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頭前溪河口段受到外海波浪、潮汐、匯流段交會之水理輸砂影響，歷年來變遷頗為顯著。水利署水利規劃試驗所、第二河川局等單位自民國94年起，陸續辦理河口段之治理規劃檢討、物模試驗、數模研究及工程執行規劃等計畫，目前河口段相關工程已完工約一年，其中舊港島分流工、苦苓腳凹岸丁壩及河口段疏濬等之效益，值得持續評估探討與研究。此外，為了提升河川生態環境之維護與保育概念，結合水文、地文、人文、生物、空間利用，以頭前溪河口段為例，整合相關水利工程措施，營造浮覆地與生態棲地環境，並結合公眾參與，研擬頭前溪河口段生態水利整體規劃，作為未來國內河口治理規劃之參考。本計畫分兩年執行，藉由動床數模工具、生態與人文調查、公眾參與等，進行頭前溪河口段生態水利整體規劃，除了評估河口段舊港島分流工、相關工程措施之效益外，配合座談、說明會等各類型公眾參與型式，結合生態與人文基本調查資料與相關水利模擬分析，綜合呈現整體規劃意涵與風貌，以供相關治理規劃與決策參考。

Influenced by the flow and sediment transport among wave, tide and river’s discharge, the morphology of Touchien River’s estuary has migrated dramatically in the past years. Several plans of Touchien River’s estuary had been proposed and executed by the Water Resources Planning Institute (WRPI), and the Second River Management Office since 2005, including the Review Improvement Planning, model experiments, mathematical tests, and engineering projects. The engineering projects of the estuary have been completed about two years ago. However, the estuary bed started to deposit. Hence, the benefit of building Jiugang Island diversion dikes, Kulingjiao concave bank dikes, and dredging the estuary should be assessed. In addition, aiming at restoring and conserving estuary’s ecological environment, both ecological environment and hydraulic engineering should be integrated in the overall planning of eco-hydraulic engineering of Touchien Estuary, which combines hydrology, geography, humanity, biology, and space utilization. This study is carried out in two years. In this (second) year, work items include taking three ecological census of indicator species, simulating the long-term morphologic change of Touchien Estuary, assessing the effectiveness of the proposed countermeasure, proposing an overall planning of eco-hydraulics engineering, and recommending land-use management. According to the sediment transport simulation result of several improvement engineering layouts of Jiugang Island diversion dike and other associated engineering works, an overall improvement engineering layout was recommended and assessed. On the overall improvement engineering layout with building a 32m in length, 2m in width, EL. 6m protection structure between Jiugang Island and diversion dike, shortening the length of no.1 Kulingjiao spur dike to 80m and dredging, it would decrease the water stage of the design discharge Q100 (8,530cms) on average about 0.5m in the Touchien Estuary, and enhance flood protection capability of Jiugang Island under Q20. By integrating the analysis of 5S model, comments of citizen participation, and the benefit assessment of the overall improvement engineering layout, an overall planning of eco-hydraulics was recommended. Through dredging, bed material size of the estuary will change and this will be helpful for ecological restoration of indicator species. Furthermore, the advantages of the existence of indicator species include guiding water course, protecting bank, purifying water, and increasing bio-diversity.

這份報告是「頭前溪河口段生態水利整體規劃及舊港島分流工效益評估研究」的第二部分。研究由經濟部水利署第二河川局執行，國立交通大學承辦，於2015年12月完成。 研究目的在於評估頭前溪河口段舊港島分流工及相關工程措施的效益，並提出生態水利整體規劃。研究內容涵蓋基本資料調查、工程改善方案研擬與模擬、河口段變遷模擬、成效評估，以及生態水利整體規劃與土地利用管理建議。 研究發現，水筆仔的分布範圍雖受颱風影響縮減，但植株數量穩定。工程改善方面，建議調整舊港島環島護岸、縮短苦苓腳丁壩長度、進行河道疏濬，並優化舊港島分流工。整體改善方案預計能降低洪水位、減少舊港島溢淹面積，提升河防安全。 生態水利規劃建議透過疏濬減少卵礫石，增加水筆仔植生範圍，利用水筆仔導水功能加深河道，並兼顧生物多樣性與水質淨化。土地利用管理則建議朝生態營造、水利功能及歷史文化保存方向發展。