Effects of Climate Change on Water Management in The

Home , Dordrecht, Hoeksche Waard, IJsselmonde (island), Rozenburg (island)

WEFTEC®.06

EFFECTS OF CLIMATE CHANGE ON WATER MANAGEMENT

Arie van der Vlies, Kees Stoutjesdijk, Hans Waals Water authority Hollandse Delta P.O. box 469 3300 AL Dordrecht, the Netherlands

ABSTRACT

The climate is changing; the first indications are already apparent. The consequences for water and flood management are evident, especially in the Netherlands. The country has the highest population density in Europe, with the most economic centers and major cities below Mean Sea Level, so it is an absolute necessity to anticipate future changes. The development of both the necessary water burden for the regional waters and the floodwater program has led to the imposition of standards. The application of these standards has led to a series of measures that have been or are to be implemented in the period 2003 - 2015. These are very radical measures and the associated costs are considerable. Nevertheless, there is support for continuing, sustainable water management. This approach will lead to continuing a safe, healthy living environment in which the Dutch population as well as many foreigners can live, work and enjoy their leisure.

KEYWORDS

Climate change, flood defense, water management, regional water burden, safety, water is life program.

INTRODUCTION

Is climate change a challenge or a threat to water management? This question is acutely relevant in light of the extremely high river levels and floods that have occurred since the end of the 1990s in the Netherlands. These drastic occurrences, coupled with the predicted changes in the Earth's climate and rising sea levels, led the national government towards the end of the last century to mandate a committee to formulate a policy for "Water Management in the 21st Century". The committee came to be called WB21.

Safety and the quantity of water are once again high on the government agenda in the Netherlands. This was reinforced once again last year thanks to the consequences of the hurricanes Katrina and Rita in New Orleans and this region. The parallel between New Orleans and the Netherlands holds to a degree, but the comparison does not hold in some respects. During WEFTEC 2005, in the session "In the wake of Hurricanes Katrina and Rita: where we go and what we know", one of the speakers called New Orleans "an 'evitable' city on an

impossible site". Can we say the same of the Netherlands, that it is an 'evitable' country on an impossible site? This paper discusses the statement.

KEY DATA ON WATER MANAGEMENT

Geographic location

Water management in the Netherlands cannot be understood without some knowledge of the geographic situation. The country, with a land area of 36,000 square km, is situated along the North Sea.

The Netherlands lies in the delta formed by the international rivers Rhine, Meuse and Scheldt. The country is sometimes viewed as the drainage sink of these major rivers.

The Netherlands can be characterized as a wet country, if one looks at the mean annual rainfall of 750 mm. The climate is moderate, evaporation and transpiration together amount to 500 mm. There is a deficit of water in summer.

About 25% of the land Figure 1 - The Netherlands influenced by the sea consists of polders which lie (brown) or rivers (blue) below Mean Sea Level. Figure 1 shows the division of the country into low and high areas. If the lower parts of the country were not protected by dunes or dikes, 65% of the country would be flooded when sea and river levels are high. The provinces of South Holland (with large cities like Rotterdam, The Hague and Dordrecht and with main industrial areas) and North Holland (with Amsterdam and its main airport Schiphol) are especially endangered by the rivers and the sea.

A polder is a typical characteristic of the Dutch landscape. The word indicates a low-lying area, isolated from the surrounding hydrological

regime. The safety of the typical "polder" territories depends on the alertness of the water authorities, which are responsible for land drainage and flood control. Figure 2 illustrates the principle of a polder.

Figure 2 - Typical water management in low-lying areas in the Netherlands

In a polder the water levels are controlled by pumping excess water into the storage canals. In dry periods it may be necessary to reverse the direction of water flow, transfering water from the canals or rivers into the polders. In the low parts of the country most of the surface waters are stagnant. Eutrophication problems occur almost everywhere, run-off of nutrients from agricultural land and the intake of river water are responsible for excessive algal and duckweed growth in canals and smaller waterways.

Managing the water in the major rivers and sea inlets is the responsibility of the Dutch Government. The management of the smaller rivers, the canals and the drainage ditches is the responsibility of the water authorities.

Demographic situation

The growth of the population is steady: from 8 million in 1930 to the present figure of more than 16 million. The population density of 450 persons per square km is the highest in Europe.

The province of South Holland contains the cities of Rotterdam and The Hague, which are situated in the lowest-lying part of the province, the most densely populated in the country. In economic terms, a significant fraction of the most important industries and activities are also located in this province. One of the water authorities in this province is the Hollandse Delta water authority.

Table 1 - Population density

Province of South Holland The Netherlands USA

Population (x 106) 3.4 16.3 294

Area (km2) 2,880 36,000 9,373,000

Population density (inh/km2) 1,180 450 31

Hollandse Delta water authority

The Hollandse Delta water authority is one of the 25 Dutch water authorities and is located in the province of South Holland in the neighborhood of the city of Rotterdam and in the western part of the Netherlands. This water authority takes care of safe dikes and dunes, treats the waste water, and ensures that the water in the ditches, ponds, lakes and other waterways is clean. In wet periods the water authority takes measures to prevent flooding. In dry periods, Hollandse Delta ensures that there is sufficient water in canals, ditches, ponds and lakes, so people can live, work and spend their leisure time safely and well, now and in the future.

Table 2 - Hollandse Delta water authority in figures

Total area under management 85,000 hectares

Municipalities in area 23

Resident population 825,000

Dikes and dunes 650 kilometers

Waste water treatment plants (wwtp) 23

Capacity wwtp 1,600,000 p.e.

Regional monitoring areas 600

Roads 1,300 kilometers

Cycle paths 170 kilometers

Water pumping stations 150

Sewage pumping stations 63

Outside the built-up areas, the water authority maintains the roads and cycle paths, mowing the verges in the summer and de-icing busy roads in the winter. The water authority works for everyone who lives, has a business, or owns land in southern South Holland.

Hollandse Delta can only keep the area safe, clean and inhabitable with the help of society at large, which is why rules have been laid down in the Regulations (Keur) and the Surface Water Pollution Act. It is under these regulations that the water authority grants under restrictions permits to private persons, municipalities and businesses.

WATER MANAGEMENT IN THE PAST

Partly due to the country's location, water management has received a great deal of attention for centuries. Some of the water authorities in the west of the Netherlands have been performing this task for ab 800 years.

A great deal has improved in many areas in recent decades.

Safety

For centuries the safety of the dikes and dunes has been an important responsibility of the authorities. The Dutch water authorities were the first democratic institutions, dating back to the 13th century. The construction and maintenance of dikes was an important task of the first water authorities. Everyone within the jurisdiction of the water authority had to pay taxes according to his interests within the region. This, however, also gave him proportional control over the water authority. This "interest", related to "tax", related to "control" has been in use for more than eight centuries for flood defense and water management Figure 3 - The Delta Works by the water authorities in the western part of the Netherlands. Despite the work of the water authorities there have been major floods throughout the country's history: • November 18, 1421: The Saint Elisabeth Flood destroyed more than 20 villages in the southwestern part of the Netherlands, causing over 2,000 casualties; • November 1, 1570: The All Saints Flood flooded large parts of the coastal area between Belgium and the northern parts of Germany and more than 20,000 people died; • December 24, 1717: The Christmas Flood. Again the northern coastal areas between

Denmark and the Netherlands were flooded and 14,000 people were killed; • January 31, 1953: A storm flood caused breaches in several dikes in the southwestern part of the Netherlands, in Belgium and southeast England. In total 1836 casualties were counted in the Netherlands. This flood is known as "de Ramp" (the Disaster).

As a result of this last disaster the "Delta Law" was implemented by the Dutch government. This law had two major impacts. The first was the "Delta Works", which closed of the large sea arms of the deltaic area in the southwestern part of the Netherlands between 1953 and 1990 (see figure 3). This involved a tremendous decrease in the length of the sea barriers. The total length of the sea barriers (dunes and dikes) along the southwestern part of the Netherlands decreased by 700 km. Only the New Waterway and the Westerscheldt remained open because of their importance as main shipping routes to the ports of Rotterdam and Antwerp. In recent years a storm barrier (the Maeslant barrier) was developed to increase the safety of Rotterdam and its surroundings.

The second impact of the Delta Law was the establishment of the necessary dike safety. After a thorough study of the risks associated with a breach of the dunes or dikes it was established that the dikes had to be constructed to resist a water level that could occur once every 1,250 to 10,000 years (see figure 4). The dikes along the rivers are mainly developed on the basis of 1:1,250 year and the dikes and dunes around the center of Holland have to be strong enough to withstand an event of 1:10,000 year intensity. Along the coast the safety level was established at an event of 1:4,000 years and the dikes open to a certain sea influence have a safety level of 1:2,000 years. (The dikes in New Orleans have a safety level of 1: 100 years.)

Dunes make up three-quarters Figure 4 - Safety standards of the dikes of the Dutch coast and cover about 40,000 hectares or 11% of the land area. The sandy coast is in continuous motion. As this can expose and increase the vulnerability of the land behind the dikes, the government has been keeping a careful eye on the coast for centuries. In 1990, the government decided on a "dynamic maintenance" approach to the coastline. This means that the coast is allowed to move, within certain limits, and that wind and water have free play. Within these limits, the level of sand is maintained by bringing it in from elsewhere. Most sand replenishments these days are taken from the sea bed.

Integrated water management

Over the course of centuries, the Dutch armed themselves against the hazards of the sea and the rivers and the nuisance of excessive rainfall using a great deal of effort, innovative ideas, clever technology and – mainly – gritty determination. This allowed the country to develop and prosper. More space was needed in which to live and work. Technology assisted the Dutch to drain large lakes and reclaim large areas from the sea by building dams. The Netherlands built up its own land area.

The area in the polders must be kept sufficiently dry. Rainfall in the Netherlands amounts to about 750 mm per annum more than is required to replace evaporation and allow crops to grow. The excess water has to be carried away. To this end, over the years a range of waterways have been dug, which allow the excess water to collect at a polder pumping station, which pumps the water out of the polder. In some locations this water can be discharged directly to the sea, but that is often not the case in polders that have been drained dry. Here we use a staged series of pumps, so that the water is first pumped into a catchment basin (called a boezem), after which a second pumping station finally raises it so that it can flow into the sea (see also figure 2).

The demands on this drainage system are gradually becoming increasingly stringent. Living and working in the polders means that both surface and ground waters have to be maintained at the right level. This has also allowed agricultural development on the land, which is often very fertile. The demands of agriculture grew, which translated, among other things, into yet more land drainage. Lower-lying areas of the country were given a modified, lower water level. The higher-lying areas drained away excess rainfall over weirs to the lower-lying areas, where the pumping station ultimately pumped off the excess water. In areas with a clay substratum, the desired difference between ground level and water level in the waterways is about 1.20 to 1.50 m. However, this desire for a lower drainage level had an adverse effect in many parts of the Netherlands. Some places have a great deal of peat over the substratum and lowering the groundwater table allowed the peat to oxidize, resulting to compaction of the ground. The workable land thus sunk lower and lower, which meant that the water table and the drainage system had to be modified once again. This vicious circle led – and still leads – to a great deal of tension between agriculture and water management. Peat-rich areas may now not be drained by more than 0.60 m.

Partly due to the increasing demands of agriculture, the demand for fresh water for irrigation also rose. Fresh water is available from the major rivers. Digging inlets from the rivers allowed the water to be used for agriculture, but it has also become important for industry, the electricity supply and other users.

"A safe and habitable country with healthy and sustainable water systems": this is the goal with which Dutch water management faced the future. The first part – ensuring a safe and habitable country – has existed for centuries. The new impetus has been described above under the heading "safety". The second part of the aim – ensuring "healthy and sustainable water systems" – has a much shorter history. It was not until the late sixties that the problem of surface water pollution led to systematic action to tackle the main sources of pollution. By that time, the poor quality of the surface water was presenting a threat not only to public health but also to wildlife habitats.

During the eighties there was a growing realization that the goal of public safety and habitability could not be viewed in isolation from that of healthy and sustainable water systems. Moreover, it became clear that water management could achieve these aims much more effectively and efficiently if the policies directed at them were not only closely interrelated with each other but also carefully coordinated with other relevant policy areas. In the mid-eighties this realization became known as integrated water management.

The policy of Dutch water management is formulated in the Fourth National Policy Document on Water Management.

Waste water treatment

When the Surface Waters Pollution Act went into effect in 1970, it gave a new impetus to the construction of sewage treatment plants. This also marked the start of the process by which municipalities and provinces transfered their treatment plants to the water authorities. Nowadays, public wastewater treatment is only carried out by water authorities, which manage almost 400 plants. In addition, various companies treat their own wastewater in some 600 plants.

The volume of wastewater treated in public sewage water treatment plants increased from 8 million population equivalents in 1970 to 27 million population equivalents in 2004. The sewerage system has been radically improved and expanded to allow for the construction of new sewage water treatment plants.

FUTURE INFLUENCES

Climate change

A number of studies have shown that the climate is changing. Measurements have shown us that the earth is warming up. This can have serious adverse consequences for an area like the Netherlands. Warm air can contain more moisture which, when it cools down over land, results in greater precipitation. This will mainly take the form of heavy, local showers. Besides excessive precipitation, we also have to consider relatively long periods of intense drought. These are expected to be accompanied by shortages in the water supply, partly due to increased evaporation. Threatened shortages can result in serious economic and ecological damage. Agriculture too may experience such adverse effects, as the system of waterways cannot be used everywhere to supply water. Modifying the system and digging fresh water basins would cost too much, incidentally, as a recent national study has revealed. Because the climate change will lead to higher sea levels, the drainage of water from the rivers to the sea may be hampered. A further consequence is that the hydraulic pressure on the groundwater from the water outside the polders will increase, leading to a greater inflow of salt water. Combating this extra salination will actually increase the demand for fresh water.

Based on observed statistical relations between large-scale atmospheric patterns and local precipitation, the scenarios by 2050 for the river Rhine area are as indicated in Table 3.

Table 3 - Climate changes in the Netherlands

Quantity low medium high

Temperature + 1º + 2º + 4-6º

Summer precip. + 1% + 2% + 4%

Summer evap. + 2% + 4% + 8%

Winter precip. + 6% + 12% + 25%

Sea level rise + 20 cm + 60 cm + 110 cm

Referring to the information presented above, the following prognosis is now generally accepted by water managers in the Netherlands, and serves as the basis for many studies of future water management options: • Rainfall rates will continue to increase both in the Netherlands and in the upstream catchments, especially in winter. • Temperatures will also continue to increase in the Netherlands and in the upstream catchments in both summer and winter. • (Summer) rainfall intensity and the frequency of extreme rainfall events are also likely to increase. • Evaporation will also increase, especially in summer. • Sea levels will continue to rise, by at least as much as they have in the 20th century, and probably considerably more.

WB 21 committee results

The extremely high river levels and floods that have occurred since the 1990s gave rise to the question of how water management in the Netherlands should be conducted in the 21st century. To answer that, central government appointed a committee in early 1999: The Committee on Water Management in the 21st Century (WB21).

The initial reasons for the WB21 Committee's investigation were: 1. Heavy rainfall had caused the near-collapse of some of the dikes along the Rhine. The local population and livestock were evacuated as a precaution. 2. Polders, including residential areas, had been inundated several times as a result of extremely heavy rainfall. Rainfall intensities have been measured of 150 mm/24h and 75 mm/3h (annual mean 700 – 800 mm). 3. The ground level in many areas is sinking due to such activities as the extraction of groundwater and natural gas, as well as the compaction of our drained peat soils. 4. The climate is predicted to change.

The WB21 Committee's major conclusions are that: - historically, technology alone was used to maintain water management, and water policy was low down on the town and country planning priority list;

- we have now reached the limits of what is technologically feasible. Increasing the capacity of pumping stations and increasing the height of the flood defenses are not (always) the solution to future problems; - more space has to be given to water in the future and water has to play a leading role on the town and country planning agenda.

The WB21 water policy acknowledges water quantity and water quality, each involving a three-pronged attack: Water quantity: 1. Retain: rainwater should be retained as far as possible at the location upon which it falls. 2. Store: if retention is not possible, the rain must be stored in the same area (polder or community). 3. Remove or drain: only if retention and / or storage are impossible.

Water quality: 1. Keep it clean: prevention is better than cure. 2. Separate: separation at source. 3. Dilute or flush through: the solution when keeping it clean or separation is impossible.

The most significant consequence of this policy is that more space is needed for water management. The practical development of WB21 leads to a long-term water management task having the following characteristics: - given the impact on the amount of space available in the Netherlands: multiple use of space, such as combined nature reserve and water storage, dike construction and recreation; - water helps to set and order the priorities of the spatial planning agenda. This principle has recently been accepted in legislation; - every item of town or country planning must pass the water test; this water test is a procedural instrument to safeguard water in spatial plans; - the water management task may not be passed on to other water managers. Each manager (national government, province, local authority water authority) must carry its own responsibility and must accept the costs of all necessary measures. The burden of the water management task falls most severely on the western and northern parts of the Netherlands. Twenty-six percent of the Netherlands lies below sea level (termed below NAP). Without dunes or dikes, 66% of the Netherlands would regularly be flooded.

"WATER NEEDS MORE" PROGRAM

As has already been stated, large areas of the Netherlands lie below the mean level of the North Sea. Without dikes and dams, large parts of the country would be inundated every day. Furthermore, the Netherlands is the drainage basin for the major European rivers. Without river dikes, great areas would be flooded for long periods. Living and working in the low- lying, water-rich Netherlands has demanded and continues to demand a great deal of effort in water management.

Threats

The water system has worked well for a long time. Over the years the Dutch have come to place their trust in its technology and design. This has given rise to a great feeling of mastery. A negative aspect, however, is that the nuisance of a surplus or a shortage of water has become difficult to accept. Historically, low-lying areas, where it was known and accepted that they were too wet after heavy rainfall, were not built on. Nowadays, homes or businesses are located there and the nuisance is no longer tolerated. The realization that we live in a low- lying country where the water simply cannot always be our friend has vanished among a large fraction of the population.

So it was a serious shock Figure 5 – Flooding in September 1998 when, in the late 1990s, parts of the water system seemed to be unfit to withstand a number of extreme weather events. At that time the country was confronted with extremely high water levels as a result of heavy rainfall upstream. Not only did the rivers burst their banks, it also became clear that the river dikes were not always high enough, nor strong enough. As a precautionary measure, 250,000 people were evacuated from low- lying areas. In the same period and in subsequent years, large areas of the country were confronted with extreme rainfall. At some places in September 1998 as much as 130 mm fell in a 24 hour period. Drainage capacity could not meet this demand. In the Netherlands the standard drainage capacity is calculated to remove 14 mm per 24 hours. The result was that large areas of agricultural and urban land were flooded (figure 5). This scenario was repeated in other regions in subsequent years. Damage ran into billions of euros. The water managers were faced with the question whether these were incidents that the system was simply not equipped to deal with, or would we have to face it more often? Would we have to abandon the water system? Serious reconsideration was an urgent priority.

A new look at water management needed: Water management for the 21st century

The floods of the 1990s gave fresh impetus to discussions of the safety of our water system at all levels: central and provincial government, and among the water authorities. The awareness arose that the water systems could not perform as expected when coping with extreme rainfall, with nuisance or damage as a result. The expected climate change, settling of the land, and sea level rise only served to reinforce this awareness. It became clear that we cannot

tackle these problems in the traditional manner. It would not be sufficient to increase pumping capacity by a factor four or five. We have reached the limits of the technology. Nor would it be feasible in cost terms. The Committee on Water Management in the 21st Century (WB21) produced the advisory report already referred to.

We needed another way of thinking about water. The resultant National Water Management Agreement [Nationaal Bestuursakkoord Water (NBW)] stated that the water authorities must test their water systems before 2006 against operating standards for regional flooding.

Standards for flood nuisance

The parties realized that tackling flooding may have far-reaching consequences. There was a need for a joint agreement on what was and what was not acceptable. This led to standardization, based on economic principles, of the probability that the water system would fail under heavy rainfall. The probability criterion, as well as the height of ground level, both depend on the type of land use. The basic premise is that the damage to areas of high economic value (cities) is greater than in agricultural areas, for instance. Table 4 shows the NBW standards and criteria.

Table 4 – Permissible probability of failure and ground level criterion: NBW standards

Normalized probability of Ground level criterion failure (area that will experience Land use NWB standard temporary flooding)

Grassland 1:10 years 5 percent

Arable 1:25 years 1 percent

High value horticultural land 1:50 years 1 percent

Greenhouse horticulture 1:50 years 1 percent

Built-up area 1:100 years 0 percent

These standards should be seen as the minimum that the water system should meet. If parts of the water system do not meet this standard, then action will have to be taken. Situations may occur, however, where the costs of the measures outweigh the reduction of damage. In such cases it may be decided that no measures will be adopted. The NBW standards govern the instant when flooding occurs. In practice, nuisance occurs even at lower levels than the standard. Discussion is therefore continuing on the application of supplementary standards for exceeding one-half of the dry area of agricultural land, or the lowest discharge level of the sewerage system.

Calculations

The standards led the water authorities to start calculating. To do this they used complex computer models to simulate the entire drainage system, including current land use, soil type

etc. Rainfall was input using a 96-year series of actual, measured rainfall. In order to determine the effects of changed rainfall in the future (climate scenarios), the specified rainfall events were increased according to the percentages included in the WB21 report (table 5). Table 5 – Climate scenarios used

Climate scenario Precipitation intensity Annual precipitation showers

Current scenario 0% 0%

WB21 mean scenario + 10% + 3%

All water authorities computed the current and future situation in this way. As an illustration, figure 6 shows the Hollandse Delta areas that do not match up to the future situation. This map forms the basis for the calculation of measures as well as discussions with the planning authorities. Figure 6 – Climate scenario results in the Hollandse Delta area

Sufficient Insufficient to NBW requirement Water Insufficient to supplementary Not tested Management area reguirement

Measures based on new thinking

The necessary measures require first and foremost a new way of dealing with water. We have to realize that it is no longer sufficient simply to quickly carry away the excess water. Often there will be no area left to which the water can flow: the main catchment basin is full, the

Figure 7 - The three-pronged attack of WB21 river is already too high and the water cannot be carried away to the sea. So we have to retain the water temporarily as far as possible where it falls. This means we need extra space. And finally, of course, ultimately we have to drain the water with the pumping stations (see figure 7).

Translation into measures Figure 8 - Consequences per water authority of Based on this, the next step is to NBW requirement calculate the package of measures, using as our point of departure the Percentage of the area per water authority which does not three-stage plan of retain–store– comply with the inundation drain. We used the computer requirements models once again to determine the most effective set of measures. A variety of scenarios can be set up for the different solutions. The first computer results were recently made public (see figure 8). Heavy investments will be required in the coming years.

Increased demands on water quality

Parallel to the concerns about too much or too little water, there are also concerns about the poor quality of the water. Towards the end of the 1980s it was realized that water quality was seriously suffering due to industrialization and different forms of land use. Measures directed to water treatment and the prevention of discharges led to considerable local improvements, but the pace

of improvement seemed to be stagnating. For example, the semi-annual change of chloride content in some areas due to a switch from drainage to supply has an adverse effect on the development of an ecologically stable water system. An extra impetus was needed. This came in the form of European policy under the Water Framework Directive. This involves an obligation to achieve results with measures intended to improve water quality. At present we do not have a clear idea of the consequences of this Directive.

Multifunctional, innovative design essential

Given the population density of the Netherlands, with the pressure this puts on space, it is no small matter to gain space for water storage. The measures will have to be combined as far as possible into a multifunctional package. This involves smart combinations, with improvements to the waterways, developments in water quality, development of natural values, retention of fresh water in periods of drought, recreation, urban development etc. (See figures 9 and 10, before and after project Strype.) This demands cooperation between many parties. The investments needed to keep the Netherlands Figure 10 - Situation before project Strype safe, clean and inhabitable were always large and they will remain so. We can never really win the fight against the water, but that does not mean we shall avoid innovative ideas based on the principle that we can also use water as a partner in the battle. This also demands that the population's awareness must be raised, which was why the campaign “The Netherlands lives with water” [Nederland leeft met water] was initiated. We also need the planning authorities to think differently. Figure 9 - Situation after project Strype Partly related to this, throughout the country it has now become obligatory to take integral account of the water aspects in every planned development – which we call the water test.

Dealing with water differently, cleverly and in good time seeking to give it the space it will eventually claim anyway, this offers the best chance to keep the Netherlands inhabitable, now and in the future.

FLOOD PROTECTION PROGRAM

Recent developments

Climate changes increase the chance of high river flood or extreme sea water levels and thus the probability of high river flows and/or high sea water levels will increase in the following decades. In 1996 a new Dike Safety Act was passed by the Dutch Parliament. According to this Act each dike and dune had to be examined every five years to establish the actual risks according to the following failure modes: • overflow and/or overtopping of water over the dike crest; • slippage of the inner or outer slope of the dike; • erosion of the dike cover (grass, asphalt or basalt blocks), which might cause a breach in the dike; • piping, causing water to run under the dike and erode the dike body from within.

In 2002 the first round of examination was reported to the Dutch parliament. In this first round only the height and the dike cover were examined. Insufficient experience meant that examination of the stability of the dike slope and the possibility of piping was postponed until the second round in 2006. In this first round 50% of the total of 3,550 km of dikes and dunes met the criteria. Final judgment on 35% of the dikes (about 1,200 km) could not be given due to lack of information on the dike itself or about the normal situation. About 15% (580 km) was judged as "not fulfilling" all criteria e.g. due to poor or insufficient strength of the basalt blocks. Measures have to be taken to improve the safety of these dikes and dunes, at a total cost of 2.55 billion euro.

The second examination also has to test stability and possible piping. This round of testing will be reported to the Dutch parliament in the latter half of 2006. It is expected that a greater length of dike will fail the new criteria and will have to be improved. The total costs of all measures will exceed the amount of money available in the next few years, so the Dutch government had to set priorities, which it did in the "High Water Protection Plan". Figure 11 – Probability of fatality in the Netherlands One can easily anticipate that even by 2005 more dikes will fail the criteria in the future. After a study by the Research Institute for Public Health and Environmental Studies it was established that in the Netherlands the probability of death due to flooding was almost the same as being struck by lightning and 20 times higher than the chance of death due to an accident in the chemical industry (see figure 11). The Dutch government, together with the provinces and the water authorities, initiated a project called "Flood Risks and Safety in the Netherlands" (FLORIS).

In this project a calculation will be made of the probabilities and consequences of flooding for all 53 dike rings. Together, the probability and consequence will constitute the risk of flooding. This calculation will be done using a new computational method that accurately quantifies the probabilities of flooding. Currently, little is known about the safety of hydraulic structures (e.g. locks and pumping stations) in particular, even though they are major elements in dike rings. This new methodology will allow the dike managers to gain insights and anticipate changes in the risk of flooding caused by climate change, population increase and the increased economic value of the area in question. In addition, the results of Floris will provide a basis for reconsidering socially desirable safety levels. Floris will also contribute to the decision- making process concerning measures to maintain or increase safety, relative to costs and benefits.

The Hollandse Delta water authority

In the region managed by the Hollandse Delta water authority the safety levels of the dikes and dunes ranges from 1:2,000 years for the city of Dordrecht and the Hoeksche Waard, to 1:4,000 years for Goeree-Overflakkee, Voorne Putten and IJsselmonde (the southern part of Rotterdam). For two small dike rings (Rozenburg and Pernis) the safety level is established by law as 1:10,000 years (see figure 12). Figure 12 - Dike rings managed by Hollandse Delta water authority

1:10,000 1:10,000

1:4,000 1:4,000

1:2,000 1:2,000 1:4,000

After the first examination only four stretches of the dikes and dunes proved to be inadequate and 'in need of improvement'. In total this involved a length of about 8 km and an estimated cost of 75 million euro. After the second examination of the dike rings with a total length of 350 km in 2005, about 70% were found to meet the criteria. However, 70 km (20%) needed to be improved immediately because the stability of the dike slope was inadequate or there was a severe probability of erosion of the inner dike by piping. About 35 km (10%) has to be examined more carefully. Some parts of the dike are near very deep rivers, which scour the

embankment. This can cause slippage of the dike embankment and subsequent collapse of the dike itself. The situation is shown in figure 13.

Figure 13 - Results of the second examination

Good Sufficient Unsufficient, to improve No verdict Dunes

It costs on average 5 million euro per km to improve the dikes and dunes, but the costs can range from 0.25 million to 25 million euro per kilometer, so the total costs for improving the dikes and dunes are estimated to be 335 million euro.

RESULTS AND CONCLUSIONS

Water management in the Netherlands has for centuries been a matter of public law and has been carried out with great success. The water authorities are the oldest public bodies in the Netherlands. The dikes and dunes have never been safer. Nevertheless, despite this great effort and the good record, much work remains to be done, to continuing this safety for a variety of reasons. • Many big cities and large areas of the Netherlands, including the most important economic regions, lie below Mean Sea Level. • The extremely heavy rainfall at the end of the 20th century. • The fact that in the Netherlands the impact falls on the highest population density in Europe. People who all live, work and take their leisure there. • The predicted climate change.

The most important conclusion reached by the committee on Water Management in the 21st Century was that water management in the twenty-first century cannot be solved with technology alone and that more "space for water" is needed in our spatial plans.

In addition to more space for water, and to ensure the future safety of the low-lying parts of the country, the flood defense standards have been raised to take account of changes in the frequency with which the dikes are overtopped due to greater run off as a result of climate change as well as the higher population density and the rising values of capital goods. The necessary measures were computed based on the standards for regional water nuisance and primary flood defenses. Implementation of these measures will demand immense investments until 2015.

Development of both the necessary water burden for the regional waters – "Water needs more" – and the floodwater protection program has led to the imposition of standards. The application of these standards has led to a series of measures that have been or are to be implemented in the period 2003-2015. The magnitude of these measures and the necessary investments are summarized in Table 6.

Table 6 - The "Dutch Water is Life program" for water management

Hollandse Delta The Netherlands water authority Water management burden regional waters in ha 80,000 1,500 – 2,500

6 Investments € (x 10 )* 2,500 45 - 85

Dune and dike improvements in km 580 70 – 105

6 Investments € (x 10 )* 2,550 400 - 560

* 1 € = 1.2 - 1.3 $

Besides these investments, new public works programs are to be implemented as a result of the European Framework Directive. The USA acknowledges that a great deal has to be invested in the water infrastructure in the coming years: the "Water is Life" program. The Dutch and of course other European "Water is Life" programs are by no means inferior. These programs are needed to guarantee safe and adequate water management, now and for the future. Apart from minor encouragement payments by the Dutch Government, the water management burden must be carried entirely by the water authorities. The investments in dune and dike improvement are financed by the Dutch Government, since these serve super-regional interests. The annual management cost of both programs has to be financed from the taxation levied by the water authorities.

The costs of water management are due to increase considerably. If these costs are to be recouped from the citizenry, an area of support has to be created. To this end, a number of campaigns have been initiated, including: • The multimedia public awareness campaign "The Netherlands lives with water" encourages support for the Dutch policy of "giving water more space".

• The Program for Adapting Space and Climate (ARK), which has as its goal making the physical planning of the Netherlands more resistant to climate change.

The Netherlands: "an 'evitable' country on an impossible site?" Not at all. Water management in the Netherlands, water management in the Hollandse Delta water authority: a splendid and imposing challenge in a beloved country.

REFERENCES

Ministry of Transport, Public Works and Water Management (1998). Fourth National Policy Document on Water Management; Government decision, The Hague, the Netherlands. Ministry of Transport, Public Works and Water Management (2000). A Different Approach to Water, Water Management Policy in the 21st Century, The Hague, the Netherlands. Union of Water authorities (2003). Normering regionale wateroverlast (in Dutch), The Hague, the Netherlands. Netherlands Water Partnership (2003). Climate Adaptation in Water Management; How are the Netherlands dealing with it?, Delft, the Netherlands. Research Institute for Public Health and Enviromental Studies (2004). Risico's in bedijkte termen; een evaluatie van het beleid inzake de veiligheid tegen overstroming (in Dutch), Bilthoven, the Netherlands. Netherlands lives with water (2004). Water in the Netherlands 2004-2005: Facts and figures, The Hague, the Netherlands. Geuze, A., Feddes, F.V. (2005) Polders (in Dutch), NAI Uitgevers, Rotterdam. Hollandse Delta water authority (2006). Water burden analyses (in Dutch), Dordrecht. Hollandse Delta water authority (2006). Report on safety examination of dikes and dunes (in Dutch), Dordrecht.

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