M.Arch Thesis Urban Flooding Typology
Ao Chin Wen Prof. Alstan Jakubiec 2016 June
M.Arch Thesis Urban Flooding Typology
Ao Chin Wen Prof. Alstan Jakubiec 2016 June
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Introduction Geography of Taipei Urban Development Cause of Flood Current Flood Prevention Case Study Design Criteria & Opportunity Site Proposal
Typhoon Time Distribution Graph
Source: Taiwan Climate Change Projection and Information Platform
Introduction
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1 Introduction DEC
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Rainfall Distribution Graph Source: Central Weather Bureau
This thesis aims to tackle the issue of flooding in the urban region of Taipei, through thorough investigation of the causes of flood, current strategies employed by the Taipei government and the future urban development of Taipei city. From there, it will be used to guide the development of an integrative solution that is aimed to improve the living quality of Taipei city in the event of a typhoon.
Due to typhoon, Taiwan has an extremely uneven distribution of rain fall across the year. During summer, rain fall depth can reach up to 400mm(Typhoon Herbe, 1996), with 4 to 5 typhoon visiting Taiwan per year, accounting for 63% of annual rainfall, while during winter, there can be little to no rain fall at all. Despite that, typhoon still plays an important role in Taiwan as it contributes to the local water supply. As Taiwan lacks huge reservoirs, she is reliant on the typhoon to replenish the water supply in the local dams. This means that in the absence of typhoon, there is a risk that there will be a drought that persist till the following summer, as the existing dams are unable to cope with the locals’ demands.
Exploring on the opportunities that allow us to provide an alternative perspective on the relationship between people and typhoon through architecture.
Being a highly urbanized city, Taipei has suffered huge losses due to typhoon. According to a report by March Insurance Agency for Taiwan Water Resource Agency, the potential loss for a flood occurrence with a 200 year return period could amount to 7.5 billion NTD of insurance compensation, with more than 60,000 units being affected.(2005 Marsh) 9
Geography of Taipei
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2 Geography of Taipei
Outline of Taipei City
Located at the northern part of Taiwan,Taipei is a highly urbanized and global city. Since Japan occupation, by placing administration HQ here in Taipei,the city has become the capital of Taiwan. Over the years, the city continues to gain importance as a major ďŹ nancial center in Asia, and currently has the highest population density (2.7 million in 271.7997 sqkm, 9,950people/ sqkm, 2016) among Taiwan cities. Surrounded by 3 main mountain ranges-Datun Volcano group-altitude 1120m,Linkou Plateaualtitude 400m,Xueshan Range-altitude 3492m, Taipei is located within the Taipei Basin, which compromises of Taipei City and New Taipei City, in which 243 sqkm of at land to be 20m below sea level. These mountain ranges could produce a phenomenon called rain shadow, where the warm air is lifted upwards due to orographic lifting, the decreased pressure and expanded air is cooled to a point of adiabatic dew point, causing rainfall on the windward side of the mountain.(Whiteman, 2000)Although Taipei is on the leeward side, most typhoon has alot more moisture content then a typical warm moist air, thus, rainfall would instead land on the leeward side of the mountain as well, and collected at Taipei Basin.
Tamsui River and Branches
There is one main water outlet in Taipei, TamSui River, which then splits into 3 sub river-Xindian Creek, Dahan Creek, and Keelung River.
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Geography of Taipei
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Source: http://tmap.geospatial.org.tw/
Urban Development
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3 Urban Development
1921
Photo of Early Da Dao Cheng Source: http://www.dili360.com/ch/article/p54128e64a576737.htm
As Taipei become the capital of Taiwan, during the Japanese occupation, rapid urban development was carried out to respond to the population growth and intensification of Taipei City.
1956
1993
However, this development has also destroyed the original landscape of Taipei Basin. During Qing Dynasty, Taipei’s economic rely heavily on DanSui River and is one of the 3 major port cities in Taiwan (一府二鹿三艋舺) where the residences used to fight over control over the port region at Meng Jia and Da Dao Cheng. From the historical maps, we can see how Taipei City starts to expand inland. Due to ill maintenance of the upstream river, sediments accumulated at the port region, rendered it dysfunctional as a river for transportation, and reduced the water capacity of
the river. （温、戴 ，1999）The rise of onland transportation such as railway and cars also causes the reduced need of water transport. Even though Taipei city manages to transform itself from a port for goods export to a service orientated industry, the rapid development comes at a cost. The rapid urbanization and influx of population into the city causes a great demand for housing, that are cheap and reliable. In respond, concrete cast building filled the earlier housing development of Taipei city, reducing public green space to 5.6%(Taipei Parks and Street Lights Office,2016), narrow alley allows a super compact and high dense residential development. Wetlands or forests are converted into roads and buildings, greatly affecting the water retention value of flat lands in Taipei city.
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Xue shan Mountain Range
Causes of Flood
Taipei City
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DamSui River
4 Causes of Flood 4000 BC
?? ~ 1683
SOURCE: http://pansci.asia/archives/55515
1683
1895 Accumulation of sediments causes water capacity for the river to reduce, causes overflow
Current Dense urban development increases impervious surface on flat land and mountain.
The 3 main causes of flooding in Taipei city are 1) low altitude terrain, surrounded by mountain ranges 2) high percentage of impervious surfaces in the developed region 3) low water retention potential for shallow river streams, causing river overflow. The cause of flood relate closely to the development of the city. From the diagram on the right, it indicates the shift in industry and the center of the city, while the development alters the environment of Taipei city, making it susceptible to flooding.
government agencies and public amenities, the average percentage of impervious surface is 82%, while the most abundant residential typology having 88% impervious surfaces.(林,2002) The impact of flooding goes beyond disruption of traffic, city functions and damages to property. The flood could transmit diseases, causes mosquitoes outbreak, contamination of water supply, hygiene issues in the city, land slide, power outage.
According to a study on Taipei’s impervious surfaces, buildings such as residential, business, industrial,school, 17
Within Taipei urban zone, the amount of impervious surface can be estimated by multiplying the percentage of impervious surface for each building typology (residential,commercial, industrial,public amenities and parks) and multiply by the area dedicated to each typology.
Using a study done on Taipei’s impervious surfaces (林,2002) ,more than 64.7% of the area are impervious surfaces. For 600mm of rainfall, impervious surface would result in 594mm/ m2 of runoff volume. Multiply by the total urban area,129.96km2, the runoff volume would be nearly 50 million liter.
Residential: 3800 Ha Commercial: 880 Ha Industrial: 411.5 Ha Public Buildings: 7341.85 Ha Park: 140 Ha (Ministry of Interior Taiwan,2014)
Causes of Flood
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Current Taipei City Development
Causes of Flood
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Corrugated metal rooďŹ ng
Ceramic tile facade
No presence of plants along roads
Asphalt Typical Taiwan Apartment Buildings
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Typical Taipei Residential Alleyways
Source:http://www.worldcitiescultureforum.com/data
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Major Public Green Space in Taipei
Taipei city’s terrain causes rain water to accumulate, while collecting rain runoff from the mountain ranges. With more mountain surface area facing the city (187.4 sqkm, outlined in red) than the flat area of the city(129.96 sqkm), there is a significant amount of rain water that enters the city. The development on the mountain does not help with water retention on the mountain as well. Residential buildings ,car parks and roads increases the percentage of impervious surfaces that were once forests.
Causes of Flood
With an average slope of around 30%, the mountain of Taipei mountain consist of mainly woods cover with hydrology group C soil (CN=73), we can estimate the rain runoff volume using the equation: Q=(P-I)2/(P-I+S) Q=precipitation(inch) P=rainfall(inch) S=potential maximum soil moisture(inch) I=initial amount of water (inch) Under 600mm/m2 rain fall, the runoff volume would be 518mm/m2, with a total volume of 97 million liter.
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With the influence of both urban and mountain rain run off, this graph shows the flooding simulation of a 200 year return period, rain fall amount of 600mm. Most of the urban region are flooded, where only regions beside the mountain are excluded.
Source Sou rce ce e: Taiw a an Climat a e Chan at ange an ge Pro Projec jec ectio t n and tio and Inf Inform ormati orm at on Pla ati atfo tform rm
Taipei 27 Flood Prediction-200 Year Return Period 650mm Precipitation
Current Strategy
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5 Current Strategy
River Side
Dadaocheng Flood Gate Source:
Two main strategies that Taipei government employed are 1)flood wall 2) 90% coverage drainage system, which include rain water drains and pump stations.
City Side
One of the most common strategies against flooding, would be to include a larger flood zone besides the river. However, due to rapid development of the city, the river bank is already saturated with buildings, hence the flood zone is unable to be broadened, resulting in a variation of river width from 400m to 150m. The narrow part of the river is susceptible to flooding when a sudden increase of water volume occur on the upstream. To counter this, flood walls
been erected around Taipei city in 1960s. Flood wall and flood gates up to 9.2m are installed along Dan Sui River and its branch, to prevent water overflow from the river into the city. Flood walls are an effective and cost effective measure to stops river from flowing into the city. However, it takes huge amount of maintenance fee each year to repair the wall, while it also disconnects the river scene with the urban living environment. The tall flood wall blocks the visual connection and impedes citizens from accessing the river that were once so important to the aboriginals and early immigrants in Taipei.
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The red dashed lines indicates the extent of the ood wall for Taipei city. It has basically surrounded the entire city, disconnecting the urban area with river. Besides blocking the river from owing into the city, it also means that water within the city has to rely completely on pumps and drainage system since the water is basically trapped within the wall.
Current Strategies
The water from the pump stations are then drained out to the river and various dams. However, during high tide or when the river itself is taking lots of rain water, and dams themselves will also be full due to the heavy rain fall, such system will not be suďŹƒcient when the total rain volume exceeds the capacity of water retention storage.
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Thesis Statement Due to the low-laying terrain of Taipei basin,frequent occurrences of typhoon and rapid urban development, Taipei city is susceptible to floods, causing significant loss to the city and disruption to citizen’s daily life. The current strategies such as flood wall along the river, and continual upgrade of drainage system could mitigate the flood issue temporarily, but it also detaches the society from the water resources. Through investigating the cause of flooding in Taipei city, this thesis propose a new residential typology that could mitigate flooding in Taipei while re-kindle the relationship that Taipei City once had with water, with a secondary function as public space when the primary function of water retention is not needed.
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Case Studies
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6 Case Studies
Benthemplein Water Square
Benthemplein Water Square Source:
Solutions to tackle flooding can be ranges from retaining, delaying, re-directing to rejecting water. In order to combat the flooding issue in Taipei, all 4 strategies should be deployed as the there is a wide range of scenarios, such as mountain side, urban run off, river over flow etc. These case studies would offer insights to strategies that can be deployed at various scale and scenarios. Situated at Rotterdam, Netherlands, Benthemplein water square is a unique public space that had the intention of flooding in mind. By combining water retention device with a recreational space, the outdoor sport facility will be used as per normal during non rainy days, during rain, it became a water retention device and a pool.
Such infrastructure is useful in places where there is a clear distinction between rainy seasons and dry seasons. Incorporating a secondary function to the retention facility could prevent under utilization during dry seasons. Most of the public spaces in Taipei are made of flat concrete floors, where the impervious surface does not help with the infiltration of water, and the public space contributes to the impact of urban rain run off.
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DOUBLE-BENCH
SHOP
GARDEN
SEATING-SHELTER
SLIDE
SINGLE-BENCH
BIKE-POINT
MEDIA
SKATE Various functions that can e attached to the wall
The Big U
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Sou So S o ource r e: e: Rebu uild ild ld By By Desig Desig De sig si ig n
6 Case Studies The BIG U
The BIG U Source: Rebuild By Design
This proposal by BIG for Rebuild by Design proposes a infrastructure installation along the shore of Manhattan island to prevent the water from flooding into the city. This design combined various functions to be incorporated with the flood wall. Recreational space, shops, sport facility or sitting area etc. This combination allow the flood wall to be utilized out of the rainy season or high tide scenario, and also provides the citizen an opportunity to connect with the water scape.
of Taipei city. However, I believe that the design should instead incorporate this periodic surge of water. Systems that hide away the presence of water will only further enhance the negative attitude towards typhoon.
Comparing with the current design strategies in Taipei City, the system that BIG proposed does not disconnect the water resource with the city itself. Both flood wall and drainage systems in Taipei focuses on making water disappear from the everyday life 37
Zhong Shan District600mm rain fall ood zone (0.5m, 1m, 3m and above)
Flooding Simulation
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Design Criteria & Opportunity
Dual Functions-Due to the uneven distribution of typhoon occurrences throughout the year, the design has to have multiple functions that can be activated during dry and rainy seasons. Integration-To fully utilize the impact of typhoon, there is a need for a thorough integration between living space and flood prevention strategies. To increase the amount of surfaces and volumes in which can retain water and reduces run off, design at multiple scales, individual apartments, buildings, blocks and urban planning, should be considered. This would also help in changing the role of typhoon in the daily life of Taipei city. Environmental Sensitivity-However, there is a need to also take into consideration on the issue of mosquito infestation that might result from the water retention design. ----------------------------------------------------------------------------------------------------------------------------------Reduction in population-As Taipei City development starts to mature, we are expecting a declination in the population. The need for cheap and dense housing is no longer a priority for Taipei citizens, but should place more priorities on improving the living quality such as public space, green spaces etc. Old and ill maintained housing-Although the old housing development has cultivated a culture that many Taipei citizens could identify with, narrow alley ways, family shops and restaurants at each corner of the blocks. Zhong Shan District is also saturated with residential housings that are in need of new development. More than 57% of the buildings are over 30 years old (Department of Urban Development, Taipei Government, April 2016), ill maintained building elements, with the lack of amenities such as lift or public spaces. Shift in housing needs-As the family structure evolves over time, the need for the size of a housing unit changes as well. Compared to the early 90’s, the major demand shifted from 3 to 4 room unit to 1 to 2 room unit. This could also be related to the shift in the age of house owners in general. Lack of green space-Compared to Singapore’s 66sqm/capita, Zhong Shan District is only 7.4sqm/ capita. The green spaces are sparsely located, some units are not near any green spaces. There is a strong need for the improvement of living quality and to improve urban rain run off. Access to river scape-Besides the flood wall that isolates the city with the river, there is also major highway that run along the river, worsen the connection between the two. The traffic network is placed along the river as the urban region is unable to accommodate such major infrastructure due to the high dense development in the earlier era. The proposal should address the connectivity issue of the residents with the river.
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Site Proposal
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Site Proposal
From the research done on causes of flood, urban rain run off and mountain runoff are equally important factors that contributes to flooding, with a volume of 50 million liter and 90 million liter respectively. Hence this proposal would focus on how architecturally mitigate flooding issue on both types of terrain, while ensuring the connectivity between the river and urban built environment is not lost. The proposed intervention will be focusing on the Zhong Shan District. This district is expected to have the worst flooding occurrences in the event of a 600mm rain fall. With the amount of flooding occured, we can expect it to be contributed from neighbouring district’s rain runoff. Being one of the early district that undergoes urban development when Taiwan government just started, the site is occupied by many old houses made up of either bricks or concrete with plenty of impervious surfaces. Zhong Shan District also span across various hydrology condition, urban, river side and mountain slope. With such a diverse landscape, a new residential typology that can responds to various conditions can be explored within this district.
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Diverse Terrain in the Zhong Shan District
Zhong Shan District’s Terrain
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Mountain
River
Urban
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Residential Housing Distribution
Compact Housing Development
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Source: National Development p Council
Population (thousands)
Taipei Population Trend Prediction
Source: National Development p Council
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Green Space Distribution
Lack of Green Space
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Zhong Shan District 7.4 sqm/capita
Singapore
66 sqm/capita
Source: Top: Department of Budge, Accounting & Statistics, Taipei Government,2016 Bottom:Siemens and economist intelligence unit, 2011
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Limited Access to River Scape
Disconnected River & City
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Highway along the river
Flood wall between city and river
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References A study on urban water cycle- the investigation on the percentage of imperviousness and the experimental analysis of surface runoff -2002, 林子平 Whiteman, C. David (2000). Mountain Meteorology: Fundamentals and Applications. Oxford University Press. 颱風洪水風險評估,美商达信保险,2005 温振華、戴寶村，《淡水河流域變遷史》，1999
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