圖書典藏及影音數位平台

新店溪支流南勢溪集水區於蘇迪勒颱風後崩坍地大幅增加，預期土砂可能逐年向下遞移，而桂山壩位處烏來老街下游，本次計畫目的係如何利用水力排砂以減緩水庫囚砂率，並評估颱洪時配合南勢溪整治將泥砂排放至下游，以減南勢溪渠底清淤疏浚量，使河床風貌重塑，恢復往日湖光山色景緻，達成增進休閒遊憩及環境營造之目標

After Typhoon Soudelor hit Taiwan in 2015, the landslide area have been increased from 22.35 Ha to 65.48 Ha in the upstream of Xindian River in Wu-Lai district, which were recognized by Forestry Bureau Aerial Survey Office in Taiwan. The sediment would transport to the river and change the direction of water impact, which could results in the safety concerns of the flood capacity and flood-control structure. Although the “Reservoir Water Gate Operation of Guishan Dam” and “Guishan dam reservoir application Guidelines” were revised in 2010 and 2011, respectively. The sediment deposition in the downstream of Wu-Lai old street has been increased during the Typhoon season, and it reduced the functional efficiency of Guishan Dam reservoir and raise the flood risk due to the serious sediment deposition of the river part. The aim of this project is to analyze how the hydraulic flushing decreases the trap efficiency of the reservoir and evaluate the effectiveness that sediment was desilted by the gate operation during the drainage period. It could reduce the dredging amount in the reservoir and drainage bottom of Nanshi River, which could maintain the environmental landscape along the river and regain the former scenery, attaining the goals of the river environment leisure and recreation. The work items in this project are multifarious and we classified them in to 4 main parts, including information collection, field measurement, model development and countermeasures development. In addition to the general situation of the river basin as the basis for the analysis at basic data collection part, the main project is to estimate the annual sediment yield and discharge in the basin. It would become the evaluation basis. In the field measurement, the basic topographic and gravel-bed River material survey, as well as information of water level and sediment station will be used as a model calibration verification. The most important part in development of flow hydraulics and sediment transport modeling ,considering at the influence by Guishan Dam in One-dimensional model, our team adopted the HEC-RAS as the tool which has a better simulation result in cross-rive structure and explore long-term erosion sedimentation trends and flood drainage capacity. The HEC-RAS simulation results will be provided as the analysis conditions to the SRH2D, a two-dimensional model, which could deal with most conditions in 2D sediment transport modeling and without divergent problems. With this 2D model as the main tool , the desilting and drainage problems once be used in Shigang Dam and Hou-Cun Weir assessment and achieve good results. In addition to the fixed wheel gate of drainage tunnel of Guishan Dam which is 5.38m wide and 4.15m high are submerged at 102.0m underwater top elevation, results in some desilting parts should consider the 3D hydraulics and sediment characteristic. Our team would evaluate with our model once developed in Shimen Reservoir. On the foundation of hydraulics and sediment model, our team will assist the stabilization project of Wulai River section, desilting operation and improvement of Guishan Dam and rainfall warning evaluation. The main dredging part in the river stabilization scheme is dredging river section, giving the suggestion of the aspect ratio and the site of dredging flow path in deep groove. Besides the dredging effectiveness evaluation, our team would assist in assessing the impact from the method in this project. The suggestion includes dredging time operation and methods, also evaluate whether the weir elevation change would improve dredging or not, and the feasibility assessment of dam removal. Moreover, we would assist the rainfall warning setting, which could be used in disaster reduction and reservoir operation also as the reference for organizers.