圖書典藏及影音數位平台

青草湖水庫位於新竹市南區客雅溪中游，於民國45年興建完成，原蓄水面積24.85 公頃，蓄水總容量1,097,700 立方公尺，為新竹地區早期兼具灌溉及觀光功能之水庫與著名風景區，惟水庫逐年淤積而蓄水容量銳減，致防洪和灌溉功能喪失，民國76年前台灣省政府公告廢除水庫使用功能，目前保留觀光遊憩，並由新竹市政府負責管理。近年來針對青草湖整治過程，分別於民國92年12月經濟部水利署完成「青草湖水庫重生規劃」、民國96年8月辦理「青草湖重生實施計畫」、民國98年9月辦理「新竹市青草湖重生工程」及民國99年3月辦理「新竹市青草湖重生工程既有構造物安全評估(溢洪道改善後蓄水前操作檢查)」等。 雖青草湖已喪失其防洪與水資源利用功能，且庫區上游係屬山谷地形，流域裸露之地層有上新世卓蘭層與更新世之沖積層，土質鬆軟易受沖蝕，加以寶山鄉山坡地大面積開挖，汛期易增土方量流失，加劇庫內庫容銳減，經統計至民國92年水庫容積僅剩完工時之8.68 %。 於防汛期青草湖水力排砂與上游泥砂入流歷線、下游客雅溪防洪減淤，及休閒景觀均與該水庫泥砂變遷息息相關；故本計畫擬配合新竹市「青草湖重生實施計畫」針對青草湖水庫因砂率之影響，洪峰削減及延滯出流效應均不明顯，喪失防洪功能，原有灌溉渠道進水口及排砂隧道均已被淤泥覆蓋而無法操作，不具取水及排砂功能，水質受污染已呈優養狀態，水庫嚴重淤積致湖面縮小及青草湖歷年改善方案檢討等，作一流域整體性之檢討。 本次計畫目的係如何利用水力排砂以減緩水庫囚砂率，並評估排洪時配合客雅溪排水整治將泥砂排放至河口之效益，以減少庫內及客雅溪渠底清淤疏浚量，維持水庫沿岸環境景觀，使地區風貌重塑，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。

Located midstream of the Keya Creek in the South District of Hsinchu City, the Chingtsao Lake (Green Grass Lake) was constructed in 1956 with an original water area of 24.85 hectares, and a total impoundment capacity of 1,097,700 cubic meters. The impoundment capacity has declined significantly over the years because of severe siltation. In 1987, the former Taiwan provincial government abolished the lake’s function as a water storage reservoir, limiting its purpose to that of a tourism and recreation destination, which is managed by Hsinchu City government even today. Statistics have shown that the volume of the reservoir in 2003 was only 8.68% of that originally constructed. Although the Hsinchu City government implemented a dredging project in 2009, the lake requires repeated desilting after a short interval of time to remove the sediment resulting from overexploitation of the land and inappropriate conservation of the slopes upstream of the Keya Creek. The aim of this study was to alleviate the sedimentation rate by discharging sediment hydraulically. The results of this study are provided below. I. Data Collection of the Current Situation of the Keya Creek and Chingtsao Lake (1) Ecological survey results show that the Keya Creek possesses significant biodiversity, including several bird species of conservation concern, such as the crested serpent eagle, sparrowhawk, and brown shrike. (2) Survey results regarding the water quality show that if the Chingtsao Lake is used as the baseline, the upstream pollution ranges between unpolluted (or minor pollution) and moderate pollution, and the downstream pollution ranges between moderate pollution and severe pollution. (3) An investigation of the Keya Creek flood control structures has shown that among the existing protection facilities primarily comprise reinforced concrete (RC) dikes, RC retaining walls, ridges, cages, and masonry revetments . Cross-creek constructions include 46 bridges. (4) Comparative analyses of the watercourse scour-and-fill effects have shown that both scouring and filling effects developed downstream beyond the Phoenix Bridge, whereas only scouring effects were observed upstream. (5) Hydrological analyses have indicated that the peak flows at the return periods are slightly lower than the figures estimated in the “2007 Plan of Water Draining and Environmental Promotion in the Keya Creek of the Hsinchu Region.” This was presumably because a different probability distribution function was selected. II. Analyzing Sediment Yield and Discharging on the Upstream of Chingtsao Lake (1) Combining remote sensing (RS) technology and geographic information system (GIS) technologies, this project obtained data of landslides and sloping land soil losses from the catchment basin. We calculated that approximately 9.1 tons of sediment are deposited annually upstream of the Chingtsao Lake. (2) Observational studies of water and sediment show that the alignment curve of the flow-sediment transport rate at the Phoenix Bridge is Qs= 14.122Q1.4241, R2 = 0.99; and the alignment curve of the flow-sediment transport rate at the Huanhu Bridge is Qs= 8.01Q1.7368, R2 = 0.98. (3) Simulated calculations based on the current impoundment capacity of Chingtsao Lake and that after the rejuvenation program indicate that its flood detention capacity is insignificant. Consequently, Chingtsao Lake should be considered an ordinary river course. (4) Operations on the rubber dam of Chingtsao Lake are still based on the water level. (5) According to the terrain data of Chingtsao Lake measured this year, the sedimentation rate in the sedimentation basin is estimated to be 23%. (6) Regarding the current situation of the Chingtsao Lake, the hydraulic and physiographic conditions for discharging sediment hydraulically are inadequate. Instead, short-term mechanical excavation-based dredging of the land surface is recommended to immediately achieve the desired effects. (7) Based on experiences of the Chingtsao Lake Rejuvenation Program, desilting operations will be performed at an average elevation of 30.8 m, and a total expense of approximately NT$44.7 million. (8) The result of the CCHE-2D simulation shows that compared to the entire reservoir area, the current channel for discharging sediment is too small to effectively transport sediment upstream. After assessments, simulations of Plan 1 (Project 0), Plan 2 (dredging the sedimentation basin), and Plan 4 (separating sediment from water) were performed. The results were used as the boundary conditions for sediment upstream of NETSTARS to determine the scour-and-fill effects hydraulic sediment discharging operations have the downstream watercourse. III. Evaluating the Keya Creek Flood Control and Sediment Reduction Simulation Results (1) Among the NERSATRS simulations, master parameter Case 7 obtained relatively ideal simulation results. The parameters included the Engelund and Hansen sediment transport formula, the scouring depth multiplication factor Alt = 0.02, and the number of flow tubes, Tube = 3 and △t = 1(hr). (2) Simulative analysis of the scour-and-fill effects in the Keya Creek watercourse caused by discharging sediment hydraulically in Chingtsao Lake indicated that the simulated watercourse scour-and-fill effects for Plans 1 and 2 were similar, both showed scouring and filling effects. Furthermore, sedimentation effects were obvious in Plan 4. (3) The simulation results of CCHE-2D and NETSTARS indicate that although the sediment discharging performance of Plan 4 was satisfactory, it caused sedimentation in the downstream watercourse of Chingtsao Lake. Additionally, the discharging of sediment in Plan 4 involved separating sediment from water, which increases engineering costs. Furthermore, plan 4 reduces the impoundment area and volume of Chingtsao Lake by half, which significantly influences the benefits associated with sightseeing. Therefore, of the assessment plans for this research project, Plan 2 has the greatest feasibility. Therefore, it should be adopted to perform regular dredging operations. In addition, regarding slope conservation and land development, the awareness of residents living in the upstream catchment area should be increased through propaganda to ensure effective operations and management of the Chingtsao Lake area.