Universität Leipzig
Fakultät für Physik und Geowissenschaften
Institut für Geographie Bachelorarbeit im Studiengang
Geographie Bachelor of Science
Sponge Cities: reimagining urban spaces as ecological landscapes in flood-prone cities
Vorgelegt von / Autor/in: Sudarshan Saravanan
Email: ss90cusy@studserv.uni-leipzig.de
Matrikelnummer: 3742362
Erste Betreuer/in: Bastian Lange
Zweite Betreuer/in: Andreas Berkner
Eingereicht am: 26.04.2022
Abstract
Rapid urbanization and climate change are testing humanity’s ability to adapt and reshape itself. Coastal cities are increasingly threatened by rising sea levels, as well more extreme and more unpredictable weather events. These precedented challenges call for transforming the approach in urban resilience. From fighting the water, to consolidating it. Instead of keeping water away, you bring into your urban spaces and help it resolve your problems. Under the large banner of nature-based solutions many alternative flood management concepts have emerged under different names in different countries. The largest country pursuing this alternative model is China, under the terminology of “sponge city”. The present thesis gives an update of the success and failures so far, by summarizing results from different survey and studies. The results are positive, despite insufficient funds and inaccurate planning. However, challenges remain, especially due to the Chinese political system, where criticism is not embraced. The studies use quantitative and qualitative data, such as remote sensing imagery and in-dept interviews from different Chinese cities. The successful implementation of the sponge city concept in China, will pave the foundation for similar projects in other large countries, such as the US, India, the EU and south-east Asian countries, which have numerous coastal cities.
Keywords: sponge city, nature-based solutions, urban design, low-impact development, urbanization
Abstract: Deutsch
Die schnelle Urbanisierung und der Klimawandel stellen die Anpassungsfähigkeit der Menschheit auf die Probe. Küstenstädte sind zunehmend durch den steigenden Meeresspiegel, sowie extremere und unvorhersehbarere Wetterereignisse, bedroht. Diese Herausforderungen erfordern eine holistisches Umdenken in der Stadtplanung. Anstatt gegen das Wasser anzukaempfen werden neue Ansätze unternommen, mit dem Wasser zusammenzuarbeiten. Anstatt Wasser aus urbanen räumen fernzuhalten, werden Verusche ausprobiert, die Wasserflächen als ein Teil der Stadt zu integrieren. Unter dem großen Banner der „naturbasierter Lösungen" sind viele alternative Hochwassermanagementkonzepte unter verschiedenen Namen in verschiedenen Ländern entstanden. Das größte Land, das dieses Alternativmodell verfolgt, ist China unter dem Begriff „sponge city“, zu deutsch „Schwammstadt“. Die vorliegende Arbeit gibt einen Überblick über die bisherigen Erfolge und Misserfolge der nationalen „sponge city mission“ in China, indem sie Ergebnisse aus verschiedenen Umfragen und Studien zusammenfasst. Die Ergebnisse sind, trotz unzureichender finanzieller Mittel und ungenauer Planung, positiv. Herausforderungen bleiben jedoch, insbesondere aufgrund des chinesischen politischen Systems, wo Kritik nicht willkommen wird. Die Studien verwenden quantitative und qualitative Daten, wie Fernerkundungsbilder und eingehende Interviews aus verschiedenen chinesischen Städten. Die erfolgreiche Umsetzung des Schwammstadtkonzepts in China, wird die Grundlage für ähnliche Projekte in anderen großen Ländern sein, wie den USA, Indien, der EU und den südostasiatischen Ländern. Die, mit zahlreichen Küstenstädten, ähnliche Ideen umsetzen könnten
Keywords: Schwammstadt, Naturbasierte Lösungen, Städtebau, Alternative Umgang mit Regenwasser, Urbanisierung
Introduction
In the beginning of the 21st century global climate change is taking place at an unprecedented rate. The earth’s thermal energy is increasing due to greater absorption of solar radiation by greenhouse gases. This increase in thermal energy in the atmosphere is creating more severe and extreme weather events, such as droughts and flash floods/excess rainfalls (IPCC, 2022) (Cai et al, 2021) The main research question of this thesis is to describe how the paradigm shift in the way urban design and planning responds to environmental hazards is unfolding, with the case study of China. How the sponge city mission in China is being implemented and how the results have been so far. In addition, the thesis intends to characterize and briefly timeline the response in planning and design to environmental hazards, throughout the history The concept of a sponge city will be summarized, ordered into a larger field of ideas of nature-based solutions around the world.
The more traditional approach, which was dominant throughout the 20th century, was to curb flooding in urban environments by building artificial structures such as levees, stormwater tunnels, water storage bunkers or reclaiming land from water bodies. These structures are usually built out of concrete and asphalt (Mallea, 2019) However, in recent years a “nature-based solution” approach called “sponge cities” has emerged as an alternative to the traditional approach (Seddon et al, 2019). Sponge cities are urban areas which have been designed to manage excess rainfall, by absorbing water, instead of draining it as fast as possible. These strategies are characterized by an effort and ability to naturally absorb rainwater, reduce hard artificial surfaces and increase absorbent spaces. Some of the strategies include creating green rooftops on buildings, storing/harvesting rainwater, building roads with porous materials and increasing the amount of water bodies in a city to serve as retention basins. Vegetation can be further selectively choosen to improve water quality and combine the sponge city concept with natural ways of treating greywater. In comparison to conventional flood management methods, sponge cities bring numerous additional benefits such as improved water quality, higher efficiency in water usage, improving air quality and reduction in the urban heat island effect. Furthermore, it has the potential to create a haven for flora and fauna, which contribute to human well-being (Jiang et al, 2019) Cities like Berlin for example, are rethinking flood management, as cited in the German online newspaper “Tagesschau” (Hilgert, 2021). The nature-based approach in fighting urban flooding is significantly cheaper than building grey infrastructure to curb urban flooding (Oates, 2020). In many countries the terminology regarding sponge cities differs, for example in the US and Canada sponge cities are referred to as “best management practices (BMPs)” or “Low-Impact Development” (LID). In Australia and New Zealand, they are called water sensitive urban design (WSUD) and in the UK “sustainable urban drainage
systems” (Liu et al, 2021). However, terminologies between Australia and UK are used universally in both countries (Ashley et al, 2013). In Singapore it is known as “Active Beautiful clean waters plan” (Liu et al, 2021). They all fall under the larger sustainable concept of“Nature-based solutions” to reduce or eliminate risk from climate change hazards with natural features (Seddon et al, 2019). The sponge city concept is part of a larger paradigm shift defined as “nature-based solutions”.
One of the first countries to implement “sponge cities” on a large scale is China (Jiang, 2018, p.136). The Chinese government pledged 60-90 million USD per city and per year for 3 years, for 30 selected cities. The financial plan beyond these 3 years is unclear, therefore the central government encourages private sector investment through private public partnerships (PPPs). In addition to overflooding, China is a country with a lot of water scarcity and, more expectedly, water pollution. It is predicted that 641 out of 654 Chinese cities are vulnerable to frequent flooding. Since 2008 more Chinese cities are experiencing urban pluvial flooding (See Figure 1). They cause widespread socio-economic damage and attract worldwide media attention. The economic loss is expected to be around 15 billion UDS every year, especially in the South of China (See Figure 2). The main causes for the increase in urban pluvial flooding are climate change, rapid urbanization and unsustainable urban development. China urban expansion has been significant, especially during the 1990s. China urban population increased from 302 million to 771 million during the 1990-2015 period. The growth in Chinas urbanized area however took place at twice the growth in urban population So urban sprawl was increasing (Jiang et al, 2018). Human space theories offer the socio-anthropological basis for sponge cities. Human beings prefer spaces, which are open have water bodies and have some vegetation, they provide shade and visibility and water resources. Landscapes with spaces to settle along rivers and streams are seen as desirable places to live by human beings, due to human evolution (Falk and Bailling, 2010) (Ode et al, 2009).
The theoretical framework will commence by summarizing the history of climate adaption in urban settlements. How urban dwellers optimized the structural resilience of their settlements, by building stilts or buildings canals. Moreover, their effectiveness will be summarized. Certain cities in the past also have committed mistakes, which are akin to mistakes made in urban settlements of the modern era. The history of Chinese urban planning and design concerning flood mitigation will be introduced, before presenting contemporary sponge city projects in China, as part of the sponge mission. Three typical case studies will be visualized. The first project is a constructed wetland in Jinhua, which features in many landscape design magazines and articles. Many prominent news channels use this project as a cover picture to first present the idea of a sponge city, like the BBC (Wong, 2021). The second project will be a broader description of the implementation of the sponge city project in the city of Wuhan, where specific interventions have been made to curb urban flooding. Wuhan is a city specially effected by urban flooding and its financial impact (Jiang et al, 2018, p.2) (Jiang et al, 2018, p.3). The next case study described will be Changde, a city located in the interior mainland of China, where an American design firm was chosen to design an urban district in the south of the city (Messner, 2016). In the following the chapter the methodology of the thesis will be outlined. The thesis will use only secondary data, collected from different studies conducted by different professionals in China. In addition, literature regarding the topic will be reviewed. In the results chapter, three studies will be presented and their results described. The study areas are Wuhan, Nanjing and Yangzhou. The Wuhan study analyzed the property value impact of sponge city projects and the readiness of citizens to financially contribute to sponge city projects. The Nanjing study focuses on analyzing remote sensing data to see the change in land use and the general change in urban agglomeration. In Yangzhou qualitative interviews have been done with professionals and technicians involved in the sponge city project. To comprehend their idea of the sponge city and their impression of its impact. The results chapter will be terminated by quoting literature review of the sponge city mission. These literature articles describe the mission more holistically and identify problems, which are structural and not based on single case studies or the geography of individual Chinese cities. In the discussion chapter the value of the results, from the three studies, will be summarized. Furthermore, practical actions, which could be undertaken, will be outlined. The thesis will be concluded by suggesting more research in specific areas. Moreover, why governments should embrace the ambition of the sponge city mission in China to emulate it in their own countries.
Theoretical Framework
After severe urban flooding in Beijing in the year of 2012, urban pluvial flooding came to increased attention in the Chinese society. A city like Beijing, which is actually a water-scarce city, faced 79 deaths from flooding (Zhou and Roswell, 2021) (Wang et al, 2017) The problems related to increased urbanized area are obvious, they increase waterlogging, a large part of rainwater resources get lost and rainwater runoff pollution increases. Urban development takes away spaces, which could have served as woodlands, wetlands and water bodies (Lu et al, 2018). Several measures are actually being planned by the Chinese government to increase water supply to Beijing, due to water scarcity, including a project to divert water from South China to the north of China, which was met with criticism and anger from Southeast Asian countries (May and Wong, 2021). This creates an ironic situation where the capital city of the second largest economy in the world, faces water scarcity and flooding. Both causing a big financial burden to the Chinese state and city officials (Mullen, 2021). Due to these developments, frustration among residents grew, which led the Chinese government to announce the” sponge city” mission. Prior to this the Chinese government had undertaken several measures to curb fluvial flooding, by building dams and using conventional flood management measures, however this was the first time the pluvial flooding events were tried to be addressed. The Chinese government laid a lot of value on large engineering projects, which were also built as symbols of nationalism, despite its significant cost on the environment and human settlements, as well as farmland (Hvsitendahl, 2008). Furthermore, due to ongoing climate change, extreme flooding events are increasing and becoming common in areas, which hadn’t seen such events in the past. The aim was to subsidize pilot projects undertaken in selected cities, with the aim of naturally absorbing, filtering and purifying 70% of the rainfall received in the urban area (Zhou and Roswell, 2021). Since 2015, 30 Chinese cities were chosen (Yin et al., 2020, p,2). Before describing sponge city projects in China, it is noteworthy to look at how urban areas in the past eras dealt with overflooding and how flood management was undertaken in ancient times. Before the existence of concepts like sponge city and sustainable city, many urban areas were designed keeping environment conditions in mind Contemporary governments give a lot priority to an efficient water supply, without considering the impacts on other important mechanisms, for example the sustainability of the water source or the degradation of the water quality during long transports. In democracies satisfying the voter before the election is the foremost priority, one of the measures to ensure electoral strength, is by subsidizing the price of water (Pandey and Bhardwaj, 2021). This creates very often a false impression of abundant water sources. High tech engineering solutions have often been seen as the main solution to water scarcity or insufficient supplies. Countries and institutions in the 21st century however are
changing this paradigm, by using nature based solutions to tackle crucial socioeconomic problems (Cohen-Shacham, 2016).
Historic background
Before the 21st century other forms of adaptation have been utilized by human beings to be resilient against extreme flood events or conventional water level fluctuations. Houses and thereby villages were more radically adapted to a hydrological environment than contemporary urban settlements today (Böhm, 2016) (Putro and Zain, 2021). In several sites around the Alps, especially towards the north of the Alps in Switzerland and Germany, archeological remains of stilt houses on water bodies have been discovered. These existed probably from 5000 BC to 500 BC. Stilt houses were usually either built on water or on bogs (a variety of wetlands). The houses were built out of wood and lichen with the walls made out of clay (Böhm, 2016). It is still unclear why prehistoric European settlements around the Alps were built partially on water. Some suggestions are that this was done to be in safety from enemies during war and safe from animals. Other suggest that the stilt houses were convenient for fishing aquatic species out of water bodies or to adapt to changing water levels (Desor, 1866). The research around this topic is fairly new as the discoveries are comparatively not very old and are still being analyzed and evaluated (Jeraj, 2009). In Asia stilt houses are extremely common and can be found in almost every south, south-eastern and east Asian nation (Das, 2016) (Putro and Zain, 2021) (Nithi et al, 2005). Traditional Thai house are almost always built on stilts. They protect against venomous animals and against flooding. Irrigation fields are regularly purposely flooded for rice cultivation and therefore, it is convenient for houses to be raised on stilts (Nithi et al, 2005). In In the Kalimantan province of Indonesia floating homes, or so-called “Rumah Lanting” houses are designed to deal with the fluctuating water levels and the surrounding environment. In Kalimantan, which is located on the Borneo Island shared with Malaysia and Brunei, communities always lived in close relation to the natural environment. Traditionally indigenous communities lived in the forests or on large rivers. The communities who live on large rivers are usually involved in trading goods and services. This is the prime interaction of indigenous people and outside communities. A floating house building typology is a way of residing alongside the river, especially in major river in west Kalimantan, without having to procure property rights over land. It is an easier option for lower-income residents to reside in more economically more attractive areas. These structures get constructed out of local materials sourced from the vegetation (Putro and Zain, 2021). In addition to designing houses in response to flooding, cities in ancient civilizations were also designed keeping flooding and water scarcity in mind. Many cities invested a lot of resources early on to ensure that the water supply was sufficient and that the city was protected against floods (Onofre, 2005) (Evan et al, 2017) (Lentz et al, 2017). Cities were also built in totally different typologies than ancient cities in later decades, they
did possess city walls and were sometimes sprawling out over spaces larger than many cities today (Evans et al, 2017) (ZDF, 2020). These are interesting discoveries for contemporary urban design.
Before the Spanish invasion in 1519 the Aztec capital of Tenochtitlan faced severe droughts and floods, furthermore it had issues in supplying good water and sanitation services. In addition to building dams, dykes and aqueducts they Aztecs built so called “floating gardens” to be more resilient to environmental changes (Sosa-Rodriguez, 2010). These floating gardens are and were called “Chinampas” they were small rectangular beds of gardens in shallow lake beds. Chinampas were built out of interweaving reeds with wooden stakes beneath the water surface to keep the garden in its position. They were designed keeping moisture retention in mind (Onofre, 2005). Parallel to the construction of the Chinampas, which were in many ways similar to reclaimed land or modern aquaculture, drainage systems were built. Their purpose is to create a constant flow of water to clean organic waste. Furthermore, once the drainage canals accumulated sediments, they were dug up and thrown onto the Chinampa fields. The sediments form the lake were usually rich in nutrients and fertilized the soil effectively, creating good harvests (Nunley, 1967). However, when it came to water management Tenochtitlan’s rulers made many mistakes, which are comparable to mistakes made by contemporary governments They established a reliance on far-away water sources, by building aqueducts connecting water springs in the mountains. The Aztecs built a dam, the Nezahualcoyotl dyke, this dam intended to divide the brackish water from the lake Texcoco and the freshwater from the lake of Mexico, this also increased the risk of a dam-burst if insufficiently maintained (Sosa-Rodriguez, 2010). Tenochtitlan was connected to the mainland by causeways, which could be cut off in case of necessity, for example during war. The city was fully connected by canals, which made it accessible by foot or by canoe. The canoe was the main from of transportation inside the city and for the transportation of goods. The conqueror of Tenochtitlan Del Castillo himself wrote in his documentations that he was fascinated by the building and towers “arising” from the water. He described Tenochtitlan like a dream city he had never seen or imagined before (Del Castillo, 1521).
Chinese cities have a long reputation of hydrologic engineering and natural adaption to water fluctuations For example, the city of Ningbo built a water diversion project in the 8th Century to access a higher volume of freshwater and enable the relocation of the city towards the floodplains. Bank embankments were planted with mulberry bushes to help stabilize the soil and create nutritious soils for silkworms. Many of these artificial embankments became identical to natural streams, thereby promoting biodiversity of human interests (Tang et al, 2018) The ancient city of Suzhou is crisscrossed with canals and streams, which were the basis of the transportation system. Furthermore, the canals prevented and limited the damage created by floods significantly, as the canals
served as spillways during floods (Xu, 2020). Another source from 1989 also states, that the city of Suzhou was rarely affected by floods (Qingzhou, 1989). Suzhou is referred to as “the Venice of the East” by many tourist portals and other sources The beginnings of the urban morphology of Suzhou can be traced to 514 B.C, when Suzhou already had 8 water gates and 8 land gates. Zhu Changwen already noted in 1084 that the canals were essential in driving out excessive rainwater. House doors very frequently opened towards a canal (Xu, 2020). This is visible even today (Sills, 2020). In 1793 a British artist who had visited Suzhou, made the connection between Suzhou and Venice (Xu, 2020). In fact, in ancient China waterways and canals were built to connect cities with each other for the purpose of freight trade (Wang and Nolf, 2020). Suzhou had a reputation of fertile agricultural and aqua-cultural production. Furthermore, its canals where a vending space, where vendors would arrive in the boats and sell goods to ongoing pedestrians. The nodal points between streets and canals were overcome by canal arch bridges. A double system of roads and canals were existent in the city, which existed in a grid plan system parallelly (Xu, 2020). These bridges played a very important role in the identity of the city and they were named differently and elegantly, with names such as “Fragrant Flower Bridge”. The bridges were ideal places to view the skyline of the city or draw paintings (Wang and Nolf, 2020). During the Southern Song period it is estimated that 82km of canals existed in Suzhou. That was 78% of the existing the city street network. That means the road network of the city was only 20% more than the canal network. As per the book “The Chinese city in space and time: The development of urban form in Suzhou” by Xu it is speculated that each canal was less than 10m in width and 3-5m in depth (Xu, 2020). Today Chinese architects of sponge city projects in China, often refer to traditional urban planning theories and concept, while presenting and designing them. It is viewed as a reemergence of Chinese traditions (Yu, 2015).
Case Study Jinhua
On such contemporary Chinese sponge city project is the Yanweizhou Park, located in the city of Jinhua, south of Shanghai. It attracts more than 40,000 people a day (Hobson, 2015). It has been designed by the well-known architect firm “Turenscape”, founded by Kongjian Ju. (Delaney, 2018). It is often used as a cover picture in many online articles about “sponge cities” in China, due to its architectural reputation and popularity (Wong, 2021). The Yanweizhou Park is a 26-hectare wetland park at the mouth of three rivers. The Wuyi and the Yiwu river converge here to the Jinhua River Before the sponge city project, most of the fluvial wetlands were destroyed by sand quarry activities. A high flood wall, to protect the area from flooding, also destroyed the aesthetics of the area. During the dry season the surface area was barren and dry. The flood wall cut off the space from the city visually and physically. However, during the wet season the erosion of the surface was high and thereby causes the water to intrude further inland. (See Figure 3) Therefore, the designers convinced the
city officials to demolish the flood wall and create a balanced earthwork by creating an erosion resilient embankment, which is covered by native vegetation (See Figure 6). The entire area has been converted into a park with pedestrian paths and pavilions, which is designed to be flooded during wet season. This forms the core of the sponge city concept, whereby the flood wall is demolished and the monsoon floods are allowed to spread, rather than trying to curb it (Yu, 2015) (See Figure 6) During the wet season the area gets fertilized by sedimented silts (Hobson, 2015). The inland area of the park is permeable, as reused gravel was used to build the pedestrian pavements. The vehicle access area, was also constructed with permeable concrete pavements. The inland pond is designed in a way to purify the water before it enters by letting it flow through gravel. The water quality is thereby good enough for swimming (Yu, 2015). The most eye-catching aspect of the park however, is a series of footbridges, which were designed aesthetically, inspired by a wooden dragon (Hobson, 2015) (See Figure 4) The architect firm which implemented the project states on its website, that the Yanweizhou park combines the river currents, the flow of people and the gravity of object into a dynamic coexistence. The design included meandering vegetated terraces, curvilinear paths, a serpentine bridge and circular bioswales and planting beds (Turenscape, 2014). The Yanweizhou Park represents a type of sponge city project that is very common in sponge mission cities in China. Landscape urban design can be sub-divided into two forms “for resilience” and “through resilience”. “For resilience” seeks to integrate hard infrastructure, which does not absorb water naturally, into an environment that is more similar to ecological landscape. By constructing bioswales and rain-gardens. It serves more as a bandage to an environment that is not planned and designed well for the water cycle and may, due to its function, never be. “Through resilience” creates entire natural landscapes in spaces where no hard infrastructure is present. It aims to copy untouched natural landscapes and serve practical functions for human settlements, such as wetlands (Katsy, 2016).
It is also mentionable than wetlands, also referred to as peatlands, store up to twice as much of carbon than forests do. This fact is rarely mentioned or put forward in public debates. Despite the fact the wetlands are also the source of methane emissions, most wetlands are carbon sinks. Especially in the tropical and subtropical regions of the world. Tropical and subtropical wetlands store 4-5 times more carbon than boreal wetlands (Mitsch et al, 2013). Furthermore, constructed wetlands are significant contributors in cleaning water, therefore they are being piloted to replace the conventional form of wastewater management in China. Through a complex form of interrelationships between organism and the water, the water gets cleaned (Stottmiester, 2003). In addition to that any kind of vegetation severely reduces the air pollution in the environment, several studies indicate this. The benefits of constructed wetland
are so vast and diverse, we will not be able to cover these in this thesis (Selmi et al, 2016)
Another project designed and implemented by the Bejing-based landscape design studio “Turenscape” is the Mei Garden, along a river in Jinhua. The designers were contracted to design a garden based on the traditional Chinese flower “Mei”, which has a high value in Chinese culture and society. The plot was an urban wasteland with building debris, garbage and urban runoff (See Figure 7). The project follows a cut and fill building concept and therefore didn’t need any additional soil from outside the plot. The garden is designed to clean eutrophic water from the nearby river. The river water is pumped into the garden at the highest level and directed threw four weirs (See Figure 8). These weirs serve as bio-filter, which contain vegetation bends. The process of biofiltration involves passing water through porous material, such as sand and gravel. This porous material is inhabited by microorganism and plants. These organisms extract necessary substances from the water and thereby purify it. Biofiltration has a main purpose of filtering organic substances, which are toxic in water beyond certain levels, such as nitrogen (Hammes et al, 2011) It terminates along the path towards the lower north end, into a lotus pond. Walled boxes, in the Lotus Pond, contain the Mei flower (See Figure 8,9) (Turenscape, 2013).
Significance of urban water run-off pollution
The general intention to clean water run-off, stems from the fact the cities unfortunately heavily polluted stormwater and thereby toxify nearby water bodies, such as rivers and lakes. Solid substances like heavy metals and polyaromatic hydrocarbons get mixed with the natural rainwater run-off. (Zhao et al, 2018) Sometimes even the components of filters are hazardous, due to insufficient knowledge of developers. The use of asphalt, geomembranes and filter fabrics are sources of micropollutants, such as bisphenol A. Biofiltration has the potential to clean suspended solids, nutrients and trace metals. Some studies have proven biofiltration to also be effective in retaining aromatic hydrocarbon. A study undertaken by Flanagan et al (2018) in Compans, France in the urban agglomeration of Paris, shows that biofiltration have a high effectivity in cleaning suspended solids, as well aromatic hydrocarbon and zinc. They were removed by 90% (Flanagan et al, 2018). Copper and octyl phenol, which is mainly caused by tire run-off pollution from cars, were reduced by 70% (Tamis et al, 2021). BPA and nonylphenol were moderately removed by approximately 50% to 60%. The effectiveness in cleaning DEHP was, however is poor, with only 8%. DEHP is found in many plastic products and is a form of micro-plastic pollution, and suspected to be a cause for cancer (Tickner et al, 2001) (Flanagan et al, 2018). In saltwater bodies oysters can help curb water pollution substantially, as oysters remove excess nitrogen, by incorporating into their shells and tissues Furthermore, they filter pollutants by solidifying them into small packets and depositing them onto the ocean floor, where they are not harmful to other organisms (Ermgassen et al, 2013).
Case Study: Wuhan
The city of Wuhan was one of the first cities to implement sponge city projects. Annually, a selected Chinese sponge city receives 63 million USD from the Chinese central government to implement sponge city projects. The focus in the Wuhan sponge city mission is to curb water logging and improving water quality. The size of Wuhan’s natural lakes has shrunken 70% from the 1950s to 2013. In 2016 the Wuhan section of the Yangtze River reached a peak of 28.37m, which is the fifth-highest recorded eve. Furthermore, Wuhan’s has an issue with water pollution Very often the sewage pipes and stormwater pipes get mixed and get discharged into natural water bodies. It also overexploits its groundwaters and suffers from an urban heat island effect (Peng and Reilly, 2021). Before implementing the first phase of the sponge city mission, pilot projects were initiated to prove the ability of nature-based solutions in reducing waterlogging and flooding, including on a school (Peng and Reilly, 2021).
During the first phase urban gardens, artificial water bodies and two new rainwater pumpstations were constructed. Furthermore, drain pipelines were repaired and at least one lake was ecological restored An area in Wuhan called Nangan Channel, suffered from serious waterlogging. This was due to a high groundwater level and a larger percentage of hardened surface. Adding to that Nangan is an older urban district and has mixed sewage and stormwater pipes This sponge city project includes several interventions like bio-retention facilities, permeable pavements, underground rainwater storage tanks and socalled ecological parking spaces. A bio-retention facility or bioswales have features, which are distinctive for grey-infrastructure projects and nature-based solutions. On the surface it visually appears to be stretch of a green landscape However, below the vegetation, the cultivated soil and the natural soil, lays a perforated pipe which discharges excess water from the catchment area during excess rainfalls. The project is an example of how many sponge city projects are implemented in Chinese cities (Peng and Reilly, 2021).
An area called Nanganqu Park was transformed in the 1990s before the sponge city mission. From being a drainage ditch in the 1980s it was transformed into a site with permeable pavements, rain gardens, grass swales and artificial wetlands. 20% of the funds came from the city government and the rest came from the private sector, which in this case is an iron and steel company (Jing, 2019). The city has four categories under which sponge city projects gets assessed, these are water ecology, water environment, water resources and water safety. The standards for these indicators are proposed to increase by every decade (Peng and Reilly, 2021). However due to insufficient funds the sponge city mission in Wuhan has slightly stalled (Maciejewska, 2020, p.15).
The Wuhan sponge city projects are incorporated into other broader urban planning frameworks. The Wuhan comprehensive plan and ecological planning framework. The ecological frameworks plan for two green inner rings in the city
of Wuhan and six wedges/green corridors and two axes. The sponge city projects will be aligned to be inside the allocated ecological corridors. Space in the city is also being dedicated as prohibited construction areas or as blue/green delineated conservation areas (Peng and Reilly, 2021)
Both the government sector and the private sector contribute towards the maintenance of sponge city projects. The technical guide of the Wuhan sponge city project advises the maintenance and operation to be organized in a decentralized manner (Peng and Reilly, 2021).
Case Studies: Changde
Changde is a city located in the inland regions of China, in a province called Hunan. Changde was an important cultural and economic center in the Ming dynasty. Changde took an even more holistic approach towards a sponge city. The city commissioned the US-based Urbanlabs to design a masterplan for the inner city. The new urban district is supposed to inhabit 600,000 residents. At the center of the plot is a highly flood prone polluted lake. The idea is to reimagine the lake in the center of the city into an asset for the city, by not building any defenses, to curb water overflowing The fact that the project intends to increase the size of the lake and make it bigger than it was before, is contradictive to the common practice in China and in other Asian cities, which have a contemporary tradition to reclaim land from water bodies and the sea. Lakes are seen to be hinderance to urban development The site is also intended to be planned as a central business district to decentralize the city
The CBD will be located on an island in the middle of the lake, with a prominent commercial building, which will be the highest on the site area (Messner, 2016). The public transport system in the form of a bus system, will be accessible from everywhere within 10 minutes. The combination of a dense urban area with a natural setting is a new way of thinking about urban design and modern cities (Maciejewska, 2020, p.15). The design incorporates so-called “Eco Boulevards”, these are canal lined streets, which pre-filter stormwater before it enters the central lake. The “Eco Boulevards” are proposed to incorporate constructed wetlands in the center, as well as a permeable hard landscape equipped with street furniture. A smaller amount of space will be dedicated to a four-lane carriageway for motorized traffic. Small stormwater parks will be located in equal distances, along with rain gardens in every block (Urbanlabs, ). Along the Chuang Zi River an ecological purification area/filtration area was created It consists of different kinds of vegetation, phytoplankton and reeds or wet grass. During the rainy season, the rainwater harvesting plants can discharge excess water into the ecological purification plant and then divert it toward the rivers. Thereby the river water quality can remain good and pollutants can be filtered out (Maciejewska, 2020, p.15). (Turenscape, ) Other sponge city projects involve rainwater harvesting plants along the Chuan river.
Methodology
The type of research aimed in this thesis is a descriptive research approach. The aim is to describe the entrance of a new paradigm in urban design and planning, which aims at alternative practices in the field of flood defense and water managements systems. By researching literature and using keywords oto search relevant papers. Implemented projects will be presented and described thoroughly, and their results on the basis of quantitative and qualitative data presented. The studies were chosen randomly without searching specifically for case studies with successful results. The data will be secondary data gathered from conducted studies undertaken by Chinese and international professionals abut sponge city projects in China. The scale and level of research regarding sponge cites in China, will be depended upon Furthermore, critics of the implementation and policies of sponge city projects were cited, some have not collected data, but interpretate the data already collected. This study uses a content analysis method to conduct a literature review of sponge cities. The result will be summarized and a general trend among all studies will be outlined.
Results
In the results chapter of the thesis will present several studies and reviews from different Chinese cities. The first study consists of an online questionnaire and in-dept interviews conducted in Wuhan to understand the perception of sponge city projects in Wuhan and the “willingness to pay” among residents. The second survey from the city of Nanjing was conducted by using a land use land cover remote sensing analysis technique to analyze the land use change in Nanjing over the years. Furthermore, Zhou and Roswell (2021) directed a qualitative survey with professional and technicians in the city Yangzhou regarding the sponge city mission In addition, several review articles are summarized, which critic the sponge city mission holistically, considering the large scale of planning and implementation. Concluding articles published by authors, who have written general reviews of floating architecture have been summarized.
Wuhan
The article published by “GrowGreen” project initiated by the European Union composed an article describing sponge city projects in Wuhan and their success a failure. The “Growgreen” project is a partnership between several cities around the world to do research and share knowledge on nature-based solutions in urban design and planning (Growgreen, 2022). The city of Wuhan has a citywide real-time monitoring program and evaluation platform to evaluate the success and failure of sponge city projects around the city and in different geographies of the city. In the summer of 2020, the sponge city projects in Wuhan were challenged and their abilities tested. The city suffered intense rainfall during the monsoon season over a longer period than the average. The cumulative precipitation was 1,3 to 2.1 times more than the usual precipitation and the duration of monsoon season was unusually long. The flood level of rivers in the surrounding areas reached a level of 4m higher than the average urban elevation However, the city’s residents experienced the floods, which were the 4th highest in the history of Wuhan, very mildly, with limited damage This is astonishing as most provinces in Southern China experienced considerable property damage and waterlogging. Wuhan did not suffer very serious damage and the occurrences of waterlogging could be dealt with ease, in comparison to previous years. In comparison to the flooding event in 2016, the sponge city projects increased the hydrological absorption capacity and efficiency. The number of waterlogging points reduced from 162 to 30. The inconvenience to traffic was greatly reduced. Another visible outcome in Wuhan is that the sponge city initiative seems to have also boosted innovation, with 58 patents applications being filed by companies and local sponge city implementation models being developed (Peng and Reilly, 2021). Another source estimates that there will a 70% reduction in water pollution in certain pilot area, due to sponge city projects. Another significant benefit of sponge city
projects is the increase in property values around areas where several projects have been undertaken (Maciejewska, 2020).
In the study Zhang et al (2018) the economic benefits of the sponge city projects for property owners were studied. Previous studies have identified that not merely the flood risk identified by hydrological professionals reduces the property values in neighborhoods, but more individual flood events. Flood resilient retrofits after such extreme weather events can rectify property values to their original value or even increase them further. The methodology used was interviews and analysis of secondary data. It is therefore a combination of quantitative and qualitative research. For collecting qualitative data, a questionnaire was used to research Wuhan’s resident’s perceptions of the sponge city mission and their perception of danger, caused by flood extreme events. In the questionnaire 27 close-ended questions were asked. Closeended questions mean, that there were a set of predefined answers from which the respondents can chose. Interviews were conducted with professionals from the public sector, for example city government and planning institutions, and the private sector, for example real estate developer and service providers 15 interviews were held from January to March 2017. 384 citizens were chosen as a minimum sample size in an online questionnaire The sample size was chosen according to calculation regarding the confidence interval in relation to the population of Wuhan. The questionnaire was reached out to all different districts of Wuhan to get an overall picture. All together 452 responses were collected and from those 423 responses were analyzed, as 29 respondents did not live in the Wuhan city area. Around 47,5% of respondents were between the age groups of 18-28 years. The majority had a college or university degree, furthermore there were more female respondents than male. Secondary data was used from land transaction price data. The result indicate that residents are willing to pay for interventions, however their main interest lies in the improvement of urban life, rather than in flood reduction measures. The perception of flood risk is dependent one different factors, these include ability to take preventive measures, past experiences and their proximity to a flood hazard. Five indicators were used to analyze the flood risk perception of Wuhan residents: flood exposure, flood frequency, flood impact perception, flood protection and impact of property values. 96,75 of the respondents had experienced severe urban floods in the last twenty years. 66,5% of the respondents experienced flooding at least once a year for the last 10 years. According to Zhang et al (2018) this exposure level is very high.
This is because the willingness to finance sponge city projects is not influenced by the scientific level of danger observed through data, but rather by an individual subjective assessment. One study has found a correlation between education/income and the willing to pay for sponge city projects. The study involving the secondary data came to the result that during a heavy rainfall period in Wuhan in July 2016, most residential areas had property values
decreases. Except two residential areas where property values were increasing, both of these neighborhoods were neighborhoods with significant sponge city construction projects. Results from the interviews suggest that a large proportion of the population of Wuhan has been affected by flooding 96,7%. The disruption in the public transport system and road systems was perceived to be the most disruptive hazards of flooding. Followed by flooding of neighborhoods, which 49% saw as disruptive. Other disruptions were flooding of offices and residences. Most residents see urban flooding as annoying; some see the floods as neutral, as they have gotten used to it. Others document their experience as traumatic. The majority of respondents take protective measures against floods, this usually involves recovery actions. The protective measures include things link flood barriers, sandbags and removing valuable items from risk areas to dry areas. Most resident agree 86% agree that the value of their properties would be lower after the floods Interestingly more than 44% of the respondents were familiar with the concept of a sponge city and 66% have heard about it. As part of the survey the sponge city concept was introduced to the interviews and their responses documented. 68% felt that this could reduce the damage caused by urban pluvial flooding and 26% wanted it its effectiveness to be proved.
Many residents actually valued the increase in green and public space as the most important measures of the sponge city mission, in addition to reducing flood related damages. The majority of 80% felt so, in comparison 74% found the flood safety improvement to be beneficial and 73% the improvement of public space (Zhang et al, 2018). The residents’ level of “willingness to pay” for sponge city related projects largely depended on how beneficial the projects would be for their property, the functional benefits and increase in property values. This hypothesis was proven by the study conducted Zhang et al (2018). Most respondents (83%) expected an increase of their property values after the construction of sponge city projects. 50% anticipated an increase of between 211% of their property value. The perception on the influence on land values in Wuhan was limited, as in China land is not owned by private individuals but by collectives or by state. Private individuals do not have the authority to participate in land sales or purchase and cannot avail renting land rights or user rights. 67% of resident’s agreed that a land price increase is likely, most respondents expected an increase in property value of around 5% (Zhang et al, 2018).
In-dept interviews were conducted to gather information from professionals. Most professionals shared the view that the flood risk exposure in different parts of Wuhan vary a lot. Certain areas are strongly affected, whereas other barely. Overall, the measures undertaken are not seen as sufficient. Interestingly Wuhan residents do not value the flood mitigation measures all year round. Rather, the multiple benefits created by additional space, additional greenery and a general increased quality of urban life was valued outside of the rainy
season by most citizens. Furthermore, additional greenery is seen to reduce air pollution in Wuhan. Only during the rainy seasons when flood risk events become more daunting and threatening, the value of sponge cites as flood mitigators is recognized. When it came to the question of who should finance sponge city construction projects, interview suggested that the cost should be taken care by homebuyers. Especially developer shared this stance, however many admitted that due to high burden this cost should be taken car by municipality funds, which are collected through taxes. It is observed that the districts which fall under sponge city districts have a more stable price during rainy seasons, whereas most district experience a drop in property price during the rainy season. Furthermore, over a longer period of time certain different pattern were observed between sponge city districts and non-sponge city district. Qingshan and Hanyang are sponge city areas. Qingshan is located in the north of the city and generally more in the outskirts. Hanyang is located on the western side of the Yangtze River is has a denser urban environment. From 2012-2014 the increase in property prices around the city were the same between both types of districts. However, in the year of 2015 the property prices in the sponge city districts dropped. The drop can be attributed however to the fact the real estate construction was higher than usual in this year. Therefore, the supply increased and prices dropped. However, in the two years after that the trend line of the property price were both better than the non-sponge city areas. This may be an indication of an increase of property prices, due to the sponge city mission. The study concludes by criticizing that the sponge city mission does not include financing models such as private public partnerships PPP, therefore more resources can be dedicated to improve the potential of a sponge city and their maintenance. In the last sentence the study warns that this study may not apply for different Chinese cities. As every Chinese city has a different cultural and geographic context. It is important to undertake studies in several Chinese cities (Zhang et al, 2018)
Nanjing
Liu et al (2021) uses remote sensing at a citywide level to analyze sponge city projects in the city of Nanjing, close to Shanghai, located on the Yangtze River (Xu et al, 2007) The paper looks at the case study of Nanjing. The study aims to calculate the volume capture ratio (VCR) of the urban area, by using a landuse land-cover remote sensing analysis technique (LULC) Essentially the study wants to know how much water the urban area absorbed. From 1985 to 2015 the built-up area of the city of Nanjing increased four-fold, from 11% to 44%. Currently an accurate spatial variation of VCRa (volume capture ratio of annual rainfall) over a city or urban area is lacking. Liu et al (2021) criticizes that the sponge city mission of the Chinese government uses a one-size fits all approach regarding indicators. This is more typical for grey infrastructure and does not consider climatical differences across Chinese cities. The study by Liu et al (2021) aims to help planners identify and prioritize sponge city
interventions at certain locations with the help for satellite remote sensing data
The volume capture ratio of annual rainfall (VCRa), is the percentage of water that is not directly discharged, but retained, absorbed or evaporated by the landscape. The target for the city of Nanjing by 2030 is to achieve 80% VCRa. Currently a short-duration coefficient is used to calculate this variable, however the calculation methods for different cities can vary and therefor make comparison difficult (Liu et al, 2021). The city of Nanjing is located on the Yangtze River in the eastern province of Jiangsu. This is China richest province, if city provinces are excluded. It has a disposable GDP nominal income of 13,000 USD (National Bureau of Statistics, 2014). The city is located in proximity to Shanghai. Since 2016 various Sponge city construction projects have been implemented in the city. Landsat satellite imagery was used by the paper to create a land use map of Nanjing. A transition matrix method was used to visualize the changes in quantity from the former into the latter. The Sankey Chart is used to depict the flow and relative visual components of variables Three years were taken as reference points of the history of Nanjing, 1985, 2000 and 2015. The mixed forest in the built-up area has not changed much throughout the period. Preferential development happened towards the southeast and the northwest. More than half of the surface area of the city of Nanjing matched the sponge city construction target goal, but none in the subzones The most built-up subzones in the center of the city had the worst VCRa indicators, which is expected. The data showed that the water bodies increased by 20%, however this is a false interpretation, as this may be because of a misclassification of the northwest shore of the Yangtze River. Most of the increase in urbanized area, took place on what used to be croplands. The paper by Liu et al (2021) concludes that the VCRa is a very important indicator for the sponge city mission, despite having some challenges Liu et al (2021) states the it has three advantages in the application in built-up areas. It evades the variability of urban administrative boundaries, it enables a comparison between Chinese cities and urban districts and it allows for a historical comparison (Liu et al, 2021).
Yangzhou
Zhou and Roswell (2021) conducted a qualitative survey by interviewing relevant professionals and questioning them about the viability of constructed wetlands in reducing urban flooding. The respondents supported the idea of constructed wetlands, but questioned its viability. They do curb urban flooding, but the dimension in which they are promoted seems too slightly political oriented, according to the respondents. Additionally constructed wetlands are a significant tourism magnet and are therefore important for the tourism sector The disadvantages of constructed wetlands are their need for a great amount of land area. The study by Zhou and Roswell (2021) aims at a city called Yangzhou in the Jiangsu province between Nanjing and Shanghai. 7 Local officials and researchers were selected, through snowball sampling and taking
advantage of social networks. Interviews took place in the summer of 2019 in the Chinese language for about 30min to 60min. The interviewees were specialists in the field of hydrology, ecological engineering, climatology, river and urban development, as well as officials responsible for flood management and relief. In the beginning the understanding of sponge city measures were gathered and the existing planning policies collected through their impressions. What institutional barriers and difficulties in adopting sponge city features. Five interviews were recorded and two interview were transcribed. It is interesting to see that different respondents saw the sponge city mission, through different lenses. The urban development specialist saw wetlands, not only as environment conservation, but also as an advocacy for low impact urban development and the hydrological specialist saw it attributed to the physical sponge, by holding water in a given space. Many agreed on the basic idea that sponge cites need to control 70% of the rainfall excess runoff. The necessity of sponge cities was welcomed by all interview participants, however lack of sufficient funds from the government were criticized. It was also narrated that coping with flooding events, with sources in the upstream regions was impossible solely with sponge city projects. The interviewees were very skeptical that green-roofs and rain-gardens have a significant impact of flood retention. Constructed wetlands have the potential to cleanse water and significantly improve the water quality in addition in storing rainwater and increasing absorption of water into the ground, according to the respondents. In addition, they significantly improve the biodiversity of an area. Most wetlands are built to clean or filter river water or serve an amenity purpose. Furthermore, due to its high demand of space or other financially more rewarding land-uses are preferred, such as real-estate development. The interviewees also criticized that in China sponge city projects are implemented in guidance and financing from different government agencies and ministries, in comparison to Western developed countries where many projects are coordinated under one government. Financial unsustainability was seen another concern for interviewees, as sponge city projects do not earn back revenues. One respondent said, it only benefits the larger well-being of the country. However, a user-pays model could help generate additional revenue, by making visitors pay a fee at the entrance of such a park (Zhou and Roswell, 2021)
Review of Sponge city mission in China
Yin et al (2020) did a holistic literature review of the sponge city mission planning, design and construction, as well maintenance, operations and effectiveness. It suggests that in the planning and design process localenvironmental conditions should be incorporated and contemplated. Furthermore, it is important to identify monitoring methods and hydrological models to assess the performance of sponge city projects throughout China. Not only should flood control and water quality be assessed, but also its effect on the urban heat island effect. In addition, the maintenance should be better
organized. The paper by Yin et al (2020) comes to the conclusion that sponge city projects can indeed alleviate waterlogging, thereby ensuring water safety, reduce runoff pollution and increase stormwater and rainwater reuse and absorption. The paper criticizes that there is a lack of local information on maintenance and operation, therefore a conducive review is not possible. In the last sentence the paper also suggests stronger coordination with smart city projects (Yin et al, 2020). Jiang et al (2018) complains about the lack of literature, which questions and deals with the practical management perspective of sponge city projects. The paper tries to identify to what extent the mission is an answer to Chinese cities woes with overflooding However, it is difficult to convince private stakeholders to invest, as the characteristics of sponge city projects are rather familiar to public goods. Adding to that a distrust between the private sector and the government exists. Jiang et al (2018) further criticizes the speed of execution without considering sufficient time for planning and consideration. The study explains the main cause of this to be the technocratic style of Chinese governance, which favors visible engineering execution (Jiang et al, 2018). Over the years growing evidence is been collected to prove that anthropological climate change is the main cause behind the increase pluvial and fluvial flooding hazards, particularly high-intensity short-duration rainfalls can be attributed to climate change. (Jiang et al, 2018). This can be attributed to China becoming to more prosperous society and therefore more people being able to afford more space, when previously not having enough space for maintaining privacy (Statista, 2020) (Hu, 2015). Grey infrastructure such as stormwater drainages have also suffered under poor maintenance and bad quality designs (Jiang et al, 2018).
Discussion
What do the results mean?
The results indicate a widespread consensus among academics, professionals and citizens that the sponge city mission is a good initiative and that it should be pursued further. This is noteworthy as in a country like China, large scale engineering projects have traditionally got a lot of attention (Zhai et al, 2020)
The Chinese government usually focuses on large scale engineering projects as a demonstration of power and to perpetrate power in regions not connected effectively or regions which have a history of different ideological views, such as Hong Kong, Tibet or Xinjang (Jackson and Sleigh, 2000). Furthermore, by marketing the sponge city mission as an emergence of Chinese values and traditions and relating this to traditional Chinese architecture, as seen in the Jinhua Mei Garden project by the architect firm “Turenscape” for example, all age groups and socio-economic backgrounds feel captivated by the urban planning approach. The Jinhua Mei Garden core idea was focused around the Mei flower. The Mei flower has a huge significance in Chinese culture and has been depicted seen decades. It is used in food, drinks and traditional Chinese
medicine. It is a symbol of the spring, after a long winter (Welch, 2013). The younger Chinese citiznes feel delighted to have cleaner and greener cities, which solve urban pluvial flooding and by carrying forward ancient traditions in modernity, the older generations may be allured. The lack of interest in collaborating with the private sector as seen in the study of Zhang et al (2018) can be attributed to the Chinese government general dislike of the private sector being very powerful (Livingstone, 2020). This can be seen in the example of the arrest of “Jack Ma”, a famous Chinese businessman, who disappeared from the public domain following a speech in which he criticized China”s regulators and banks. The speech took place during a Chinese financial market forum (Peach, 2021). Since then, he has disappeared and is only visible intermittently, for example on vacations. Such criticisms in the implementation of the sponge city mission can be counterproductive in a political system like Chinas. However, the strong participation of younger people in the survey conducted by Zhang et al (2018) proves that the younger generation are interested and passionate about this idea of urban planning. The younger generation might take this forward in a more enthusiastic way than the current generation. Therefore, it would be important to further analyze sponge city projects in democratic countries.
Why do the results matter?
The results collected in the city of Nanjing by Liu et al (2021) indicate that there is a serious demand for space in areas severely affected by flooding. The risk of flood has no negative effect on urbanization and the socio-cultural appeal of bigger Chinese cities. Urban space is still going to be on demand in coastal and fluvial regions throughout Asia especially in countries in south Asia or Southeast Asia, despite climate change. Emerging countries have a considerate amount of urbanization yet to take place yet (Hugo, 2019) Countries like Bangladesh, which is one of the largest floodplain regions in the world, have no high elevation areas and are entirely located on lower elevation (Rajagopal, 2020) This mean that amphibious and floating architecture could more essential in the coming years. To achieve that, floating and amphibious architecture would need to be destigmatized as extravagant architecture, as it is practiced in Asia since centuries (Putro and Zain, 2021). If throughout the history, human beings have built houses on stilts and even on water, combining it with modern technology does not seem imprudent Many respondents had a minimum of an undergraduate university degree in the Zhang et al study (2018) which may make the study inaccurate unless the city of Wuhan has a large population of people with minimum of a bachelor’s degree. The interest of citizens in improving urban public space, increasing greenery and thereby quality of life, shows the desire of urban residents to increase proximity to natural landscapes. The research in this multi-disciplinary field, there can be therefore intensified. Urban landscapes should try to emulate natural ecosystems and their material
cycles. Combining the sponge city project with water management is crucial, as well as with waste management.
What practical actions should follow?
Pilot project should be undertaken and initiated by the government or private construction and architecture firms, to gather more data on this typology of architecture. The data could improve the construction of such architecture and increase safety and security. Suitable locations can be identified with further studies on water bodies to help the expansion of such initiatives. Water bodies require a stable water level to make a residence more pleasant and avoid disturbance by wind-driven waves. Furthermore, studies should also be taken forward to analyze the environmental impact and if they outweigh the benefits. Concept of sponge city and amphibious/floating architecture should be combined for severely affected regions. Countries which lie predominantly in floodplains may need technologies, which can help them adapt to changing climates (Adetunji, 2019). In these areas reforestation and amphibious and floating architecture can be a viable solution against loss of land. Land can be utilized and financially productive through controlled environment agriculture rather than the conventional agriculture, which is also aesthetically less appealing and hazardous for residents
Conclusion
What is noteworthy about the paradigm of nature-based solutions and associated with it the sponge city concept, is that it is not seen simply as a solution to an existing problem, but an overall enhancer of urban and human life. More and more human beings are moving into urban areas and do not want to sacrifice their quality of life experienced in rural landscapes (Sher et al, 2018) In fact, many estimate that then current estimation of urban residents is an underestimation, due to inaccuracies in emerging countries. The informality of residents and urban dwellers, as well an inaccurate data comparison and regions classification underestimates the number of the urban population. In India for example many urban areas are classified as rural areas, due to political reasons. Having the classification of an urban area gives the local government more power than the state or central government, therefore politicians aspire to not classify densely populated urban neighborhoods as urban areas. Furthermore, the threshold for a settlement to be called an urban area is different in every country. It is estimated according to independent studies that 50% of the Indian population live in cities with a population of more than 5,000 inhabitants. The Indian government however states the urban population to lie around 30% (Onda et al, 2019)
The value as inhibitors of urban flooding is in fact given lesser recognition by Chinese resident in the city of Wuhan for example. The findings of the study done by Zhang et al (2018) indicate that urban designers, landscape architects, architects and planner can make use of these multifunctional benefits to market
sponge city projects. Sponge city projects can be better financed if they incorporate a variety of benefits to citizens. Financing sources could then attract private stakeholders, this may be citizens, companies or societies. PPP private public partnership could be very promising according to the findings by Zhang et al (2018). Throughout the history urban life always offered more jobs opportunities and societal perspectives, such as better gender roles (Bricker and Ibbitson, 2019) However, cities were rarely an enjoyable residence to live for all residents universally over the last centuries (Harvey, 2016) Rural life always offered the charm of better air quality and better aesthetics values, which benefited mental and physical health (Baumann, 2018) (Bilde, 2004) Rural life never offered the same amount of employment, diversity and alternative societal lifestyles. Individuals who did not succumb to gender roles or patriarchal values were sidelined. To overcome this urban life was desired, however the quality of life had to be sacrificed, especially for lower-income groups (Yamagishi et al, 2012). In the 21st century this contradiction may be diminished for the first time. For the first time cities are achieving good air quality levels, including cities in China (Lo, 2022). A study undertaken in Switzerland even proved that biodiversity can be higher in urban areas, than in rural areas. However, this is due to agricultural practices, which are environmentally hazardous (University of Berlin, 2015). Urban settlements should try to emulate the natural environment and ecological cycles Rather than simply exploiting natural resources it could create resources for itself, in the form rainwater harvesting of water recycling and cleansing of greywater. The sponge city concept can also be further adapted to rural areas and agricultural landscape to really enhance its effectiveness. As mentioned by a respondent in the city of Yangzhou, urban flooding can only be curbed by undertaking changes at its water catchment sources. The sponge city concept could help agricultural patterns to be more biodiverse and aesthetically appealing too, in the same way it’s being attempted in urban areas. Furthermore, technology and artificial intelligence could assist rural areas in maintaining polyculture agricultural landscapes, which were maybe financially unviable before due to increased labor costs. Aquaponics, aeroponics and generally so-called controlled environment agriculture could improve the biodiversity in rural areas and in cities (Benke and Tomkins, 2017) (Shamshiri et al, 2018).
Research limitations
One of the limitations of this research is the unavailability of Chinese language literature. As I cannot speak or read the Chinese language, furthermore a lot Chinese government data is inaccessible if you’re outside of China or if you’re part of the general public of China. A large part of the literature regarding sponge city missions in China is in Chinese, these literature documents are inaccessible for non-Chinese speakers. Related sponge city projects in other
countries, which are termed under other names were not analyzed in this thesis and are therefore the results are limited to one national and cultural context. The implementation of sponge city projects in democratic societies would have given a more holistic insight into the style, way and motivation for implementation. Furthermore, the aspect of public opinion and public participation could have been researched more thoroughly. Furthermore, because China not being a democratic country, many issues may have not been addressed in interviews (Bell, 2016) The sponge city mission serves as a generally positive role model for other countries to imitate. The results are largely positive. Spillover effects are also visible, in fact more than the inhibition effect on flood risk. The ambition, speed and state-of-the-art designs inspire urban designers around the world to think differently. However, democratic countries may have to look at other role models for implementing sponge city projects, for it to be politically successful.
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