圖書典藏及影音數位平台

頭前溪河口段受外海波浪與河川流量交匯等複雜因素影響，歷來變遷頗為顯著。水利署第二河川局(以下簡稱二河局)為確保河口段之河防安全與落實分流治理規劃，於101年完成辦理河口段治理工程，包括舊港島護岸與分流工、苦苓腳凹岸堤防與丁壩群及河口段疏濬等措施。完工迄今河床已有回淤情形，故二河局於103~104年度辦理各項工程之效益評估研究，並整合水文、地文、生物、空間利用及相關水利工程措施，研擬頭前溪河口段生態水利整體規劃，提出改善建議。然治理工程完工後，河道水理輸砂條件改變加上外海波浪推移作用，對於河口與臨近海域沖淤之影響尚待評估研究。此外，河口段河道整治工程完工後仍有待相關監測資料收集，以進一步評估與驗證，且整治工程對於溝貝、豆子埔溪等排水之影響亦須進行評估。爰此，成立本委託專業服務計畫。

Influenced by the flow and sediment transport among wave, tide and flood, the morphology of Touchien River estuary has migrated dramatically in the past years. In order to enhance flood protection of the estuarine area, Second River Management Office had implemented the regulation plan of Touchien River estuary, including setting Jiugang Island diversion dikes, Kulingjiao concave bank dikes, and dredging the channels, and all were completed in 2012. However, Touchien estuary supplies sediment to surrounding coast. After the regulation plan completed, the sediment transport conditions of Touchien estuary would change. Therefore, It is necessary to evaluate the impacts of Touchien estuary sediment transport on surrounding coast such as Kangnan and Shangyi coast. For this purpose, numerical model will be utilized to simulate the migration of Touchien estuary and surrounding coast. Then, the function of coastal defense structures will be reviewed, and improvement measures will be recommended to be the references of the regulation plan. This study is carried out in two years. In this (first) year, this plan performed in three principal parts. First, supplementing with channel and coastal sectional survey has been executed. Comparing with the past survey result, it shows that the river bed of Touchien and Fengshan have been raised up about 0.12m and 0.26m respectively. Both Kangnan and Shangyi coasts presented erosion respectively in the region of seabed elevation EL.0m to 50m and 200m. Second, a two dimensional mobile-bed coastal model (named CCHE2D-Coast) was adopted to simulate the estuarine and coastal morphological changes during the storms and monsoons. By analyzing the simulated seasonal morphological changes, it shows several important characteristics of sediment transportation such as: (1) the sediment would be flushed to estuary by flood currents, and deposit in the north region of Hsinchu fishery harbor in the range of seabed with EL.-3.0m to EL.-7.0m; (2) the larger flood would flush sediment to further area, and erode the river mouth more; (3) in the monsoons, the offshore currents would erode the deposition in the north region of Hsinchu fishery harbor, and transport sediment to the toe of breakwater dike of the harbor or pass it to the south of the harbor; (4) The monsoons play a role of a recovery to compensate the bed changes by the storms. Finally, according to the simulation of several improvement dredging cases, case 2 with the width ratio 2:3 of left and right channel in the Jiugang Island reach would decrease the deposition from 2.5m of existing layout to 1.7m.