Thesis Booklet Chinwen

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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


3/26

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

4


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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.

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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

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