圖書典藏及影音數位平台

經濟部水利署南區水資源局（以下簡稱本局）所轄管之曾文水庫、阿公店水庫及牡丹水庫係供應南部地區水源之水庫，鑑於氣候變遷之影響，致使水庫汛期間防洪操作需嚴密搭配氣象水情之推估及預警方能有效達到水庫防汛減災及蓄水利用之效果。 因此由本計畫進行入流基本資料之蒐集及更新藉以分析庫區上游降雨時間與空間分佈特性及庫區水位歷線等關係產出之成果來作為防汛應變之用。廠商須提供氣象及水情資訊簡報，依本局需求進行水情資料蒐集、預估及分析等，提供本局於緊急應變操作參考。 近年因氣象預報技術亦有新的推展，可藉由蒐集與研判分析提升水情預估準確度。本局為確保緊急應變期間水情掌握及預警推估之準確性，爰擬辦理本計畫進行資料蒐集、分析與觀測系統整合、氣象與水情資訊提供等工作。 另因應本局防淤隧道完工啟用在即，未來除防洪功能外亦兼負排砂操作任務。為精確研判水庫異重流到達之條件與時機，使曾文防淤隧道利用達最大化，進行排砂操作模擬，以利本局未來排砂操作時之重要參考依據。

Reservoir operation during flood period needs closely matched rainfall forecasting and warning information to ensure dam safety, flood mitigation, sediment venting, venting downstream deposition from previous dredging and securing future water supply. After Zengwen Reservoir Sediment venting Tunnel construction is completed in 2018, simulation of sediment venting operation and estimation of turbidity current arrival conditions and time are regarded necessary reference to maximum efficiency of this tunnel. The working items of this project are include：(1) Collecting, maintaining and extending basic data of Zenwen, Mudan, and Agongdian reservoir, such as meteorological data, geographical data, hydrological data and essential facilities data. Data collection is focus on watershed precipitation and inflow/outflow discharge of each reservoir with different path of typhoon, and proposing analysis advice of probably impact by typhoon track. (2) Supplying weather forecasting information. (3) Flood operation consulting service: during typhoon or heavy rainfall event period, personnel stationed for supporting while authority is designated as level-2 and level-1 facility. (4) Flood information integration and consulting service: Developing an integration user interface to display hydrological observation data of Mudan and Agongdian reservoir, including the rainfall data from Central Weather Bureau (CWB). Maintaining Zengwen reservoir hydrological observation data display website built in 2017 according to demands of Southern Region Water Resources Office (WRASB). Services of website operational assistance and hydrological information advisory were held during normal time. (5) Simulation of Zengwen Reservoir sediment venting operation：First, with historical disaster databases, improvement had been suggested, which is sediment venting operation of Water Resources Planning Institute of the Water Resources Agency (WRPI). Second, according to forecasting inflow, sediment concentration and the result produced by WRPI hydraulic model, simulation of sediment venting operation will be launched and operation advice will be proposed. Finally, providing relevant information and advisory when Central Weather Bureau and Emergency Response Center of Southern Region Water Resource Office upon second level. (6) Decision support of Zengwen Reservoir flood control operation: Producing flood control operation decision support interface founded on result as mention above, include observation data displaying, analysis path of typhoon model and sediment venting operation model of Zengwen Reservoir. In this project, the website is extended to display the real time and historical observation rainfall and water level data for each reservoir in jurisdiction area of WRASB. During typhoon season, typhoon information, support on system operation and techniques are provided in the torrential rainfall events of 13-June, 19-June, 02-July, 22-August and 26-August, and Typhoons Maria and Mangkhut. This project made the flood warning and operation integration services improved and more efficient. This annual project provided consultations of flood control operation of Zengwen Reservoir during 7 events, which are the torrential rainfall events of 13-June, 19-June, 02-July, 22-August and 26-August, and Typhoons Maria and Mangkhut. The most significant event during which the spillway and desilting tunnel were both operated is the torrential rainfall from 22-August to the end of August. In the beginning of this event, the reservoir water surface level (WSL) was only 223 El.m. It was expected that the inflow volume could not elevate the WSL to attain El. 230 m after the flood, therefore pre-release operation was not recommended. The reservoir release was kept at lower discharge until the evening of 23-August, when rainfall was significantly increased due to the unexpected slower movement of tropical depression. The reservoir release was increased progressively to achieve a maximum discharge as 2,650 m3/s. The actual and forecasted discharges of reservoir peak inflow were 3,266 and 3,363 m3/s respectively, and the WSL of reservoir was maintained below 230 El.m when the peak occurred. Afterwards the operation partially switched the spillway release into desilting tunnel for sediment venting, and the release was gradually reduced to store the recession inflow to achieve the desired end-of-operation WSL, El. 230 m. Generally, the operation satisfies multiple objectives including ensuring dam safety, flood mitigation, sediment venting, venting downstream deposition from previous dredging and securing future water supply. According to historical flood data analysis, we review the turbidity current venting rules that are conducted by Water Resources Planning Institute of the Water Resources Agency (WRPI) using physical model experiment. According to the results of the physical model tests, the turbidity current venting rules and operational recommendations are based on the estimated inflow and on-site observation data of sediment concentration. The research results of this project show that the operational rules of the WRPI (2017) can be slightly modified to a total storage capacity of more than 160 million m3 or the ratio of total inflow discharge volume and the initial water level storage capacity is more than 0.65. The timing of turbidity current reaches the dam can be slightly corrected to the average inflow discharge is greater than 1,400 m3/s when inflow discharge in more than 300 m3/s, and the ratio of total inflow discharge volume and the initial water level storage capacity is greater than 0.5. In addition, if the inflow discharge reaches more than 2,700 m3/s during the flood event, it may also generate a turbidity current to reach the dam. However, the operational rules established by the WRPI should not be easily changed or adjusted at this stage because of its argument and background. Therefore, we suggest it is necessary continue to track the results of field observations as the future work. Most of the density current plunge points in Zengwen Reservoir are located between section 18 and section 21, except for the Typhoon Mindulle in 1993 and the Typhoon Morakot in 1997. The movement velocity of turbidity current is between 0.24m/s and 0.61m/s, with an average of about 0.39 m/s. The velocity coefficient is between 0.054 and 2.11, with an average of about 0.54. Due to the movement velocity is estimated from the location of the plunge point to the dam and the arrival time of turbidity current is based on the estimation of the velocity coefficient, the range of velocity coefficient value is more diverged. However, the Zengwen Reservoir has not yet discovered the phenomenon that the turbidity current gradually migrates from the upstream to the dam. Therefore, it is recommended that the project continue to collect more data from the field, and gradually correcting the velocity coefficient to be more feasible. Therefore, this project proposes an average velocity coefficient of 0.54 tentatively for calculating the movement velocity of the turbidity current, and then calculates the transportation time and arrival time of the turbidity current. Then, the simulation of turbidity current venting operation is provided and reference source is suggested.