The green track to urban
revitalization
An interdisciplinary analysis on design criteria for
optimizing socio-ecological improvement regarding
‘de Hofbogen’ project in Rotterdam
Kiran Aluvihare, Dana van Bentum, Veerle Tuijnman, Brian Wals
Student number 10578781, 10571949, 10597476, 10571418
Course Interdisciplinary Project
Supervisors Myrte Mijnders & Kenneth Rijsdijk
Date 22-5-2016
Abstract
During this study ‘De Hofbogen’ project in Rotterdam will be assessed by way of an interdisciplinary analysis, inspired by ‘The High Line’ in New York and ‘La Coulée verte René-Dumont’ in Paris. This will be done in order to determine what design criteria contribute mostly to socio-ecological improvement if an urban linear park would be realized. Results include that the multifunctional aspect of the park is of great importance. Socio-ecological improvement measured in the form of biodiversity, water balance, heat balance, health and gentrification are expected to improve when design criteria regarding waterproofing, vegetation choice, soil choice, drainage and social structure are implemented.
Table of contents
Abstract...2
1. Introduction...4
2. Research questions...5
3. Conceptual framework...6
4. Theoretical framework...8
5. Study area...14
6. Methods...15
7. Results...16
8. Design criteria...24
9. Discussion...25
10. Epilogue...26
11. References...27
1. Introduction
Cities are of major importance to society and are continuing to grow as urbanization rates are globally increasing. Many social, practical and security related factors are to be considered with the development of new neighbourhoods. When parts of a neighbourhood lose their function, they are often exposed to decay. It is in these parts of cities that urban revitalization is necessary. Redevelopment of these neighbourhoods could be put in motion by investing in urban green space.
Multiple studies have provided sufficient evidence for the positive effects of green spaces within an urban area regarding self-reported health and longevity (Takano et al. 2002). In addition, studies have shown that urban green spaces could have a significant effect when it comes to the energy balance of a city (Slingerband, 2012).
Urban green space projects have been implemented in several cities to challenge current environmental changes and to revive socio-economic conditions. ‘The High Line’ in New York and the ‘Coulée verte René-Dumont’ in Paris are successful examples. But what aspects of these green spaces makes the project actually contribute to social and ecological improvement of the adjacent neighbourhoods?
Both these green spaces are linear parks: greenbelt corridors that belong to the category of green urban infrastructure. In contrast to conventional parks, linear parks are green belts within a city that not only provide recreational spaces, but dynamic places that allow visitors to experience the city in a completely new way with big influences on social, ecological and environmental aspects of the city.
Since a green urban space has interplay in different levels of disciplines, such a space could be seen as a complex system. An urban linear park could be seen as a complex system with different depended factors of which each should be approached from a different discipline. For example, a linear exists of a recreational function, while it also has effects on the hydrology of an urban area. It would therefore require an interdisciplinary approach.
Currently, the city of Rotterdam is looking into the possibilities of implementing a 1.9 km long green corridor on an old railway track called ‘De Hofbogen’ in order to revitalize the area of ‘Rotterdam North’ in several aspects. In order to make this park successful, specific design criteria need to be drawn. For each aspect of the green corridor, a different discipline-related sub research will be performed, to eventually draw combined conclusions. The interdisciplinary research exists of social and ecological studies as well as an earth science approach.
In this paper, we will contribute to the understanding of urban green space and the positive effect of green spaces regarding the revitalization of neighborhoods. The following research question will be answered in this paper: What design criteria have to be implemented in the Hofbogen linear park project in Rotterdam in order to optimize socio-ecological improvement of that area and mitigate physical environmental pressures? This question will be answered through an interdisciplinary approach. Not solely focusing on a distinctive discipline, but using a wide scale of specialized researchers in different disciplines and to use their particular forms of information, data collection, techniques, concepts and theories is often the only form of problem solving to understanding complex systems (Menken & Keestra et al., 2014).
2. Research questions
In order to comprehend the full scale of the research and understand its interdisciplinary approach, it is important to know in what way the different disciplines have done their research. Following question is the main research question, succeeded by the disciplines driving questions.
Research question
What design criteria have to be implemented in the Hofbogen linear park project in Rotterdam in order to optimize socio-ecological improvement and mitigate physical environmental pressures?
Sub questions general
What is the current situation in social, ecological and physical environment regarding the Hofbogen project in Rotterdam?
Social Structure and human well-being
How does the implementation of a linear park influence the socio-economic process of gentrification?
How does the implementation of a linear park influence the socio-ecological processes of human health and productivity?
How does the implementation of a linear park influence the social processes of crime, public safety and social cohesion?
Physical environmental pressures
What drainage systems are best to be implemented in a urban linear park in order to contribute to the recharge of groundwater?
What drainage systems are best to be implemented in a urban linear park in order to contribute to reduce urban storm-water?
How can the Park Cool Island effect in the Hofbogen area contribute to the mitigation of the Urban Heat Island of Rotterdam?
Ecology
How can biodiversity be increased by a linear park? Main focus on bird species richness. How can the public best be engaged in the ecological improvement in a linear park? How can an urban linear park contribute to an enhanced affiliation with nature?
3. Conceptual framework
Green infrastructureThe concept of Green Infrastructure has been introduced to upgrade urban green space systems as a coherent planning entity (Tzoulas et al, 2007). Green infrastructure consists of all natural and artificial practices in urban areas that contribute to urban environmental and sustainability goals. Simply said, Green Infrastructure encompasses all urban multifunctional ecological systems (Sandström, 2002). Examples are green roofs, trees, bioretention and infiltration, rain gardens and permeable pavements, green walls, urban agriculture etc. (Center for neighbourhood technology, 2010; Foster et al., 2011.). Every action that is taken in a city in order to achieve environmental goals could be seen as ‘green infrastructure’. Therefore, practices like green, blue and white roofs can also be seen as green infrastructure since they increase the albedo effect which in turn has positive effects on the temperature balance of a city.
Multiple studies have provided sufficient evidence for the positive effects of green infrastructure within an urban area regarding self-reported health and longevity (Takano et al. 2002). The benefits of green infrastructure can be divided into five categories: Land-value, quality of life, public health, hazard mitigation and regulatory compliance (Foster et al., 2011.). However, the climate adaptation benefits of green infrastructure depend widely on its type and design.
Linear park
For this research the typical specifications of a linear park will be used. This concept can be seen as a combination of different aspects of green infrastructure. A linear park is a park that is substantially longer than wide, also, it is a type of green infrastructure that can provide several services at the same time. Linear parks can be seen as innovative urban green space. Two famous examples are situated in New York and Paris. The linear park in Paris is called the Couleé Verte René-dumont and was established in 1988. The High Line in New York is known as a famous and successful linear park project and was constructed in 2009 (Patrick, 2014).
Urban revitalization
Urban revitalization or urban renewal consists of redevelopment and investment in a particular area in order to restore or ameliorate the economic flows of that area. This can be done, for example, by renewal of the physical structure, job creation, economic assistance, aggregation of housing units, changing housing criteria, and offering or creating new public services or activities (US Department of Housing and Urban Development, 2007).
Socio-ecological systems
When integrating social science into long-term ecological research, combining social, earth, and life sciences, to get understanding of the social dimensions in ecological change and ecological dimensions of social change, it becomes possible to merge the often separated natural and human systems. It becomes the principle of the socio-ecological system (SES) (Redman, Grove & Kuby, 2004). It is essential to study the socio-ecological system from an interdisciplinary approach, in order to grasp full understanding of its complexity.
Social structure
The term social structure was first introduced in the social sciences by Robert K. Merton (1938), to describe the interconnectedness between different sociological changeables. This encompassed all participants of society and their behavior towards each other, and the interaction with both cultural and institutional influences. It is often used as an overarching term to describe all the influences that are at play when studying social entities and to be able to identify these variables and stratify them (Deji, 2012).
Physical environmental pressures
Indicators of environmental pressures describe pressures exerted by human activities on the environment that have effects on quality and quantity of natural resources and on the functioning ecosystems (Eder & Narodoslawsky, 1999). These derive from the developments of human extraction of materials from the environment and the release of materials back into the environment. Also, these pressures reflect trends in the state of the environment and monitor the progress made to realizing environmental policy targets (Smeets & Weterings, 1999).
The human produced emissions are of lower quality than the original material and are placed at locations remote from their source. The size of these flows of material is tremendous and causes excessive stress on the environment (Eder & Narodoslawsky, 1999). Examples of physical environmental pressures that will be used in this research are CO2 emissions, groundwater depletion, storm water and heat emissions.
Design criteria
The final outcome of this research will result in a list of design criteria for the Hofbogen project in Rotterdam. Design criteria can be seen as the explicit goals that a project must achieve in order to be successful. The design criteria in this research will be focused on optimizing socio-ecological improvement and mitigation of physical environmental pressures in the city of Rotterdam. The design criteria that will be the outcome of this research can be seen as the physical requirements of the linear park. For example: the amount of vegetation, what kind of vegetation, the presence of footpaths and/or playfields, soil type etc.
4. Theoretical framework
During this interdisciplinary analysis many concepts and theories have been used. This section of our report provides an overview of the most important concepts and theories. A setup of our research can be seen in table 1. Further elaboration upon the concepts and theories are subsequently given in order to make them understandable.
Table 1: Theoretical Framework Research Rotterdam ‘ Hofbogen’
Per subject
● What is the current situation in Rotterdam?
● What should be improved in Rotterdam?
● What changes should be implemented to reach the desired result/ urban revitalisation? Introduction per subject Research Research + specific results Subjects Green Infrastructure Biodiversity Affiliation with nature Social structure Human Health Hydrology Temperature Limited vegetation and niches Flagship species Fluctuations in crime rates Increase in (mental) health Ground water recharge Urban heat island Human disturbance Wildlife acceptance capacity (WAC) Increase social cohesion Increase in productivity Storm water reduction Park cooling effect Lack of resources Public safety Increase in human well-being Gentrification
SOCIAL ECOLOGY EARTH SCIENCE ‘Physical environmental pressures’
As the proportion of urban residents increases annually, the nature of urban ecosystems will become increasingly important in shaping people’s views about natural ecosystems (Savard et al., 2000). Enhancement of biodiversity in urban ecosystems can have a positive impact on the quality of life and the education of urban residents can thus lead to an enhanced affiliation with biodiversity in natural ecosystems (Savard et al., 2000). That sensitivity to environmental issues is majorly dependent on the exposure to natural things in everyday life is also suggested in multiple evidences (Sebba; Rohde; Kendle in Savard et al., 2000). According to Savard et al. (2000) flagship species are charismatic species which attract attention and which can be used to galvanize public support for conservation efforts. They have the capability to capture the imagination of the public and induce people to support and/or to donate funds to institutes devoted to preservation (Walpole, 2002). It is through flagship species that a public association with biodiversity conservation efforts is wanted to be realized.
Social structure
There are two important factors that are constituent to the social structure and which are utmost interesting to take into consideration when looking at the influences a linear park can have on its adjacent neighbourhoods. There are the closely related social factors: crime rates, public safety and social cohesion. Also, from a more socio-economic perspective, gentrification processes have a large influence on the present social structure and affect the three social factors too.
In Rotterdam Noord, the borough of Rotterdam that comprises the adjacent neighbourhoods of the Hofbogen, there is currently a higher residency to business ratio for all the housing units relative to the rest of Rotterdam, see table 2 (Wijkprofiel Gemeente Rotterdam, 2016). Also, looking at the official fair market value in table 2, these neighbourhoods include many lower and middle class housing units, compared to the rest of Rotterdam (Wijkprofiel Gemeente Rotterdam, 2016). When comparing municipal statistics (between 2014 and 2016), visible in table 3, it shows that Rotterdam Noord has experienced some deterioration in the last two years, but redevelopment has already been initiated which will generate gentrification processes to occur.
Table 2 Relative difference between Rotterdam and Rotterdam Noord
Difference (Rotterdam-Rotterdam Noord) Residents/workers ratio -15% (33%-18%)
Official fair market value <180.000€
+18% (60%-78%)
Source: Wijkprofiel Gemeente Rotterdam, 2016
Table 3 Statistics of Rotterdam Noord between 2014 & 2016
public services -2%
people’s perception of the environment -8%
people’s perception of public space -5%
municipal investment in public space +11
statistical social binding -1%
people’s perception of social binding +13%
engaging the people +2%
properties +1%
Source: Wijkprofiel Gemeente Rotterdam, 2016
Gentrification processes are a complex mixture of variables that are interlinked with each other and influence each other reciprocal (Atkinson & Bridge, 2004: Lees, 2008). In general, the term "gentrification" is used to describe the anomalies in the housing market (Smith, 2002) and although it has always been and will remain a broadly interpreted concept which is often demarcated slightly different (Galster & Peacock, 1986; Kennedy & Leonard, 2001), we tend to speak about the following urban processes (Smith, 2002; Atkinson & Bridge, 2004; Lees, 2008): • Displacement of the lower working class (or any displacement)
• Influx of the middle and upper class • Crime rates reduction
• Increased social mix and increase in creative class (Florida, 2004) • Increased property values and loss of affordable housing
• Change in consumption, leading to a different supply and demand in services • Rent gap, potential higher rent prices give impetus to re-invest in properties • Deindustrialization and shift to service sector
• Allows more local organisations to exercise power and influence in policy making (Vu, 2012) • With more capital comes more investment
• Increase in public facilities like playgrounds, supermarkets and green spaces
Smith (2002) states that the erratic dispersion of gentrification in a city can differ enormously by the presence of anything like parks, architecture or water. Moreover, Troy & Grove (2008) and Crompton (2001) proved that park proximity in any of their researched cases was positively linked to higher property prices.
During our participating observation of the Hofbogen area, we already acknowledged these developments. The gentrification processes have already been put in motion with the start of the revitalization of the Hofbogen area. This could prove to have a significant effect on the public safety and crime rates by improving the overall social structure of the whole area (Crewe, 2001; Troy & Grove, 2008).
Table 4 Safety Index Rotterdam Noord
changes between 2014-2016
perception of violence -19%
theft -1%
burglaries -1%
vandalism +4%
nuisance complaints +1%
Source: Wijkprofiel Gemeente Rotterdam, 2016
Crewe (2001) found that a new linear park in an urban environment can have several effects on crime rates and the perception of public safety by the local community. It has several distinctive characteristics that separate it from a common park. Linear parks connect a much vaster area together and appeals to a much broader public and therefore could draw and connect criminal activities from other regions to a much wider area, known as crime-spillover (Crewe, 2001). However, Crewe's (2001) research showed that there was no significant increase in crime fueled by the presence of the new linear park compared with rates on commercial streets, and also that nearby residents showed an overall perception of high safety by day. This resulted from an increase in the social cohesion. Linear parks are used heavily by the elderly and families with children, and become a green corridor to escape urban life and a social meeting point (Crewe, 2001).
In Rotterdam Noord, the municipal data shows that there has been an overall increase of the safety rating of 1% (Wijkprofiel Gemeente Rotterdam, 2014). However, this comprises both the perception of residents as factual statistics of incidents. As table 4 shows, there is still an increase in objective crimes. It is the perception that causes the overall rating to increase. Considering crime-spillover, it is vital to look at the connected neighbourhoods. As visible in figure 1, the most northern part of the hofbogen (Hillegersberg-schiebroek) will connect the whole length of the neighbourhoods Bergpolder and Agniesebuurt. It will also bring a new environment to connect people from adjacent neighbourhoods like Oude Noorden and Liskwartier. In order to prevent crime-spillover, it is crucial for the quality of life of the Hofbogen area to control the different crime rates, as the Agniesebuurt and Oude Noorden score a lot lower than the connected neighbourhoods (table 5).
Table 5 Safety Index Rotterdam
2013 Hillegersberg-schiebroek 10
Bergpolder 8,3
Liskwartier 8,2
Oude noorden (Noord) 5,5
Agniesebuurt 5,8
Rotterdam 7,2
Source: Veiligheidsindex Gemeente Rotterdam, 2014
Human health
Urban green space becomes increasingly important to sustain ecosystem health but also
human health and well-being. Tzoulas et al. (2007) explain that Green Infrastructures are
Figure 1 Neighbourhoods of Rotterdam, obtained from: bergpolder-liskwartier.nl
directly linked with the well-being and health of the urban population. The links between the socio-economic status and health are well established, thus for productivity to maintain or improve a healthy lifestyle is recommended (Tzoulas et al., 2007).
Urban green space has proved to have a positive effect on people's longevity (Tanaka et al., 1996; Takano et al., 2002). To add, De Vries (2003) states that a positive link has been found between citizens self-reported health and well-being and the amount of contact with urban green space. Also the social bonding and cohesion strengthens through the interactions with other members of the community, which is a common element that comes forward with green urban spaces Kim & Kaplan (2004).
Urban green space also has a physical characteristic that enhances human health, for it improves air quality and the negative effects of the urban heat island, which means a healthier climate for urban life (Tzoulas et al., 2007).
Groundwater
The Dutch region in which Rotterdam is situated in a low-lying delta which is threatened by an increasing sea level, water extraction for domestic, agricultural and industrial purposes and a decreasing water quality (Oude Essink et al., 2006). Contamination of the groundwater in the Netherlands is mostly caused by the salinization through the process of saline water intrusion (Ranjan et al., 2006). Also, a result of climate change, the sea-level will continue to rise and the physical and ecological environment will continue to change which accordingly will have effect on the groundwater system. Therefore, a continued decline of fresh (not contaminated) groundwater is to be seen in the area of Rotterdam. Especially in urban areas, the recharge of the groundwater is minimized because of the impermeable surfaces throughout a city (Oude Essink, Van Baaren, De Louw., 2010).
It is found that this pressure on groundwater systems is similar throughout the world (Oude Essink et al., 2006). To meet the increasing water demand, due to a rapid expansion of urbanization, industrialization and agriculture, conservation of fresh groundwater supplies is very important (De Vries, Simmers, 2002). The cause of groundwater problems delta areas are facing can be divided into two subject: the decrease of the available amount of groundwater and the contamination of the groundwater.
Storm water
Storm water is the water runoff after a precipitation event. Stormwater management is very important, especially in urban areas. Considered the increasing urbanization rate of the Netherlands and the rising sea level nowadays, storm water runoff is a primary stress factor on surface water in urban areas. Research done by the Environmental Service Division (2007) shows the significant impact of urbanization on runoff. They stated that the volumes of surface runoff exceeds 50% of a precipitation event, while runoff volumes over natural landscape surface range between 10 and 30%.
Urban Heat Islands (UHI’s) are characterized with a higher temperature compared to their outlying rural surroundings, which is due to the fact the built surfaces change radiative and thermal properties of urban infrastructure. In most cases the temperatures of the UHI’s are calculated by comparing data from rural and urban meteorological stations (Alcoforado & Andrade, 2008). The annual mean temperature of a city with a million inhabitants can be 1 to 3°C higher than its surroundings (Wong, Akbari, Bell & Cole, 2011). A rise in mortality and decrease of work productivity are only some of the consequences (Slingerland, 2012). The main causes of the development of an Urban Heat Island are visualized in figure 2. The heat radiated by the sun is trapped in between buildings by absorption of shortwave radiation. Air pollution and obstruction of the sky by buildings decrease the longwave radiative heat loss from street
canyons. Combustion
processes and decreasing urban vegetation are leading to higher temperatures within cities (Kleerekoper, van Esch & Salcedo, 2012). UHI’s can also be detected with the usage of remote sensing imagery.
The Netherlands is a densely populated country, and rural green space is regarded as a limited and valuable resource (Heusinkveld et al., 2014). As the Netherlands has a humid mid latitude climate, the UHI guidelines in city planning were never incorporated. However, since first research in Utrecht (1969-1970) showed that this city experienced the presence of an UHI, guidelines were adjusted. Investigation of UHI of several cities, by calculating the maximum difference between urban and rural temperatures, showed that UHI is related to the amount of green that is surrounding a weather station in a 600-meter radius (Heusinkveld et al., 2014). The area of lower temperature associated with the green fraction of a city is referred to as a Park Cool Island (PCI). The extent of the cooling mechanism of a park reaches about one park width (the diameter of a park) into the surrounding urban neighborhood (Spronken-Smith & Oke, 1998).
The impact of the effects of a PCI will vary depending on the type of park and the size of the park. Irrigated parks are much cooler than non-irrigated parks, because the water in the ground can easily trap heat from the surrounding area. The most apparent controls of PCI’s during daytime are the presence of water, shade and surface albedo. They control the absorption of solar radiation and the evaporative cooling. PCI is calculated by subtracting the minimum park temperature (Tp) from the maximum urban temperature (Tu): PCI=Tu – Tp (Spronken-Smith & Oke, 1998).
5. Study area
The 1.9 km long abandoned railway viaduct ‘The Hofbogen’ is situated in the North of Rotterdam. The railway and the buildings supporting the railway are owned by Hofbogen BV while the rail itself is owned by ProRail. By both companies, it is desired to eventually transfer the ownership to the community of Rotterdam. The railway was built in the beginning of the 20th century and formed a connection between Rotterdam, The Hague and Scheveningen. The connection is not in use anymore since the 90s and the railway viaduct was assigned to national monument in 2002. Nowadays, several projects aim to renovate the Hofbogen railway line as well as the building underneath the railway. 3000 square meter of commercial space situated underneath the railway station was officially opened in 2015. The aim for the railway viaduct is to build a linear park. Several ideas have arisen amongst different stakeholders, however, no set plan for the linear park has been created yet.
6. Methods
In order to comprehend the massive complexity that the implementation of an urban linear park will bring, an interdisciplinary approach is needed. Therefore, this research involves the disciplines of social geography, ecology and earth sciences. A wide scale of specialized researchers in different disciplines have used their particular ways of information gathering and data collection. Also, different concepts and theories are found in different disciplines. Since this method offers a wide scale of information, solutions for complex systems can be found. Besides the interdisciplinary research, full understanding of all involved disciplines is needed.
The research of the individual disciplines consists of a literature research. For every research, concepts and theories have been studied according to the current situation in Rotterdam. Also, in order to solve these problems, the possible techniques regarding the implementation of a linear park were studied. For example: the discipline social geography studied current crime rates and biology focussed on affiliation with nature and biodiversity, whereas the earth science discipline looked at current problems regarding the hydrology and temperature of the study area. After this analysis, a study on the implementation of a linear park was done. For every discipline, the possible design criteria for a linear park were analized. Examples like the High Line in New York and the Promenade Plantee in Paris were used in this part of the research. The possible design criteria per discipline were tested on the study area in Rotterdam. Eventually, the results were integrated in comprehensive and overarching design criteria, specific to the Hofbogen in Rotterdam. These design criteria can therefore be used as a template for other potential linear parks.
Besides the literature research, the study area was visited. Also, there has been contact with different stakeholders in order to complement the information that was obtained in the literature research.
Common ground
The theoretical framework shows the relevant subjects and concepts for this research amongst every discipline, as can be seen in table 1. Common ground can be found between the different disciplines and their concepts. When studying the interaction between humans and fauna, the social and ecological disciplines have to exchange information for their research. Ecology and earth science cooperate when the connection between the role of ecology and the urban sink function of a city is made. Furthermore, the hydrological aspect of earth science is connected to ecology when looking at the through fall of water caused by the canopy cover of an area. The urban sink function can also be linked to human health and productivity, which connects the social discipline with earth science. The different aspects within the earth science discipline can also be linked to each other. The hydrological aspect can be linked to the temperature aspect. The process of increasing groundwater recharge can reduce the Urban Heat Island effect. All of the aspects within the earth science discipline search for methods to mitigate problems caused by climate change. And what connects all of the disciplines in this research is the main subject
of green infrastructure. The disciplines are investigating different aspects of implementing green infrastructure in Rotterdam.
Figure 5 Visualization of the common grounds between the different disciplines
7. Results
For every individual discipline, a literature research was conducted on the theories according the discipline and the area of the Hofbogen. Furthermore, with the knowledge obtained during every individual research is integrated in a complete overview of the design criteria of the Hofbogen project in Rotterdam. The following section describes, per discipline, the theories related to the project and the design criteria that are related to these theories. Every discipline is subdivided in two subjects.
Affiliative function of urban ecosystems
An affiliation with nature can be formed by engaging the public with biodiversity conservation efforts. This study has focussed on birds as primary group of organism because they are very audible and visible and can be excellent indicators of urban ecosystem aspects such as biodiversity; vegetation structure and contaminants (Savard et al., 2000). The three main ways of engaging the public in biodiversity conservation efforts are: (1) the creation of suitable conditions for birds. Examples of this are the hanging of nest boxes but also by plantation of selective native trees which is beneficiary for multiple species and also can potentially enhance the value of property (Gilles in Fernandez-Juricic & Jokimäki, 2001); (2) environmental
education. This increases public awareness and participation; (3) research: is necessary in order to acquire new information and to redefine management strategies.
Though an urban ecology centre would be a good way of turning all three ways mentioned above into social priorities for the improvement of urban life (Fernandez-Juricic & Jokimäki, 2001), it is unlikely that appropriate funding will be available in the near future. Focus should therefore lie on management and environmental education related design criteria. A conceptual model, including short elaborations on these subjects, for improving bird conservation in cities can be found in figure 6.
Figure 6 Conceptual model for improving bird conservation in cities (Fernandez-Juricic & Jokimaki, 2011)
Biodiversity
Studies of bird communities in urban parks have shown that parks are considerably richer in bird diversity than other urban habitats (Tilghman; Jokimäki and Suhonen; Hadidian et al. in Fernandez-Juricic & Jokimäki, 2001). In order to increase biodiversity in the Hofbogen linear park designers can enhance certain aspects of the park (Leedy & Adams in Fernandez-Juricic & Jokimäki, 2001).
First of all an enhanced habitat diversity/complexity is desired. This can be expressed in the form of vegetation being present in multiple layers and the availability of trees of different ages. Bird diversity is known to increase as vegetation develops and as the area of woodland increases in size so does the number of species that it can sustain.
Wooded routes and streets have proved an important mitigator of bird movement restrainment. They show to have a positive influence on the number of species present, species persistence, guild densities (species with a similar role within the ecosystem) and probability of occupation by individual species (Fernandez-Juricic & Jokimäki, 2001). A correlation can be seen between
the amount of vegetation and the species richness as well as a negative correlation between the amount of pavement and the species richness.
Another design that can be taken into account is that of enhanced resource availability. Do to the occurrence of fragmentation, some urban environments lack key resources needed by species such as nest sites, shelters or food. When availability of the lacking resources is enhanced biodiversity is likely to increase. Permanent water sources are also important to foster bird diversity (Tilghman; Jokimäki in Fernandez-Juricic & Jokimäki, 2001).
The third design criteria that should be taken into consideration in order to optimize biodiversity is the control of human disturbance in the park. A high visitor count has been found to diminish species richness and temporal persistence of pairs in various locations in southern and northern Europe (Fernández-Juricic et al., 2001). Disturbance by humans has the same effect on birds as predator disturbance. Birds will therefore spend a larger amount of time flushing, resulting in less food intake. The flushing distance of a bird is dependent on the habitat complexity and the bird size. More complex habitats result in lessened flushing distances whereas an increase in bird size correlates with increased flushing distance (Fernandez-Juricic & Jokimäki, 2001). With regard to conservation implementations this information can be used when deciding matters such as path location.
Social structure
Enforcing on any of the related gentrification processes can be used as a neoliberal urban strategy to revitalize neighbourhoods (Smith, 2002). And that is exactly what the case is in Rotterdam with the Hofbogen linear park, if it would come off the ground.
The park will require many public facilities; to address all participant of the public space it has to become. This would include, playgrounds for families with children, benches, food supply, water taps, sport equipments and elevating transportation services. It needs to be attractive in such an extent that a person would want to bypass from the daily route in order to experience the little extra quality of life. This will instigate several economic flows.
Reinvigorating the old railway track and building a park alongside it, and also redeveloping the arches for cultural and other services would instigate processes affiliated with gentrification. This will show an increase in property values (Crompton, 2001; Troy & Grove, 2008), the location becoming a cultural hotspot (Florida, 2004) and people collaborating for the local community, which proves to be cost-effective and beneficial for all local parties. Because of the investment in revitalization, it will be more likely that the area will revive by more investments en money flows.
There will be an expected drop in crime rates, due to more social control and cohesion the linear park will induce. But to ensure there will be no crime-spillover the park needs to comply with some criteria. We suggest closing times of the park between dusk and dawn, seasonally bound and specific parts of the park. Also it is most advisable to have cctv camera surveillance on crucial locations (like entrances) and city guards are a viable option. For maintaining the
public safety, it is also suggested to plan the park in such a way that there are no dead zones in which criminal activities could take place.
There are potential adverse consequences too. Because of the appealing force of most gentrification processes, the housing prices will rise. Consequently, lower class people will become displaced to poorer outer neighborhoods in Rotterdam and a community of higher class will settle. Another problem is the rent gap, which establishes when the rent could and should be much higher than the current residents are paying (Smith, 2002). These positive and negative effects of gentrification and changes in the social structure are problems many cities face. In order to revitalize the Hofbogen area, including the adjacent neighborhoods, it will have to come down to what extent gentrification processes may take place. It is necessary to monitor all aspects of the social structure to be able to react immediately on any negative impacts.
Human health
In Rotterdam, with the harbor being one of the most industrialized platforms in the world, any pollution captured from the air by flora is required. It is however, not only the physical aspect of the linear park that will contribute to the well-being of society. It will also have a social aspect which will have a great impact in an area like the Hofbogen. Implementing more green infrastructure in the area has a binding and mental effect on humans which will improve work productivity, health and well-being of residents of the Hofbogen area and other participants of the linear park (Tzoulas et al., 2007).
Hydrology
With the implementation of the linear park in Rotterdam, several techniques need to be applied in order to improve the hydrology of the park. In the area of Rotterdam, there are two problems according to the groundwater. At first, the extraction of groundwater for several practices causes a decline in groundwater level. Next to this, in the south delta of The Netherlands there is an upward groundwater flow with a higher salinity, as a result of groundwater extraction further inland inland (Oude Essink et al., 2006). This causes salinization of the groundwater in Rotterdam. Furthermore, urban storm water runoff can cause floods and erosion and this can be seen as another problem with hydrology in Rotterdam.
In order to face the impact from future stresses related to further climate change, adapted groundwater management is needed in delta areas like Rotterdam, to tackle to mentioned problems according to the hydrology of Amsterdam (Ranjan et al., 200).
Converting grey infrastructure (which can be defined as buildings, roads and other impermeable pavements) into green infrastructure could contribute to the recharge of groundwater. In urban environments, precipitation finds its way through grey infrastructure into surface waters, instead of infiltration in the soil to eventually end up in the groundwater. Therefore, there is no recharge of groundwater in Rotterdam (Ashley & Evans 2011).
When implementing a linear park, it needs to sufficiently transport precipitation water in order to decrease the amount of storm water and to make sure the water finds its way to the
groundwater system. This can be done by artificial infiltration systems (Bucheli, Muller, Heberle & Schwarzenbach 1998).
The linear park in Rotterdam can be seen as a green roof, since it is an elevated park. Storm water management, such as artificial infiltration systems, involves the retention principle in order to delay the surface runoff (Geiger and Dreitseitl, 2001). With the implementation of a soil layer on top of the linear park, a part of the water evaporates, a part of the water is used by plants, a part of the water is added to the groundwater (groundwater recharge) and a potential part can be drained off to surface waters (Gobel et al., 2004).
As Zobrist et al. (2000) states, it is very important to take into account the polluting effect of the infiltration of groundwater. If precipitation is polluted, the infiltration pathway could get polluted as well. However, since the linear park in Rotterdam will become a natural system that is physically not connected to other natural areas, the potential contamination can be cleared out without any side effects present. Whenever contaminated water infiltrates in the soil of natural areas, the contaminants can have effect on the present ecosystems and can disperse throughout all connected areas. Since Hofbogen green space will not be connected to other natural areas, the contaminants stay concentrated in one place and can therefore be cleaned out without any dispersion.
In order to tackle the problems Rotterdam is facing according to the hydrology, design criteria for the Hofbogen linear park project are created.
The study area at the moment consists of a non-permeable concrete roof. Some parts of the railway viaduct have raised edges, some part have no edges at all (see
figure 7).
First of all, in order to implement the linear park concept, it is needed to create uninterrupted raised edges along each side of the linear park. These edges will prevent seeping water along the ridges and will ensure optimal performance of filtration techniques.
The current drainage system of the Hofbogen consists of drain pipes, situated approximately at every 8 meter, on both sides. Figure 8 is a photo of the current situation at the Hofbogen viaduct, drain pipe are present every 8 to 10 meters. It is unknown if these water pipes are connected to a sewage system or not. There is a high probability that these drainpipes are connected to a sewer system. In order to optimize the hydrology of the study area, it is needed to place soakaways at the end of each drain pipe. The soakaways are systems that dispose water into the groundwater, by slowly dissipating water into the groundwater (Ashley & Evans 2011). The soakaways in Rotterdam must be installed at the end of each drain pipe and will provide recharge of groundwater after a precipitation event. The soakaways must be designed
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in a way that the drain pipe is still connected to the sewer system. However, this connection to the sewer system may only be opened with the occurrence of a heavy rain event and the soakaway system cannot drain away the rainwater immediately. Therefore, the recharge of groundwater is optimized and there is still an emergency option to drain away surplus water. Furthermore, in order to assure the water will be transported towards the drain pipes, it is needed to make sure the start of the drainpipes is situated below the average altitude of the railway.
In order to improve the hydrology of Rotterdam, the subsurface of the park is also really important. Overall, the linear park will consist of four different layers. Underneath the vegetation layer, there will be a soil substrate, a filter and drainage material (Berndtsson, 2010).
The construction of the linear park will consist of different layers on which vegetation will grow. There are different types of green roofs, the Hofbogen linear park will consist of a mixture of intensive and extensive vegetation. Since different vegetation types will be placed, different soil layers need to be present. For example, fruit trees which can be seen as intensive vegetation, will need a soil thickness of approximately 150 cm, while shrubs will only need around 70 cm of soil. Therefore, some elevated parts in the park will be created (Getter & Rowe, 2006).
Further research will have to provide information about the exact soil substrates that need to be used. The desirable infiltration rate needs to be assigned and thereby, the annual rainfall and the properties regarding the soil, temperature and vegetation needs to be taken into account. For example, for a particular soil it is calculated that the difference between field capacity (45%) and wilting point (15%) there is a measured water storage of 9 mm for 30 mm soil substrate (Brengtsson, Grahn, Olsson, 2005). The temporal storage of water in vegetated areas of the park can be considered as bio retention areas (Ashley & Evans 2011).
The third layer will consist of a filter. This filter will prevent the loss of soil particles and the contamination of the runoff water with large particles (Berndtsson, 2010).
Underneath the soil substrate an artificial layer consisting of permeable material must be applied: drainage material. This layer must be permeable for water but impermeable for roots. This ensures that the concrete construction of the Hofbogen will not be damaged by the roots of vegetation. This also ensures that the water that infiltrated all the way through the soil and sand layer can freely flow towards the drain pipes.
Since the park will not only consist of vegetated areas, another drainage method needs to be implemented in the non-vegetated areas, like concrete pathways. In these areas, it is needed to place infiltration trenches along sides of the pathways. Runoff from the non-permeable area will infiltrate into the infiltration trenches which will be connected to the layer with drainage material.
Temperature
Above park characteristics, such as temperature and air pollution, are important for urban planning. Heusinkveld et al. (2014) mapped the Urban Heat Island of the city, using novel bicycle traverse meteorological measurements. As figure 9 and 10 show, the UHI is accumulated above the city centre and the harbour. Daytime measurements already conducted in Rotterdam found that there is rural air temperature of 30.1 °C , a slightly warmer city center 31.3 °C, and most importantly a cooler park 27.3 °C (Heusinkveld et al, 2014).
The research site is marked as a black star and is located within the area with a high UHI value. Spatial variation of the Rotterdam UHI is strongly affected by local vegetation cover
(Heusinkveld et al., 2014). Note that green roofs, green facades, trees shrubs or grass may have a different cooling effect. For example, a dense tree cover limits the nocturnal cooling effect and causes higher temperatures in the park at night (Heusinkveld et al., 2014). Overall,
Figure 9 The Urban Heat Island above Rotterdam (Heusinkveld et al., 2014)
Figure 10 The location of the fieldwork area of this research marked by a black star. The X and Y axis represent the longitude and latitude respectively.
the implementation of a linear park will increase the Park Cool Island effect within this area. It can contribute in two ways, cooling with water or cooling with vegetation. In this part of the research the focus will be on the cooling by using vegetation in addition to the influence of the size of the park. Vegetation can contribute to the mitigation of the UHI in two ways; providing shade and evaporation (Slingerland, 2012). However, evaporation will only occur when the vegetation is provided with enough water.
Earlier research by Cao et al. (2010) shows the relation between the landscape index (size of a park) and the influence on the PCI of that park. The linear park that will be renovated in Rotterdam is 1.9 kilometers long and approximately 6 meters wide, which means that the size of the whole park is 11.400 km2. The shape of the park corresponds to the shape of figure 11 (e).
From the research done by Cao et al. (2010) can be concluded that this park shape is correlated to highest values of PCI in spring, summer and autumn.
Apart from the shape of the park, PCI intensity is mainly determined by the projected cover of vegetation inside the park. This refers to the area covered with trees and shrubs as seen from the air. From the research of Cao et al. (2010) can be concluded that in spring trees, grasses and shrubs are the most significant variables with an effect on PCI intensity. For summer these significant variables are the area of trees and shrubs. There were no significant values found for autumn.
Furthermore, Heusinkveld et al. (2014) found a specific formula according to their research in Rotterdam that can help calculating the percentage of vegetated area necessary for a certain amount of cooling of the Hofbogen linear park. They say that 1.5 km2 has a nocturnal cooling of 0.06°C per % aerial greenery. When looking at the differences in daytime average temperature between the urban heat island and the surrounding rural area of the city, a decrease of 1.5°C should be realised to minimize the UHI effect above Rotterdam. This means that 25% of every plot of 1.5 km2 should be planted with aerial greenery. This is approximately 17% per square kilometer and refers to about 1940 km2 of vegetated area in the hofbogen linear park to realize a reduction in temperature 1.5°C above and in the surrounding area of the park.
Figure 11 The LSI value of different park shapes (Cao et al., 2010)
8. Design criteria
The results of studies of the individual disciplines were integrated in comprehensive and overarching design criteria, specific to the Hofbogen in Rotterdam. See scheme:
Social Structure Temperature Biodiversity Public engagement Hydrology Closing and opening times between dusk and dawn, 17% per square meter should be vegetated area Enhanced habitat diversity/ complexity Creation of suitable conditions for birds Upraised edges along the whole track Cctv camera surveillance on crucial locations 940 km2 of vegetated area Enhanced resource availability Environmental education Soakaways at the end of the drainpipes Childrens playground Realise a reduction in temperature of 1.5°C above and in the surrounding area of the park Control of human disturbance in the park Subsurface consisting of: - Vegetation layer - Soil subtrate - Filter - Drainage material Benches
Slope entrance & elevators
Food & Drink supply
Visualization of design criteria
9. Discussion
Crime ratesCrime rates are likely to drop when implementing a linear park in an urban environment, but there is a theory that claims a linear park can have negative impacts on the crime rates in adjacent neighbourhood (Crewe, 2001). It connects a much wider area than regular parks, which can result in crime spreading more easily from areas with higher crime rates to areas which were considered more safe, the so-called crime-spillover (Crewe, 2001). Taking into account that in the North of Rotterdam (and Rotterdam as a whole) there has been significant improvement in crime rates ever since 2001 (Gemeente Rotterdam, 2014) and considering all subjects of improvement, the linear park should have a positive effect on the social structure in such an extent that crime rates should drop. There is however not enough research available on this matter to state anything conclusively and crime rates should therefore be monitored after implementation of the linear park and future research concerning crime rates influenced by implementation of a linear park should be conducted.
Hydrology
When looking at the effects of implementing techniques that reduce the groundwater extraction, a critical look on urban hydrology is required. This is because the hydrology of an area strongly depends on climate factors. For example, the statement on precipitation of study of Asley & Evans (2011) is based on research in an unknown location in the USA. It might be tricky to implement these findings in the study area of Rotterdam, since different initial hydrology and environmental characteristics of the area may be present. The study on hydrology of the linear park of the Hofbogen is based on findings in other park that might have another climate. Therefore, the reliability of this part of the research might be influenced.
Further research should be done on the implementation of the soil. To evaluate which soil type will be the best option for the Hofbogen linear park, an integration between the eventual design criteria on vegetation and the desired storage volume is needed.
Temperature
When looking at the reduction of the UHI of Rotterdam, a lot more factors can be involved in this process next to the usage of vegetation. As already mentioned, water can also account for an increase in the Park Cool Islands effect. The evaporation function of vegetation will only be effective when there is enough water available for the plants. This will be dependent on the hydrological choices of the project, for example the type of soil will determine the amount of water that can infiltrate and the different drainage systems used. Next to these factors, the type of plants will also be important for the different cooling mechanisms, but this exceeds the scope of this research.
10. Epilogue
After having conducted this interdisciplinary analysis it can be concluded that there are many design criteria that can be considered when a linear park is implemented in an urban environment. Having taken into account ecology, hydrology, temperature and social geography, a set of design criteria has been created that will optimize socio-ecological improvement in the surrounding area. These design criteria have been visualized by a graphic designer and elaborated upon in the ‘results’ and ‘design criteria’ sections.
Because the design criteria that have been selected are not necessarily site specific they can be implemented in urban linear parks in cities all over the world. We hope to see cities implement urban linear parks more frequently in the future as they can contribute to a neighbourhood from an ecological and social point of view as well as by mitigating environmental pressures.
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