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Yuan-San-Tsu Flood Division Tunnel 1、 Introduction
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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 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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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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.
Photo 1. Keelung river field of recent years. (Source : Water Resources Agency, Ministry of Economic Affairs.)
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Chart 1. Statistics of Keelung River Typhoon Flood Water.
Typhoon (year)
Lynn (1987)
Reib (1998)
Babs (1998)
Xangsane Nari (2000) (2001)
Flood Area (hectare)
3,332
345
338
771
4,806
Flood Depth 0.2 - 7.5 (meter)
0.2 – 7.5 0.5 – 3.8
0.5 – 7.5
0.3 – 8.5
Death (person)
32
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.
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2、 Yuan Shan Flood Division Tunnel Structure Introduction 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.
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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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(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.
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.) 6 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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2.1.3 Side Weir (1).
(2).
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. 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).
(2).
(3).
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 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. 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).
(2).
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. 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).
(2).
Structure: open channel, bottom elevation descents by a fixed 10% slope starting from 60 meters high, and connects to the flood division tunnel entrance. 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).
(2). (3). (4). (5). (6). (7).
Structure: tunnel standard section is round hollow section, internal diameter 12 meters, total length 2,484 meters, grade 1/100. Intake: RuiGan New Village of RuiFang Township in Keelung County. Outtake: Provincial Highway 2 (Taiwan), coastal highway. Tunnel 1: 1,160 long, grade 1/100. Giufeng River Crossing Section: 33 meters long, grade 1/100. Tunnel 2: 1,290.5 meters long, grade 1/100. Function: automatically diverse the flood water that naturally overflow the flood division weir into the sea outside of Ruifang for discharge.
Photo 8. Left : tunnel intake; right : tunnel intake model.
2.2
Outlet Structure Introduction
2.2.1 Outlet Transition Section and Chute (1).
(2).
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. Function: improve water flow at the tunnel exit.
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2.2.2 Outlet Stilling Basin (1).
(2).
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. 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.
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 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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, 16 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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 20 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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. 22 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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
Tunnel Construction
Fault Deserted
Massive Mine Pits
Inflow of Water
Flammable Gas
Photo 15. Problems encountered during tunnel construction. │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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 26 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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 28 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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) │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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Chart 3 Statistics of Historical Flood Discharge of Yuan Shan Tzu Flood Division Tunnel Year
Name of Typhoon
Emergency Flood Discharge
2004
9/11/2004
Regular Flood Discharge
2005
2006 2007
2008
2009
Maximum Flood Discharge (CMS)
0911 Extremely Heavy Rain 10/25/2004 Nock-Ten 12/03/2004 Nanmadol 7/18/2005 Haitang 8/04/2005 Matsa 8/31/2005 Talim 10/02/2005 Longwang 9/10/2006 Extremely Heavy Rain 6/15/2007 Extremely Heavy Rain 9/18/2007 Wipha 10/06/2007 Krosa 11/26/2007 Mitag 7/28/2008 Fung-Wong 9/12/2009 Sinlaku 9/27/2009 Jangme 9/29/2009 Extremely Heavy Rain 10/05/2009 Extremely Heavy Rain 10/23/2009 Extremely Heavy Rain Total 18 flood divisions
Total Flood Discharge (M3) (per million) 200 600 450 211 78 382 115 140 35 76 636 91 75 247 351 296 94 168 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. │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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 36 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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
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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 40 │員山子分洪道│Yuan-Shan-TSU Flood Diversion Tunnel│
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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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Part II : Use your hands
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.
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