Protection against flooding: a new Delta Plan in The Netherlands

Transcription

1 Destructive Water: Water-Caused Natural Disasters, their Abatement and Control (Proceedings of the Conference held at Anaheim, California, June 1996). IAHS Publ. no. 239, Protection against flooding: a new Delta Plan in The Netherlands FRANK P. HALLIE Ministry of Transport, Public Works and Water Management, PO Box 20906, 2500 EX The Hague, The Netherlands RICHARD E. JORISSEN Ministry of Transport, Public Works and Water Management, Road and Hydraulic Engineering Division; PO Box 5044, 2600 GA Delft, The Netherlands Abstract In 1993 and 1995 both the Meuse and Rhine achieved seriously high water levels caused by heavy rainfall. The consequences of these two events were significant water damage along the Meuse (in 1993 and 1995) and along the Rhine (in 1995). The local waterboards could no longer guaranty the security against flooding of various polders. As a result of this and an evaluation of the risk of a possible dike collapse it was decided on the preventive evacuation of more than people and millions of animals. This mass evacuation gave rise to considerable social unrest. During the high waters of 1995 the government decided to accelerate rapidly the existing programme of river dike reinforcement. Therefore a new "Delta plan" was announced by the Prime Minister of The Netherlands. Special legislation was necessary to be sure that the most weak dike sections were reinforced by the end of A total of approximately 650 km of dike fall under standard law. Special consideration is given to the recommendation of the Committee for the Review of River Dike Reinforcement Principles. This takes into account characteristic values of the river area, e.g. landscape, nature and cultural history. By environmental impact reports, more sophisticated designs and public hearings it is possible to execute the river dike reinforcement programme in such a way that all participants are involved. To cope with future developments it became more clear that river dike reinforcement alone does not ensure a long lasting solution. A new approach is needed including physical planning, land use development, (international) river management and finally building and reinforcement of dikes. INTRODUCTION The Netherlands is situated on the delta of three of Europe's main rivers: the Rhine, the Meuse and the Scheldt (Fig. 1). Half of The Netherlands lies below sea level, including the most populated western part that contains Amsterdam and Rotterdam. Much effort and billions of dollars (or guilders) have been invested in protecting our land. High storm surges that push sea water inland are the main threat. In 1953, following a storm surge from the sea that drowned many people, updated plans were created and implemented to protect the threatened area. The Delta project in the southwestern part of The Netherlands was launched. As a result of lying in a river delta the country has been able to develop into an important industrially and densely populated nation. Construction, management and maintenance of flood defences are essential conditions for the development of the

2 362 Frank P. Rallie & Richard E. Jorissen Fig. 1 The Netherlands and the major rivers. towns and cities and further economic development of the country. The Rhine, the Meuse and the Scheldt are the most important source of our fresh water and support local culture, natural biodiversity and offer also a beautiful landscape. Economically, they are also vital: Rotterdam is one of the principal ports in the world, obtaining its position due to its excellent inland water transport routes, especially into the heavily industrialized hinterland of Germany. To some extent the rivers main natural purpose, to carry water, sediment, and ice out to sea, is easily forgotten. Over the centuries, human use of the river basins has inhibited the rivers' abilities to perform these natural functions. Deforestation,

3 Protection against flooding: a new Delta Plan in The Netherlands 363 urbanization and canalization have produced significantly higher peak discharges than those recorded in the nineteenth century. Protection against flooding is in a way a popular business in The Netherlands. In times long ago people lived near the river but mainly on the higher ground, so there were in fact no threats to be feared. Then flooding of the river over its normal banks was rarely seen as a disaster. As a result of drainage, the peat and clay marshes were made suitable for agriculture. This drainage lowered land level and the threat of floods increased. To protect property, dikes were built from the early Middle Ages. Farmers also started building small dikes to protect their land. The drainage activities became more professional, sluice systems and windmills were used to raise the water into the drains from low-lying "polders". This again resulted in further lowering of the ground level. One could say that the Dutch pumped themselves under the sea level. Since the early Middle Ages ground levels have dropped several metres as a consequence of drainage, oxidation and settlement. It is clear that the building of dikes was the only solution to survive. The increasing population and the need for more land resulted in a more intensive use of the low-lying polder areas. This whole process resulted in a land more and more vulnerable to flooding. The population increased and the value of property also. Therefore the regular floods were more and more seen as disasters. The damage was often significant and could cause many deaths by drowning. The rivers were used more and more for other activities, like shipping. The rivers were forced into a narrow bed and this resulted in more disastrous flooding. A continuous dike reinforcement programme was needed to protect the people from flooding. The most important failure mechanism of a dike at high water levels are: wave overrun, sliding of the outer or inner slopes, erosion of the outer slope and piping. To withstand these mechanisms the dike needs sufficient height and stability. In the safety assessment of dikes, each relevant section of the entire dike is judged on these two aspects. The most important mechanisms that can result from a dike's inability to fulfil the water retaining function can occur during or shortly after high water. In the seventies and eighties the reinforcement plans of the river dikes came under fire. The attitudes of society towards the river landscape did not always parallel the need for significant strengthening of the river dikes. As a result of social discord, committees were established in both the eighties and nineties to investigate the need for reinforcement of the river dikes. In both cases the recommendations clearly emphasized the need for reinforcement but with proper care so that a large part of the characteristic river landscape could be retained. The river dikes serve many other purposes besides the control of water, for example living space, transport, recreation and wildlife. The awareness of these functions relating to landscape, nature and culture has grown strongly over the last decade. After the most recent study in 1993, government and Parliament agreed that the strengthening of the river dikes along the Rhine and parts of the Meuse should be undertaken and completion of the programme by the year 2008 was agreed.

4 364 Frank P. Hallie & Richard E. Jorissen FLOODS IN 1993 AND 1995 In 1993 around Christmas and in early 1995 both the Meuse and Rhine obtained extremely high water levels caused by heavy rainfall. The consequences of these two events were significant water damage along the Meuse (in 1993 and 1995) and along the Rhine (in 1995) (Hillen & Jorissen, 1995). The discharge at Borgharen (the first control point on the border with Belgium), the first control point) was measured at 3120 m 3 s" 1, a level that will occur only once in 150 years (1/150 per year). As a result, along the undiked banks of the Meuse the river broke its banks. The consequences of this were significant damage in the province of Limburg (approximately 250 million Dutch guilders). Immediately after this high water period, the Minister of Transport, Public Works and Water Management established the Meuse Flood Emergency Committee with the instructions to research into how the consequences of such flooding could be addressed in this part of the country. A first example of this research was the reassessment of our flood control standards. The high water of 1993 in the Rhine gave rise to no further policy initiatives, because it was judged as a normal high water period. The established programme of dike reinforcement was not changed. The Meuse Flood Emergency Committee investigated the possibilities of further protection against flooding. The main results of this Committee are as follows: - to a large extent the widening and deepening of the river bed can largely prevent the effects of high water (Fig. 2); - the material removed (sand and gravel) can be used for nature development projects in the neighbourhood of the river; - in certain cases retaining walls are required to give additional protection, particularly in urban areas; - certain areas that were flooded in 1993 cannot reasonably be protected against flooding; - planning policy must be better adapted to the different functions of the river. The results of the activities of the Committee show that the recovery of the natural character of the Meuse was seen as the most important element in the restriction of future flood damage. The reduction of water levels at high river discharge must principally be achieved by widening and deepening. A significant difficulty here major bed minor bed major bed normal discharge 1 minor bed deepening 4 branch channel 2 minor bed widening 5 high water channel D high water 3 major bed excavation Fig. 2 A new approach.

5 Protection against flooding: a new Delta Plan in The Netherlands 365 is that the work will take between 10 and 20 years. At that moment, almost one year after the flood of 1993, it was deemed acceptable, especially because the report of the Committee showed that the cost of the extensive plans could be met by the profits of selling the raw materials which will be excavated, especially sand and gravel. In 1995 again the Meuse and Rhine reached very high water levels. The maximum discharge in the Meuse was less than in 1993, but the high water levels in 1995 proved much more persistent. The damage along the River Meuse in 1995 was significantly less than in The reason for this lay in the slightly lower water levels and especially in the better state of preparedness of both citizens and the authorities. The 1993 experience was very important. All this created a climate in which short-term measures for the protection against high water were deemed necessary. The maximum discharge in the Rhine during the high water period in 1995 reached almost m 3 s" 1 at Lobith on the border with Germany (Technical Advisory Committee on Retaining Structures, 1995). The design discharge is however significantly higher ( irrv 1 ). Although the difference in maximum water heights between 1993 and 1995 was only some decimetres, the local waterboards along the Rhine could no longer guaranty security against flooding of the various polders. As a result of this and an evaluation of the risk of a possible dike collapse, it was decided on the preventive evacuation of more than people and millions of animals. This mass evacuation gave rise to considerable social unrest. A NEW DELTA PLAN During the high waters of 1995 the government decided to accelerate the existing programme of river dike reinforcement. Therefore a new "Delta plan" was announced by the Prime Minister of The Netherlands. In fact everybody knew that most of the river dikes did not meet the required standards. Earlier it was stated that in 1993 the Parliament agreed to the river dike reinforcement programme that will be completed in 2008 AD. So it is obvious that in 1995 not much was done in respect to the reinforcement programme. The aim of this new Delta plan is, in general, to complete the dike reinforcements along the River Rhine and along some parts of the River Meuse in the year 2000 AD. The repairs of the weakest parts of these dikes are considered as urgent and it was decided to reinforce these dikes before the end of Special legislation was necessary to be sure that the weakest dike sections are reinforced by the end of A total of approximately 150 km of dike along the Rhine are to be considered as weak and thus requiring urgent attention. Along the Meuse approximately 150 km of retaining walls had to be built before the end of Special legislation was needed to accelerate the pace to complete the required actions. Within a period of 10 weeks the actions necessary had to be completed, including actions of appeal. As this special legislation is a bit controversial with respect to the care needed which was promised for the remaining river dike reinforcements, only the most urgent dike sections could benefit over a period of only two years.

6 366 Frank P. Hallie & Richard E. Jorissen After this work over 2 years the state of the remaining river dikes will not require urgent attention and a normal reinforcement schedule will be carried out. The new Delta plan contains the framework into which the reinforcement plans must be fitted. No objections can be allowed, the main goal is completion in the year 2000 AD to make The Netherlands safe against flooding. For the undiked section of the River Meuse the recommendations of the Meuse Flood Emergency Committee serve as guidelines. By widening and deepening the river beds, a lower water level has to be created. In places where these measures do not lead to a sufficient reduction of the risk of damage, retaining walls will be built to reduce the average chance of water damage in the nearby towns and cities. The new Delta plan launched an accelerated implementation of these plans. The restoration of the Meuse must be finished by the year of Along the Meuse extensive plans are being developed to recover the natural character of this river, which is seen as the most important element in the restriction of future flood damage. Widening of the river winter bed and deepening of the river summer bed must create more storage capacity in the river system itself in order to reduce the water level during a flood period. FLOOD PROTECTION ACT A total of approximately 650 km of remaining river dike fall under standard law. Special consideration should be given to the recommendation of the Committee for the Review of River Dike Reinforcement Principles. This means taking into account the characteristic values of the river area, e.g. landscape, nature, and cultural history. Using environmental impact reports, more sophisticated designs and public hearings it is possible to execute the river dike reinforcement programme in such a way that all participants are completely involved. This standard law is called the Flood Protection Act and came into operation at the beginning of this year (15 January 1996). This seems strange, because in The Netherlands there is a tradition in protection against flooding and the building dikes. In fact it is a renewal of and complementary to an old act in operation since Nature Cons. Org.: - natural values Province: - coordination - physical planning Municipalities: - local interests Water Boards: - upkeep defences <^ State: supervisor Fig. 3 The Flood Protection Act.

7 Protection against flooding: a new Delta Plan in The Netherlands 367 This law provides for the supervision by the national government of the activities of the lower water administrations, and for the foundation of waterboards by the provincial governments. The Flood Protection Act describes the competencies of the administrations on every level concerning flood control (Fig. 3). The waterboards play an important role in the system of flood control which are very old institutions and are responsible for the maintenance of the dikes, and the protection of the dikes from damage. The costs of the tasks of the waterboards are met by the landowners inside the territory of the waterboard. They pay their waterboard taxes proportional to the area they own. Nowadays buildings too are taxed and there are so many buildings that the owners of buildings together pay more than the landowners in some waterboards, but all proportional to the value of their properties. The waterboards are supervised by the provincial government in the execution of their technical duties, but also their administrative and financial powers. The Ministry of Transport, Public Works and Water Management supervises the provincial governments in the same way, it fulfils the role as the chief supervisory body. The Ministry is also responsible for maintaining the existing coastline. Furthermore, it provides the necessary information on water levels, waves and other information necessary for the design and safety assessment of the flood defences. The research on flood defences is carried out by the state in cooperation with provinces and the waterboards. The Technical Advisory Committee on Water Retaining Structures advises the state on the detailing of this research. The managers of the primary flood defences are required to check the technical condition of the flood defences and assess the actual safety against requirements every five years. An overview of this assessment is reported to the provinces. The supervising provinces report to the Minister of Transport, Public Works and Water Management, who, in turn, informs the Lower House of Parliament on the safety of the flood defences. The waterboards have the task of maintaining the strength of the river dikes to meet the safety standards. The Flood Protection Act gives standards for every dike-ring area, the system constructed long ago. For each individual area a safety standard is set. The safety standard should be based on weighing the costs of the construction of flood defences against the possible damage caused by floods. At this moment the standard is expressed in terms of the probability of failure. This probability is transformed into a specified design water level. The Flood Protection Act sets new standards for the dike reinforcement programme. Preparation now needs more time in respect to the dike sections in need of attention approximately 2 years is required. The Act contains a lot of standard actions which can be dealt with simultaneously. It includes a so-called Environmental Impact Assessment, in which all relevant alternatives must be shown. Also the water board must give information on how the landscape, nature and cultural values are taken into account. Appeal is possible to only one official institution: the State Council, a definite decision will be given within 12 weeks or at the most 6 months.

8 368 Frank P. Hallie & Richard E. Jorissen A NEW APPROACH To cope with future developments it is evident that river dike reinforcement alone will not ensure a long lasting solution. A new approach is needed (Fig. 2) including physical planning, land use development, (international) river management and finally building and reinforcement of the dikes. Raising the river dikes (again) is only a temporary solution for the problem of high water. But there is no doubt about the necessity of this round of dike reinforcements. Behind the dikes millions of people are living and enormous investments have been made. But in addition to the reinforcement of dikes, other kinds of measures are necessary, if only to prevent to the extent possible the necessity of future dike reinforcements. The measures to be taken in the river basins should be aimed at enlarging the area occupied by the river itself and at limiting the probability of damage during periods of high water levels. The physical planning in the river basin should ensure that the area available for the river between the dikes should be kept free for the main functions of the major rivers: discharge of water, shipping and as a habitat for wild life. Developments that negatively affect these main functions should be actively prevented, e.g. by implementing a ban on building. A new river basin policy is in discussion now. The policy is aimed at enlarging the area of the river itself, sustainable protection against flooding and limiting the potential for damage. Also sustainable compensation is needed where water levels are increased by certain kinds of activities, e.g. by hydraulic engineering structures like bridges, sluices and flood defences; waterway improvements works and building in the flood plains. All other activities are not acceptable, except if it is quite clear from research that particular activity is of importance to society. The only place where it can take place is within the river or flood plain and there is no harm to increase of the river discharge capacity. By storing rain and melt water within the basin the maximum flows of the major rivers can be lowered. Sustainable river management should be aimed at structural maintenance and, where possible, the increase of discharge, and the recovery and development of the natural character of the particular river. When the above mentioned measures offer insufficient protection against flooding, then (additional) technical measures can be implemented. Upstream on the River Rhine in Germany there are plans to build eleven storage basins for retaining flood water. The Netherlands the choice of dikes as the method for protection against flooding by the major rivers was made long ago. By combining all measures described it might be possible that new dike reinforcements can be avoided in the future. Last but not least: there is no such thing as complete protection from floods and all these plans and measures they contain cannot prevent our country from being flooded. They will, however, reduce the potential damage of future floods. In addition instruments are needed to predict and warn against flooding and to make people aware of the consequences of living in flood-prone areas. This new approach will be dealt with in the 4th National Policy Document on Water Management which is scheduled for 1997.

9 Protection against flooding: a new Delta Plan in The Netherlands 369 CONCLUSIONS Reassessment of flood control standards in The Netherlands has led to the following conclusions: - Sometimes it takes a near calamity to draw the public's attention to a problem. High water levels in The Netherlands in 1993 and 1995 created a climate in which the resistance to dike reinforcement decreased. - The results of the Meuse Flood Emergency Committee shows that the recovery of the natural character of the Meuse was seen as the most important element in the restriction of future flood damage. The reduction of water levels during floods must principally be achieved by widening and deepening of the river channel. The new Delta plan for the major rivers contains special legislation for accelerated reinforcement of the most urgent river dike sections, by setting aside some regular legal procedures for appeals law and actions. The new Delta plan also supplies a framework for the further river dike reinforcement projects. - The Flood Protection Act contains safety standards for the primary flood defences. It also provides a framework for planning within a limited preparation time, of at the most 2.5 years. This was necessary to be able to realize the main goal: The Netherlands safe against flooding in 2000! - In The Netherlands an increasing number of people are becoming convinced that reinforcing dikes alone cannot offer real sustainable protection against floods. - All future measures and activities in the basins of large rivers need to be tested as to how they affect water discharge. - The risk of damage must be limited, for instance, by good warning systems and suitable safety measures. Increasing the potential damage must be prevented through various measures in the area of town and country planning, and especially by avoiding constructions in high risk areas. High water levels are a part of the natural river system. Full protection against flooding cannot be guaranteed. Therefore information services, to make people simply aware of the fact that high water levels are and will always be a real possibility. - One thing is clear: high water levels will always be part of our future. REFERENCES Hillen, R. & Jorissen, R. (1995) River flooding and flood management in The Netherlands. Ministry of Transport, Public Works and Water Management; 30th MAFF Conference of River and Coastal Engineers; Keele University; Ministry of Agriculture, Fisheries and Food; Flood and Coastal Defence Division; July Technical Advisory Committee on Water Retaining Structures (1995) Under pressure 1995; the condition of the Dutch river dikes during the flood period of January-February Technical Advisory Committee on Water Retaining Structures; Delft, The Netherlands, December 1995.