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Civil Engineering, National Taiwan University, Case Study.
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土木工程概念設計
Conceptual Design Studio
│員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│ 1
Yuan-San-Tsu Flood Division Tunnel
ainstream Keelung River runs 84.6 kilometers, it originates
from Mount. Jintong of Pinxi District in New Taipei City, and
is one of the main branches of the Tamsui River. Keelung River
runs through Ruifang, Qidu, Nangang, Xizhi, into Taipei City and
finally merges with Tamsui River in Guandu. There are three
major branches to Tamsui River: Xindian River, Dahang River, and
Keelung River. When Keelung River enters into the Taipei basin,
the river way curves and winds causing inadequate discharges.
During the raining season when there is ample perspiration, cities
along the river banks such as Xizhi and Wudu suffer from severe
flooding problems and people complain about it. In the previous
years, we could still see on the TV news the flooding footage in
Xizhi and Wudu. Although the government adopted the cutting the
bends of the river to improve the Keelung river flooding problem,
the original natural river way is now occupied by houses. During
the high-water season, storm water and river were left with no path
to discharge. Water overflowed into the housing areas, leaving
people along the river banks again suffer from the flooding problem.
Typhoon Nari in 2001 turned northern Taiwan into water world,
and both banks of the Keelung River suffered heavy blow from the
flood. People voiced out to the government, demanding the
government to face the flooding problem along the Keelung River.
The lashing from the public stressed the urgency of the improvement
work of the Keelung River. The government also sensed people’s
demand to never suffer from the flood, and began proactively
M 1、 Introduction
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promote the Keelung River Improvement Project. In 2002, Yuan
San Tzu Flood Division Tunnel was approved for construction.
The idea of Yuan San Tzu flood division tunnel was to diverse the
flood water using a tunnel to contour the over flowing water to the
East Sea outside of Ruifang. This measure would prevent the flood
water from overflowing into the residential area.
The concept of Yuan Shan Tzu flood division tunnel was
initiated in the 70s; however, the planned tunnel crossed three fault
zone and the geological criteria were inadequate for the construction.
In addition, there was also concern that the massive amount of fresh
water being poured into the sea would impact the coastal ecology.
The government thus was reluctant in approving the construction.
The ample perspiration brought by typhoons was the unceasing
nightmares to the people that lived along the Keelung River before
the improvement construction. After accessing the public need and
the maturity of the tunnel construction technology, the government
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Photo 1. Keelung river field of recent years.
(Source : Water Resources Agency, Ministry of Economic Affairs.)
finally decided to begin with this improvement idea that existed for
over a decade. Yuan San Tzu flood division tunnel was finished in
2004 and it was a successful case of water treatment. With Yuan
Shan Tzu flood division tunnel, the people in Xizhi, Wudu ,and other
cities along the Keelung River were no longer the victims of flood.
The successful water treatment case brought fame to the Yuan
Shan Tzu flood division tunnel and made it the role model for the
future flood division constructions. However, there were great
many hardships and trouble solving wisdom behind this construction.
There are also issues raised by this construction that await better
methods in the future to solve and tackle.
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│員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│ 4
The main intake construction site of the Yuan Shan Flood
Division Tunnel situated in the RuiGan New Village of RuiFang
Township in Keelung County. The key categories of the
construction included: flood division tunnel, flood division weir,
stilling basin, side weir, and barrage weir. Each structure has its
own purpose and function in design. In photo 2, you can see the
location of each structure. We will introduce the main design and
function of each structure in the following.
Typhoon
(year)
Lynn
(1987)
Reib
(1998)
Babs
(1998)
Xangsane
(2000)
Nari
(2001)
Flood Area
(hectare)
3,332 345 338 771 4,806
Flood Depth
(meter)
0.2 - 7.5 0.2 – 7.5 0.5 – 3.8 0.5 – 7.5 0.3 – 8.5
Death
(person)
32 0 0 59 104
Damage Before the treatment project, there were already 195
lives taken in the recent few years; the lost of property
reached over hundreds of billion dollars.
2、 Yuan Shan Flood Division Tunnel Structure Introduction
Chart 1. Statistics of Keelung River Typhoon Flood Water.
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Photo 2. Intake of the Yuan Shan Flood Division Tunnel.
(Image taken from : Water Conservation Quarterly, volume 48)
2.1 Intake Structure Introduction
2.1.1 Barrage Weir
(1). Structure: concrete gravity wide weir, 8 meters high, 30 meters
long, top of the weir marked 68 meters high.
(2). Function: 3 comb type check dams built in the upstream to block
huge rocks and drift woods from floating to downstream.
2.1.2 Sediment Releasing Tunnel
(1). Structure: concrete gravity broad crested weir, 9 meter in height;
weir top length 20 meters and marked 69 meters high.
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Photo 4. Elevation of the Barrage Weir, flood division tunnel is on the
left, and the sediment releasing tunnel is on the right.
(Source : Water Resources Agency, Ministry of Economic Affairs.)
(2). Function: releasing the stilling basin sediment to Keelung river
downstream, as well as ensuring the ecology of the downstream and
preventing the sediment from over depositing in the stilling pool.
Photo 3. Upper left and right: barrage weir; bottom left is a corner of
the downstream; bottom right is the sediment releasing tunnel.
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2.1.3 Side Weir
(1). Structure: concrete gravity weir with flat crest, 2.5 meters in
height, 184meters in length, top of the weir marked 62.5
meters high, free overflow, connecting to the flood division
stilling pool.
(2). Function: separating Keelung River and the stilling basin.
When Keelung River waterline exceeds 62.5 meters, water
would flow over the side weir and enter the stilling pool.
2.1.4 Flood Division Stilling pool
(1). Structure: bottom of the pond marked 60 meters in depth.
Two sediment tunnel gates were set at the river way that led to
the downstream of Keelung River. Flood division weir was
built at the entrance that connected to the flood division tunnel
(2). Function: main function is for sediment deposit to prevent
sediment from being flushed into the tunnel and blocking the
tunnel. When the water level of the stilling pool exceeds 63
meters, the water will overflow the flood division weir and
enter the flood division tunnel.
(3). Maintenance: stilling pool deposit massive amount of
sediment, the sediment tunnel often opens for discharge.
There will also be one desilting on the stilling pool each year
in order for the stilling pool to function normally.
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Photo 5. Upper left and right: side weir; bottom left and right,
stilling pool.
2.1.5 Flood Division Weir
(1). Structure: curved ogee weir, 3 meters in height, weir top
length is 80 meters with the height marked as 63 meters.
Middle section of the weir body on the upstream has a 7 meter
high division block, using free flowing method to connect to
the contraction section.
(2). Function: separating the contraction section between stilling
pool and intake, when the water line of the stilling pool
exceeds 63 meters, the flood water will overflow the flood
division weir and enter into the flood division tunnel naturally.
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Photo 6. Left : flood division weir. Right : water level marking of
the stilling pool.
2.1.6 Contraction Section and Transition Section at the Entrance
(1). Structure: open channel, bottom elevation descents by a fixed
10% slope starting from 60 meters high, and connects to the
flood division tunnel entrance.
(2). Function: improve the tunnel entrance flow. The sophisticated
design allows the water to speed up and carries the sediment
away swiftly without blocking the tunnel.
Photo 7. Contraction and transition section at the entrance.
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2.1.7 Flood Division Tunnel
(1). Structure: tunnel standard section is round hollow section,
internal diameter 12 meters, total length 2,484 meters, grade
1/100.
(2). Intake: RuiGan New Village of RuiFang Township in Keelung
County.
(3). Outtake: Provincial Highway 2 (Taiwan), coastal highway.
(4). Tunnel 1: 1,160 long, grade 1/100.
(5). Giufeng River Crossing Section: 33 meters long, grade 1/100.
(6). Tunnel 2: 1,290.5 meters long, grade 1/100.
(7). Function: automatically diverse the flood water that naturally
overflow the flood division weir into the sea outside of Ruifang
for discharge.
2.2 Outlet Structure Introduction
2.2.1 Outlet Transition Section and Chute
(1). Structure: dicth, transition section bottom elevation descends at
1% slope, chute bottom grade at 1:1, inner net width transits
from 12 meters to 35 meters.
(2). Function: improve water flow at the tunnel exit.
Photo 8. Left : tunnel intake; right : tunnel intake model.
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Photo 9. Left : tunnel outlet transition section model; right : tunnel
outlet stilling basin.
Photo 10. Construction process of the Yuan Shan Tzu Flood Division
Tunnel Outlet
2.2.2 Outlet Stilling Basin
(1). Structure: close conduit and open channel, inner net width 35
meters, net height 20.8 meters; elevation of the bottom marks
-6 meters, end sill elevation 4 meters, normally maintains 10
meters pool for energy dissipation.
(2). Function: stilling basin dissipates massive flood energy before
flood water is discharged into the East Sea, preventing coastal
erosion that might damage the ecology and the view.
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Photo 11. Yuan Shan Tzu Flood Division Tunnel Outlet, at the
Provincial Highway 2 (Taiwan), the coastal highway.
(Source : Water Resources Agency of the Ministry of Economic
Affairs.)
2.3 Sediment Tunnel Gate Regulations
2.3.1 Regular Operation: when the water level at the upstream
of the barrage weir is below 63 meters, the gate will remain
opened at all times.
2.3.2 Flood Division Operation: when the water level at the
barrage weir rises over 63 meters, the sediment tunnel gate
will be closed until the flood water subsided and the water
level is blow 62.5 meters. The sediment releasing gate will
be opened again, resuming regular operation status, of
which the gate will remain opened at all times.
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2.4 Alert Policy
According to the operation regulation of the Keelung River Yuan
Shan Tzu Flood Tunnel Division, currently there are three types of
alerts :
2.4.1 Pre Flood Division Alert: when the barrage weir upstream
water level reaches 62.5 meters, alert the Tamsui River Flood
Prevention Command Center, and the Command Center will
post the warning along with the Tamsui River flood alert.
Control Center uses intake and outlet broadcasting stations to
distribute the flood division alert, and notifies the New Taipei
City Emergency Management Center at the same time.
2.4.2 Flood Division Alert: when the barrage weir upstream water
level reaches 63 meters, the flood division is commenced.
The Control Center notifies the Tamsui River Flood
Prevention Command Center, and the Command Center will
issue the warning together with the Tamsui River flood alert.
Control Center uses intake and outlet broadcasting stations to
distribute the flood division alert, and notifies the New Taipei
City Emergency Management Center at the same time.
2.4.3 Emergency Alert: when the barrage weir upstream water
level exceeds 67.2 meters and the tunnel is filled, the Control
Center notifies the Tamsui River Flood Prevention Command
Center and the Command Center posts the alert with Tamsui
River flood alert. Control Center uses intake and outlet
broadcasting stations to sound the emergency alert, and
notifies the Emergency Management Center of Taipei City,
New Taipei City Keelung City, and town office, police
departments and fire departments of Ruifang district
simultaneously.
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2.5 Flood Discharge Design
When Keelung River water level is below 62.5 meters, it is in
the safe range. However, when the water exceeds 62.5 meters, the
flood water will overflow into the side weir and enter in the stilling
pool for sediment deposit. At this time, the sediment releasing
tunnel is closed. After the sediment deposits for a period of time,
the flood water will be cleaner. When the water level of the stilling
pool exceeds 63 meters, the flood water will naturally overflow into
the flood division weir and enter into the division tunnel. The
contraction design before the flood division tunnel will speed up the
flood water and swiftly carry away the sediment particles in the
flood water. This will prevent the sediment clotting the walls of the
tunnel to shorten the tunnel life span.
The sediment deposit in the stilling pool will be over
accumulated after operating for a period of time. When the water
level is yet reaching the alert line, the sediment releasing tunnel will
be opened to flush the sediment in the stilling pool to the
downstream. This is because after being scrubbed by the river
water for a while, the downstream will suffer from the riverbed
erosion problem, and supplementing the sediment is very crucial to
the eco maintenance. The design of the sediment releasing tunnel
flushes sediment downstream so that the sediment volume would not
be insufficient, which in turn stabilizes the downstream eco function.
However, the problem of sediment over deposit results from the
sediment in the stilling basin being not flushing downstream
through sediment releasing tunnel. Government will perform
annual desilting to ensure the normal function of the stilling pool.
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Once the flood water enters the flood division tunnel, it
discharges into the sea at the Provincial Highway 2 (Taiwan), the
coastal highway. The flood water carries massive amount of energy
from the long flowing, if it discharges directly into the sea, the
energy will cause erosion and damage the north east coast.
Therefore there is an stilling basin at the outlet, allowing the flood
water to dissipate the accumulated energy before entering the sea.
Once the flood water sits in the stilling basin for a while and the
energy is dissipated, the water then is discharged into the sea. This
shall reduce the erosion of the northern east coastal area.
The flood discharge principle of the Yuan Shan Flood Division
Tunnel is by discharging the excessive flood water into the sea
through the division tunnel. This is like setting up a large manual
draining pipe, and drains away the excessive water. The choice of
the construction site, the detail design of each structure are carefully
connected and associated. The design is so ingenious that if we
closely study the function of each structure, we will know how much
work was dedicated to the detail design of this construction.
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Photo 12. Automatic flood division process
Upper left: flood water overflowing the flood division weir; upper right:
flood water discharging into the tunnel.
Bottom left: Intake of the flood division tunnel; bottom right: open sea
near Ruifang, the East Sea.
(Source: Water Resources Agency of the Ministry of Economic
Affairs.)
2.6 Hydraulic Modeling Verification
According to the related reports on the Public Construction
E-paper, in order to verify whether the detail design of the Yuan Shan
Tzu Flood Division Tunnel matched the design requirement which
specified that when Keelung river discharge was at Q200=1,620cms,
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the tunnel division flood discharge was at Q200=1,310cms; a
hydraulic model was utilized for testing. The key objective was to
test on a hydraulic model at the ratio of 1/100 to closely examine the
design details of the intake structure, inside of the flood division
tunnel, the outlet structure physics and the flood routing capacity.
The research result of the testing was provided to the design unit as
the reference for detail design modification and environment
evaluation.
The focus points of the hydraulic model testing research were on:
1) flood division structures function and hydraulic physics under peak
discharge in different recurrent duration; 2) sediment distribution of
the river way and the stilling pool at the downstream of the side weir;
3). sediment density distribution at the river downstream, tunnel
entrance and exit.
Photo 13
Hydraulic Model
(Source : Water Resources Agency of the Ministry of Economic Affairs.)
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3. Yuan Shan Tzu Flood Division Tunnel Construction Plan
Using a flood division tunnel to discharge the flood water was
an idea that started during the Japanese occupation era; however the
typhoon damage statistic at the time did not show any imminent
need for the Yuan Shan Tzu flood division tunnel. At the time, the
professional technology was not yet developed to overcome the
geological criteria such as fault zones and deserted mine pits;
therefore the construction was put on hold. In year 2000, flood
from Typhoon Xangsane took 59 lives of the coastal residents,
making the government aware of the inevitable action in improving
the Keelung River. By year 2001, Typhoon Nari claimed 104 lives
and uncountable property lost, the improvement project became of
great urgency. In addition to the imminent need of the people, the
government also wanted to demonstrate its determination to improve
the Keelung river. Yuan Shan Tzu Flood Division Tunnel project
thus was approved for construction immediately.
Yuan Shan Tzu Flood Division Tunnel construction was one
of the construction categories of Keelung River Yuan Shan Tzu
Flood Division Tunnel Construction Project. There were other
construction projects that aimed at the improvement of Keelung
River; however, Yuan Shan Tzu Flood Division Tunnel was the
most effective one. It is now the role model of many other flood
division construction projects. The main construction of Yuan
Shan Tzu Flood Division Tunnel cost approximately NT$3.994
billion. The construction began on June 5th 2002 and was
originally scheduled to finish on October 4th, 2004, giving the total
construction duration a little over 2 years to finish. The timing
was very tight, and many works were needed to be done within
such a short time: intake, tunnel, outlet, check dam, and the
clearing of the residual soil and rocks. At that time, government
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adopted the most advantaged turn-key method, having the turn-key
contractor responsible for both construction detail design and the
actual construction work. The detail design also required using
hydraulic modeling to verify the flood division function, ensuring
the flood discharge would reach the expected goal.
Before the construction was completed, typhoons with ample
perspiration struck Taiwan and resulted flood water overflow.
Government must make a decision immediately to execute
emergency flood division in order to discharge excessive flood
water. Three emergency flood divisions were executed before the
completion of the Yuan Shan Tzu flood division tunnel. These
three flood divisions successfully protected people’s lives and
properties and the emergency measure was validated. However, it
was also because the divisions that the completion of the
construction was postponed to October 28th, 2005. In just a short
3-year for Yuan Shan Tzu Flood Division Tunnel to be finished for
operation, naturally there existed many obstacles to be overcome
one by one. This construction also caused a few ecological issues
that brought the attention of the ecological protectionists. There
are many things that we have not done and things we could do
better for Yuan Shan Tzu flood division tunnel construction, or in
the design of flood division constructions in other regions in the
future. In chart 2 we will have detailed description on the
construction plan.
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4. Construction Obstacles
4.1 Timing: Short Construction Time
From the design and the structure we can see the enormous scale
of the Yuan Shan Tzu flood division tunnel construction. There are
several detail constructions for different functions, such as the intake,
tunnel, outlet construction, et al. If government adopted the usual one
step at a time construction progress - waiting for one construction stage
completed to begin the next stage - then how long will it take for Yuan
Shan Tzu flood division tunnel to complete? From the need of people
at the time, we could understand that, if such a construction indeed was
capable of relieving people from the flood problem, people would
naturally want the construction to finish as soon as possible. The
government also expected this construction to effectively discharge the
flood water and reduce the harm of flood. Taiwan goes through
several strikes from typhoons every year, and typhoon normally carries
heavy perspiration. With the early completion, we could prevent the
recurrence of the catastrophic tragedy of casualties and property lost.
Government ruled on the commence of the construction on June 5th,
2002 with completion date set on October 4th, 2004, giving only a little
over 2 years for the construction to complete. Such a large-scale
construction would take a fairly long time if were to finish gradually;
however, the purpose of this construction was to prevent disaster, it was
a disaster prevention construction urgently needed by people; the
government thus must adopt an effective and shorter duration
construction procedure to deal with the compressed timing.
To ensure the flood division function and the early
completion, Water Resources Agency of the Ministry of
the Economic Affairs adopted the most advantaged
turn-key method to execute the main construction.
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Under the basic design framework, the turn-key
contractor shall be responsible for the detail design and
construction. The detail design of the flood division
structure shall require hydraulic modeling to verify the
flood division function. United Geotech Inc. is entrusted
with the construction supervision, and the CTCI
Corporation will be in charge of environmental
monitoring and evaluation during construction and
operation.
--Water Conservation Quarterly, Vol.48
Turn-key method can reduce the waste of time as the turn-key
contractor is responsible for detail design and construction, which
reduces the communication problems between design and construction
detail. This will decrease the obstacles in design and construction to
the minimum and move forward the completion date. In order to
bore through the tunnel expeditiously, multiple adits were set up inside
the tunnel. This would increase the cross sections during the tunnel
construction and helped to shorten the work schedule. The measure
made it possible for the tunnel to bore through within one year.
What the government did was to simultaneously undergo several
detail constructions to reduce the waste of time. Finally the
construction was able to finish within the shortest possible time,
providing one more protection to the lives and property of the people
at the middle and downstream of Keelung River.
4.2 Geological Obstacles: Faults and Deserted Mine Pits
When the concept of Yuan Shan Tzu flood division tunnel was
generated in the 70s, the first and foremost obstacle was the geological
instability. The planned route of the tunnel crossed several faults
including Ruifang fault, Yuken fault and Fantzeou fault. The geo
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rock formation of the planned route was mainly composed by
sandstone, shale and sandstone/shale interlayer, in which the rocky
stratum was coal-bearing seams. The stratigraphic faces were
complicated, there lacking complete geographical data base to
encounter different geological conditions, and the estuary of the
division tunnel was a slope formed by the wasted coal cinder; these
made the stability questionable and require further investigation. In
addition, there were many deserted coal mine pits within the tunnel
excavation route, there most certainly deposited some flammable gas
such as fuel gas and methane gas. Inappropriate construction would
cause disastrous consequences or collapsing due to the mine pits.
Also there could be massive inflow of water during construction as the
stratum was saturated with ample underground water. All these
elements added uncertainty to the excavation process.
The technology inherited from Japanese occupation era was
insufficient to overcome all these problems. As the technology
matured through time, the geological database was established and
geological exploration equipments were developed. Yuan Shan Tzu
flood division tunnel construction finally was able to cope with these
complicated and uncertain issues and tunnel 1 and 2 were bored
though within one year. Overall speaking, the tunnels were able to
bore through so smoothly was a reflection of people’s urgent need, the
government’s respond with policies, and the maturity of the
construction technology. In short, this is a successful case of all
elements come together. When all elements came together, Yuan
Shan Tzu flood division tunnel was made possible. Naturally there
were many problems to be solved to help the smooth progress of the
construction.
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Photo 14. Location of the adits
Photo 15. Problems encountered during tunnel
construction.
Fault
Deserted Mine Pits
Massive
Inflow of
Water
Flammable
Gas
Tunnel Construction
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4.3 Public Resistance: NIMBY Effect
NIMBY effect actually is a grass rooted and advanced
movement; it is even a chance to promote social
collective review. Because NIMBY (Not In My Back
Yard), hence NIABY (Not In Anybody’s Back Yard),
thus NOPE (Not On the Plant of Earth), and further
pondering the review of the over all structural question,
making it the power to push the society to grow.
--Wei-Chieh Lai, Secretary-General, Green Citizens’
Action Alliance
NIMBY truly reflects the tug of war between the need of a
partial of people and the large group. How to reach a balance
where both side wins is a challenge to the wisdom of the decision
making organization. All construction come from the need of
people; any construction that does not originate from people’s need
is unwanted and is not possible to exist. However, a question is
pulled from this that is “the construction itself satisfies whose need?”
Some constructions may protect the lives of some people, and thus
has its reason to exist; however at the same time when some people’s
need are satisfied, would some others’ interests/benefits be deprived
or damaged? This is like the two ends of a seesaw: when someone
wins, someone else looses.
The construction itself not always has a positive impression on
people. If a construction is in the neighborhood and it results in the
rising of the estate value, people of the neighborhood naturally have
a higher acceptance to the construction. However, if the
construction brings negative impression, people of the neighborhood
for sure would receive it differently. Construction as such that
brings negative impressions tend to bring in problems that would
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induce people’s resistance. For example, air pollution, decrease of
the estate value, damaging of the nearby environment, etc.
However, if the construction is associated with the daily lives then
this construction must find a place to work on. If everybody is in
the “NIMBY” state of mind, then the actual collective meaning
would be “NIABY” which in further concludes as “NOPE”. This is
a very realistic public phenomenon that is very difficult to overcome.
Everybody needs to get rid of garbage, but no one
wants the garbage yard to be right next to my house,
this is NIMBY effect. We have to solve this NIMBY
effect. It does not matter if Ruifang suffers from
flood, when the flood division tunnel is finished, Xizhi
is the area that will be benefited from it. This
involves the social welfare. Namely the
government allows houses to be built in Xizhi, forcing
the government to spend top dollars in building flood
division tunnel in the upstream, does this make
sense at all? Or is it to say that since we have flood
division tunnel at the upstream to relieve
downstream from flood problems, the area in the
downstream thus can be developed without any
limitation or restriction? This is a question of
chicken and egg.
-- April 12th, 2010, Zhen-Yu Du, Chief, Yuan Shan
Tzu Flood Division Tunnel Management Center
At the planning stage, government heard the opposing voices
from the local residents that were against the construction of Yuan
Shan Tzu flood division tunnel. This was because that the outlet of
the division tunnel located in Ruifang, but the beneficiary of this
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construction would be the people in Xizhi district. Construction
proposals such as these where the construction site ‘would be in my
neighborhood but I would not be benefitted from it’ normally could
not receive full support of the local residents. NIMBY effect can
be found in many construction cases, especially the ones that
associated to the negative perspective of the public; for example,
garbage incinerator, landfill etc. How to smooth away public’s
rejection to the construction was a big challenge the government
faced at the time. To change the public’s perspective towards a
construction and further to make people accept the fact that they
would not be the direct beneficiary of this construction was a test to
government’s wisdom.
Zhen-Yu Du, the chief of Yuan Shan Tzu Flood Division Tunnel
Management Center pointed out that, due to the uncontrollable
development in the Xizhi district, the flood discharge became a
problem which contributed greatly to the Keelung River flood
problems. In order to improve the flood problem in Xizhi district,
was it really reasonable to install a flood division tunnel at the
upstream in Ruifang district? With such a solution in operation,
could Xizhi district keep on developing for commercial reasons?
This indeed worth careful considerations.
According to the 10th River Management Office of the
Hydraulic Engineering Office, Yuan Shan Tzu Flood
Division Tunnel Improvement Project that scheduled to
complete in 2004 was scheduled to contract out for
construction in the middle of May. However, there was
resistance in the land acquisition, and conflict of mining
and fishery rights that waited communication. If these
problems could not be resolved, the construction
progress was likely to be stalled. Yuan Shan Tzu Flood
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Division Tunnel construction mattered greatly with the
Keelung River Improvement Project. Executive Yuan
ordered the construction to be completed before end of
2004; Hydraulic Engineering Office hoped to finish as
early as possible. However, resistance lied in the
execution process. On the land acquisition, the basic
principle was that any land with the overburden depth
below 40 meters, the 10th River Management Office shall
levy the land use; when the overburden depth exceeded
40 meters, the office shall register the user right and
render reasonable compensation. However, no
measure was able to satisfy all parties. Despite the
estimated land acquisition being not much, the attempt to
resolve it in a short time may not be as easy.
--- February 28th 2005, China Times.
In order to begin the construction of the flood division tunnel
smoothly, the government adopted forceful land acquisition and
provide reasonable compensation to solve the public resistance issue.
Though government listed compensation standard, there still lacking
recognition from the upstream residents whose land were forcefully
acquired. Acquiring land for flood discharge policy is bond to
encounter public resistance and opposition. Government
summoned several coordination councils and continued to
communicate and explain to the public, hoping that the public would
understand the effect behind the policy and turn to support and
recognize the policy. This process was rather painstaking and
difficult.
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Dr. Jihn-Sung. Lai of the Hydrotech Research Institute at the
National Taiwan University pointed out that people at the time was
in great concern over the safety of Yuan Shan Tzu flood division
tunnel construction. It would be very difficult for the government
to convince people by answering all their questions. Dr. Lai’s team
used virtual animation so people could understand immediately the
influence of the flood division tunnel construction have on their
future. After the video presentation, people learned that the
construction imposed no threat to their safety and that there would
be better environment for their leisure use. The construction would
help solve the flood problem for the people at the downstream and
create better and safer lives in the future. After people understood
the Yuan Shan Tzu Flood Division Tunnel better, the acceptance
level was greatly increased. However, after people accepted the
project, there came issues of profit groups and local residents
demanding compensation. How to receive reasonable
compensation has always been the primary concern the people have
after accepting the construction projects. Government at the time
issued a set of compensation standard. Despite adopting forceful
acquisition and reasonable compensation to settle the public
resistance issue, the government still could not make all the involved
parties satisfied with the compensation. One comforting note was
that during the coordination process, there was no large scale public
resistance in stopping the operation of the construction. When
Yuan Shan Tzu Flood Division Tunnel was finished, the effect was
recognized by the local residents, and it indeed relieved people in
Xizhi of the flood problems, shaking off the nightmares that had
been haunting the residents in the middle to downstream of Keelung
River.
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Photo 16. Computer simulated flood division tunnel operation
status during flood.
4.4 Flood Before Completion: Emergency Flood Discharge
Before Yuan Shan Tzu flood division tunnel was completed,
there were three occasions that required flood discharge, we called
them the “emergency flood discharge”. In 2004, Yuan Shan Tzu
flood division tunnel went through 0911 extremely heavy rain,
typhoon Nock-Ten and Nanmadol total 3 emergency flood
discharges, the combined flow was approximately 1.278 million
square meters, effectively reduced the flood water level at the middle
and downstream and prevented flood damage at the downstream.
The government then faced a decision making issue. Before
they issued the emergency executive order for the emergency flood
discharge, they must evaluate how much damage would the
emergency flood discharge do to the tunnel, and the positive
economic effect on the society after the flood damage on the middle
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to downstream was relieved. The government thus must draft a
plan in advance for emergency flood division, evacuation and
control operation. These three emergency flood divisions displayed
the positive effect on protecting the lives and properties of the
residents. According to the Water Resource Agency’s report, the
appearance of the concrete lining inside the tunnel remained intact
from the three divisions, the damage was mainly on the lining steel
mold and the heavy machineries inside the tunnel. After re-order
the steel mold, the tunnel concrete lining was fully completed in
March 2005. The decision of emergency flood discharge was
approved and recognized by the residents; it was also a direct proof
to the flood division effect of the Yuan Shan Tzu flood division
tunnel. The opposition voice was finally diminished.
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Photo 17. Emergency flood division damage to the tunnel portal.
Before the flood division tunnel was finished, in order to protect the lives
and properties of people, the government ordered emergency flood
discharge after overall evaluation. The heavy flow of the flood from
typhoons severely damaged the heavy machineries and steel mold of
the concrete lining. However, the emergency flood discharge also
protected the lives and properties of the downstream residents. This
decision won the unified recognition.
(Source : Water Resource Agency, Ministry of Economic Affairs)
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Chart 3 Statistics of Historical Flood Discharge of Yuan Shan Tzu
Flood Division Tunnel
Year Name of
Typhoon
Maximum Flood
Discharge
(CMS)
Total
Flood Discharge
(M3)
(per million)
Emergency
Flood
Discharge
2004 9/11/2004 0911 Extremely
Heavy Rain
200
10/25/2004 Nock-Ten 600
12/03/2004 Nanmadol 450
Regular
Flood
Discharge
2005 7/18/2005 Haitang 211
8/04/2005 Matsa 78
8/31/2005 Talim 382
10/02/2005 Longwang 115
2006 9/10/2006 Extremely Heavy
Rain
140
2007 6/15/2007 Extremely Heavy
Rain
35
9/18/2007 Wipha 76
10/06/2007 Krosa 636
11/26/2007 Mitag 91
2008 7/28/2008 Fung-Wong 75
9/12/2009 Sinlaku 247
9/27/2009 Jangme 351
2009 9/29/2009 Extremely Heavy
Rain
296
10/05/2009 Extremely Heavy
Rain
94
10/23/2009 Extremely Heavy
Rain
168
Total 18 flood divisions 79.94
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4.5 Ecological Issue : North East Costal Ecosystem
Yuan Shan Tzu flood division tunnel solved the flood problems
that troubled Xizhi and Keelung River downstream for years. The
effect and achievement won praises and affirmation; however, such
construction arose issues that require our further thinking in how to
improve it in the future.
Although each flood discharge was merely 2 to 3 hundred
CMS, the worst scenario did happen. Flood water carried large
amount of sediment, garbage, fresh water life forms out of the tunnel
and entered the sea directly. The sea at the flood division tunnel
exit became the new Yin-yang sea.
Typhoon initiates the Yuan Shan Tzu flood division, and
the flood discharge flushes sediment, plankton, aquatic
lives to the sea. Ming-Xiu Zhen explained the formation
of the yin-yang sea, one is because the sediment flushing
into the sea, suspends, floats and results in shading; the
other one is because fresh water is lighter than the sea
water and would retain on the upper layer of the sea,
making the fresh water layer that carries sediment even
more obvious.
In addition to the visual impact of the fresh water, with large
amount of aquatic lives flush into the sea unexpectedly,
those that suffer the most would be the innocent fresh
water life forms that are forced out of their homes. Taiwan
Coral Reef Society receive many reports from their
members reporting that many mouthbreeders are found
lost in the sea area at the outlet of the flood division tunnel.
These mouthbreeders swim blindly, unable to find familiar
shelters and food to feed.
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Flood water with high slit content causing the sea area to
be covered by debris, and this is a fetal blow to the life
forms in the sea area. As pointed out by Zhen, if the
sediment volume in the flood water is not too much, coral,
sea urchins would still be able to blow out the sediment
that covers their breathing mouths. However, if the
sediment amount is high and covers the mouth and
choking the anthozoa, it would for sure kill the anthozoa.
As for algae, since it is co-dependent to the coral and is
unable to move, when the flood sediment keeps covering,
death is inevitable.
--October 2nd 2005, United Daily
Flood water normally carries massive amount of sediment, so
we have stilling pool design at the intake entrance to deposit
sediment and allows it to discharged into the sea by way of the
flood division tunnel. Even so, the amount of the sediment
carries by the flood water is still in a big volume and causes
problems to the north east sea eco system when the flood is
discharged to the sea from the outlet exit. These issues have been
the concern of ecological protectionists. When the government
planned the Yuan Shan Tzu flood division tunnel, the main concern
was human lives and property safety. Here we find that the
ecological system of the nature should be included in the
consideration, because we are closely associated to the nature. It
is not what we would like to see if the survival of other species are
deprived for the need of human being, or that their ecological
habits are forced to change.
We can see from the ecological protection reports that, over
discharge sediment would choke the mouth and pharynx of coral
and prevent it from getting rid of the excessive debris. In the long
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run, this would cause the death of the coral. There are even
disoriented fresh water lives that find it difficult to find shelters or
food. When our government was building the Yuan Shan Tzu
Flood Division Tunnel, did they realize such flood discharging
method would affect the ecosystem?
Honestly speaking, people in the past did not think much
about the ecology. Making money was all that mattered.
However, it works the other way around now. Ecology is
important because NGO groups are deeply involved and
they are eager to contribute to the issue. What the
result of the flood division would be, no one dares to
guarantee.
Flood water is generally yellow and dirty. The most
serious influence on the sea area is that “the sediment is
the number one killer to coral”. Once the sediment
deposit on the coral, especially the fine sand, coral would
not be able to grow. For this, when we made the design,
we tried to use the current at the exit to carry the find
sand away and disperse the find sand. Because the
current at the north east coast is stronger. So far
everything is fine, though there is most certainly influence
on the ecology. No one is to say there is none. Any
construction has its impact on ecology. Right now the
condition does not get any worse. We hope that when
the catchment basin at the upstream is better improved,
the sediment in the river would decrease in the future.
The influence of the flood water discharge to the coast
would be less and less.
-- April 12th, 2010, Zhen-Yu Du, Chief, Yuan Shan Tzu Flood Division Tunnel Management Center
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In the interview of Mr. Du, we understood that government put
the outlet exit of the Yuan Shan Tzu flood division tunnel on the
north east sea coast where the current was stronger, hoping that the
current could swiftly and naturally carry the sediment away without
depositing on the coral and affect the natural ecology of the area.
From the stilling pool at the upstream to the location of the estuary,
we saw that the government had already putting the ecology issue
into concern when designing the Yuan Shan Tzu flood division
tunnel. The actual effect on the ecology surfaced when Yuan Shan
Tzu flood division tunnel was finished and the flood division was in
operation. Indeed, the sediment deposit problems still exist.
From the ecological protection point of view, the ecological
protection measure of the Yuan Shan Tzu flood division tunnel is not
good enough. Right now what we can do is to make sure the
situation not to get worse. Mr. Du thinks that the current situation
is well under control. If in the future we can do better in sediment
process at the upstream catchment basin, prevent large quantity of
the sediment from being flushed down to the outlet, then perhaps we
could actually improve the damage to the north east sea ecology.
Whether the current condition is truly improved, this
construction case inspires us in many ways. There are many factors
for a construction to consider. It is more than just construction
itself but also human needs, ecological needs, environmental needs,
etc. How to find the balance in so many different needs does worth
our time and effort to study and review. We expect to find better
designs to solve these problems that are not yet processed adequately;
or to design better construction role models to put an end to the
negative effects.
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5 General Discussion – Successful Water Improvement Model
Taiwan is an island with many rivers and encounters high
frequency of typhoons. Many rivers in Taiwan have flood
problems, and a successful water improvement case could be the role
model for other disaster prevention constructions. Yuan Shan Tzu
flood division tunnel is the most recent construction case with the
best flood division effect. It successfully improves the long term
flood problem at the Keelung River downstream, and brings a safety
living for the residents in Xizhi District.
Government had the idea to have a flood division tunnel in
Ruifang District since the 70’s, but the geological uncertainty and
that the flood problems from typhoon were not very serious made
the construction remain an idea. In recent years, high rise buildings
were built in Xizhi District, many commercial buildings resulted in
the over development of the area. Typhoon Xangsane in 2000 and
Typhoon Nari in 2001 altogether took away over one hundred lives
and countless property damage. Government then realized the
situation and approved the construction of Yuan Shan Tzu flood
division tunnel.
The construction of Yuan Shan Tzu flood division tunnel includes
1) intake, 2) outlet, 3) tunnel, 4) check dam, 5) residual soil and rocks
clearing process, etc. As the construction time span was only three
years, the government adopted turn-key contract, having one turn-key
contractor in responsible for all the detail design and construction
works to reduce the construction time. Tunnel construction used
multiple adits to perform multiple cross sectional construction, using
the fastest speed to bore through the tunnel within one year. The
excavated soil and rocks from the tunnel construction were collected
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in the residual soil treatment plant first then processed according to
the remaining soil process policy. The challenges faced by the tunnel
construction at that time were 1) geological uncertainty, 2) crossing
multiple fault zones, 3) water inflow, and 4) hidden crisis of
flammable gas.
On the construction of outlet and intake, in order for the flood
discharge to operate smoothly when completed, the detail design
utilized “hydraulic modeling” to test and verify the flow speed
analysis or sediment deposit. A stilling pool was designed at the
intake and the main function of this stilling pool was for desilting,
preventing excessive sediment being flushed into the tunnel. An
stilling basin was set at the outlet with design to dissipate the energy
carried by the flood water, before discharging into the sea and
resulting erosion at the coastal area. Despite that, the flood
discharge still carried massive amount of sediment and inflicted the
north east coastal ecology. Coral in that sea area suffered from
breathing problems from the excessive sediment in the sea. When
designing the Yuan Shan Tzu flood division tunnel, north east sea
area was chosen as the estuary of the tunnel for its strong current.
The idea was for the natural current to carry the sediment away
swiftly. There is still room for the improvement on the issue
involving ecology. If the sediment releasing job at the catchment
basin on the upstream can be better improved in the future, the
influence on the outlet ecology naturally would be decreased.
In addition to the above challenges, Yuan Shan Tzu flood
division tunnel also faced public resistance issue since was approved
for construction. There were also three emergency flood discharges
before the construction was completed to encounter the flood from
the typhoon perspiration. The government must assess between the
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construction lost and the lost of lives and property on both sides of
the river to make the best decision. Building the Yuan Shan Tzu
flood division tunnel helped the middle to downstream residents
shake off the flood problem. The contribution is so great that it
becomes the role model for the future flood prevention
constructions.
From concept to birth, a construction overcomes many
obstacles along the way. Each process challenges the wisdom of
the construction team. However, use better, faster and more
diversified measures to achieve the final goal is the skill that
everyone in the construction field must learn. Through the
introduction to the Yuan Shan Tzu flood division tunnel, we hope
people in the future would come up with better solutions for flood
prevention; we also hope for more of the fine constructions in the
future to improve the lives of the future human being.
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Practice Part I : Use your brain
1. Find a construction case in life, try to analyze its initial planning,
construction process and operation after completion, what are the
problems that this construction might encounter?
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2. Find a river in Taiwan that requires flood discharge design and
explain why.
3. If you are the person in charge of the Yuan Shan Tzu Flood
Division Tunnel construction, since government only grants 3
years for the construction to finish, what measures would you
adopt to meet the short construction span?
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4. If you are a member that participates the tunnel construction, and a
large inflow of water (underground water) happens half way
through the excavation, how will you discharge/drain the water?
5. Suppose you are a government official who is in charge of an
important construction decision making, and you are answering to
people’s demand to build a garbage landfill yard somewhere.
The nearby residents of the site raise strong opposition, how will
you solve the NIMBY effect issue?
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6. Think of the soil and rocks from the tunnel construction
excavation, how to utilize them for further use?
(Please ignore the fact that government will solve this problem
based on policy, and come up with your own re-use method.)
7. Think of the positive effects of the flood water that normally
brings disaster, how can we use it to help and help with what?
Try to come up with the positive functions that can be created out
of the negative natural catastrophes.
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8. Suppose your are a government official who is in charge of an
important construction decision making. If one day the rain is
highly acid or carries poisonous materials, and it would seriously
imperils the ecological safety of the sea area if the water is
discharged into the sea, i.e., causing the massive death of the
marine lives in the sea; when the flood strikes, would you choose
to discharge the flood or not? Why? Or, if you can come up
with a measure to protect human lives and property and the
ecology at the same time?
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1. At the estuary of the Yuan Shan Tzu flood division tunnel there is
an “stilling basin” designed to prevent flood water overly eroding
the estuary. Now try and design another protective installation at
the estuary to prevent fresh water life forms to be flushed into the
sea during flood.
Part II : Use your hands