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M.Arch Thesis
Urban Flooding Typology
Ao Chin Wen
Prof. Alstan Jakubiec
2016 June
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M.Arch Thesis
Urban Flooding Typology
Ao Chin Wen
Prof. Alstan Jakubiec
2016 June
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Content
Geography of Taipei
Introduction
Case Study
Cause of FloodUrban Development
Site Proposal
Design Criteria & Opportunity
Current Flood Prevention
1
5
3
2
6
7
8
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Source: Taiwan Climate Change Projection and Information Platform
Typhoon Time Distribution Graph
Source: Central Weather Bureau
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 thatthere will be a drought that persist till the
following summer, as the existing dams are
unable to cope with the locals demands.
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)
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.
Exploring on the opportunities that allow
us to provide an alternative perspective
on the relationship between people
and typhoon through architecture.
Rainfall Distribution Graph
JAN
FAB
MAR
APR
MAY
JUNJUL
AUG
SEP
OCT
NOV
DEC
Introduction1
8 9Introduction
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Located at the northern part of Taiwan,Taipei
is a highly urbanized and global city. SinceJapan 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 financial 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 Plateau-
altitude 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 flat 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.
There is one main water outlet in Taipei, TamSui
River, which then splits into 3 sub river-Xindian
Creek, Dahan Creek, and Keelung River.
Outline of Taipei City
Tamsui River and Branches
Geography of Taipei2
10 11Geography of Taipei
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1312Geography of Taipei
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SOURCE: http://pansci.asia/archives/55515
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.
According to a study on
Taipeis impervious surfaces,
buildings such as residential,
business, industrial,school,
government agencies and
public amenities, the average
percentage of impervious
surface is 82%, while the most
abundant residential typology
having 88% impervious
s u r f a c e s . (
The impact of flooding goes
beyond disruption of traffi c,
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.
Xue shan Mountain Range Taipei City DamSui River
4000 BC
?? ~ 1683
1683
1895
Accumulation of
sediments causeswater capacity forthe river to reduce,
causes overflow
Dense urban
developmentincreasesimpervious
surface onflat land and
mountain.
Current
Causes of Flood4
1716Causes of Flood
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Current Taipei City Development
Within Taipei urban zone,
the amount of impervious
surface can be estimated by
multiplying the percentage
of impervious surface for
each building typology
( res iden t ia l , commerc ia l ,
industrial,public amenities and
parks) and multiply by the area
dedicated to each typology.
Using a study done on Taipeis
impervious surfaces (more than 64.7% of the areaare 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 HaIndustrial: 411.5 Ha
Public Buildings: 7341.85 Ha
Park: 140 Ha
(Ministry of Interior Taiwan,2014)
1918Causes of Flood
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Corrugated metal roofing
Ceramic tile facade
Typical Taiwan Apartment Buildings
Typical Taipei Residential Alleyways
No presence
of plants along
roads
Asphalt
20 21Causes of Flood
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Source:http://www.worldcitiescultureforum.com/data Major Public Green Space in Taipei23
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Taipei citys 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 aswell. Residential buildings ,car
parks and roads increases
the percentage of impervious
surfaces that were once forests.
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.
2524Causes of Flood
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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.
27uSource: T:: Taiwaii an Climatte ChangeProP jece tioi n annd InInfII ormatiatat on Platfoorrm Taipei Flood Prediction-200 Year Return Period 650mm Precipitation
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Two main strategies that
Taipei government employed
are 1)flood wall 2) 90%
coverage drainage system,
which include rain water
drains and pump stations.
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 disconnectsthe 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.
River Side
City Side
Source:
Dadaocheng Flood Gate
Current Strategy5
28 29Current Strategy
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The red dashed lines
indicates the extent of the
flood wall for Taipei city. It
has basically surrounded
the entire city, disconnecting
the urban area with river.
Besides blocking the river from
flowing into the city, it also
means that water within the
city has to rely completely on
pumps and drainage system
since the water is basicallytrapped within the wall.
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
suffi cient when the total ra in
volume exceeds the capacity
of water retention storage.
3130Current Strategies
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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 citizens daily life.
The current strategies such as flood wallalong theriver, and continual upgrade of drainage systemcould
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 typologythat
could mitigate floodingin Taipei while re-kindle the
relationshipthat Taipei City once had with water, with
a secondary function as public spacewhen the primary
function of water retention is not needed.
33
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Case StudiesBenthemplein Water Square
6
Source:
Benthemplein Water Square
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 theimpact of urban rain run off.
3534Case Studies
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SHOP
GARDEN
DOUBLE-BENCH
MEDIASEATING-SHELTER
BIKE-POINT
SINGLE-BENCHSLIDE SKATE
uuurcerrcerce: R: R:::::::::::: ebuebui d y eeesisiiii
Various functions that can e attached to the wall
Case StudiesThe BIG U
6
Source: Rebuild By Design
The BIG U
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 providesthe citizen an opportunity to
connect with the water scape.
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
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.
3736The Big U
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Design Criteria & Opportunity7
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 therole 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 ateach 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 90s, 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 Singapores 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 majorhighway that run along the river, worsen the connection between the two. The traffi c 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.
Zhong Shan District600mm rain fall flood zone (0.5m, 1m, 3m and above)
38 39Flooding Simulation
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Site Proposal8
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 districts rain runoff.
Being one of the early district that undergoes urban development
when Taiwan government just started, the site is occupied by manyold 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.
4140Site Proposal
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Mountain
River
Urban
Diverse Terrain in the Zhong Shan District
4342Zhong Shan Districts Terrain
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Population (thousands) Taipei Population Trend Prediction
Source: National Development Council
ource: National Development Council
Residential Housing Distribution
4544Compact Housing Development
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7.4 sqm/capita
Zhong Shan
District
Singapore
66 sqm/capita
Green Space Distribution
Source: Top: Department of Budge, Accounting & Statistics, Taipei Government,2016 Bottom:Siemens and economist intelligence unit, 2011
4746Lack of Green Space
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Limited Access to River Scape
Highway along the river
Flood wall between city and river
4948Disconnected River & City
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Whiteman, C. David (2000). Mountain Meteorology: Fundamentals and Applications. Oxford University Press.
A study on urban water cycle- the investigation on the percentage of imperviousness and the experimental analysis of surface runoff -2002,
References
5150
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Case StudiesCheonggyecheon River Restoration
6
5352Geography of Taipei