圖書典藏及影音數位平台

近年水利署為維持現有水庫之蓄水功能，積極推動水庫更新改善及防淤工程，以期水庫淤積情形得以減緩；水庫下游河道也因此得到上游集水區泥砂之補注。目前台灣典型河川中下游河道河槽之下切、拓寬、側向變遷與縱向沖淤等行為研究，均著重於河防安全與河道穩定影響之探討，對於水庫排洪排砂兼顧下游河道河槽建立之關係較少著墨。因此基於流域整體土砂平衡概念，探討下游河道河槽建立與上游水砂關係，研擬兼顧水庫防淤操作與下游河道河槽建立之策略方案，來提升水庫壽命與河防安全，值得研究探討。 本計畫擬藉由歷年水文地文資料及動床數值模式，探討水庫排洪排砂與下游河道河槽建立之關係，研析水庫下游河道短期與長期之沖淤、河口段變遷、河防安全等影響，研擬合宜之水庫排洪排砂與下游河道動態穩定河槽建立策略方案；並提出維持下游河道動態穩定所需之上游來水來砂條件，以供河川、水庫堰壩規劃及管理單位參考。

With the sediment yields increased in the upper watersheds, large sedimentation was transported and trapped in the reservoir. In recent years, to make sure the sustainable usage of reservoir, hydraulic desilting strategies were planned and assessed its feasibility in the future. Although many researches had discussed the impact of hydraulic desilting on downstream channels, seldom articles focus on the relationship among them. In this study, we take Zengwen Reservoir for an example to discuss the forward issues by using comprehensive methodologies. First of all, six periods cross section data in Zengwen River were collected and several fluvial morphological approaches, including the variation of the river hydraulic geometry relations, bed materials distribution, bankfull discharge, slope, the ratio of channel depth and width, average bed datum, thalweg, water level, channel cumulative sediment yields, and channel trough-line shifting were used to assess the river characteristics. In addition, the channel stability is also discussed by analyzing the river dominate discharge, the transverse and perpendicular stability, and its scouring/deposition trend. After a series of fluvial morphological analysis, the Zengwen River could be separated into three regions with different river characteristics. Second, one dimensional dynamic bed model, CCHE-1D, was used to simulate the bed change. Differing from the model parameters calibration and validation with a whole channel in tradition, the channel modules was constructed separately and the parameters for each module were calibrated and validated according to the reach characteristics. Third, we assume that the sediment amounts of maximum hydraulic desilting are 5.04 million cubic meters per year with sediment particle 0.055mm. Three hydraulic desilting ratios, 0.01, 0.55, and 1.0 were planned and simulated with two flood sluicing scenarios, the short term and the long term period. The short term period refers to the two hundred recurrence interval of flooding in Zengwen Reservoir; the long term periods assume that the pass ten year’s typhoon events in Zengwen Reservoir would be repeated in the future decade. Furthermore, the discharge and the sediment concentration for all tributaries and the tidal effects were taken into accounts in the simulation. The impact on the downstream channel with the hydraulic desilting, tributaries’ discharge and sediment input, and the estuary reaches were all discussed in this study. The results of numerical simulation reveal that large amounts of sediment could deposit in the middle reaches due to the milder slope. In the current hydraulic desilting planning, to avoid the severe deposition problem in these regions, artificial dredging is still a necessary engineer approach. Therefore, suitable hydraulic desilting strategies should consider the artificial dredge capacity and negotiate with the reservoir manager to draw up practicable sediment releasing amounts from the reservoir.