into adapting the current system will be used for the insurance and compensations of any potential flood damage. This means that the inhabitants of the floodplain will face floods more often than now, largely caused by a changing climate. In case of a flood however, the gathered money can be used to compensate all the damage. The IVM Project has assessed the cost of the project. In Figure 10.5 To reduce the vulnerability and increase the safety, the urban this assessment, it is stated that these costs (2.0 billion euros for areas should be raised. Limburg) could compensate four floods. (Ministerie van Verkeer en Waterstaat, 2006) Such a flood would occur every 50-75 years, and since the IVM project reaches until the year 2100 it might be a more economical approach statistically speaking. It should be pointed out however that the high-water levels of 1993, 1995 and 2003 also had statistical return rates of 50-75 years and happened within a ten year period. The large advantage of this approach is the lack of effort that needs to be taken. The current situation will be maintained and any proposed measures will never be implemented. Naturally this will have a very low cost, apart from the maintenance of the current dike system. The large disadvantage is that this calculation did not include human casualties or injuries. It is already shown in previous chapters that the water levels and flow speeds are potentially lethal and thus 104 Analysis of Arcen
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105 11. Analysis of Arcen
In the last chapters, it was proven that making the urban landscapes in the valley of the Meuse complete or partial flood-resilient won’t result in an acceptable level of safety. The only possible flood protection approach that can guarantee a sufficient level of safety for the Meuse floodplain seems to be raising the urban landscapes. The possibilities of raising an urban landscape will be investigated in the next chapters. To test whether a raised urban landscape can become safe and whether it will still be attractive and functioning, it is necessary to zoom in on the Meuse floodplain and choose a specific area to design and test in. The village of Arcen was chosen for this.
11.1 Choice for Arcen
Arcen was chosen as one of three different urban landscapes in the Meuse floodplain. Originally, the goal was to design and test three different urban landscapes, one of every category that is present in the Meuse floodplain (see chapter 5). These three urban landscapes were partly chosen for their location and partly because of the data that was available on these urban landscapes. As time passed and the process went on it became clear however that three different urban landscapes would take more time than was available for this thesis. Therefore, this thesis focuses on Arcen, as an example of a Figure 11.1 Location of Arcen within Limburg floodplain village. The two other urban landscapes were Maastricht and Oost-Maarland as examples of valley towns and terrace villages respectively. The choice for a floodplain village is based on the fact that most flood-prone urban landscapes are floodplain villages. Moreover, the flood problems are the largest in these urban landscapes, with the highest water levels and the highest flow speeds. If these problems can be solved here, then it should be possible to export the found solutions to the other urban landscape categories.
11.2 Description of Arcen
Arcen is a small village in the northern part of Limburg, comparable in size to other villages in the floodplain. It is situated approximately 10 km north of Venlo and 3 km west of the German border. It is situated in the terrace landscape of Limburg, in the floodplain of the Meuse, on the eastern bank of the Meuse
Figure 11.2 Topographic map of Arcen
106 Landscape Arcen is thus situated in the so-called terrace landscape of Limburg. This landscape is known for its terraces that are situated alongside the river and are situated above one another like a staircase. In the landscape, these terraces are flat areas on different levels with steep, sudden rises to other terraces. They have their origins in the last ice age, when the sea level dropped and the erosion of the Meuse increased because of the bigger difference in height between sea and source of the river (see chapter 2 for the exact process). The resulting landscape can be divided into three categories: the plateau, the terraces and the floodplain. The plateau is the original landscape through which the Meuse has cut its way and is essentially the highest situated terrace. It largely consists of small-grained sand called loess, deposited after the last ice age. The terraces are old floodplains of the river Meuse. Since the second-last ice age the river has moved westwards, cutting deeper Figure 11.3 Aerial photograph of Arcen. (Google-earth, 2009) and deeper into the landscape, leaving the terraces east of Arcen. After the last ice age these terraces were covered with sand by the wind, resulting in the Maasduinen (Meuse dunes) The only terrace edge that can still be seen, is the one on the edge of the floodplain, the others are underneath the Maasduinen. On the western side of the floodplain, there is a steep rise to the old plateau. Here the river has eroded away the plateau directly as it moved westwards. The floodplain itself is not entirely flat. As can be seen on the relief map (figure 11.4), there are old, deeper river arms and small, higher situated islands, which is the result of a constantly changing riverbed.
The land use of these different landscape categories differ widely. The loess that covers the plateau is ideal for agriculture. Therefore, the plateaus are mainly used as agricultural land. The terraces are normally also used as agricultural land, but since the terraces near Arcen were covered with unfertile sand, which was unsuitable for agriculture, this was impossible. As a result, nature flourished here and this has resulted in one of the most valuable nature reserves of Limburg. It mainly consists of forest, with some heath lands and ponds. The floodplain is also well suited for agriculture because of the fertile sediment that the Meuse has deposited. Yet, the high groundwater levels make agriculture difficult on many places, especially the old river arms. Therefore, the old river arms mainly consist of grassland, while the higher areas are used for agriculture, or even tree nursery on the very fertile parts. The village of Arcen itself is situated near the river Meuse, on the eastern bank of the river, actually bordering it directly at the southern tip of the village. It was built on one of the higher situated ‘islands’ in the floodplain.
Figure 11.4 Relief map of Arcen.
107 History Arcen is an old village; it first appeared on the map around the year 0. The Romans built a fortress (arx in Roman, hence the name Arcen) near the river for protection against the barbarian forces from the north and to improve the movement of troops along the Meuse river. When the Romans left and the Franks took over, the village began to decline and it was not until the 14th century that it became an important settlement again. During this period, Arcen was acknowledged as a free town, which was allowed to govern itself. The lords of Arcen made sure that every ship that passed the town was forced to trade goods on the market of Arcen. This made Arcen a very wealthy town. The old buildings and forts in an around the village are a testimony of these times. At some point during the middle ages, Arcen even had its own town wall with gates. Arcen never became a big town though, mostly because of the river Meuse, which was a constant Figure 11.5 Aerial photograph of Arcen. (Blieb, 2007) threat to buildings built outside the higher ground on which Arcen was founded. Another reason why Arcen remained small was the constant fighting over the strategic important settlement. Especially the 80-year war with Spain was harsh for the inhabitants of Arcen since it was burned to the ground on several occasions. (Stichting Heemkunde Arcen, 1997)
Current situation Nowadays the village of Arcen has a total number of 2546 inhabitants. (Gemeente ArcenenVelden, 2008) The economy has changed a lot since the middle ages and is now mainly focused on the many tourists that visit the old castles and gardens around Arcen or enjoy the landscape of the Maasduinen. Apart from the many cafes and restaurant for the tourists, the village has very little industry or other businesses. It mainly consists of houses where people live who work elsewhere, mainly in Venlo. Figure 11.6 Aerial photograph of Arcen. (Blieb, 2007) The buildings in Arcen were mostly built after the Second World War. There are some buildings left from before the war, mainly around the village square, but these are rare.
Flood and flood protection Arcen was one of the villages that were flooded during the floods of 1993 and 1995. The water levels were relatively low, compared to the potential water levels. Nevertheless, the damage to buildings and the public space was substantial. Luckily, there were no casualties. The minister of water affairs at that time ordered protective measures to be constructed to protect the flood stricken areas in 1993. Most of these measures were not finished in 1995, which is the reason why Arcen was flooded again, even though the water levels were lower. (SchrojensteinLantman, 2004) Figure 11.7 A memorial in the centre of Arcen on a relatively As a result, many of the houses were damaged, although nobody was high part of the village, showing the water levels of the flood of 1993. The water levels during a 4600 m3/s will be 1.5m higher. injured. The former minister of water affairs ordered that emergency
108 quays were to be constructed around the flood stricken areas. As a result, Arcen is now protected by quays that are supposed to hold water levels with a return rate of 1/250 which corresponds with a discharge of 3150 m3/s. This quay doesn’t completely surround the village but is connected to the higher grounds to the east. These higher grounds and the quays themselves, are not high enough to stop a 1/1250 event however and therefore the village could easily be flooded, even in the current situation.
11.3 IVM around Arcen
Even though the only safe way of living in the Meuse floodplain is to heighten the current urban landscapes, there are some interventions that can be taken in the floodplain itself that might make this task an easier one. The IVM project is a good example of a set of interventions that lower the water levels, creating a safer urban landscape. Since this set of interventions is placed outside the urban landscape and contribute to a lower water level in the Meuse floodplain, there is no reason to not implement them. This is why the proposed interventions around Arcen are used for the remaining part of this project.
Figure 11.8 Quays around Arcen, which are connected to the higher grounds 11.3.1 The IVM measures around Arcen in the east.
A list of proposed IVM interventions can be found below. The total effect of all these interventions will be that the water levels of a 3950 m3/s discharge will be lowered to the current dike level, which currently can deal with a discharge of 3150 m3/s, a difference of 80 cm in water level.
1. Green river Broekhuizervoort This green river starts as a 500 m wide corridor at the village of Broekhuizervoort. After 4.5 km it splits up in two separate green rivers of 250 m wide. The eastern branch leads to Blitterswijck. The western branch leads to Wanssum and flows back into the Meuse through its harbour. (Very high effectiveness, low costs)
2. Green river Wanssum Figure 11.9 A part of the quay that protects Arcen against flooding. This is a variation of the green river Broekhuizervoort. The eastern branch still leads to Blitterswijck but the western branch bypasses Wanssum and Meerlo until it flows back into the Meuse near Maashees. It makes use of old stream-valleys, which need to be connected by excavating the intervening higher grounds. (Low effectiveness, high costs)
109 3. Retention at Broekhuizenvorst North This elongated retention area is situated between Broekhuizenvorst and Wanssum. The area mainly consists of meadows but some are planted with production-forests. (High effectiveness average costs)
4. Mix of stretch-bound measures The IVM project has proposed several large-scale interventions within the river forelands of the Meuse along the zandmaas stretch of the Meuse. In the vicinity of Arcen these are: Lowering of the summer-bed. Along the zandmaas stretch the summer-bed of the river will be lowered with 2 meter. Lowering of the river-banks Along a 250 m wide stretch on both sides of the river the river- banks will be lowered with 1 meter. Lowering of the river-foreland The winter-bed of the river can be lowered with 0.5 to 3 meters on both sides of the river, depending on the local conditions. Widening of the winter-bed On some locations the winter-bed of the river can be widened by digging away some of the terraces. Near Arcen this could be done near Grubbenvorst-Broekhuizen on both sides of the river. Figure 11.10 IVM measures around Arcen (Low to very low effectiveness, high to very high costs)
5. High-water trench Grubbenvorst This trench makes use of the natural depression in the winter- bed near Grubbenvorst. The trench will be 2.5 km long and will be situated in an area that is mainly used as agricultural land. The relation between Grubbenvorst and the Meuse can be enhanced with this trench. (Low effectiveness, average costs.)
6. High-water Trench Aastbroek This high-water trench is situated on the western side of the river. It is around 2 km long. (low effectiveness, low costs)
110 11.3.2 Effects of the IVM measures
It is assumed that the IVM measures will keep the water level during a 3950 m3/s flood event below the height of the quays that have to protect Arcen (see figure 11.11). The height of this quay is currently set at 17.00m N.A.P. (Limburg, 2008) We stated before that the discharge that we will design for is 4600 m3/s, the middle scenario of the KNMI predictions. A rule of thumb now shows that the water level will become then 17.65 m N.A.P. at Arcen. (RIZA, 2005) With this information, it is possible to see what the new water levels will be in Arcen during a flood that will occur in case of a discharge of 4600m3/s. It’s clear that when the water levels of the river exceed the water level that accompanies a 3950 m3/s discharge, the quays are overflowed and Arcen is flooded. Figure 11.12 shows the impact of a 4600 m3/s discharge.
11.4 Conclusion : The village of Arcen is taken to do research by design on how an Figure 11.11 When a discharge of 3950 m3/s appears, the water is kept urban area in the valley of the Meuse can be raised to make them below dike level and Arcen remains dry. safe against floods. When the IVM is taken into account, the village of Arcen will still face a flood when the discharge is higher than 3950 m3/s and this is the case with the middle scenario predictions of the KNMI. Therefore it’s necessary to raise this village to a safe level. It is expected that the design principles that will be found can be projected on other floodplain villages and possible also on parts of the valley towns and terrace villages.
Figure 11.12 With a discharge of 4600 m3/s Arcen is almost entirely flooded..
111 112 The concept of raising Arcen
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113 12. The concept of raising Arcen
Within this chapter the most important questions that accompany the assignment of creating a higher situated, static urban landscape on a mound within a dynamic floodplain will be discussed. When an urban landscape is raised to a certain height, an artificial island will be created in the floodplain of the river. From now on, this island will be called a mound. (An artificial heap of earth or debris.) Such a mound will have a large impact on the urban landscape itself but it will also have a large impact on the surrounding landscape. Figure 12.1 Large objects in the floodplain dam up the water and raise water Moreover, since an artificial heap of earth has a higher density than levels further upstream. Consequently the ground level needs to be raised an urban landscape with spaces between the houses, there will be further and further. less space for water during a flood. This will have an effect on water levels and increases the flow speed directly around the mound, but Since safety is the ultimate goal of raising an urban landscape, the also further upstream and downstream. (Rijkswaterstaat, Dienst mound will have the highest allowed ground level. The quays around Limburg, 2009) Arcen have a height of 17 m N.A.P. and therefore the mound will get Flood-resilience may not be the best solution for the flood problems this 17 m N.A.P. of Limburg by itself, but the basic ideas of the theory can still be Currently the quays will protect Arcen against a flood accompanying used. Measures that are implemented in the floodplain should have a discharge of 3150 m3/s (1/250 year). The IVM project proposes as little influence on other parts of the floodplain as possible. This can measures in the floodplain around Arcen. In the future, the water be achieved by taking the flow speed, flow direction and water levels levels will rise and the discharge accompanying a chance of 1/250 into account when creating design suggestions for the mound. year will become 3950 m3/s. The IVM measures are supposed to This raises three main questions that will now be addressed. First, reduce the water level far enough to prevent a future discharge of what should the height of the mound become? This question can 3950 m3/s from overflowing the current quays. This does implicate be answered by looking at international policy. Second, what shape however, that the mound will overflow during a higher discharge, should the mound get? This question can be answered by looking at such as the 4600 m3/s that this thesis maintains as the standard. nature. Lastly, what is the best location for the mound? This question During a discharge of 4600 m3/s, the water levels on top of the can be answered by looking at the present landscape. mound will be 65 cm. This is enough to cause serious damage to the urban landscape. Therefore, further flood protection is needed. In chapter 8, we stated that the use of flood-resilient techniques in the floodplain was impossible because the water levels were too 12.1 The height of the mound high. Since the water levels on the mound will only be 65 cm, it becomes possible to implement the flood-resilient techniques. This If a mound is to be designed to create a safe living environment way, the urban landscape can be protected against a flood of 4600 for the inhabitants of the floodplain, then it should be given such a m3/s without causing problems elsewhere. These measures will be height that even the extreme water levels will be unable to flood the discussed later in this chapter. First, the shape and location of the mound. That would be the ideal situation for a mound. mound are discussed. One of the criticisms against the use of dikes is the effect that they have on the water levels further upstream. (Neuvel, 2007) These water levels will rise, thus the creation of a dike actually worsens the problems elsewhere. The placement of a large solid object, like a mound, in the floodplain will have a similar effect on water levels in the upstream area. This shifting of problems is considered unsocial. As a result, the government has strict laws that forbid any measures that shift the problem to other areas. Even on an international level, there are laws and agreements that state that problems cannot be Figure 12.2 When the discharge of 3950 m3/s is exceeded, the mound will shifted to other areas, upstream or downstream. (Bos, 2009) flood. Therefore flood-resilient techniques have to be applied. These laws have a direct effect on the potential height of the mound. The mound cannot become higher than the current quays that protect Arcen. If the mound is designed with a higher ground level, there will be a negative influence on water levels elsewhere. (Dijksma, 2008)
114 12.2 The shape of the mound
A mound will have a large influence on the water levels. According to the theory of flood-resilience, it is necessary to reduce this impact. Therefore, we will study the best shape for the mound with the least influence on the water levels. To find the best shape for a mound, which is a shape that has the least effect on water levels, nature can be a good example. Everything in the universe has to comply with the laws of nature, like gravity. As a result, many shapes are common in nature, simply because they work according to the rules. This is shown by parallel Figure 12.3 Hydrodynamic shape of a carp (Bulmash, G. 2007) evolution, which is the development of similar characteristics due to adaptation to similar environments and strategies of life in organisms that are not closely related. (Farabee, 2000) An example of this is the development of wings by birds and the bat (which is a mammal). The same is true for hydrological efficient shapes, also called hydrodynamic shapes. Many animals live in or around the water. The best example is, off course, the fish. This animal has a distinct hydrodynamic shape, broad in the front and becomes narrower near the end (figure 12.3). Such a shape is the most cost-efficient for the fish.
Another good example is the natural shape of islands within rivers. Fluctuating water levels and currents erode the land and leave island in the river. Since water seeks the course with the least friction, the shape of the islands that are left after erosion is the most hydrodynamic shape possible. To get a good impression of the shape of such an island, the untouched rivers of Siberia can serve as Figure 12.4 Naturally formed islands in Siberia (Google-Earth, 2009) a good example (figure 12.4). These islands have the same shape as the fish has, broad front, narrow end. In the past the Meuse also had this kind of islands, but they were removed to improve the flow rate of the river and increase the shipping capacity (see figure 12.5). (Ven, Van de, 1993)
Humankind has been inspired by these shapes when it comes to making objects that are exposed to water. One of the best examples is the canoe, which has existed in the same shape for thousands of years. (AScribe, 2006). Here some difference is found comparing to the more natural shape however (figure 12.6). This can be ascribed to the more functional use of a canoe. Humans and goods had to be transported for which room was created in the back of the boat by making it wider. Figure 12.5 Naturally formed island near Borgharen, Limburg on the map of the The shapes of these examples can be reduced to the following year 1825 (Chart Room, 2008) measurements. The shape of the objects is 4.5 times longer than the width of the object. The widest part is situated on one-third of the length of the object, seen from the front. The centre line of the object does not always need to be straight. The end point of the object can move away from the centre and curve the whole centre Figure 12.6 Hydrodynamic shape of a canoe (REI, 2008)
115 line, just like an island in a river bend or the tail of a fish would do when it is swimming. From these examples, it can be concluded that this shape is the most hydrodynamic shape that can be created in the floodplain of the Meuse. (see figure 12.7) Water will easily move beyond the mound while causing the least friction. This improves the durability of the mound and therefore the safety level. In addition, it will have the least effect on other parts of the river since it has little effect on the natural course of the water. Furthermore, the shape will be beneficial to the water levels in upstream areas, since the river can discharge water quicker because of the streamlined form of the mound. The mound will therefore be created with this shape as a starting point.
12.3 Location of the mound
This still leaves the question of where this mound should be located. To answer this question we look at the current landscape in which Arcen is situated.
The process of creating a mound in the floodplain will take a long Figure 12.7 Hydrodynamic shape of the mound time, possibly 50-100 years. Technically, the new mound could be created anywhere in the floodplain. However, if the urban landscape will be raised over a long time span, this could mean that the village consists of already raised parts and lower situated parts for a long period. When building on new locations around Arcen, this could result in a divided Arcen and a village consisting of two half villages or even more for decades is unacceptable. Therefore, the new mound has to be created within 500 m of the current village. This distance will guarantee that the village will never be separated in different parts. The relocation of this many houses to a new area could also pose many legal issues, especially when a municipal boundary is crossed. These are prevented by staying close to the original location of the village.
Figure 12.8 A new mound has to be created within 500 m of the current village.
116 Another aspect of finding the right location for the mound is the location of the current quay. This quay can be used as a starting point of the new mound. It provides a relative save area behind the quays, outside the dynamic winter bed of the Meuse. On the riverside of the quays, the river is more powerful. High water situations may make it difficult to build a mound on the riverside of the dike. In that case, the mound is built in the floodplain and there you do not have control over when and how strong high water levels will appear. Therefore, it is logic to construct something around the construction location of the mound in this case to prevent the construction location. This will take an extra part of the floodplain and will thus create higher water levels upstream, which is strictly forbidden. So constructing the mound behind the dikes in an area that is much less influenced by the river is much easier.
Figure 12.10 The current quay around Arcen.
Figure 12.9 The current quay around Arcen.
Figure 12.11 The area behind the current quay.
117 During a 4600 m3/s discharge the flow speeds of the river can become very high in the lower areas of the floodplain, where water levels are higher. The flow speeds in such areas can become high enough to erode away the mound. Therefore it is crucial to place the mound in a relative calm area of the floodplain. These calm areas can be deducted from the flood map. The deeper parts of the floodplain will flood earlier during a high water event and will also have a faster flow rate. The higher parts of the floodplain will be safer to build on. The height map shows that an old meander runs on the eastern side of Arcen. (figure 12.12) This meander is likely to flow faster than the other parts of the floodplain when the dikes are overflowed. Another, smaller meander runs west of the current location of Arcen. When these currents are drawn in a map, it is possible to deduce the calmer areas of the floodplain.
Figure 12.12 This flooding map shows an old meander east of the village.
Figure 12.13 The currents that appear around Arcen
118 When these three aspects of finding the right location for the mound are combined in one map, the overlapping part will show the best location for the new mound. Figure 12.14 shows the result. The ideal shape of the mound should be projected now on this remaining location area and needs to be adapted to the currents that occur during a 4600 m3/s flood (figure 12.15). The shape of the mound is not straight but has been slightly curved towards the river to accommodate the influence of the currents in the meander on the eastern side of Arcen during a flow rate of 3950 m3/s or higher. When the mound is built, the quays will cease to have a function, since the houses will be safely placed on top of the mound. Therefore, they can be removed. This produces an opportunity to create a new high-water trench on the eastern side of the mound. This trench would follow the old meander. This has some effect on the shape of the mound since the meander does not follow a straight line but meanders a little. The result is shown on the map in figure 12.16.
Figure 12.14 Combining the diked area, 500 m zone and appearing currents gives the location for the mound of Arcen.
119 Figure 12.15 The location of the mound. Figure 12.16 The final location and shape of the mound.
120 12.4 Concept of appearance of the mound
Now that the location, shape and height of the mound are known, the appearance of the mound can be designed, at least on a conceptual scale for now. There is a multitude of different aspects, which could be used as a guideline for the design of the urban landscape, ranging from small-scale climate to ecology. However, since this thesis focuses on the flood-resilience and flood risk of the urban landscape we will discuss the aspects that give answer to the following questions.
1. Is there space and necessity for areas that need extra protection on the mound? 2. Which measures can lower potentially dangerous currents in the urban landscape? 3. What design will allow a safe flooding of the mound? 4. How will the water act inside the urban landscape? 5. How will the connectivity of the mound be maintained during a flood?
12.4.1 Is there space and necessity for areas that need Figure 12.17 Relief map of Arcen and surroundings. extra protection on the mound?
From a safety point of view, some buildings and urban functions should never be allowed to flood. These include the emergency services and other services like supermarkets. These functions are of such an importance to the lives of the inhabitants and the functionality of the urban landscape that they should not be allowed to flood. For a small town like Arcen at least the following buildings should have a safer area where they could be situated. • Doctor • Police station • Fire department • School and gym (if extra accommodations are needed) • Church • Supermarket • City hall (coordination centre during a flood)
When an urban landscape is larger or located far from other cities, this list could be extended
Whether there is room for such an area, can easily be checked by comparing the required area with the available area. The mound was planned on a location where the floodplain was already relatively high. Some parts are that high that they won’t be flooded by the Figure 12.18 One part of Arcen isn’t flooded when a discharge of 4600 m3/s appears
121 highest predicted water levels, as shown in figure 12.18. Compared with the space required for the services this location seems to be large enough, as shown by figure 12.19.
The shape of this higher area is very irregular, which will have consequences for the currents on top of the mound during a flood. The currents become less predictable and as a result, the erosion damage and danger to humans will increase. Therefore, the higher area should be shaped hydrodynamic, in the same way the mound has been shaped, which results in a shape as shown in figure 12.20. This area will henceforth be called the sub-mound
Figure 12.19 The higher situated area is big enough to contain all the important buildings.
Figure 12.20 The sub-mound should have a hydrodynamic shape to guide the currents.
122 12.4.2 Which measures can lower potentially dangerous currents in the urban landscape?
The Meuse is a very calm river for a large part of the year. The speed at which the river flows is quite slow and sometimes the river can even be crossed by foot. (Provincie Limburg, 2004) This all changes when the water level rises. As the water level rises, the rate of flow increases and the force of the water increases with it. Eventually the rate of flow can reach speeds of 3 m/s. (Rijkswaterstaat Dienst Limburg, 2008a). To make a calculated guess of this speed and possible effects, we can make a comparison. In tropical swimming pools in the Netherlands it is very common to have a small part where water is accelerated to produce a “wild water” effect. The water level in these parts of the pool is mostly around 1 meter. Even grown men have trouble standing upright such a stream, while the rate of flow is only 1 m/s. If 1 m/s is already life threatening to people, then 3 m/s would be completely devastating for the urban landscape. Therefore, the rate of flow on the mound has to be slowed down to an acceptable level. The front of the mound is however located near the river, right near a bend. The kinetic energy of the flow is pointed directly at the front of the mound. Within the river itself a flow speed of the water of 3 m/s can be reached. A large amount of water with such a flow speed has the power to destroy buildings. Therefore, a barrier has to be erected to guide the kinetic energy around the edges of the mound. Figure 12.21 The barrier on the head and the submound direct the currents and slow down the flow speed. Once the flow is parallel to the mound the forces are not directed at the mound and water is allowed to flow into the urban landscape. Behind the barrier, a relatively calm area will exist where it is possible to build a flood-resilient urban landscape. Apart from the forces of the river, there is also a high-water trench on the western side of the river, proposed by the IVM project. This will force water against the western side of the mound; therefore, the barrier has to be extended here. Because of the barrier the currents on the mound will be altered, therefore the shape of the sub-mound has to be altered again. The shape of the barrier and new shape of the sub-mound are shown in figure 12.21.
123 12.4.3 What design will allow a safe flooding of the mound?
Flood-resilience is based on the principle that it is better to cope with a flood than fighting against it, because the consequences are too big when the fight is lost. Applying this way of reasoning, urban landscapes can be flooded during very high water levels, but at the same time, they are prepared for it. The main question is however how they are prepared. When a look is taken at other areas in the floodplain that are designed to be flooded, like a bypass, it can be concluded that they are designed to start flooding from the most downstream point towards the most upstream point. Put otherwise; first, they fill up with water from the downstream point and then they start flowing along with the river. They never flood from the upstream part because this causes a lot of erosion. It is better to fill the bypass with water before it starts to flow with the river, because this reduces the force of the water on the construction of the bypass. Figure 12.22 The higher the water level, the higher the flow speed and Near the bottom, a stream always flows slower than in the top layers thereby the chance for erosion. of the stream because of the irregular surface. Water always takes the path of least resistance and therefore the water in the upper water layers flows a lot faster since there is less friction here. When the kinetic energy of the water is high, more energy is directed against the irregular surface. In most cases the surface will loose this battle and will be swept away, which is called erosion. Figure 12.22 shows this process.
The same erosion effects occur in the urban settlement. When water is allowed to flow in the streets of the mound at the same speed as in the river, there will be a lot of damage and injuries. That is why the village needs to be flooded in a slow and controllable manner. It is also the reason why there is a barrier at the front. This way the river will flood the urban landscape slowly and the water on the mound will have a very low flow speed. The eastern and northern sides of the mound are the best places where water can flow into the urban environment. The flow speeds are the lowest at these locations and the direction of flow is faced away from the mound, which results in less damage. To make the flooding controllable, the water should only be allowed to enter the mound at several locations. This way the currents within the urban landscape are more predictable. Therefore, another barrier with openings is built on the edges of the mound. These openings should be large enough to let enough water in though; otherwise, the water in the floodplain will rise faster than on the mound. As a result, the pressure will rise and the water will pour through the opening with higher speeds than allowed. A speed of 0,1 m/s seems appropriate for the flow speed in these openings. The water levels can rise with 3.5 cm/hour during a high-water event. (Ministerie van Verkeer en Waterstaat, 2001) With these numbers, it Figure 12.23 Inlets will let the mound flood in a controlled way. is possible to calculate the required size of the openings.
124 The area of the flooded mound is 734,290 m2. Therefore, every hour 25700 m3 of water will need to flow through the openings. This amounts to 7.1 m3 that flows into the urban landscape every second. Knowing this, the size of the opening can be calculated. If the flow speed should be 0.1m/s then the opening should have a circumference of 71 m2. The height of the openings varies during time. At the start of the flood, the water levels are only 1 cm above the ground level of the mound. At the highest point of the flood, the water level will be 65 cm above ground level. The height of the opening is therefore variable. To complete the calculation, the average water level of 32.5 cm is taken. As a result, the length of the openings should accumulate to a total of 218 m. The eastern side of the mound is the best place for the situation of these openings. The flow speed is lower here as the floodplain is less deep. The eastern side of the mound has a length from front to end of 2.1 km, which means that the openings are roughly 10 percent of the total length of the eastern side of the mound, as seen in figure 12.24.
The openings can be spread out equally over the eastern side of the mound. Through these openings, the water will enter the mound. Once the mound is flooded, the water will begin to flow northwards Figure 12.24 10 percent of the eastern side needs to be “open”. The upstream part will have more openings than the downstream part to slow down due to the gradient of the mound and the influence of the river. The the currents on the mound. exact flow speed is unknown; nevertheless, it should be kept to a minimum. Therefore, a better solution is to have more openings on the upstream side than on the downstream side of the mound. In this way, the water can easily flow onto the mound but is partially blocked when it flows back into the floodplain at the end of the mound. Effectively this slows down the water flow speed, which increases the safety level. (Dijksma, 2008) Lastly, when water is allowed to flow onto the mound, it should be slowed down, otherwise the flow speed might be too dangerous. This can be done by placing the objects around the openings in such an angle that the water has to make a turn of more than 90 degrees to flow onto the mound. Effectively it will first hit the side of the openings, which slows down the water, after which it gently flows onto the mound. What the appearance of these openings can look like will be discussed in chapter 13.
125 12.4.4 How is the water guided inside the urban landscape?
Water will always flow in Arcen. The reasons for this are the natural gradient in the landscape and pressure differences between bodies of water on the mound and in the floodplain, when the water level rises or dwindles. To improve the safety of the urban landscape during a flood, it is important to make these currents predictable and reduce their flow speed. There are two simple categories of objects that have an influence on these currents, namely three-dimensional objects and flat surfaces. The three-dimensional object impedes the flow of water and can be used to guide water in the desired direction. Flat surfaces on the other hand, do not impede flow but are the areas where water flows. For a small urban landscape like the village of Arcen, where urban green is little present, these objects can roughly be categorized as buildings and streets. Gardens can also have a large influence, but since they are privately owned and therefore very irregular in appearance, they will not be used in this concept. The situation of the streets is crucial to the currents within the urban landscape. There are two separate ways in which the streets can be aligned with the currents. The fist one is where al the streets are diagonally aligned with the currents. This will lower the flow rate of the water equally in every street. The question is whether this will be enough though. The other method is to place some roads parallel to the currents while others are placed in a right angle to the currents. This way the parallel streets will direct the water while the streets that are situated in a right angle will have a very low rate of flow. Effectively, this will create zones in the urban landscape where the flow speed is very low, which is safer. The diagonally placed streets would not have these zones; therefore, we dismiss this method and adopt the parallel-right angle method. The parallel-right angle method has as a result that streets will be constructed in a grid pattern. This has one mayor drawback however. When the streets that run perpendicular to the current are too long, they will begin to flow also. When streets do not form a grid, the hooked streets will be shorter and will not begin too stream since the streams are impeded at two sides. This layout is shown in figure 12.25.
The currents that are present on the mound after the previous design interventions are roughly shown in figure 12.27. These currents will be the guidelines for the streets that run parallel to the currents. Side streets will be placed perpendicular to these currents. The exact location will be discussed later in the design phase.
Figure 13.25 Buidlings and streets are used to make the currents predictable with a low flow speed. The streets have to be placed perpendicular and parallel to the flows of the water.
126 12.4.5 How will the connectivity of the mound be maintained during a flood?
One of the goals of this thesis is that urban landscapes should still be livable during a flood. This means that inhabitants can still sleep in their houses and are able to move outside if necessary. This does not take away the need for an evacuation route though. Emergency services should be able to reach the inhabitants during times of need and inhabitants should always be able to leave the mound if they wish to do so. It is impossible to connect every building with an evacuation route however. Therefore, there shall be one route through the urban landscape, with 2 connections to the higher parts of the landscape. This route should be designed in such a way that every building on the mound lies within a zone of 300 m around the evacuation route. This would mean that every person is able to move outside the settlement when he/she wants to and that the settlement is easy to reach in case of emergency. The evacuation route is never allowed to flood, not even during the highest floods. This is very important since cars are very susceptible to the force of water and they will be caught by the current even before a human is swept away. Yet, the route should not obstruct the water flow inside the urban settlement. Therefore, the route is likely to be placed on poles. Another method is to make a floating road Figure 12.27 Roughly the main currents on the mound. that rises with the water levels. These possibilities will be explained in the design phase.
Figure 12.28 An evacuation route will keep the mound always connected to Figure 12.26 Floating road (Waterforum online, 2003) the higher part
127 12.5 The process of raising an urban landscape should then be raised, creating a dike around Arcen in the shape of the mound. This will free up more floodplain that can be used during We have concluded that the safest approach to protect an urban high discharges and lowering the water level. landscape in the floodplain of the Meuse is raising the ground level After this, the head of the mound should be constructed. This area will of that urban landscape. In this chapter, we have shown what shape keep the remaining part of the urban landscape safe by guiding the and height such a mound needs to get to minimize the impact on forces of the water around it. Nowadays, the front side of the mount the floodplain. However, at the location where this mound should be is the centre of Arcen. This centre houses many of the important built, an urban landscape already is present. This means that all the functions of the urban landscape, which should be moved to the houses will have to be demolished, the ground raised and then the highest part of the mound, the sub-mound. So, at the same time houses have to be rebuilt. It is impossible to transform the complete that the head is constructed, the sub-mound should be constructed urban landscape at once. It has to be a gradual process that allows also. Once the head is finished, the buildings on it can be occupied the urban landscape to function normally during the transformation, by inhabitants that live in areas that have not been raised yet. The minimizing the inconvenience for the inhabitants. The next question areas where the inhabitants come from can then be raised. From a is what this process will look like. safety point of view, it is best to move the inhabitants from the lowest areas first. This process can be continued until the complete mound First, the material that is needed to create a mound does have to has been build. come from somewhere. Not every material can be used to create a mound. Sand and clay, in the right combination, are the best materials This process will require a lot of time. However, the climate will also for dikes and therefore also for mounds. This material can be bought require time to change. At the beginning of this thesis, we have and shipped to the locations of the mound, but since the IVM project stated that the scenario that we use will run until 2100. This gives lowers the floodplain around Arcen and other urban landscapes, 90 years before the mound has to be completed. Yet, it appears material will become available locally. The use of this material can that the climate changes faster than was predicted. (KNMI, 2009) lower the costs of raising an urban landscape like Arcen. therefore, we state that the whole process should be finished within Figure 12.29 shows the amounts of material that becomes available the next 40-50 years. when the measures of the IVM project are implemented and the amount that is needed to create a mound in the location of Arcen. In cubic meters, the available material exceeds the amount that is needed for the mound. Yet, not all this material will be suitable to create a mound. Especially the top soil will have some degree of pollution and will be unsuitable. Moreover, the top soil is very fertile soil, which should not be wasted if the floodplain around Arcen is to remain an agricultural area. Therefore, the top soil will have to be removed and stored for later use. The layers of soil beneath the top soil can then be used. This layer consists mostly of sand and gravel. The sand can be used for the mound, the gravel can be sold and the money can then be used to buy material for the mound. Once the mound is created, the original top soil will be redeposited and used as agricultural land.
Second, the process itself. The first areas that need to be adapted are the areas around the mound. The buildings that are situated here should be adapted or moved to higher grounds. Then, the eastern side of the mound should be raised and connected to the dike. This will create a dike around Arcen, which will allow a high-water trench to be built on the eastern side of Arcen. The high-water-trench will allow more water to pass Arcen during high discharges, which will buy the urban landscape time to complete the process. Next, the western side of the floodplain should be adapted by Figure 12.29 The amount of material that becomes available by implementing removing or adapting the buildings. The western side of the mound the IVM project and the amount of material that is needed for the mound.
128 Design principles for a flood-resilient urban landscape on a mound
13
129 13. Design principles for a flood-resilient urban landscape on a mound In this chapter several of the design principles that could be 13.1.1 Urban green implemented on the mound of Arcen are discussed. Applying these design suggestions will guarantee the safety of the inhabitants of Urban green is a term that is used for all the plants in the public Arcen during a flood. We have chosen to show design principles space, ranging from grass to trees. Urban green is used for a number because, although in an ideal situation, a new layout of Arcen would of functions. Trees, for example, can be used for shade, guidance, be designed, there is too much uncertainty about the future for such beautification, etc. Apart from different functions for every plant, a design. Moreover, the actual realistic value of such a layout would every combination of plants can also have different functions. They not be worth the time and effort that is needed to create such a can form a park, roadside, garden or even a parking lot. Urban green layout, largely because such a design would be too specific for one therefore is very important for the functioning and attractiveness of urban landscape (Arcen) and would have little value for other urban the urban landscape. If Arcen should become a flood-resilient urban landscapes in the Meuse floodplain. landscape then one question is how urban green can be made As a result, this chapter will discuss the design suggestions of flood-resilient. several parts of the mound, instead of the whole. The design principles of these parts will illustrate how the most important The effects of floods on urban green are mainly dependant on the technical measures will work and at the same time how they can species of plants. Every plant reacts in a different manner to water improve the attractiveness and functioning of the urban landscape. and even within a species the individual plants react differently. Because these individual design principals are more focused on Some plants can withstand water for a large part of the year while the underlying principles of flooding, it should be possible to export others will begin to die after a couple of days. them to other urban landscapes. Before the actual design principles of the mounds are discussed, some more general design principles for the mound are discussed. First, the design principles of the urban space are discussed (chapter 13.1). Afterwards the design principles of the private space are discussed (chapter 13.2).
13.1 Design principles of a flood-resilient urban space
In the urban landscape, there is a multitude of objects present that does not belong to the category of buildings, which are discussed frequently throughout this thesis. These objects are mostly situated in the public space. Most of these objects differ from each other in many aspects like construction, shape and usage. Therefore, it is Figure 13.1Flooded trees need to have most of the leaves impossible to find a solution that makes every object in the public above water level (Lewis, 2007) space flood-resilient. As a result, the most important groups of objects in the urban space will be discussed, after which a solution The damage done to plants increases proportionally with the amount or list of solutions will be given for every group. These solutions will of leaves covered by water. Trees are therefore more resistant then be used in the design principles of the several parts of the to flooding than bushes, since their leaves are higher situated. mound. The main groups of objects in the public space include in Moreover, some species’ roots are highly susceptible to floods and no particular order: die off after a couple of days, after which regeneration does not take - Urban green place and the tree dies. - Infrastructure The effects of a flood on plants are also not always immediately - Public utilities noticeable. A plant may survive the flood, but can be severely weakened by it. Later it can be killed by other causes like a harsh As a general rule these measures should be “no regret measures”. winter, a disease or insects. This can still be attributed to the flood. This means that they are designed to be flooded and that they won’t (Iowa State University, 2008) fail during a flood, or that their failure won’t have an effect on the safety of the urban landscape.
130 Plants are difficult to heal after a flood and are even more difficult to adapt to a flood, contrary to manufactured objects like buildings. The only thing that can be done for urban green in a flood-resilient landscape is to choose flood-resilient species of plants for the planting scheme of the urban landscape. Some species are native to landscapes that are naturally prone to flooding. As a result, these species have evolved to resist or endure the effects of water. Such species should be used in a flood-resilient urban landscape. A couple of flood-resilient/resistant trees that can be used in a flood- resilient landscape are:
High tolerance Acer rubrum - red maple Fraxinus nigra - black ash Fraxinus pennsylvania - green ash Larix laricina - Eastern larch Figure 13.2 Acer negundo - Figure 13.3 Acer rubrum - Salix nigra - black willow Boxelder Red maple Taxodium distichum – baldcypress (Ayuntamiento de Sevilla, 2009) (Troy Highschool, 2009)
Intermediate tolerance Abies balsamea - balsam fir Acer negundo - boxelder Acer saccharinum - silver maple Alnus rugosa - speckled alder Betula nigra - river birch Celtis occidentalis - hackberry Fraxinus americana - white ash Gleditsia triacanthos - honeylocust Liquidambar styraciflua - American sweetgum Platanus occidentalis - sycamore Populus deltoides - Eastern cottonwood Populus tremuloides - quaking aspen Pyrus calleryana - callery pear Quercus macrocarpa - bur oak Quercus palustris - pin oak Quercus phellos - willow oak Salix alba - white willow Figure 13.4 Betula nigra - Figure 13.5 Liquidambar Thuja occidentalis - Eastern arborvitae River birch styraciflua - American sweetgum (Fishing Creek Tree Farm, 2009) (Van den Berk boomkwekerijen, Ulmus americana - American elm 2009)
Figure 13.6 Tree grate embedded in infrastructure (Tauntondeane, 2009)
131 13.1.2 Infrastructure
Infrastructure is a term that is used for the surfaces in the urban landscape that are used by people to get from point A to B. Examples are roads and squares. Most of these objects only have two dimensions and are flat. Since they are flat, the water will flow on top of these objects. This causes less damage since the energy of the currents is not directed against the objects, which is the case with buildings and other three- dimensional objects. Figure 13.7 shows this difference between buildings and infrastructure. As a result, little adaptations have to be made to the two dimensional infrastructure of a flood-resilient urban landscape. Nevertheless, some improvements can be made.
Infrastructural objects that do have a third dimension have to be more hydrodynamic to reduce to damage done by the flow of water Figure 13.7 Degree of loss related to depth of inundation (Messner & Meyer, against the object. 2005) Although the damage to infrastructure is relatively low, it can be further reduced by making the surfaces as smooth as possible. Pavement stones for example have cracks between them filled with sand. This sand will erode away during a flood and the pavement will get uneven as a result, which will have to be repaired after the flood. A smoother surface like asphalt or concrete will not have this problem; therefore, smoother surfaces are preferred in a flood- resilient urban landscape.
Even though the effects of water on infrastructure are small, the effects of a flood-resilient infrastructure on the safety of people can be large. People still use the infrastructure to move around during a flood. Usually the water is turbid and people cannot see the surface they are walking on. In such a case, a sudden difference in water level caused by height difference in the infrastructure can lead to personal injuries or worse. Therefore, sudden changes in height should be kept to a minimum or should be clearly noticeable during a flood. An example is given in figure 13.8. Figure 13.8 Sudden differences in height should be avoided. Lastly, infrastructure should be easy to clean after a flood. Sediment is deposited during a flood, which will stay behind in any irregularity and sudden height differences. When the infrastructure in a flood- resilient urban landscape is smoother, there will be less sediment in the streets after the flood. This, in turn, will speed up the process of going back to a normal live in the urban landscape, which improves the flood-resilience of an urban landscape.
132 13.1.3 Public utilities of fossil fuels (IPCC, 2007), it might be better to tackle this problem at the same time. When every building is able to produce their own ‘Public utilities’ is a term that is used for a multitude of objects that electricity, the use of fossil fuels will go down, eventually causing less deliver/remove substances or energy to individual buildings from flood-related problems in the future. Moreover, since the buildings outside the urban landscape, together with objects that are needed are not part of an electricity network anymore, there are fewer to control the delivery/removal. Examples are sewers for wastewater consequences when something goes wrong. When one electricity- removal and electricity cables for the delivery of power. Public producing object fails, only one building will be affected, instead of utilities are essential in the daily lives of a person, but they are highly a whole area. This works well with the flood-resilient principle, since vulnerable to floods. During a flood, it is common that most utility it lowers the risk of the overall urban landscape. networks are damaged and shut down. Because some of the public For the production of electricity, there are several possibilities, which utilities are extensive, sensitive networks, the influence of the flood work on different scales and have different prerequisites. For the may be noticed far beyond the flood-struck area. This can be the urban landscape, the following two options will work for sure, as case when a part of an electricity network is flooded and takes out they are already used elsewhere, namely: silent windmills and solar the whole system.(TMO, 2008) panels. These two options will have less effect on the appearance Since flood-resilience is a relatively new concept, there is no research of the urban landscape than a complete flood-resilient electricity data available about how to make these utilities more flood-resilient. network, and will lower the flood-risk of an urban landscape. Yet, since these utilities are essential for an urban landscape we will give some suggestions for them. These suggestions can be used as a starting point for future designs for public utilities. Since the public utilities are largely different and take a lot of time to examine separately, we will discuss the following larger categories of public utilities:
- Electricity - Gas - Water & sewage
Electricity Electricity is important for the functioning of many of the devices in a Figure 13.9 Solar pane.l (HeijTech Services, 2006) house. It is transported to the individual houses by an underground network of cables. This network is protected against the effects of small amounts of water, such as can be produced by heavy rain or groundwater. A flood will however cause problems for the distributor stations above the ground. These stations are not protected against large amounts of water and will fail, causing the complete local electricity system to fail. To safeguard the distribution of electricity, the network has to be protected against large amounts of water. This can be done by using some of the point-adapt techniques that are used for buildings. Placing distribution station on mounds or on poles will keep them out of reach of water. The same will have to be done with the electrical wiring underground, as these are not fail-safe. The negative effects on the appearance of the urban environment of this method can be called considerably. The network is now hidden from view by placing it underground. Placing these cables aboveground will create an untidy appearance of the public space, which we think is undesirable. Figure 13.10 Wind-energy generated by Quietrevolution. (Quietrevolution, Since the climate change is caused by men with their extensive use 2007)
133 Gas Gas is mainly used inside buildings for heating or cooking. It is transferred to these homes by pipelines underground. If people should be allowed to heat their house and cook, the gas delivery should be maintained during a flood. The gas network is a lot less susceptible to water, compared to electricity networks. Yet, if the Figure 13.11 Building on fire in flooded area (Spitsnieuws, 2009) network fails, it can create very dangerous situations where gas leaks catch fire and cause explosions or infernos. (U.S. Consumer Product Safety Commission, 2007)
It is however difficult to create enough gas on-site for every building, as is possible with electricity. Some machines do exist that are capable of producing gas for households. Yet, they require a lot of fuel, like waste and sewage, which is not always present, esspecially during a flood. Furthermore, they also require lots of space in most cases. There is a solution to this problem however: not using gas. Since the buildings already can produce their own electricity, it is better to use electricity instead of gas. Gas is nowadays used, because it is cheaper than electricity. This will change when electricity can be produced on-site. Moreover, electricity is much more efficient in converting energy to heat and it is cleaner. (Howell et al., 1987) Therefore, the buildings in the floodplain should not use gas anymore, just electricity. If this is impossible due to financial or other reasons, then a study should be made into how the gas network can be made flood-resilient. For the remaining part of this thesis, we will assume that it is possible.
Water & sewage Water is one of the most important substances for live on this planet. Humans cannot live without it and as a result, a lot of space is used for the transportation of water. Most of this system is placed underground however, just like the gas and electricity networks. It does take up more space though, as most of the network consists of large tubes, instead of wiring. There is also a difference in the tubes that lead to and away from buildings. When humans use water it gets dirty. This dirty water is potentially dangerous to humans and is therefore separated from the clean water. These two systems are called ‘clean water network’ for the clean water and the ‘sewage network’ for the dirty water. These systems work differently and the consequence is that there cannot be one method to make the water network flood resilient. Let us begin with the clean water. Drinking water may be the most important use of water for humans, but in actual litres, it is only a small portion (2%) of the total water usage that is transported to the house. Water is used in large quantities for the shower or for flushing the toilet. (TNS Nipo, 2008) Drinking water is however still Figure 13.12 System for private water supply (GWT Projects, 2009) the most important for humans, especially during a flood. Water
134 should always be available during and directly after a flood. Since 13.2 The private spaces in a flood-resilient urban the quantity of drinking water is comparatively low (1.8 l per person landscape. per day), it should be possible to produce drinking water on-site. This should lower the risk of the urban landscape even further as Private spaces are the areas that are owned by the inhabitants of there is no risk of a drinking water network failure. Several systems the urban landscape instead of the municipality. Mostly they consist are available that can create drinkable water from undrinkable water. of a plot with a building in it. The municipality has less to say about These have the size of a coffee machine and should be available in these areas because they are privately owned. This can cause some every building. problems for a flood-resilient urban landscape. Inhabitants can place This only solves the problem of clean drinking water however. A objects in their gardens that can pollute the water or hinder its flow. flood can last a whole week. During this time, people still need to Buildings can also be placed incorrectly or be adapted incorrectly. prepare food and clean themselves. Therefore, there is a need for The dangers for the safety are too big to let every person decide large quantities of water. Nowadays, an average person needs 126 what they want to do with their plots, gardens and houses. There litres of water every day. This amount is too big for a small machine should be strict rules that state what a person can do with their to produce. Even if it could produce such an amount, it would still houses and gardens. These rules should be focused on the safety need to get the water from somewhere and floodwater is not always of the complete urban landscape during a flood. We as landscape an option. Therefore, the current network should be adapted in such architects are unable to produce these rules, but for the remainder a way that it can withstand floods and deliver water during floods. of this thesis we will assume that it is possible. The personal water cleaners should still be available in very buildings As for the buildings, since the mound can be flooded, the buildings for extra safety. on the mound can also be flooded. Therefore, the buildings on top of the mound should be adapted to the flood. The water levels on Sewers are used to transport wastewater away from buildings to a the mound are a lot lower than they would be without a mound. As a cleaning facility, where it is cleaned and dumped. It also transports result, it is possible to use every flood-resilient point-adapt measure rainwater that falls on hard surfaces in the urban landscapes and that is described in chapter 7. The choice for the measures and that cannot seep into the ground. Because the rainwater is also where they are used should however be made by the municipality transported by the sewer system, the system is highly susceptible to and designers, not by the inhabitants. A house on poles will have an flooding. Openings are required at the surface that let the rainwater entirely different effect on the flow of water than a house on a small in, but these openings can also let floodwater into the network. When mound. A free choice of measures for every inhabitant will not result this happens, the sewage will flow into the streets. This sewage is in an urban landscape with predictable flows during a flood, which very dangerous for human beings as it carries all kinds of germs and will create unsafe situations. The designers of the urban landscape other dangerous substances. The extra nutrients can also pose a should investigate where the currents of the flood should be and severe threat to nature. Therefore, rainwater and the sewage network place the different point-adapt measures accordingly. It may be should be separated from each other. In the newer neighbourhoods possible to create areas in the urban landscape where there are less that have been built during the last years, this separation of waste currents and where it does not matter what kind of flood-resilient water systems does already exist. The rainwater can be cleaned building is placed. This could be the case behind the wall at the further by placing helophyte filters in the urban landscape that clean front of the mound, where the flow speed could be zero. Where the the water before it is dumped. When these filters are flooded, there different point-adapt measures should be used will be discussed will be little damage to the environment. For sewage water this is further in the different design principles for the several parts of the impossible and dangerous, therefore the current network should be mound in the next sub-chapters. improved and be made waterproof. One other condition is that water For the remaining parts of the privately owned plots, there should treatment plants should be placed outside the reach of floodwater; also be strict rules. This is especially true for the gardens that are otherwise, all the effort will be wasted. situated along streets that are used to guide water. These gardens should not be full with objects that hinder the flow of water. Stone surfaces have a preference above green. Gardens that are not situated along a street can still pose a threat to the safety of the urban landscape when there are no rules for them. The placement of a tree that can topple during a flood can take down a house and completely alter the direction of flow in the urban landscape, creating unsafe situations.
135 13.3 The design principles of several crucial parts of the still an important function for the controlled flooding of the complete mound urban landscape.
During this thesis, we have made many reasoned assumptions. This 4. The floodplains around the mound was necessary because of the lack of research that has been done When a mound is placed in the floodplain of the Meuse, the quays on the subject of flood-resilient designs. With the help of hydrologists that currently protect the urban landscape will become obsolete. and translational research, it was possible to come up with a concept What will happen to the areas that will become part of the floodplain for the town of Arcen that could be translated into a safe-fail flood- again? Two options are given. resilient urban settlement. With a lot of time and effort, it is actually possible to translate this concept into a completely designed layout Since there will be no design of the complete urban landscape, the for Arcen. This would not have any real value for the safety of the current layout of the urban landscape will be used as a guideline inhabitants of the Meuse floodplain however. Such a design would be for the development of the design principles. If any chances are too specified for Arcen and would be difficult to export to other urban present that could further improve the safety or attractiveness of the landscapes. Instead, we have chosen to translate the concept into urban landscape, these will also be utilized. design principles for crucial parts of the mound. A well-considered design principle for e.g. the front of the mound will have more value for other urban landscapes as we can cover more of the problems that will also be present in other urban landscapes. For some parts, design principles of two extreme options will be given, as this will increase the value for other urban landscapes. These design principles are mainly focused on the technical details of the measures that will improve the safety of the urban landscape, while at the same time a functioning and attractive urban landscape is created, as described in the goal of this thesis. The several parts of the mound and the reasoning behind them that will be discussed are:
1. The head of the mound This is most likely the most important part for the safety of the urban landscape on the mound. The measures shown in the design principles of this part have the function of directing the flow of water around the mound instead of through it. Two extreme options are given, a subtle green option and an option that makes use of hard materials.
2. Internal measures that improve safety The mound can still flood when the discharge of the river exceeds 3950m3/s. When this happens, the water will flow through Arcen. Two options will show how this water can be guided through the streets in a safe manner. In addition, some design principles will be given as to how the water can enter the urban landscape in a safe manner. Lastly, the evacuation route in the urban landscape will be discussed.
3. The sub-mound and the tail The sub-mound is a higher situated area that will not flood when the mound is flooded. Here, the most important buildings of the urban landscape are situated. In addition, the tail of the mound will Figure 13.13 Locations of the several parts of the mound that will be dis- be discussed. In this area, fewer buildings are present but there is cussed in the next chapters.
136 13.3.1 The head of the mound
The main function of the measures at the head of the mound is to direct the energy of the flowing water around the mound. Therefore, a barrier needs to be erected that forces the water around the mound. The proposed mound has a height of 17.00 m N.A.P. This is high enough to prevent a river discharge of 3950 m3/s to flood the village of Arcen. When the discharge exceeds this amount, the water level will reach a height that enables it to overflow the mound and the urban landscape will be flooded. During such an event, the rate of flow of the river will be around 3m/s. (Rijkswaterstaat Dienst Limburg 2009) Such a flow speed will only be reached in the summerbed of the river. When the water levels are less high, the flow speed will drop accordingly. This means that the flow speed on top of the mound will be less than 3 m/s. Compared to a floodplain with a similar water level the flow speed is likely to be somewhere between 0.5 and 1.5 m/s. Still, this flow speed has enough force to damage many, if not all, of the objects in the village of Arcen, even when these are designed to be flood-resilient. Only houses on poles and amphibious houses could be built in that case. In an urban landscape with only houses on poles and amphibious housing the direction and speed of flow will be very difficult to control. Even though the buildings may be safe, the complete urban space surrounding the buildings will be an unsafe area, because of the currents. Figure 13.14 The head of the mound should become 18.15 m N.A.P. to prevent overtopping. Therefore, it is clear that the currents need to be regulated. This can be done by placing a barrier at the head of the mound that directs the water around the mound, effectively creating an area with little or no speed of flow behind it. This barrier should be impermeable, no water should be allowed to flow through it. When there is an opening in the barrier, the water will be forced through it because of the force of the river water. The flow speeds can be very high at such a point and create considerable damage. Houses cannot be used as a barrier to guide the water. The force of the water is simply too strong. Houses that are currently situated in the floodplain of the Rhine in Germany need to have a wall of at least 60cm thick to withstand comparable flow speeds. The best solution would be a wall or ground body that is solid enough to withstand the forces. Whether this wall takes the shape of a wall of stone or a grassy dike will be discussed in the options. The wall should have a height of at least 17.65 m N.A.P. to withstand a discharge of 4600 m3/s (1/1250 year). When the water flows against the barrier, it will be directed to the sides, around the mound. The force behind the water will also push some of the water upwards however. When the barrier is only 17.65m N.A.P. high, the water will flow over the barrier. Therefore, another 0.5 meter is added to the height of the barrier. This height is currently added to dikes to cope with similar effects. (Kok, De and Hoekstra, Figure 13.15 Flood-resilient species of trees to filter debris out of the 2008) water.
137 Figure 13.16 Trees have to be used to filter debris out of the water to prevent damage of the mound.
Apart from the force of the water itself, the river also carries all sorts of debris. This debris (tree branches, timber, etc) can be a serious threat to the houses in Arcen and the barrier that protects them. The debris needs to be filtered out of the water or be directed around the mound, before it reaches the mound. The filter needs to be permeable to water; otherwise, it will disturb the currents too much. On the other hand, it needs to filter larger objects out of the water. This could all be done with large steel fences with wire mesh, but this would not fit nicely in the current landscape. Instead, lines of trees and brushwood are more suitable to protect the mound against debris. The species of trees is dependent on the location in the floodplain, but they need to be flood-resilient, fast-growing trees with many branches. Otherwise, the trees will fall down during a flood or otherwise fail their task.
These patches of wet forests will be placed at the southern and south-western part of the mound. Here, the currents are pointed directly at the mound. This is shown if figure 13.16
138 The above-mentioned basic principles concerning the currents and flow speeds will be the guidelines for the two options. The two options will show two extreme appearances of the head of the mound. The first option shows what the design principles of a hard alternative are. The second option will discuss the design principles of a soft alternative for the head of the mound.
Option 1: a rigid appearance Option 1 explores the possibilities of a mound with a stony and rigid appearance. It is inspired on the city walls that, in history protected the urban landscapes against enemies. At the same time, the walls also protected the urban landscapes against flooding, like the city walls of Nijmegen. In the case of Arcen, this seemed appropriate, with its history of flooding and being a fortress. Figure 13.17 City wall of Valkenburg (Vosbergen 2008)
The sides of the mound will therefore look similar to a city wall. The materials should be more durable than the old bricks of such a wall however. Large blocks of granite will be used instead. This will give a rigid and durable look to the mound, giving the inhabitants of Arcen a more secure feeling.
To protect the buildings on the mound against the currents of the river, the barrier should have the shape of a 1,15 m high and 1m broad wall. This wall will be placed at the edge of the mound and will be part of the edge of the mound. The buildings will be placed with their fronts faced towards the Meuse. Since the mound can still flood these buildings, they need to be adapted to a water level of 65cm. At the head of the mound in this option, this should be with the resist method. The use of resistant buildings will further improve the rigid appearance of the head. The street that currently connects Arcen with the higher grounds will be elongated and broadened. This will create a small boulevard behind the wall. The height of the wall itself will allow to the placing of terraces at the head of the mound while keeping contact with the Meuse. To improve the contact with the Meuse further, another boulevard can be placed at the foot of the wall, near the river. This boulevard can be used during low water levels e.g. in the summer.
Figure 13.18 Map with the locations of the sections and birdviews that are shown on the next pages.
139 Figure 13.19 Frontside of the head, consisting of public space on both sieds of the barrier - 1:200
Figure 13.20 The head along the Meuse, consisting of private space behind the barrier - 1:200
The section in figure 13.19 shows the front of the mound where there is no direct contact with the Meuse. There is a height difference of 2 meter with the surrounding floodplain. The barrier on top of the edge is high enough to prevent overtopping during a high water event and will create a calm zone behind it. People will be able to look over the wall and enjoy the view. The edge of the mound is high enough to prevent people from looking over the mound when they walk on the path at the foot. The section in figure 13.20 shows the western side of the mound at the point where there is no road between the houses and edge of the mound. Here, there is room for a small garden. The houses will have the same alignment as the houses that do have a road at the front. This accentuates the hydrodynamic shape of the mound that protects them. The gardens are therefore not as large as they currently are.
140 Figure 13.21 Western side of the head with rigid appearance, on the transistion of boulevard into gardens.
Figure 13.22 Western side of the head with rigid appearance, on the transistion of boulevard into gardens in flooded situation. 141 The appearance of the western side of the mound, where the mound is situated right next to the Meuse is shown in figure 13.21. This is the point where the road enters Arcen and where the houses start to have gardens. The height difference between a normal water level in the summer and the top of the mound is 5 meter at this point. The alignment of the buildings is the same to accentuate the hydrodynamic shape. The houses are protected by using the resist method, which keeps the water outside during a flood. The result is a more resistant appearance that goes well with the rigid appearance of the whole.
During a large flood, the water runs along the boulevard (figure 13.22). The currents behind the wall are low and therefore it is safe to walk there, even though it is close to the river. The alignment of the stair between the higher and lower level will reduce damage during a flood.
Figure 13.23 shows the eastern side of the mound at the point where the head of the mound transitions in the side of the mound that does not need extra protection. This transition is the point where the evacuation route enters the urban landscape. The transition between a vertical stonewall and a diagonal grassy slope is created with the use of gabions (schanskorven). The houses on top of the mound are protected from the currents by an extra wall on the edge of the mound. The current on top of the mound is therefore low during a flood. As a result, the houses can be adapted to a 65 cm water level, according to a technique the inhabitants like.
Figure 13.24 shows the same location of the transition during a flood accompanying a 4600 m3/s discharge. The evacuation route is situated above water level and keeps Arcen connected to the higher grounds in the east. All the houses are protected against the water by their own point-adapt measures. Seen from left to right the measures are amphibious, resist, endure, poles and again resist.
142 Figure 13.23 Transistion of the head into the flank on the east side of the mound, with entrance of the evacuation route.
Figure 13.24 Transistion of the head into the flank on the east side of the mound, with entrance of the evacuation route in flooded situation.
143 Option 2: a soft appearance like granite to prevent damage from the currents. Again, the road is elongated along the Meuse before entering Arcen, which results The soft option looks at the design principles of a mound with a again in a boulevard. On this boulevard, the people can walk along more smooth character. Instead of the sudden height differences the river. At the foot of the mound another path is situated that can and stonewalls of option one, the soft option makes use of green be used during low water levels. elements and slopes. The height of the mound will still be 17.00m N.A.P. Instead of a stonewall at the front side of the mound, the These images show sections of the mound at the front and at the complete front side of the mound will be used as a barrier against western side of the mound. the currents. This means that the first 22 meters from the head of The section in figure 13.25 is of the front side. The currents can the mound will be constructed at a height of 18.15 m N.A.P. The first be strong during a flood and it is not clear whether grass will be row of houses is therefore part of the barrier. Since these stand on strong enough to resist these currents. Therefore, the front side of a higher area that theoretically will not flood, they need no further the mound is still covered in hard materials to prevent damage. measures to protect them against flooding. Figure 13.26 shows the western side of the mound where there is no road between the houses and edge of the mound, but only a The result of this broad barrier is a more smooth transition between boulevard and bicycle path. The houses will have small gardens. the mound and the surrounding floodplain or river. To improve the smooth appearance even further, the slopes will be covered with Figures 13.27 and 13.28 show the appearance of the western side grass. The foot of the mound still has to be coated with hard material according to the smooth option, without and with flooding.
Figure 13.25 Frondside of the head with steep slope of basalt blocks to withstand the currents - 1:200
Figure 13.26 The head along the Meuse with grass and only basalt blocks at the foot of the mound - 1:200
144 Figure 13.27 Western side of the head with soft appearance, on the transistion of boulevard into gardens
Figure 13.28 Western side of the head with soft appearance, on the transistion of boulevard into gardens in flooded situation.
145 13.3.2 Internal measures that improve safety
This section will discuss the design principles of the internal measures that should be taken on top of the mound to improve the flood-resilience of the urban landscape. The locations where water will enter the mound during a flood will be discussed first.
The inlets The mound will be overflowed by the river when a discharge of 3950m3/s is exceeded. Dangerous situations are a possibility when no measures are taken on the mound to guide this water through the urban landscape. In the concept, some statements were made on this subject. One of these was that the water should not be allowed to flow into the urban landscape directly. Water should be guided and the speed should be slowed down, since this would improve the flood-risk of the urban landscape. It is impossible however to guide the water through the urban landscape when it is unknown where the water will enter the mound. This problem can be solved by constructing locations where water can flow controlled into the urban landscape and where the public Figure 13.29 Inlets of water can be used as carports and are placed in a turn space has been adapted to guide this water. These locations should of 100o from the edge of the mound also slow down the water and filter debris from the water at the same time, further reducing the risk. In the concept, we concluded that the eastern side of the mound would be the best place to construct the inlets. A small calculation shows that the inlets should take up one-fifth of the total length of the eastern side of the mound. To slow down the water on the mound the southern, upstream side will have more inlets than the northern side. The figures 13.29 untill 13.32 show how the inlets will be constructed. We have chosen to construct paved roads that will function as inlets during a flood. During dry periods, these inlets can be used as a carport. They are 6 meters wide and can be used as a carport for two corresponding buildings. The inlets are situated in such a way that the water first needs to make a turn of 100o. During a flood, the water will first hit the sides of the inlets before entering the urban landscape. This action will slow down the water. Since it is unknown what the exact flow speed of the water on the eastern side of the mound will be, we have chosen to construct rigid, stonewalls at the side of the inlets. These walls will be able to sustain the force of the water and guide it safely into the urban landscape. An extra barrier is built into the walls of the buildings that are opposite to the inlets. During a flood, the water will hit these walls and slow down even more, as a redundancy. Figure 13.30 Inlets of water can be used as carports and are placed in a turn The water needs to be filtered before it enters the flood. Since there of 100o from the edge of the mound in flooded situation is a bypass on the eastern side of the river, it is likely that there will be a fair amount of debris in the currents. This debris is capable of damaging the walls on the sides of the inlets, which could threaten
146 Figure 13.31 Appearance of the inlets that can be used as carports, with trees on the slope of the mound to filter debris
Figure 13.32 Appearance of the inlets that can be used as carports, with trees on the slope of the mound to filter debris in flooded situation
147 the urban landscape. By placing a row of trees and shrubs in the predicted current that enters the town, the water will be filtered. The largest pieces of debris will be caught in the branches of the trees and will not be able to cause any damage. The inlets and corresponding walls will also protect the buildings that are surrounded by these walls against the currents. The flow speed will be near zero as a result. Therefore, the people are able to choose their own point- adapt method that will protect heir house against he flood. This is shown in figure 13.31.
The risk-reducing situation of the internal streets With the construction of inlets, it is possible to predict the currents within the urban landscape once it is flooded. By placing buildings and infrastructure in these currents, these currents can be guided. In the concept, it was concluded that placing infrastructure parallel and perpendicular to the currents, the buildings will create safe areas where there is less flow. Here, two options will be shown of the design principles of an urban layout that creates such safe areas. The first option shows an option with small streets where the currents flow and the safe areas perpendicular to them. The second option shows a variant with more room for gardens and trees within the scene.
The figures 13.33 untill 13.36 show the design principles of an intersection, where flowing and safe areas meet. The street where the water will flow (with a low flow speed) has been constructed Figure 13.33 Main streets are connected with other streets by slightly angled similar to a pipeline. Every surface between the buildings is paved. connections. Earthen bodies prevent the flowing water to cause damage to the The buildings themselves are built on mounds, which will force the buildings on the crossing and can be used as terrace. water in one direction, making the currents predictable. Other point adapt techniques allow water to flow under or through the building, which makes the flows unpredictable and therefore makes these techniques unsuitable. The flow speed in these streets will be low enough to allow trees to be planted. The street perpendicular to the flowing street will be connected to the flowing street with the same measures that slow down water at the inlets. The road will be slightly angled towards the flow direction. This will slow down the water as it hits the buildings on the intersection. The points where the buildings are hit need to be reinforced to make sure that they will not be damaged. This is done by strengthening the walls and creating an earthen body before the building that guides the water. These places on the earthen bodies can be used as a terrace for the adjoining building. The streets with a low flow speed will allow the placement of gardens and trees. In addition, since there is little flow, all the point-adapt techniques can be used. The inhabitants are free to choose their Figure 13.34 Slightly angled connections of streets create main streets with own technique to protect their house. a higher flow speed and streets with a low flow speed. Earthen bodies prevent the flowing water to cause damage to the buildings on the crossing (flooded situation).
148 Figure 13.35 Appearance of a crossing of a fast flowing street with a slowly flowing street.
Figure 13.36 Appearance of a crossing of a fast flowing street with a slowly flowing street.in flooded situation.
149 Figure 13.37 Main street where the water has a flow speed, only hard materials can be used - 1:200
Figure 13.38 Street with hardly flow speed, soft materials like plants in gardens can be used. - 1:200
Figure 13.39 Second variant of main street where the water has a flow speed. The water is guided by earthen bodies, so behind these, soft materials can be used. - 1:200
150 The evacuation route float. Problems begin with lower water levels however. Driving a car First, if all the measures on the mound work correctly, no evacuation may already become impossible as the car loses contact with the is necessary. The urban landscape should be safe enough for ground during water levels as low as 30 cm. (United States Search people to stay in their houses during the week that their settlement and Rescue Task Force 2007). Since the water levels can potentially is flooded. However, an evacuation route is always a necessity. rise as fast 3 cm per hour, this means that cars cannot be used Although the inhabitants of Arcen should be safe during a flood, ten hours after the mound is overflowed. Forecasters will be able to people should not be forced to stay in Arcen. If they want to leave predict whether the water levels will rise far enough to overflow the to safer areas then there should be a way to do so. An evacuation mound however. This should be known 12 hours before the mound route can give the inhabitants this possibility. is actually overflowed. This gives the inhabitants roughly a day to Another reason to construct an evacuation route is the accessibility leave the mound with their cars after the warning is given. of the mound during floods. Even though the measures on the mound create an environment that can flood safely, there is always a possibility of unforeseen damage caused by flooding. During such an event, it may be necessary to evacuate an area for safety reasons. In addition, there is always a chance of emergencies without a direct 13.3.3 Sub-mound and tail of the mound link with the flood. Fires and other calamities may occur during a flood. During such an event, it is necessary that the mound can be Sub-mound reached by emergency services like the fire department. The sub-mound is located on the eastern side of the mound. It is a In addition, the lives of the inhabitants go on during a flood. People natural higher-situated area, which will be shaped according to the may need to leave the mound during a flood to go to work or school. most hydrodynamic shape. The height of the sub-mound has to be A dry connection with the higher grounds will make this possible. at least 18.35 m N.A.P. This is high enough to prevent any predicted water level from flooding the sub-mound even in the highest KNMI It is impossible to connect every single building with the evacuation models. route directly. This would require too much space and would have a The shape of this sub-mound has already been discussed in chapter very large impact on the currents in the floodplain. All the connections 12. It should have the same hydrodynamic shape as the large mound would need to be placed above the highest potential water level. where it is situated on. There are three options for this; small dikes, connections on poles or On the sub-mound, there is enough space to build the new centre amphibious connections. Small dikes would have a large negative of the settlement. All the important buildings and services should be influence on the currents within the urban landscape during a flood. placed here. This improves the safety of the total urban landscape Connections on poles would create large differences in height over and also the recovery time of the urban landscape since the most very small distances (between roads and sidewalks for example), important services can be resumed immediately. which is undesirable. The last option, amphibious connections, There is more than enough space on the sub-mound to accommodate would simply be too expensive. the new services and buildings. The space that is left can be used Therefore, we have chosen for a single evacuation route with for housing or other buildings that require an extra safety level, two connections to the higher grounds on the eastern side of the like electricity-distribution buildings if an electricity network is still floodplain and mound. There are two connections to ensure that present. Since the sub-mound is not susceptible to floods there are there will always be a connection with the higher grounds, even if no special measures that need to be taken, for both the buildings one of the connections fails due to e.g. an accident. The evacuation and the public space. The urban landscape can be built according route in the urban landscape will be made amphibious. Although to what is most appropriate. We will not give design principles for the expensive, it will create a better functioning infrastructure during sub-mound because the sub-mound will not flood. normal water levels. In addition, it will not disrupt the flow of water in The list of important buildings that should be built on top of the sub- the urban landscape during floods. mound includes: The route will run through the middle of the mound. The route will - City hall: the coordination centre of the settlement, both be situated in such a way that every inhabited area will fall within a during a flood and during normal water levels. 300-meter radius of the evacuation route. Such a distance is enough - Church: for the shelter and relief of people, if needed. to allow people to move to and from the road during a flood. - Doctor/ First aid station: for the treatment of any sustained During a flood, it will become difficult to get to the evacuation route injuries or other emergencies. with motorized vehicles. For every 30 cm, a car will weigh 680 kg - Police station: for the aid of the inhabitants and the keeping less. This means that with 65 cm water, most cars will begin to of the law.
151 - Fire department: the ultimate people for the handling of large that runs on the eastern side of Arcen. The high water trench flows amounts of water. towards the mound at this point and as a result erodes the sides - Supermarket: essential for the daily lives of people. of the mound. Therefore, the materials that are used at this point - School and gym: for the shelter and relief of people, if should be robust to negate the effects of erosion. The sides should needed. also be steep to control the erosion factor further. - Burial site: dead bodies should never come in prolonged contact with water.
There are many kinds of buildings that should not be allowed to flood, but which are not present in Arcen. These buildings could include: - Wastewater treatment plant: large environmental damage if it is flooded. - Electricity-distribution centre: large economic damage if flooded. - Industry with potential dangerous waste: large environmental and health damage if it is flooded. - Other buildings with a large impact on the environment if flooded.
Apart from buildings, the sub-mound should have a large square where people can come together during floods and where loose objects can be stored which are susceptible to floods e.g. cars.
The sub-mound is at least 1.35 m higher than the rest of the mound. This is not a large difference, but it can be accentuated to improve the safety of the urban landscape. The clear knowledge of where safe places are will improve the feeling of safety as well. This can be done by making the transition from mound to sub-mound within a very short distance, in other words, with steep walls.
The eastern side of the sub-mound borders the high-water trench
Figure 13.40 Section of the eastern side of the sub-mound - 1:200
152 Figure 13.41 Western edge of the sub-mound. The most important buildings are situated here. The submound needs a large village square that can be used as parking lot during floods.
Figure 13.42 Western edge of the sub-mound in flooded situation. The most important buildings will never flood, which increases flood- resilience. Cars are parked on the village square to prevent them from floating away.
153 “Tail” of the mound The expected size of the mound exceeds the total built-on area of Arcen. In this way, future expansion of the settlement and an increase in required space per building can be incorporated. Nevertheless, the northern or “tail” part of the mound will not be required in the immediate as building area for the people of Arcen. Nowadays this area is mainly used for agriculture and greenhouses. It is likely that this land-use will continue in the future. Therefore, the tail of the mound will have a rural appearance with small amounts of houses and more agricultural related buildings. The space between these buildings will be larger than within the urban part of the settlement. Consequently, there are no possibilities to use the buildings and streets to guide water and create safer places. Therefore, every building should be prepared for this by using flood-resilient measures that can cope with currents, like small mounds or poles.
In the concept, we have shown that the water on the mound should be slowed down by preventing the water from flowing back into the floodplain too fast. When water is unable to freely flow back, it stagnates and is therefore safer and causes less damage. This can only be done by building an obstructing object, like a wall or dike, along the edges of the mound. This should be an earthen wall and will have a height of at least 17.65 m above N.A.P. It will have about 25% of the total openings, while the southern part of the mound will have 75% of the total openings. Because the water pressure builds up behind the wall, the water will be pushed through the openings, which will result in a higher flow speed at these points. The flow speed on the mound will be lower however, since the extra flow speed in the openings will not be enough to discharge all the water on the mound. The openings themselves need to be built in such a way that they can withstand the higher flow speed. It is unknown what the flow speed will be in the openings, but they will be built with stone and concrete to be sure that the openings can handle the extra pressure.
Figure 13.43 Design suggestions for the floodplain surrounding the mound.
154 Potential water levels influence possible land-uses.
155 13.3.4 The floodplain surrounding the mound remain the most important in the floodplain the next 100 years. The floodplain is however flooded by the Meuse whenever the discharge The last important part that is discussed is not part of the mound is high enough. Nevertheless, because the floodplain does not itself. We will discuss the floodplain surrounding the mound, since the have a uniform height, not every part of the floodplain is flooded arrangement of objects in the floodplain can have a large influence every time the Meuse exceeds its summer bed. Depressions in the on the currents and therefore on the safety. landscape will be flooded a lot more often that higher parts, which Again, we will discuss two different options. The first option will gives a good division in the current land-use. This division should discuss an empty flood, where most objects are moved to the mound remain the same in the future. The lower parts of the floodplain or to higher grounds. The second option will discuss an option where can be used for dairy and stock farming. Grass is highly resilient to most objects are adapted using the point-adapt techniques. flooding and the animals are mostly inside during winter, when most floods can be expected. (Ministerie van Verkeer en Waterstaat 2006) The areas of medium height can be used for agriculture. The ground Option 1 floodplain: moving threatened buildings will be more suitable because of the lower groundwater levels and again the floods will not damage the crops since these will already Western floodplain be harvested. The highest parts of the floodplain can be used for Apart from adapting the buildings on the western side of the mound, tree nurseries. Trees are less resilient than grass and are still present they could also be moved to a more safe area. Apart from leaving during the winter months. Yet, the highest parts of the floodplain the floodplain of the Meuse altogether, there are two main locations may be flooded once every 150 years or so, this gives the grower for these buildings. The first and most obvious one is the newly more security. created mound on which the village of Arcen is now located. The second option is a smaller, natural mound in the floodplain, located Eastern floodplain northwest of Arcen. This mound is higher than 17.00m N.A.P which The eastern floodplain has more houses compared with the western means that it won’t be flooded until a discharge of 3950 m3/s is floodplain. Many, if not all of these houses are located within the reached, which gives it the same safety level as the artificial mound floodplain of the river during a 3950 m3/s discharge. Apart from of Arcen. The natural mound is ideal for buildings, which have to be adapting these houses, they could also be moved to safer locations. moved but are difficult to fit into the urban landscape. An example The mound is such a safe place but the more logical safe place is the Hertog-Jan brewery. This brewery is known for emitting a would be the terrace on the eastern side of the floodplain. This penetrating smell. This smell is very likely to be a nuisance to people terrace is high enough to protect the houses against a flood event living near the brewery. Therefore, it is a better idea to move the of 4600 m3/s or higher. The height of the terrace easily exceeds a brewery, and other “smelly” buildings to this natural mound, away height of 18.00 m N.A.P. Nowadays the terrace is heavily forested from other inhabitants of Arcen. If some people are willing to endure and is intensely visited by tourists during the summer. Therefore, the smell, they are of course free to build their house near the brewery the forest cannot be completely used and half of the houses will on the natural mound, but the available space is limited. be moved to the mound. Since the houses are currently located This brings us to the other buildings in the floodplain. Since the along the edge of the floodplain, the new houses will be situated on available space on the natural mound is limited, they need to be similar places: along the edge of the mound or along the edge of moved to the artificial mound. To provide a similar living environment, the terrace. In this manner, the living quality of the current inhabitants these buildings will be placed near the edges of the mound on the will be safeguarded and the safety will be improved. The houses that northern side. The living environment is comparable to the living are moved to the mound will be placed on northern, quieter, side of environment of the floodplain, which is rural and quiet. the mound to safeguard the living quality. Both the artificial mound and natural mound are not high enough to Apart from the houses in the floodplain, there are also two large protect the buildings against extreme flooding. When a discharge farms. One of these is situated on a natural mound while the other of 3950 m3/s is exceeded the mound will be flooded. The water is situated in a lower part of the floodplain. The natural mound will levels are low on the mounds however, and the currents will be be adapted to improve the flow of water in the floodplain. The farm slow. Therefore, the buildings can be adapted with the point-adapt itself will have to be adapted to a possible water level of 1 meter. This techniques. is easy to do and has been done for centuries in Freesia. The other Apart from some sheds and other small buildings, the floodplain is farms will be moved to the terrace, away from most of the houses. now clear of buildings. There is still a multitude of other land-uses Here, it will keep contact with the floodplain, while minimizing the left however. Nowadays the floodplain is used mainly for agriculture, inconvenience to other inhabitants. stock farming and tree nursery. It is very likely that these land-uses will The floodplain itself will be mainly used as agricultural land. The
156 bypass is ideal for the breeding of livestock and growing of grass. does not have a large influence on the currents and water levels, The higher areas near the terrace can be used as tree nurseries, which gives it a preference above the other types. It is however as they are used nowadays. Farming can also take place on the susceptible to damage from floating debris. Therefore, it needs eastern side but space is limited and tree nursery might be more protection against floating debris in the form of a filter. profitable in such a situation. Concluding from the analysis of point-adapt measures, it can be said that only some of the flood-evading measures can be applied Option 2: adapting the buildings in the floodplain in the floodplain of Arcen. Amphibious buildings and buildings on The second option for this area is adapting the buildings instead of poles will be the only two typologies that suffice. Which typology will moving them. This can be done by the before mentioned options be applied to which building is a choice that has to be made by the of point-adapt. Looking at the conditions that belong to the point- stakeholders of these buildings. Nevertheless, we think that in case adapt solutions (see chapter 7), it can be concluded which solutions of the Hertog-Jan brewery, the best solution is to make it amphibious. can be used in this area. The reason is that building such a company building on poles will have an enormous impact on the surrounding landscape. Floating building Another fact that is crucial to the arrangement of buildings in the Floating buildings always need water beneath them. This option can floodplain is that the floodplain will flood a lot more often than the therefore only be used when a part of the floodplain is dug out. mound. The buildings might be protected against the water levels that occur during such a flood, the roads are not. This means that Flood-resistant buildings during a small flood the buildings will lose their connections to the Water levels of 2 meters are expected during a flood near Arcen. higher grounds. This can be solved by placing the roads on poles, Resistant buildings can only cope with a water level of 1 meter. but this will cost too much, compared to the amount of people that Therefore, the resistant option is impossible, except for a few buildings benefit from it. Therefore, the people who live in the floodplain will near the higher grounds on the eastern side of the floodplain. simply have to get used to this.
Flood-enduring buildings The endure buildings also cannot be used, because they can just handle a water level of 1,5meter, which is too less, because a water 13.4 Exporting the design principles to other areas level of at least 2 meter is possible to appear. During our analysis of the landscape of the Meuse floodplain, we Amphibious buildings concluded that there are three different urban landscape types, The amphibious building is applicable in this area because it can which are: function in case of every water level. It also has little impact on water • the floodplain village levels in the river. This building type is however susceptible to high • the valley town flow speeds. Therefore, this option can only be used in areas with a • the terrace village low water level, where the flow speed is low. In addition, filters need In an ideal situation, we would have made design principles for every to be placed in front of the buildings to lower the chance of damage single urban landscape category. This was impossible due to time by floating debris. constrains however and therefore we chose to study the floodplain village category, since these have the largest problems of all types. Building on a mound Now that it is clear which design principles can reduce the flood Building on a mound is one of the safest options available. All risk of a floodplain village, it is possible to see which of these buildings can be placed on a rigid body of soil. This option does design principles can be used in the other two urban landscape have a large influence on currents and water levels however. Because categories. of that reason, several extra little mounds in the floodplain are not desirable. Valley towns Valley towns are rare in the floodplain of the Meuse in Limburg. These Building on poles towns are located on both banks of the river. They are many times This type of building can withstand water levels up to 3 meters. In the larger than most floodplain villages and occupy the complete valley, floodplain around Arcen, such water levels are not likely. Therefore, from high ground to high ground. As a result, these urban landscapes this type of building can be used in the floodplain. This type also also act as a bottleneck, where water is dammed up because there
157 Figure 13.44 Valley town. Figure 13.45 Terrace village. is less room for the river to flow during high discharges. Therefore, Terrace villages these urban landscape types have a large influence on water levels The terrace villages are situated on the current edge of the floodplain. further upstream. Currently these urban landscapes are protected People decided to build their villages above the last known water by dikes and quays along the river. levels, but near the fertile floodplain. Mostly this was the edge of The water levels during a flood are comparable to the floodplain the first terrace bordering the floodplain. These locations have been villages. Therefore, the only way to reduce the flood risk is to raise safe for centuries and therefore the villages do not have any form the urban landscape. It was however concluded that such a method of flood protection. The changing climate will increase the potential requires more space than the current urban landscape requires. In water levels however and the terrace villages will be able to flood in the case of valley towns, this could become a problem because the future. there is not much space available. These urban landscapes already Because the water levels on the terraces are relatively low, compared take up too much space in the floodplain. to the other urban landscape types, there is no need to raise the A solution is to take the design principles of the mound and utilize ground level of these villages. The water Levels in these villages will them for every neighborhood. A neighborhood of a valley town is become 80cm at most, but will be less in most cases. comparable in size with a complete floodplain village. The town The buildings and public space can be adapted to cope with should be transformed in a series of mounds, with bypasses in these water levels by employing the design principles for the urban between. During periods of low water levels, these bypasses can be landscape on top of the mound, as shown in this chapter. used as roads or parks. The process of rebuilding and adapting the buildings in the floodplain A consequence of the use of mounds is that there will be less space can be more gradual as the buildings can be adapted whenever available for all the buildings that are currently situated in the urban they need to be rebuilt because of age. landscape. This problem can be solved by either moving a certain A sub-mound will not be necessary since the terrace villages are amount of the buildings to the higher areas that are situated outside connected to the higher grounds of the valley. These high grounds the floodplain or by building more high-rise buildings. are easily reachable. Important buildings should therefore also be The use of mounds will improve the amount of water that can flow rebuilt in the higher situated parts of these urban landscapes, where through the floodplain during a flood. As a result, the water levels will there is less flood risk. drop significantly during flood in the upstream area. The same laws that prohibit the use of a high mound in Arcen will also prohibit large high mounds in the valley towns. Therefore, the mounds cannot become higher than the current dike levels. This will imply that the mound can flood during a large flood. The dikes around the valley towns are higher already though, since they protect more people against flooding. Nevertheless, the mound will flood during discharge of 4600 m3/s and therefore the same design principles will have to be used to lower the vulnerability of the buildings on top of the mound.
158 13.5 Conclusions regarding the design principles
Although the water levels and flow speeds on top of the mound are low, there is still a need for further protection of the buildings and urban space. The design principles in this chapter have shown how the flow within the urban landscape can be regulated and guided. The fast flowing water in the floodplain can be deflected around the mound by a barrier, creating an area with low flow speeds behind it. Such a barrier needs to be a solid object, so houses cannot be used. We have shown that the construction of such a barrier can improve the urban landscape. We have also shown that water can be guided and slowed down in the urban landscape, without lowering the liveability of the urban landscape. The same counts for the sides of the mound, where water enters the mound during a flood. The floodplain around the mound can also be adapted to higher water levels by rebuilding the buildings there and changing the land- use. Moving the buildings to higher areas is also an option. The urban green in the urban landscape should be replaced with plants that can cope with flooding. Especially trees should be able to cope with water since they can damage the urban landscape when they die or fall over. There are enough plants available that can be used in the urban landscape, which are currently also used. Public utilities can be adapted to flooding. Yet, in the spirit of flood- resilience, it is better to produce energy and water on-site. This reduces the flood-risk of the complete urban landscape. We have shown that all the design principles can be implemented while keeping the urban landscape functioning and liveable, even improving it at some points.
159 160 Conclusions, discussion and recommendations
14
161 14. Conclusions, discussion and recommendations
The thesis started when two dikereefs in Limburg made the The first question proved to be the most important and time- statement that people in the Meuse floodplain have to get used consuming of the whole thesis: which innovative techniques can be to floods. They stated that the capacity of the current system of used in the specific landscape of Limburg? resisting water and keeping them out of the urban landscapes This question was approached in several steps. First, the predicted with large dikes and quays was limited. Also, there, was no space rise of potential water levels in the future was studied. The current available in the upstream area to solve the problem. Therefore they discharge of the Meuse is held at a standard of 3800 m3/s for dike wanted that science explored other methods that could protect the design and in the future this would become 4600 m3/s because of inhabitants of the Meuse floodplain. In literature we found the theory the changing climate. For the Meuse in Limburg this meant that the of flood-resilience, which tries to cope with flooding by reducing the water levels during a high river discharge will increase with 80 cm. vulnerability against floods of the urban landscape. Afterwards, the landscape of the Meuse floodplain was examined. In order to show the possibilities of more flood-resilient urban With the data obtained from the previous study, it was possible landscapes along the Meuse in Limburg, while keeping them to determine the future floodplain of the Meuse. Since the Meuse functioning and attractive, the following research question was lies in a valley, the floodplain grows larger when water levels rise. addressed in this thesis: what are the appropriate techniques that More urban landscapes will be flooded as a result, because many can contribute to more flood-resilient urban landscapes along the urban landscapes were built at the edge of the floodplain. There are Meuse in Limburg, taking the predicted rise of water levels into differences between the urban landscapes in the Meuse floodplain, account and how can they be implemented? This question has been which can be categorized in three categories. divided into several sub-questions, which are: 1. Floodplain village (small, surrounded by dikes.) • Which innovative techniques can be used in the 2. Valley town (large, bottleneck, protected by dikes) specific landscape of Limburg? 3. Terrace village (small, no flood defences) • How can these measures be implemented while The water levels in the floodplain village and the valley town can keeping the urban landscape liveable, or even become as high as 4 meters during a discharge of 4600 m3/s. The improving it? water levels on the terraces will never be higher than 80 cm. • How could this transformation be realized in time? Subsequently, a study was made on the available methods and techniques that can make an urban landscape flood-resilient. Other The research findings will enable us to state whether the hypothesis projects and literature produced a range of possible techniques. is true or not. The hypothesis for this thesis was stated as: the Further research was done on how these techniques worked and vulnerability of urban landscapes along the river Meuse in Limburg what their limits were. A distinction was made between techniques can be lowered by making them more flood-resilient with the use of that used a large area of the urban landscape to lower water levels innovative techniques, thereby reducing the flood risk. (area-adapt) and techniques that only adapted the buildings and other important objects to reduce damage to them (point-adapt)
With this knowledge of potential water levels and available techniques, 14.1 The conclusions it was possible to test whether these techniques would actually work in the Meuse floodplain. First, area-adapt was tested on a small scale. This thesis has been a real revelation for us as landscape architects. This was according to the architectonic vision. Calculations were Before we started with our research, we had a vision of an urban made on the effects on water levels of a street that would transport landscape that could cope with large quantities of water by adapting water and a park that would store water. Both were not able to lower the urban space. We envisioned streets and parks able to transport the potential water levels to safe levels. Not even multiple streets and store water at times of high water levels. Dikes would no longer and parks would work. With the results, larger versions of the area- be necessary and flood risk would be reduced. The result would be adapt methods were tested. But even a channel through an urban a vision of an innovative and safe method of adapting existing urban landscape or a basin bigger than the size of Maastricht were not landscapes in the floodplain. able to lower the water levels far enough. But we were too ambitious. Just because we as landscapes Next, the point-adapt techniques were tested. The limits of the architects can imagine a solution for a problem, it does not mean techniques were compared to the potential water levels in the Meuse that such a solution is feasible or realistic. Below, we will answer the floodplain. Most of the techniques failed this test, since the water questions as posed above and describe the real research findings levels were too high. The techniques that were able to cope with the behind the answer. water levels, were however not able to cope with the flow speeds during such water levels.
162 At this point, the conclusion was that flood-resilient techniques were low flow speeds, the eastern side in Arcen. The openings need to not able to completely replace the current method of protecting slow down and filter the water before it enters the urban landscape. the urban landscapes against flooding with dikes. Still, the current Since it is now known where the water will enter the mound, it is method was at its limit and the goal was to produce a safe urban also known how the water will flow. By placing streets and the landscape. So next it was tested whether the flood-resilient accompanying buildings parallel and perpendicular to this flow, techniques could complement the current system. The test proved it is possible to create areas with an even lower flow speed. This however that the two methods cannot complement each other. Only predictability will lower the flood-risk. after failing of the dikes the flood-resilient techniques can do their There should always be an area on top of the mound that will never work. The water levels remain the same however, and therefore the flood. This area is used for the most important buildings of the urban resilient techniques will not be able to protect the inhabitants. landscape, like fire departments. This area should also have an At this point it was clear that flood-resilience would not be able to hydrodynamic shape to improve the predictability of the currents on create an urban landscape with a low flood risk. At least, not with the the mound. Furthermore, the urban landscape should also have a water levels those are currently predicted in the Meuse floodplain. road that will never flood that connects it with higher grounds. Therefore, we searched for other options that could create a safe living environment for the inhabitants of the Meuse valley. There are To show how these measures could be implemented in the urban three options. The first is leaving the floodplain and rebuilding the landscape, while keeping it liveable and attractive, we have given settlements outside the floodplain. The second is to abstain from any some design principles for the most important parts of the mound. improvement of the current flood-defence system. The money that is To show the range of possibilities we have also shown two extreme saved with this action can then be used to pay for any damage that options. Mostly these consisted of a hard, rigid variant and a softer occurs during a flood. and greener one. The images produced during this phase show that The third option is the one we chose to further examine. In this option a flood-resilient mound can be both attractive and functioning. the current urban landscape is raised. This would create a mound in the floodplain on which the inhabitants could live safely. Laws It was difficult to answer the last question of how this transformation prohibit however that the mound becomes higher than the current could be realized in time. When we first asked this question, we had dike levels. A high mound would have negative effects on the water a completely different view of the actual transformation. Nevertheless levels further upstream. The predicted water levels will overflow we did find out that the IVM project will produce enough soil to create the current dikes and therefore the mound will also overflow. The the mound with. The urban landscape itself has to be raised from the water level and flow speeds on top of the mound will allow the flood- upstream part towards the downstream part. This will create a safer resilient techniques which we discarded earlier however. urban landscape during the transition phase. Large areas should be adapted at the same time, because the situation of the buildings is The village of Arcen was chosen to model this option. Arcen is crucial to the concept. a floodplain village and floodplain villages have to endure the largest floods. If raising the urban landscape would work here, the knowledge gained from the test could be used in other urban Main conclusion: landscape categories. The IVM project should be used to lower the water levels in the The hypothesis as posed at the beginning of this chapter is true; the floodplain of the Meuse, with the help of measures outside the urban flood-risk of the urban landscapes along the Meuse in Limburg can landscape. To further improve the flood-risk of the urban landscape, be lowered by reducing the vulnerability of these urban landscapes. the mound should be placed in an area with low flow speeds, near Lowering the vulnerability of the urban landscape with the use of the current settlement and in a hydrodynamic shape. This will reduce flood-resilient techniques will however not create a safe urban the chance of damage and thereby reduce the flood-risk. The water landscape, as the techniques are not able to cope with the huge level on top of the mound during a discharge of 4600 m3/s will be amount of water during a flood. 65 cm. Only if the water levels in the urban landscape are lowered with the The mound should have a barrier on top of it at the upstream part. help of measures in the floodplain and the ground level of the urban Without such a barrier the full force of the river is directed straight landscape itself is raised, is it possible to create a urban landscape over the mound, which makes it impossible to place buildings on that can safely be flooded. So urban landscapes in the floodplain of top of it. The barrier deflects the force around the mound, creating the Meuse can be made flood-resilient, provided that they are raised an area with low flow speeds behind it. first. During a flood, the water should enter the mound from the side with
163 14.2 Discussion of what could be done with the remaining floodplain and where there would be space available to move all the people to. The most-cost- Flood-resilience is a relatively new concept and there is little literature effective approach would likely be to do nothing and pay for any on the subject as a result. The available literature is manly focused damage that occurs during a flood. From the costs of the IVM2 project at the theory behind the concept, yet no research has been done on alone already 4 floods that occur every 75 years can be paid. Yet, the how landscapes should be designed to make them flood-resilient. As limitations of the hypothesis and goal made us explore a different a result, it was necessary to make many assumptions on individual path. We wanted to know if flood-resilience can still be implemented. techniques and what their effects would be on water levels and To compensate for this we have shown what the consequences of flow speed. These assumptions have been presented to experts other paths, like moving, are. Nevertheless, the question of what the and those that were approved have been used during this thesis. actual value of the final product is, still remains. Nevertheless, we suspected that a large collection of individual The value of this thesis is that it is a pilot study into some of the approved assumptions could result in a range of design principles possibilities for solving the flood-problem in Limburg. It takes a long with undesirable effects. Therefore, we contacted Rijkswaterstaat time to adapt the floodplain to the changing climate and the choice and made a calculation of the proposed interventions and their for an approach has to be made well before the first large floods will effects. These calculations showed that many of the assumptions occur. When it is clear what efforts are needed for every approach, proved to be right and that placing a mound in the floodplain would then the politicians can make a well-considered choice for which have a positive effect on water levels elsewhere, compared to the approach they will take. This thesis has shown what efforts are current situation. In addition, raising the mound above the current needed if the inhabitants of the Meuse floodplain want to continue dike level did indeed raise the water levels elsewhere. It did however living in the floodplain, while increasing their safety. This knowledge raise the water levels with only 0.5 cm. This low rise in water levels can be compared to that of other systems, like the current system is because more floodplain becomes available when the dikes are and leaving the floodplain. From this comparison, the politicians can removed and water can flow east of Arcen. This is more an exception decide how the increase in potential water levels will be dealt with. than rule with floodplain villages however since most villages are surrounded by water during a flood and this extra area is not gained. The last subject we want to discuss here are the social aspects of The result would be much a higher rise in water levels. this thesis. In this thesis, we have given an alternative for the current Lastly, since the mound of Arcen can still be flooded in our research, flood protection system. The current system is mainly focused at we calculated the flow speeds and water levels on top of the mound. guaranteeing an urban landscape with flood defences that will The water levels were indeed as assumed and the flow speeds, never fail, in other words: a fail-safe system. We have shown that although 0.15 m/s lower than assumed, were also too high for a safe this system has some large limitations and that a system can never urban landscape. The proposed barrier at the front of the mound, be fail-safe. A flood can always occur because of neglect, extreme the hydrodynamic sub-mound and the entrances of floodwater will weather etc. Since the urban landscape is very vulnerable because reduce the flow speed to 0 m/s at the head of the mound to 0.3 m/s it is deemed to be safe, the results of such a flood will be dramatic. at the tail. This flow speed is already safe enough for the inhabitants Our system approaches the problem from another side. Instead of of Arcen, which raises the question whether or not the design guaranteeing an urban landscape that will never flood, we propose suggestions for the internal layout of the urban landscape should an urban landscape that can flood. Yet, the flooding will be in a also be implemented. We think that since the complete layout of the controlled way and the urban landscape will be prepared for it. We urban landscape has to be redesigned that, for extra redundancy, it have shown that such an urban landscape will be safe to live and would be better to implement a more flood-resilient layout. A flood can cope with a flood. In theory the inhabitants will be safer than can always be larger than 4600 m3/s they currently are. But how will the inhabitants react to a proposal that not only changes At the end of this thesis, we asked ourselves the question what the their whole settlement, but also says that they can be flooded at actual value of this thesis for the community is. This thesis had the every moment. People don’t like floods and they certainly don’t like intention to show that flood-resilience would be a good vulnerability- to accept that they are not stronger than water. In the province of reducing alternative for the current flood-chance reducing method. Zeeland, people protest when the state wants to surrender a single Because of this limitation, we did not always explore the path that meadow to the sea. What would happen when people learn that would lead to the most safe or most cost-effective solution for the their whole settlement can not be protected anymore and that it will Meuse floodplain. For example, we think that the safest solution for flood, even though it will be a safe flood? the floodplain would be to leave the threatened areas altogether and This change will require a shift in thinking of the inhabitants of the move to the higher parts of Limburg. This creates a lot of questions floodplain. They will need to learn that the current approach is a
164 lot more dangerous than our proposed system, even though they are more likely to be flooded. They will have to get used to the displeasures of a flood. Maybe one week in their lives, they will have to change their lifestyle and cope with 65 cm of water. This is possibly the biggest problem when our proposed flood-resilient system is adopted. But it is necessary when we want to go from a dangerous fail-safe system to a safe-fail system.
14.3 Recommendations
This thesis explores a new terrain in spatial planning and design. Many of the flood-resilient techniques were never intended to be used within the floodplain of a river. Engineers should take a look at these techniques and see if they can be adapted to more severe conditions.
At the beginning of this thesis, it was stated that it is difficult to use the upstream area of the Meuse for the retention of water because the riverbanks are very urbanized and the political situation in Belgium is very unstable. During this thesis, it became clear however that solving the problem in the Dutch part of the Meuse river basin might prove to cost even more effort. Therefore, we recommend that more energy is put into finding ways to use the Belgian floodplain for the protection of the Netherlands. This might be a good thesis assignment for a GIS related study. It may very well prove to be worth the effort.
Some of the safest solutions have not been explored yet. For a good comparison of potential flood-protection systems, the option of leaving the floodplain should also be explored. How many buildings have to be removed and where can they be moved to? What can be done with the leftover areas? These are very interesting questions, which can result in a solution that might prove very safe and profitable. It may even be able to protect the lower-lying western areas of the Netherlands. This could be researched by landscape architects, with the help of spatial planners.
As discussed before, people are not willing to cope with flooding. Nowadays the government guarantees a dry urban landscape and the people expect nothing less. Our proposal states clearly that an urban landscape can flood. People will protest against this. It is important that a study is started into how the inhabitants can be made clear that the current system is unsafe and that flooding is only a bad thing in the current system. A flood-resilient landscape is safer and should be adopted as the new flood-protection system.
165 166 References
167 References
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