Which tools can be used in urban areas with dynamic water levels?

WHICH TOOLS CAN BE USED IN URBAN AREAS WITH DYNAMIC WATER LEVELS, IN ORDER TO PROTECT THE COMMUNITY? Marloes Dijkink Student Eindhoven University of Technology (TU/e), the Netherlands m.dijkink@student.tue.nl Abstract: It is well known that countries as the Netherlands, Japan and Vietnam have dealt their entire existence with water. This fact is no longer unique: due to climate change, also other countries have to face this problem. In fact, not only the sea level will rise but also the intensity and frequency of storms will increase. Hurricane Sandy proved that countries, who never had to deal with water, suffered major damage. This paper will provide insight in the water management of the Netherlands, Japan and Vietnam. And will present applicable solutions for urban areas to protect communities.

To understand these urban solutions, the context of the location will be analysed first.

Each country has its own threats, climate as well as governmental approach and therefore different solutions are provided in case of dynamic water levels. Thereafter case studies in the cities of Hamburg, Tokyo and Ho Chi Min will illustrate how cities deal with dynamic water levels on a small scale. However, each location has its own challenges. Hafencity Hamburg had to deal with a lack of space for creating flood protection, while Tokyo has to deal with earthquakes, typhoons, volcanism and even tsunamis. The fast development of Ho Chi Min City, combined with the slower process of climate change, has forced their government to take a progressive approach. The applied tools in the different case studies are all dealing with the threat of climate change, even though some solutions are high-tech and others low-tech. The difference in applied tools depends on the local characteristics, policy and the available means.

International collaborations and sharing knowledge can help to improve tools in urban areas in developed and underdeveloped countries.

Keywords: Water management, dynamic water levels, protection of community, climate change

CONTENTS

5 1. Introduction 5

1.1 Climate Change and water related problems 5 1.2 Water management tools 5 1.3 Methodology 5 2. Water managing countries: The Netherlands, Japan, Vietnam 5

2.1 Threats caused by climate change 5

2.1.1 The Netherlands: effect on rivers and sea 5

2.1.2 Japan: direct and indirect effects on rivers and ocean 6

2.1.3 Vietnam: effect on different River Deltas 6

2.2 Governmental approach on threats 6

2.2.1 The Netherlands: Protecting from to living with water 7

2.2.2 Japan: risk reduction, awareness and limiting impact 7

2.2.3 Vietnam: National Strategies and international collaborations 7

2.3 Tools applied to protect the community 7

2.3.1 The Netherlands: Dikes, Delta Works and creating more space for the river 8

2.3.2 Japan: public retention areas and super levees 8

2.3.3 Vietnam: National Strategy for Natural Disaster Prevention, Response and Mitigation 9 3. Case studies: Hamburg, Tokyo, Ho Chi Min City 9

3.1 Hafencity Hamburg, Germany 9

3.1.1 Threats and challenges: dense area with lack of space for protection tools

3.1.2 The local Strategy: no failure strategy in a sustainable and unique location near the city center 9 9

3.1.3 Applied tools: waterproof buildings and elevated safety routes 10

3.1.4. Review: Modelled risks in combination with climate change 10

3.2 Tokyo, Japan 10

3.2.1 Threats and challenges: river and sea in extremely dense area 10

3.2.2 The local Strategy: Disaster proof city 11

3.2.3 Applied tools: Storm surge measures, diversion channels and river channel improvements.

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3.2.4. Review 11

3.3 Ho Chi Min City, Vietnam 11

3.3.1 Threats and challenges: the combination of urbanization and climate change 12

3.3.2 The local Strategy: creating a Unique Delta City 12

3.3.3 Applied tools: basic protection tools for a flood proof city 12

3.2.4. Review 13 4. Conclusion 13 Bibliography 14

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1. Introduction 1.1 Climate Change and water related problems

The world’s climate is changing due to global warming. On the long term, temperature of land and sea will rise, the rainfall patterns will change, and the intensity and severity of storms will increase. Every country in the world will be affected by these changes. As a fact, dry countries will become dryer, wet countries will become wetter. (IPCC, 2007a) Already the effects are noticeable; icecaps are melting, heavy storms have occurred and the global temperature is rising. (IPCC, 2007b) Water managing countries have plenty of challenges ahead. Lower lying countries need to find a strategy to protect their inhabitants from the rising sea level. With the expected increased rainfall, rivers will discharge more water, but also the combination of the rising sea level and the expected increasing intensity of storms needs to be taken in consideration.

1.2 Water management tools

Every country needs to develop tools to protect their inhabitants, these tool may vary from fixed defense structures to local policies. Dikes, super embankments, retention areas, or even floating houses are known tools of protection and have been utilized in several countries.

And even though the communities need to be protected, the suggested tools need to integrate measures for a pleasant environment for their users.

The following question arises: “Which tools can be used in urban areas with dynamic water levels, in order to protect the community?”

1.3 Methodology

This evidence-based research will provide insight in applied tools to protect communities from dynamic water levels due to climate change.

The possibility for each tool to work in a specific area depends on location specific characteristics, such as the threats in the area. But also authorities’ position is relevant, whereas some governments appreciate the value of nature, others act from an economical point of view.

With this knowledge, described in chapter 2, the used tools to protect the community will be better understandable.

The Netherlands, Japan and Vietnam are all countries that have to deal with water and are seriously threatened by the climate change, despite each country having their own individual challenges.

Since the focus lies on the urban areas, case studies in the cities of Hamburg, Tokyo and Ho Chi Min City will be analyzed in chapter 3. The threats of the area due to climate change, the regional and local strategy of the government and the developed tools will be analyzed and illustrated with clarifying sections.

2. Water managing countries: The Netherlands, Japan, Vietnam 2.1 Threats caused by climate change

Each of the three countries has several areas below sea level, which will be threatened by the rising sea level. In case of a storm surge, these areas will become extra vulnerable. The expectancy of heavy storms will cause the rivers to be of further threat compared to earlier time. The water-related threats of each county will be explained in combination with the expected consequences of climate change.

2.1.1 The Netherlands: effect on rivers and sea

The Netherlands are known for their constant battle against water, the coastline is challenged by the sea, while the inlands are endangered by rivers and the subsidence of the polders. Dikes, dunes, dams, retention areas, Delta Works and pumps are protecting the country.

Several times a year, the water level in rives will rise due to snowmelt upstream in Germany and Austria or the country will be threatened by heavy storms on sea.

(Bolwidt, 2007)

The frequency of intense storm events is expected to increase in many parts of Europe, which contributes to the risk of floods. Since the temperature will rise, the snowmelt floods will decrease, but the amount of rainfall will increase. Due to many uncertainties, the actual effects on rivers are hard to predict, but expected is the increase of river discharge in case of storms.

Since 27 % of the country lies below sea level, water in this area is constantly pumped out by electric pumps in order to keep a low water level within the polders. (State, 2008) This results in land subsidence, caused by the oxidation of organic components due to the water detachment. As a counter effect, dikes are being raised, causing more stress on the soil, which results in an even quicker subsidence of the ground. (Katsman, 2013) (Rojas, 2013) This effect will be intensified by the sea level rise, causing the groundwater level to rise along with it.

Due to the sea level rise and the expected increase of intensity of storms, protection tools near the coastline need to be redesigned and improved.

2.1.2 Japan: direct and indirect effects on rivers and ocean

Japan is known for series of nature disasters such as earthquakes, typhoons, landslides, volcanism, tsunamis and storm floods. The east coast of Japan is very dense and rivers leading to the Pacific Ocean are crossing the urban areas. Many big cities in Japan are built on ground that lies below sea level and since the sea level is rising, the land will be even more vulnerable in case of flooding. (Yasuhara, 2012)

The sea level is expected to rise, as a consequence the tidal movement will increase, causing a higher flood 5

risk, especially in the low-lying areas, often reclaimed land from the river. Also sandy beaches and tidal flats will disappear due to the sea level rise, as will it result in increased salinity of rivers, because the seawater will invade the river further inlands.

The intensity and frequency of heavy rains will increase. The Southeast coast of Japan is expected to be exposed to extremely high rainfall, and other areas, such as the Japanese Alps will have a 1.2 to 1.3 greater amount of rainfall. This will cause a higher discharge level of rivers, needing improvements in water protection facilities.

The previous consequences are all direct effects from the global climate change. Earthquakes, tectonic movement and land subsidence are not climate change associated, but their impact will be increased in combination with climate change related consequences.

Since the seismic intensity of earthquakes is rising, special attention must be paid to earthquake-proof water protection tools in order to secure the inhabitants.

(Nakajima & Umeyama, 2007).1 2.1.3 Vietnam: effect on different River Deltas

Vietnam is located in the tropical monsoon belt of Southeast Asia. The country is already experiencing changes in fundamental climatic elements as well as extreme weather phenomena such as storms, heavy rains and droughts. (ISPONRE, Viet Nam Assessment Report on Climate Change, 2009) Expected is that the rainfall will be increased by 0.3-1.8 % in 2020 and by 1.8-10.1% in 2100 in the worst case high emission scenario. The sea level will be risen with 100 cm in 2100 and the temperature is expected to rise between 0.5 and 0.7 °C per 50 years, while the frequency of cold fronts is decreasing.

The frequency of tropical storms from the East Sea will increasing with an average of almost 7 storms yearly. It is already is experienced that the tropical cyclone frequency has increased by 2.15 in the last 50 years.

There are 5 main terrain groups in Vietnamese territory, namely: mountains, karst, valleys, sedimentary deltas and coasts. The deltas can be divided in 3 zones, namely the Northern Delta, the Central Region and the Mekong Delta.

With the climate change having a negative impact on the country’s safety, even the current situation does not comply to protect the inhabitants. The Northern delta and the midlands of Tokyo were subjected to big floods and storms in the last 10 years. In 2003, highly concentrated torrential rains caused an area of 120,000 hectare to be inundated. (ISPONRE, Viet Nam Assessment Report on Climate Change, 2009)

Also the central coastal provinces have been threatened by floods in the past. Each year the region affected by storms causing huge losses in human lives and properties. Severe storms with strong winds and heavy rains caused river water level to rise and flood. These storms in combination with cold fronts can in this area result in a prolonged rains causing floods in the Central 6

Region. In 1999 tropical storm no. 1 occurred. Rainfall of 1,384 mm in 24 hours were measured. The flooding inundated nearly 1 million houses and 715 people were killed. (ISPONRE, 2004)

The Mekong Delta provinces, located in the south of Vietnam, has the highest frequency of flood recurrence interval of the country. In 2000 a heavy flood occurred, killing 481 people. The area has a low discharge capacity and deals with long inundations, riverbank erosion and transportation failure. Large areas are flooded every year due to floodwater flows from the upstream Mekong River.

In case of severe flooding, the inundation area has a size of approximately 1.9 million hectare, where usually the area remains inundated between two to six months.

Since the sea level is rising, the inundated area of the Mekong River Delta is estimated to increase remarkably.

More than one-third of the Delta, were 17 million people live and half of the countries rice-production is located, will be inundated by a high emission sea-level rise expectation of 1 meter. Even in case of a low-emission scenario one fifth of the area would be flooded.

2.2 Governmental approach on threats 2.2.1 The Netherlands: from protecting from to living with water

After the flood disaster of 1953 the Delta Plan was launched, to protect the Netherlands from flooding.

Several Delta Works; enormous dams, sluices and storm barriers where build in order to shorten the coastline and to protect the Rhine-Meuse-Scheldt delta. After another flood disaster in 1995 occurred, where 100.000 people near the Rhine and the Meuse had to be evacuated, the approach on threats was being questioned. With the expected sea level rise, soil subsidence and increase of river drainage level, a new strategy was formed. Instead of continuously strengthening dikes, the dynamic and characteristics of the rivers became the starting point. Therefore in 1998 the Fourth National Water Policy document was published, stating that in order to increase the durability of water systems, areas for nature conservation needed to be implemented as well. The natural river dynamic was not taken in consideration for decades, resulting in less space for the river and canalization, causing the water pressure level of rivers to increase. (Brouwer, 2004)

In 2006 the Room for the River policy was presented, designed to create more room for rivers and by that causing an improved flow capacity. Designing to live with floods instead of only protecting from it, appeared to be an effective way to reduce the risk of flooding, but it also creates space for new wildlife inhabitants and increases the public awareness. (VROM, 2006)

In 2010, when all the Delta Works were completed, the Delta Program was launched, with the main goal to protect the inlands from floods and to protect fresh water supplies. The Delta commissioner was appointed

to work in behalf of the Ministry of Infrastructure and Environment and works closely together with provincial authorities, the government, water regulatory authorities, companies, knowledge institutes and civil-organizations.

In the Netherlands, the Government creates the national policy and is responsible for the norms of water safety and the primary protection structures such as the Deltawerken. (Rijksoverheid, Waterbeheer in Nederland en Europa, 2014) The provinces translates these national goals to a regional policy. The local city council is only responsible for the groundwater in urban areas. This all is stated in the Water Law and the Nature Conservation Law. Rijkswaterstaat and the Water Boards, manage the water and its protection facilities, they prevent floods, take care of enough ground and surface water and monitor the water quality.

2.2.2 Japan: risk reduction, awareness and limiting impact

Already during the Yayoi period (between 300BC until 300AC) flood management policies were implemented. Between 1890 and 1930, in the Meiji period, specialists from Europe were hired to advise in Japans flood management strategies. Their “low water flood management” was based on the Dutch flood management, where rivers were drenched and groynes were added. Coversely this approach proved to be inadequate after some floods, given the different climate and threats compared to the Netherlands.

Currently Japan has a well organized risk management. The government aims at limiting disaster damage by risk reduction, creating awareness and limiting the impact of a disaster. The Japanese mentality is based on risk reduction; trying to influence and control nature. As a consequence, the country built enormous overprotecting concrete dikes. Only since the 1980’s the ecology and environment became an aspect in the flood management of Japan. (Alphen, 2007)

On national level the water management is currently supervised by the Ministry of Land, Infrastructure and Transport (MLIT), but also by The Ministry of Economy, Trade and Industry (METI), the Ministry of Health, Labour and Welfare and the Ministry of Agriculture, Forestry and Fisheries. There is no coordinating Ministry, which causes conflicts of interest affecting the decision making processes to be slow.

(Alphen, 2007)

Japanese people are aware of their situation and have learned to live with the constant risk of floods, earthquakes and tsunamis. To achieve a higher evacuation rate, the government is trying to create awareness of this constant threat. In 2006 each household received a flood evacuation map, to inform them where to go and how to act in case of a flood. Only recently the Netherlands started a campaign to inform their inhabitants how to react in case of a threat, to strengthen the self-reliance of communities. (Rijksoverheid, 2014)

2.2.3 Vietnam: National Strategies and international collaborations

In 2007 the prime minister of Vietnam approved the National Strategy for Natural Disaster Prevention, Response and Mitigation to 2020, which was a milestone in the disaster prevention development of the country.

The Ministry of Agriculture and Rural Development and the Central Committee for Flood and Storm Control supervise the implementation of the National Strategy.

Each ministry, sector and locality is responsible for effectively implementing the measures. The Central Committee for Flood and Storm Control works together with the relevant ministries to divide the responsibilities, available budget and act according the law. (CCFSC, 2007)

Vietnam cooperates on international level with several other countries. It has an active role in disaster management and information sharing with other countries of the South-East Asian region in the ASEAN committee, founded in 1967. (ISPONRE, 2004)

Vietnam is since 2010 a partner within the Netherlands Global Water program, called Partners for Water, in which the Dutch government collaborates with Vietnam to develop joint solutions for global water problems. (VCAPS, 2013) 2.3 Tools applied to protect the community 2.3.1 The Netherlands: Dikes, Delta Works and creating more space for the river

Dikes have been the most important means to protect the inhabitants from dynamic water levels in the country’s history. More than 50 dike enclosures have been constructed for lowland areas, but dikes alone do not comply to withstand high water levels.

Already in 1937 Rijkswaterstaat investigated that the safety of the southern coastal areas could not be guaranteed by the dikes at that time. It was too expensive to reinforce all the sea-dikes in this area. Therefore the decision was made to build dams in the river mouths, based on the idea of shortening the coastline, with as result fewer areas that were threatened by the sea. These damming structures were called the Delta Works, of which some are dynamic and others are fixed. In case of a threat from sea, the dynamic structures will be closed, so no water from the sea can enter the inland waters.

(Deltawerken Online, 2004)

River dikes work according to the following principle. In the summer the threat of high water levels is usually low, a summer dike is built to protect the riverforeland often used as farmland or nature reservation.

In the winter, the water levels are usually higher due to melting-water from upstream. A second dike, the winter dike, is used to protect the lowlands, whereas the riverforeland will be flooded. (Moser, 2006)

Due to climate change the amount of water flowing through the rivers will increase. Raising the river dikes might be a possibly, but it would increase the impact 7

summerdike summerdike figure 1. principle of river dikes, summer situation

winterdike

winterdike

of the super embankment. This concept is comparable to the Dutch dike houses, rescaled times two or three and with a gentler slope. On top of the super embankment, new residential and commercial zones are created, covered with greenery. Due to the gentle slope of the levees, they are able to withstand large-scale earthquakes and contribute to a better and safer local environment.

But this concept is very expensive, since it requires a lot of soil and redevelopment of the existing structures.

figure 2. principle of river dikes, winter situation

in case of flooding. Chosen is to create more space for the river according the policy document Room for the River.

(VROM, 2006) Several tools have been implied to create more space: the wash lands are lowered, obstacles will be removed, groyns are being lowered and waterways are being deepened. In some areas dikes are reinforced or even moved.

2.3.2 Japan: public retention areas and super levees

Today’s policy of Japan is based on preventing an overflow scenario, but also designs for scenarios in case of flooding. For the prevention Japan used detailed computer models to carefully map the threats. The flood protection program in Japan is based on flood proof building, runoff control and river flow improvements.

(Luo, 2015)

Runoff control is based on the idea to store the water in retention areas in case of high water pressure.

In Japan the expropriation of land is nearly impossible, therefore the applied tools are nearly all on public ground.

(Oosterberg, 2006)These buffer zones are usually utilized as recreational zones for the inhabitants. In Yokohama, a city regularly affected by high water levels of the Tsurumi River, the Tsurumi River Multipurpose Retarding Area was developed. This area contains a football stadium, sport pitches and a large parking lot. The passing highway was elevated, to ensure a safe evacuation route. This area will overflow in case of a high water level of the Tsurumi River, releasing pressure on the other water protection facilities.

In a flood scenario within the city, several flood proof storing areas in the urban grid are created in order to store the water in case of flooding. Underground shopping malls and tunnels are constructed to be flood proof.

In 1987 the Japanese government proposed Protection Policies for Extreme Floods for urban areas, to raise the level of flood protection. One of the proposals was to build super levees, also known as super embankments, which have an increased volume and size compared to a standard embankment. (Luo, 2015) The residential areas protected by this standard embankment are between ten to fifty meters below the embankment, in case of a flood, the lower lying residential buildings would be inundated. To solve this problem, the super embankment was proposed.

These have a size of two hundred to three hundred meters wide, and in this the houses are situated on the top level 8

figure 3. principle of a standard embankment

figure 4. section of a super levee

Japanese researchers of the Tokyo Metropolitan University proposed another concept (Nakajima T. &., 2007) They developed as model, where the soil is moved and a man-made basin is created. The removed soil is used to enforce the current embankment, while the banks of the inlet are protected with a concrete dam. Fresh water will be added and a canal will be created. Through this canal floaters, made elsewhere, can enter the basin, on which new structures can be build. The floaters are semi-supported by piles underneath them and is moored.

This system minimizes the influence of earthquakes and makes the buildings less vulnerable in case of floods.

2.3.3 Vietnam: National Strategy for Natural Disaster Prevention, Response and Mitigation

The National Strategy for Natural Disaster Prevention, Response and Mitigation to 2020 has indicated several tools that should be applied in the different areas. (CCFSC, 2007)

For the North of Vietnam, the strategy of the government is to implement and improve structural measures such as dikes, diversion channels and improving the safety standards. The discharge capacity of rivers channels will be improved by the removal of obstructions in river plain and by dredging channels. (Pilarczyk, 2008)

The Central Region’s policy is based on ”proactive prevention, mitigation and adaptation”, by creating upstream reservoirs and dike systems combined with irrigation systems for agricultural production. The coastline’s dikes will be strengthened, dunes will be preserved and storm shelters for boats and ships will be build. The coastal communication stations for typhoon and tsunami warnings will be updated.

The Mekong River Delta is regularly threatened by the floods, although these floods bring various benefits to the communities, such as soil enhancement. Therefore the strategy of disaster mitigation for this area is “living with flood and flood control”. Residential zones and

infrastructure need to be planned in flood-proof areas, the discharge level of rivers and canals need to be improved and sea dikes need to be built or reinforced.

(ISPONRE, 2004)

3. Case studies: Hamburg, Tokyo, Ho Chi Min City

Case studies in the cities of Hamburg, Tokyo and Ho Chi Min City are analyzed to display the differences between the cities in local policies and applied tools to manage the threats of climate change. Each of the cities has a different approach, on the one hand due to the location specific threats, on the other hand due to available means.

Hamburg and Tokyo are located in developed countries, while Ho Chi Min City is located in a developing country, therefore this chapter displays explains also the correlation between applied tools in combination with the level of advancement of the countries and its cities.

3.1 Hafencity Hamburg, Germany

Hamburg is located in the Elbe estuary in the north of Germany and it is the largest port city of the country.

Hamburg adapted their environment to tides and extreme high water levels, with the use of an extensive network of dikes in order to protect the inhabitants. Hafencity Hamburg is a new development in an old harbor area near the inner city. The area is still is able to flood, due to the lack of dikes, but in case of inundation, the area is still able to function due to smart design solutions. This is a new perspective on how people can coexist with water, without being in endangered by it. (Nillesen, 2011) 3.1.1 Threats and challenges: dense area with lack of space for protection tools

The sea level of North Germany is expected to rise to 30 cm in 2025, 50 cm in 2055 and 90 cm in 2085.

This rise increases the possibility of a flood in Hamburg, but it is not expected to have a major influence on the city’s safety. Since dry areas will become dryer and wet areas will become wetter, the river flow will increase in the winter and decrease in summer. (Monbaliu, 2014)

Even though the minor influence of the climate on the safety, the redeveloped area of HafenCity area needed to be protected. For economic reasons, it was not possible to build a dike around the area. Not only would it cost a lot of land and money, it would also have damaged the visual relationship between the land and water. Therefore the challenge was to find other tools which would be able to protect the community. (Nillesen, 2011) (Zanuttigh, 2014) 3.1.2 The local Strategy: no failure strategy in a sustainable and unique location near the city center

The governmental policy is based on a no failure strategy supported by analyses from past disasters and on the future effect of the sea level rise. Several stakeholders,

from the city council (Hamburg Agency of Roads, Bridges and Waters and Hamburg Port Authority) to the Ministry of Environment of Lower Saxony, cooperate in keeping the areas safe by maintaining and building flood defenses in the Elbe statuary. Flood defenses in Hamburg are for 70% financed by the State, where the city pays the remaining 30%.

The city founded the company Hafencity Hamburg GmbH to manage the redevelopment of HafenCity, which had the responsibility of enhance the sustainability of the area. (Zanuttigh, 2014)

As mentioned before, the visual relationship with the water was very important for the new master plan.

Buildings were carefully planned and sightlines are kept open, to remain the inner-city’s contact with the water.

The other way around, the building regulations stated that the buildings had a maximum height of 8 stories, this to keep the old inner city visible from the Elbe River.

(Nillesen, 2011)

The historic buildings in the area needed to be integrated in the new master plan. The idea was to create a public and lively area for the inhabitants of Hamburg, therefore a good connection for pedestrians and cyclist was desired. (Zanuttigh, 2014) 3.1.3 Applied tools: waterproof buildings and elevated safety routes

Along with all the flood protection tools in the Elbe estuary, HafenCity Hamburg is designed to be protected against a storm surge in the year 2085. Chosen is to use a flood proof construction, where each separate block is flood-proof. The old dikes remained on the same level of NAP +5 (Amsterdam Ordinance Datum) and are still able to protect the area from the daily tide. A new infrastructure has been built on NAP +7.5, which crosses the lower lying existing infrastructure and is designed to keep the houses and emergency services accessible in case of a high water level. HafenCity has many public connections to the inner city of Hamburg, by creating an extended network for cyclist and pedestrians the developers hoped to create a lively and involved area.

(Nillesen, 2011)

figure 5. Hafencity Hamburg, principle section of the flood proof area

The new buildings have a flood proof plinth, where parking areas, commercial properties or cafes and restaurants are located. Because of this space utilization, there is no need for above ground parking, since there a 9

sufficient amount of parking lots underneath the buildings.

In case of a high water level, the plinth functions become flood proof with the use of floodgates. Because of the development of the area in stages, where each building is flood proof, the risk of flooding of vulnerable structures remains low.

houses were damaged by rains exceeding 100 mm per hour. (Mambretti, 2012)

Tokyo is no exception to the constant threat of earthquakes in Japan, one of the most known earthquake generators is located near Suruga Bay, about a hundred kilometers from Tokyo. (Velasquez, 1999)

3.1.4. Review: Modelled risks in combination with climate change

In the paper Risk assessment of estuaries under climate change, the HafenCity area was analyzed with the use of computer models for future threats based on the predicted sea level rise in 2025, 2055 and 2085. This research concluded that the threat of storm surge, wave height and river flow was low for the predicted sea levels.

Only the sea level rise of 2085 could form a moderate threat. In summary, the flooding area will be increased by 18% (2025), 34% (2055), and 54% (2085) on the predicted peek flood levels. The areas flooding currently, low lying embankments and unmovable historical buildings, will be flooded as well in the future. (Monbaliu, 2014)

The flood proof investment made the houses in HafenCity approximately 10% more expensive, but given the unique location and gradual development of the project, it has not disturbed the sale of apartments.

(Nillesen, 2011)

This plan is an example for many other riverside cities in Germany and the Netherlands. In Dordrecht, a city in the Netherlands with similar challenges and a similar design is currently under development.

3.2.2 The local Strategy: Disaster proof city

Tokyo is an regional government consisting of 23 special wards, which is governed by the Tokyo Metropolitan Government, also known as TMG. They are responsible for the formal decision making of Tokyo Metropolis and therefore the water management policy of the city. Government leaders of the TMG have elaborated to construct a ‘disaster-proof’ city that is believed to withstand extreme floods and earthquakes.

Several bureaus within the TMG work together to create this disaster proof city. The Bureau of Urban Development is responsible to make Tokyo resistant to disasters such as earthquakes and floods by promoting the seismic retrofitting of buildings, improving flood control measures and securing evacuation areas and roads by which to evacuate. (TMG, 1999) The Bureau of Construction manages the roads, rivers and parks of the TMG and is similar to the Dutch Rijkswaterstaat. The bureau manages 105 rivers with a total length of 711 km, while the Ministry of Land, Infrastructure, Transport and Tourism is in charge of the remaining rivers within the area.

(TMG, 2010) To protect Tokyo’s residents from floods due to typhoons or torrential rains, the Bureau has been carrying out improvements on small and medium-sized rivers, river structures in the lowland areas and river control structures. Their strategy is not only based on protection, but also on implementing facilities that produce a relaxing and pleasant atmosphere in water front areas for the inhabitants. (Inoguchi, 1999)

The Tokyo Metropolitan Government has instituted several policies and acts in order to protect the communities. The Tokyo Metropolitan Government instituted “the Tokyo Metropolitan Regional Disaster Prevention Plan”, which is based on the Basic Act on Disaster Control Measures of Japan, providing basic measures for Urban Disaster Prevention and “the Tokyo Metropolitan Earthquake Disaster Measure Project Plan” based on the Tokyo Metropolitan Ordinance for Earthquake Disaster Measures with measures related to the Earthquake Prevention. (Mambretti, 2012)

Since the intensity and frequency of heavy rains of 50 to 100mm/hour was increasing, the Basic Policy for Intense Rainfalls was instituted in August 2007, which consisted of basic mitigation and response measures in case of heavy rains. Since then, the TMG got more focused on river improvements, improved sewers, basin measures and integration of town planning within a regional setting. (Sugai, 2009)

3.2 Tokyo, Japan

Tokyo is the capital of Japan, where 10 percent of the Japanese total population is living. In 2012, the population of Tokyo was estimated to be 13.216 million with a density of 6,000 inhabitants per square kilometer.

(TMG, Tokyo’s History, Geography, and Population, 2014)Because of this high density, clever solutions need to be applied to protect the community from the dynamic water levels.

3.2.1 Threats and challenges: river and sea in extremely dense area

Tokyo is being threatened by the sea, rivers, extreme rainfall and earthquakes. Many flood disasters have occurred due to typhoons, heavy rains and storm surges. Some areas of the city are 1.5 meters below sea level, while in case of a storm surge from sea water levels of 5 meters above sea level can be reached, nevertheless 1.76 million people live beneath this storm surge level.

(Alphen, 2007)

In Tokyo the annual rainfall is 1,714 mm, which is twice the worlds average. The urban area of Tokyo has a size of 2,187 km2, the hardening of this dense urban area causes it to have a relatively poor water retention and flood prevention properties. (ARUP, 2011) As a consequence, many areas have had extreme damage during times of heavy rainfall. For example, in 2005 6000 10

3.2.3 Applied tools: Storm surge measures, diversion channels and river channel improvements.

As stated before, one of Tokyo’s threats is the poor water drainage and flood prevention properties due to the city’s heavy urban development. Water Sensitive Urban Design and Green and Blue structures appear to be possible solutions, but since the expropriation of land is nearly impossible and there is very little public space left within the city, ‘above-ground’ flood control measures are not always realizable. Tokyo therefore turned to ‘below-ground’ flood prevention measures. The city has been constructing regulating reservoirs and diversion channels. (Mambretti, 2012) (TMG, 1999)

Meguro River Underground Reservoir is an underground regulating reservoir which temporarily stores floodwater from the Meguro River. When water flows in Meguro River reach a high level, water overflows via a side weir into an underground storage reservoir.

Land above the underground storage reservoir has been designated for high-rise housing development. (ARUP, 2011)

figure 6. Meguro River Underground Reservoir principle section

Another regulating reservoir is the Kanda River/ loop road no. 7 underground regulating reservoir. It has a length of 4.5 km, a storage volume of 540.000 cubic meters and a tunnel diameter of 12,5 meter and is located below the Tek highway. It manages floodwater from the Kanda River, Zenpukuji River and Myoshoiji River. With the use of intake facilities, floodwater is being guided from the rivers into the underground tunnel, using side overflows, discharge pumps and ventilation facilities.

The tunnel reserves the inflowing water. The hydraulic storm water tunnel system discharges floodwater to the downstream. A control building monitors, operates and controls the inflow and discharge facilities. river A

river B

river C

river D

figure 7. principle section of an underground regulating reservoir

Diversion channels are used to divert a portion of flood waters, and applied underneath a highway or other urban fabric. The Kanda River was known for its frequent overflows, since many people live near the river, many housed flooded regularly. The Kanda River Diversion Channel was constructed; a 4,5 kilometers long tunnel with a diameter of 13 meters. The reservoir can hold 240,000 cubic meters of water, equivalent to the runoff of

50 mm of rain falling in one hour. (ARUP, 2011)

figure 8. diversion channel principle section

River channel improvements, such as channel widening and deepening, are being implemented on the length of 324 km of 46 rivers in Tokyo.

In addition to flood control purposes, river channel improvements are also designed to make rivers more accessible to people and more favorable to plants and animals. An example is the Kyu-Naka River, were the water level has been lowered, this enabled river environment restoration and contributed to the earthquake resistance of the area. (TMG, 2010)

On riverbanks, super levees and gently sloping embankments are being constructed to make the areas better protected against a potential strong earthquake and to improve the riverside environment. The old concrete tidal defense walls are being replaced. Super levees are built in harmony with urban community development in areas along the rivers.

(TMG, 2010) 3.2.4. Review

Tokyo has applied multiple public reinforcing adjustments to protect the inhabitants from possible floods. These highly sophisticated technologies and ordinances have constructed to turn Tokyo into a disaster proof city.

Super levees provide greater protection against large earthquakes compared to the conventional tidal defense walls. They also improve accessibility to the waterfront and enhance river side scenery. (TMG, 2008)

Other protection facilities, such as retention areas, diversion channels, river widening and deepening are expected to protect the city from flooding. In October 2004 Typhoon 22 struck Tokyo, at that time the Loop Road No. 7 underground regulating reservoir, along with other river disaster control projects, were in operation.

(ANMC21, 2009) This typhoon had a similar magnitude to Typhoon 11 from august 1993, however instead of 3,117 houses, 46 houses were flooded and the flooded area went from 85 to 4 ha. This proves that the applied tools significantly contribute to protect the community, since the flooded area was brought down by 95 percent.

(Mitchel, 2000) 3.3 Ho Chi Min City, Vietnam

Ho Chi Minh City, also known as HCMC, is a vibrant metropolis with a population of 8 million inhabitants, located in the Mekong River Delta. The city serves as an international trade hub with its seaports lying near strategic maritime routes. The population growth is 11

increasing and due to the lack of space, the living areas are expanding to lowland areas. As many other large cities in developing countries, HCMC is facing challenges in developing a better knowledge of preparedness, vulnerability, flood damage and flood management. (Tu, 2010) Several foreign institutions help the city get insight and provide tools to improve the inhabitants safety.

3.3.1 Threats and challenges: the combination of urbanization and climate change

Ho Chi Mihn City is the largest city in Vietnam.

The increase of population densities caused a decrease in green space and therefore a decrease in the permeability of the soil. During urbanization of the city between 1989 and 2006, the impermeable surface area has been doubled (Van, 2009) Regulated and unregulated buildings in HCMC are built on riverbeds, which narrow the floodplain areas of the rivers. (Schwartze, 2013) As a result frequent inundations by rainfall and high river flows occurred. Already there are problems managing the high volumes of rainwater in many places of the city, due to an insufficient sewage system and limited water storage areas within the city.

60 % of the city is barely build above sea level an land subsidence causes the land level to decrease 4mm a year in the city center. (Schwartze, 2013)Since the sea level is rising, rain patterns are becoming more extreme and average temperatures are increasing, the area will in the future be even more vulnerable to flooding. (ADB, 2010) 3.3.2 The local Strategy: creating a Unique Delta City

The HCMC has only recently stated to create awareness of the climate change. Although the climate change is not the main factor of threats, since it is mainly caused by inconvenient urban planning. The current urban development on the lowlands and the lack of sustainable design is one of the cities greatest concerns.

Therefore the government is now focusing on urban planning as an adaption method to the climate change threats. (Schwartze, 2013)

The city has a partnership with the Dutch city Rotterdam, which also located in the delta of large river system. By facing similar challenges, knowledge and effective adaption methods can be shared. A Climate Adaption Strategy has been made, in collaboration with the City of Rotterdam and the Dutch Ministry of Infrastructure and Environment, guiding Ho Chi Minh City to a “Unique Delta City”. It emphasized the need for education and public awareness regarding climate change, other methods of project developing and it proposes an adaptation strategy and action plan.

3.3.3 Applied tools: basic protection tools for a flood proof city

In contrast to the other case studies in Tokyo and Hamburg, many of the proposed tools in this chapter are not build yet and are already applied as ‘basic protection’ 12

in other more developed countries. Therefore this chapter gives insight in the basic applications needed to modernize and protect a city.

A key element to protect the inhabitants from future floods is to plan new urban development in less vulnerable areas. The current center of HCMC needs to be protected because of the social and economic activity in this area. With rising sea levels, structural tools are inevitable. A cost-effective method is a ring dike, whereas tidal gates should be integrated at the entrances of the inter-city canal. In case of high water levels, the tidal gates can be closed to protect the inner city and its inhabitants. (VCAPS, 2013) In case of a higher sea level rise than expected, where dikes and other flood measures appear not to be effective, a large tidal gate near the sea might be needed comparable to the Dutch Delta Works.

In the area outside the protective ring-dike, other options should be considered to make the buildings floodproof. The houses could be raised, on poles or mounds and in case of clustered buildings, local ring dikes could be a solution. In case of a large development exceeding 100 to 150 hectares, it is even more cost-effective compared to raised buildings. (VCAPS, 2013) Another possibility is to zone protection structures near the waterfront. Soft structures, such as parks and sports fields can be used to accommodate water in case of flooding.

Due to the large urban growth, private property and motorways block many waterfronts. So, appropriate city planning is necessary in the design process of the waterfronts. The floodplains could be designed in different zones; the taboo zone and the buffer zone. In the taboo zone no building structures are allowed, this area is used by the river in case of extreme tidal movement.

The buffer zone floods occasionally and can therefore be used for parks, playgrounds, farming or raised residential buildings. By implementing areas for water retention and integrating blue and green structures, the water storage capacity of the urban area improves, resulting in fewer floods within the urban fabric. (VCAPS, 2013)

taboo zone

buffer zone figure 8. floodplanes in zones, principle section

In general the strategy for urban planning is first addressing the flood-sensitive areas, subsequently creating space for flood water and thereafter, when the protection is still insufficient, apply physical production structures such as dikes. (Schwartze, 2013) Even when all the suggested protection structures are applied, the risk of flooding is always present. Therefore its necessary to create a reliable early warning system and a clear emergency planning. (VCAPS, 2013)

3.3.4. Review

The biannual report of the Steering Center of the Urban Flood Control displays the flooding mitigation of the past years. It revealed that the areas prone to tidal flooding had been reduced by 75% from 2009 to 2010.

From 2010 to 2011 the floods in the inner city had been reduced as well, but the risk of flooding in suburban areas had increased slightly. The next year the risk on both flood prone areas was reduced again. The reduction was mainly achieved due to engineering measures, such as applying drainage, tide gates and pumping. The reason of the flood risk increase in 2010 has not been addressed yet. This research demonstrates that the applied tools in Ho Chi Min City appear to be effective. (Schwartze, 2013)

 

4. Conclusion

Climate change affects the flood protection of many countries, which is mainly caused by the rising sea level and the increased frequency and intensity of storms.

Already great parts of the Netherlands, Japan and Vietnam are located below storm surge level and are constantly being threatened by the consequences of climate change.

Where the Netherlands and Japan are able to protect their inhabitants from inundations for now, Vietnam is still struggling to manage this. During frequent heavy floods, many houses are inundated and people’s lives are lost.

Tools are needed to protect the inhabitants from floods in urban areas.

In general, the provided tools can be subdivided into building regulations and urban planning, structural measures, retention areas and warning systems. Whereas all tools are designed to protect, at the same time they are designed considering the water dynamics. The developed tools vary from low-tech to high-tech, but the effectivity and applicability depends on the local threats, policy and available means. Vietnam is currently implementing a ring-dike in the city center of their largest city, while Japan and the Netherlands have already applied the basic tools and are now focusing on creating and implementing climate change-proof structures. Due to the high density of Tokyo high-tech tools are being applied below ground, creating more room for water storage in case of flooding.

Also in HafenCity Hamburg the basic protection tools did not suffice, therefore the area was redeveloped to be flood proof with the help of smart design solutions.

The implemented tools show significant improvement on risk reduction, however more research is needed to develop knowledge about the other effects on the local communities. In the future countries will continue to gain more experience on dealing with water related issues. By sharing knowledge about the applied tools and by cooperating on an international level, the threats of climate change can be effectively tackled.

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