圖書典藏及影音數位平台

民國97年10月經濟部水利署(以下簡稱水利署)針對東港溪流域之河川特性、防洪問題、河川資源開發利用及自然生態環境保育等問題探討後，完成「東港溪流域中上游段治理規劃檢討」，研擬各項綜合治水對策及治理措施，其中因東港溪流域上游因萬安溪、牛角灣溪之入流輸砂量大，長期而言導致主流河段易淤積，使通水斷面積減少，為期能同時能使東港溪達到河道穩定平衡之渠坡設計與降低洪患，擬於兩支流由淺山地區流入平原地區之匯流口設置滯洪設施以降低中下游水患問題，經規劃後河道滯洪設施之合適地點為萬安溪與牛角灣溪匯流口處之保安林地。 前述規劃之滯洪池用地係為行政院農業委員會林務局屏東林區管理處(以下簡稱屏東林管處)轄管編號第2414號保安林，原作為防災保安林之用，目的在於水害防備，以儲蓄洪水，調節洪峰水流，延緩下游水患發生，與滯洪池設施之功能相當；爰此，透過民國97年3月25日審查會議及民國97年9月11日滯洪池協調會議，屏東林管處同意經濟部水利署第七河川局(以下簡稱七河局)於保安林地規劃設置沉砂滯洪池。然保安林於歷經民國50~60年間之濫墾與盜伐，林相已不完整，爰當地居民於民國60年迄今已多次陳情期能解除保安林之限制，變更為非公共財產，以利民眾合法取得承租耕種權。 爰上，民眾意見顯然與七河局於保安林用地規劃設置滯洪池計畫產生歧異，爰經民國103年7月24日行政院簡政務委員太郎於行政院農業委員所召開之「屏東縣萬巒鄉成德村五溝水地區編號第2414號保安林辦理解除程序時，因部分保安林地已在100年3月份由水利署公告規劃為滯洪池，後續土地應如何處理協商會議」結論，表示請水利署重新檢討滯洪池施設之合理性、必要性及實益性，以期能兼顧人民權益與生命財產之目的。水利署於103年8月26日經水河字第10353168640號函請七河局辦理檢討，七河局於104年9月15日研提「東港溪上游萬安溪及牛角灣溪匯流口滯洪池檢討」報告，經水利署於104年10月19日召開研商會議，依會議結論因報告內替代方案水理分析對東港溪通洪能力與兩岸排水影響尚不完整，請七河局再進一步分析檢討。 爰上，本計畫主要係對於東港溪上游(依據前述治理規劃檢討報告，上游為自萬巒大橋以上)滯洪池方案研擬對其通洪能力檢討及其影響分析之研究。

In October 2008, to reduce the possibility of flooding in the lower and middle reach of the Donggang River, Water Resources Agency schemed to build detention pond in the protection forest at the confluence of the Wan-An Creek and the Niu-Jiao-Wan Creek. However, the local residents petitioned for the release of the ban on the protection forest, and ask the Water Resources Agency to assess the appropriateness, necessity and benefit of the project on the conference on July 24th 2014. Thus, Water Resource Agency held the conference on October 19th 2015 to discuss the alternatives. As a result, due the incompleteness on the assessment of the alternatives, 7th River management Office was requested to conduct a more detailed analysis on the project. Hence, this project will focus on the assessment on flood carrying capacity and impact of the alternatives. Due to the flat terrain, drainage in the tributaries, and influence of the flood prevention projects in the flood-prone areas, only part of the run-off will flow into the main stream of the Donggang River. The peak discharges of 100-year return period at each control point was assessed with SOBEK under one-dimensional unsteady routing model. The result showed that the flood carrying capacity in most cross-sections meet the requirement except for the cross-section 23, 29, 50, 52, 54, and 55. The flood carrying capacity in the tributaries is required to meet the standard of 25-year return period scenario. The flood carrying capacity in most of the cross-sections in Wan-An Creek meet the requirement, except for the cross-section 1005 and 1006. However, in Niu-Jiao-Wan Creek, flood carrying capacity in part of the cross-sections only meet the standard of 2 to 5 year return period scenario. After assessment on each factors and aspects in this project, the detention pond is suggested to be built at the confluence of the Wan-An Creek and the Niu-Jiao-Wan Creek (left bank of the cross-section 57 in Donggang River). Besides, in cross-section 48 to 51 and 53 to 56 of the Donggang River, the stream channels need to be cleaned. The total project cost was estimated to be 80.23 million NTD including 44.55 million in construction cost and 35.68 million in land acquisition with the overall benefit-cost ratio of 1.37. The implementation of the project will improve the condition on bank scouring, which better ensure the safety of the residents. Furthermore it can relief the fear of the flooding and strengthen the faith on the government, which make the project necessary.