圖書典藏及影音數位平台

本計畫主要目的為針對計畫範圍蒐集整理計畫範圍水利建造物基本資料，進行風險評估及檢測使用狀況與內部損壞狀態，以便未來做為管理、維護之參考依據，以及尋求有效維修與補強方案，爰此，擬委外辦理淡水河流域水系風險評估及水利建造物安全性檢測計畫。

I. Project cause and objective Tamsui river system flows through cities and towns of major economic developing area in metropolitan Taipei area. Owing to rapidly growing on population and the concentrated development in river basin, its hydraulic structures are related to millions of people's safety. Tracing back "Taipei flood control project", it's planning started from 1960, and "Suggested scheme of flood control project in Taipei area" was proposed in 1973. Construction of the Project was divided into three stages, and started its construction in 1981, thereby completed in 1997. Most of the hydraulic structures have been used over 30 years. Owing to recent global warming and rapid weather change, typhones, storms as well as concentrated and short duration rainfall frequently occur. Moreover, Taiwan is influenced by earthquakes. All of them affect the safety of hydraulic structures tremendously, therefore, it is needed to reinforce the inspection of most hydraulic structures. Presently, inspection framework of each hydraulic structure is integrated and complete. However, they still have the threats of unpredictable damage induced by typhoons, storms or earthquakes. For sustainable use hydraulic structures, we plan to collect and manage the basic data of hydraulic structures in the Project scope, to perform hydraulic structures' safety assessment, and detect their use condiction as well as internal damage state for reference of future management and maintenance as well as looking for effective maintenance and reinforcement schemes. II. Review on "Instrument for Hydraulic Structure Inspection and Safety Assessment" After comprehensive processing each factor of waterproof structures governed by the 10th Rver Management Office, WRA, and giving score, structures included as "A certain sizes" are as follows: Luzhou dike, Sanchong dike, left Erchong floodway dike, right Erchong floodway dike, Xixzhuang dike, Sinjhuang dike, Shulin dike, Banqiao dike, Tucheng dike, Zhongyuan dike and Yonghe dike, with a total length of 61,171 m. Given that functions and structures for water storage, diversion, waterproof and drain are various, their safety assessment items and contents should be performed based on their characteristics. Based on Article #16 of "Instrument for Hydraulic Structure Inspection and Safety Assessment", the safety assessment scope is outlined in Table 1. The Table also references Item #1, Article #18 of "Instrument for Hydraulic Structure Inspection and Safety Assessment", include "onsite inspection and assessment" and "stability assessment for structure's surrounding" (i.g. structure safety comment) into safety assessment items. Among them, as shown in Table 1, no intake, outlet, storage, diversion, delivery and grit function for waterproof and drain structures, hence the related items are not applicable. Operation and warning system is also not applicable for waterproof structures, but is applicable for drain structures. For safety assessment category, it is recommended to perform regular assessment mainly for waterproof, diversion, delivery and grid facilities. Their performance frequrecy could be once in each 5 years. III. Results of Visual Inspection on Hydraulic Structures The scope of visual inspection on hydraulic structures in the Tamsui river system governed by the Water Resources Agency, MOE, includes the main stream of Tamsui river, Erchong floodway, Tahan creek, Sanxia river, Heng creek, Xindian creek, Jigmei creek and Keelung river, the lengths that they were inspected are summarized in Table 2. Totally, the grand inspection length is 167,634 m. In order to understand the conditions of deficiency portion, the inspection results of 2016's "Structural safety inspection project on metropolitan-Taipei-area water control structures" and those of this project in 2017~2018 are collected together and made statistics. It is understood that concrete breaking has the maximum percentage (28.51% approximately), vegetation(21.72%) on hydraulic structures is the second, the others are cracking(20.81%), deficiency of expansion joint(19.00%). It is obvious that the major deficiency of dikes and revetments in the Tamsui river system is from normal natural deterioration. IV. Inspection Results of Non-destructive Testing on Hydraulic Structure For the structures with visual inspection doubt or being more important, non-destructive testing is performed by using ground penetration radar (GPR) and concrete strength hammer. The total performed inspection length of GPR is 21,774 m in 2017~2018. Among them, the results of 2017 found that there are dense holes and dike's soil settlement on Erchong floodway. The settlement is estimated being due to dike and bridge co-structure with long-time-range car's moving as well as vibration with inducing dike's soil compaction. Besides, results of inspection in 2018 also show that there are serious hole-signals locally on Bazhong revetment of Keelung river. Concerning the part of concrete strength testing hammer, the inspection results of 2016's "Structural safety inspection project on metropolitan-Taipei-area water control structures" and those of this project in 2017~2018 are collected together. Totally, there are 647 sites. As shown in Table 3, statistics data of the inspection results shows that the integrated mean and the lowest strengths of concrete, etc. The lowest strengths of concrete is located at 16K+100 of Sanchong dike. However, results of repeated inspections at many points nearby show that the concrete strength is not lower than the specified standard value 210 kgf/cm2. It is gust that the former inspection point is specially located at the location of old-structure degradation. V. Assessment Results of Hydraulic Structures Concerning this project's assessment results, deficiency locations are compared based on hydraulic structure facility and the inspection scope (Jingmei creek, Keelung river) in 2018. One assessment dike length is defined between 200~500 m (400 m mostly) upstream and downstream from the deficiency location. They are combined, if there is another deficiency location in neighbor. There are totally 26 assessment-dike-length. Among it, there are 25 project-improvement dike-length and 1 attention- improvement dike-length. The attention- improvement dike-length portion is slope toe scoring on Yong-An dike's highland beach. However, the deficiency location is under a bridge. Thus, it is needed to visit the site and clarify responsibility for quick improvement. Based on the assessment after ground penetration radar (GPR) inspection, Bazhong revetment of Keelung river is the one among project-improvement dike-length cases. However, the deficiency location belongs to walkway on dike top, thus it is recommended to ensure the rehabilitation site and quickly enter the site for improvement. Concerning the part of Jingmei dike, its deficiency is sporadic on surface, but the site is located at population intensive area. Thus, it is recommended to be quickly improved by using open contract method for preventing problems such as public complaint. VI. Inventory and Description of Cross-River Structures By onsite exploration and relevant information comparison, all of cross-river structures and facilities in the Tamsui river system were checked. They are used as the basis for building the hydraulic model to assess the effect of bridges on river flow (such as river water run-up) and the sufficiency of bridge-girder bottom-face elevation. Among 8 rivers, the grand total number of cross-river structures/facilities is 188. The number of cross-river structures/facilities on Keelung river is the maximum, 81, including no-pier steel arch-bridges. The second larger number of cross-river structures/ facilities is 27 on Xindian creek. Among these 8 rivers, main stream of Tamsui river and Erchong floodway include co-structures between bridge and dike. VII. Characteristics of River Catchments Tamsui river system flows through cities and towns of major economic developing area in metropolitan Taipei area. The upstream of Tamsui river main stream is Tahan creek at Shihmen reservoir's afterbay-weir. At further upstream, Tahan creek originates from elevation of 3,529 m on a mountain top. Tahan creek flows downstream-ward to confluence of it and Xindian creek. Then, the Tamsui river main stream flows from the confluence of it and Xindian creek through Erchong floodway outlet further downstream-ward to the river mouth. Jingmei creek (tributary of Xindian creek) flows from Shenkeng's Caodiwei (village on boundary of Taipei city and New Taipei city) in the upstream to "Water source expressway-bridge" in the downstream, then to the confluence of it and the Tamsui river main stream. Keelung river flow from Houtong's Jieshou- bridge in the upstream, through Nanhu-bridge in the mid-stream to the confluence of it and the Tamsui river main stream. VIII. Analysis on Flow Scouring Effect on Dike/Revetment Based on the chart-explanation (also with English) of iRIC-Nays2DH two-dimensional hydraulic modeling and analysis results as shown in Appendix 5, the flow-scouring effect on structures is expressed by high flow velocity and high shear-stress on riverbed. The results reveal the scouring vulnerability on the left of river cross-section 22.0~22.1 (as shown on Fig. 1(h) of Appen.5) on main stream of Tamsui river, the left edge of cross-section 8.0 (as shown on Fig. 2(h) of Appen.5) on Erchong floodway, the middle-left of cross-section 38.0~38.1 (as shown on Fig. 3(h) of Appen.5) on Tahan creek, the right of cross-section 12.0 (as shown on Fig. 4(h) of Appen.5) on Xindian creek, the right channel of cross-section 53.0 (as shown on Fig. 5(h) of Appen.5) on Keelung river. IX. Inventory of Subsidiary Hydraulic-Structures Based on the related specification, if the subsidiary hydraulic structures (such as pumping station, automatic water gate or transverse water-door) on the interface of water-proofing structure cannot be operated, also can induce failure of flood-control function to make disaster-risk. Taipei City Government owns 40 water gates or transverse water-doors, as well as 87 pumping-stations. New Taipei City Government owns 692 water gates or transverse water-doors, as well as 81 pumping stations. Keelung City Government owns 16 pumping-stations. X. Results of Risk Assessment on River System After integrated collecting results of 1-D hydraulic analysis, inspection of hydraulic structures, usage behavior, hazard degree and vulnerability degree, hazard degree and vulnerability degree are further assessed. Then hazard degree and vulnerability degree are multiplied to obtain the risk degree. Among them, the downstream plain which is undeveloped, unused or low risk degree flooding area belongs to tolerable flooding area. It is recommended that the portion without dike installation is changed to fellow No. 65 of "Water Resource Act" to limit the usage of land usage in the floodplain. Water Resource Agency made management project lines and lines of use land scope on the middle stream and upstream river reaches through mountain slope areas or high mountain area. However, no necessary to manage or no economic value for manage is actually un-managed river reach. Therefore it is delineated as low-risk scope. XI. Defining Protection Scope and Importance of Structures Considering population dense area, whether the population dense area near back of dike, whether there having important protecting objects or important facilities, this project selects Erchong floodway left dike, Erchong floodway right dike, Zhongyuan dike, Yonghe dike, Eucalyptus dike and Xinzhuang dike are selected for study and analysis. The software of iRIC-Nays2DH Flood is also used to be used as hydraulic analysis tool. Concerning topographic, the 20 m DEM data issued by National Land and Survey Center, Ministry of Interior, is used as data of topographic modeling. Bsed on the aforementioned model, the color fringe map of ground inundation depth and depth isolines due to overtopping of the project flood over dike are obtained. XII. Countermeasure to Reduce Risk Countermeasure to reduce risk is the same as risk management. Based on results of risk assessment, several risk reducing schemes are provided in the risk treatment and effects of these scheme usages are assessed. Manager should assess risk reduction schemes based on risk reduction degree, the needed cost, creatable benefit and opportunity. For hydraulic structures of Tamsui river system, this project assessed hazard and risk based on the related data collected and results of hydraulic analysis. For hydraulic structures of Tamsui river system, risk matrix is used to assess risk degree and risk light after hazard and risk have been multiplied. For the most high risk, it is explained and the needed cost is estimated. XIII. Assessment on Short Time Recovery – the Second Defense Line Due to people let flow-paths naturally developed, the middle and downstream river path of Tamsui river system continuously extended to river bank and low-lying area. It makes the type of hydraulic structure cannot be selected as earth dike with larger volume, and only flood-wall can be used to reduce the installation space of hydraulic structures. Therefore, raising of flood-wall has to be adopted as countermeasure against occurring rainfall exceeding design standard. Key Word：Tamsui River, Hydraulic Structures Inspection, Risk Assessment