圖書典藏及影音數位平台

為因應基隆河近年來保護標準下洪水量上升，防洪能力日益不足之問題，惟目前基隆河兩岸防洪牆皆已施做完成，其防洪工程不易再加高加強，加上兩岸社區亦已發展完成，宜辦理研究，謀求綜合治理措施來降低洪災風險，故為找出適應策略，辦理本計畫。故本計畫擬以務實面探討洪水量增量下防洪基能影響及因應目前所遭遇的防災課題，以符合綜合流域治水作法，提升防護效能，減低人民財產生命損失。爰此，辦理基隆河防洪機能改善方案初步研究。

Recent hydrologic analysis suggests the of flowrate of 200-year recurrence at Keelung River mouth should be 6,600 cms without considering diversion from Yuanshanzih. Comparing to the original design flood 2,480 cms, it increases almost 59.3%. With considering diversion from Yuanshanzih, the discharge of Keelung increases 1,660 cms from 3,690 cms to 5,350 cms, around 45% more. Now flood protecting capacity now is much lower than the protection standard, but current flood embankments are not easy to be enhanced because both sides were filled with completed flood protecting constructions. As a result, integrated flood management may be a solution to reduce the risk of flooding for Keelung River. This study indicates the 77% of flood discharge increase in the Keelung River mouth, around 1,900 cms, is caused by the change of rainfall, the other 23%, 580 cms, is due to land development. The one-dimension HEC-RAS model analysis results revealed that the main overbank flood risk sections in Keelung River, under the 200-year recurrence flood, are the SheZi Island river section (from river mouth to section 9th of Keelung River) and Xizhi river section (from section 50th to section 70th of Keelung River) where 28 bridges, including 7 recently completed bridges, did not have adequate flooding transited sections. The flooding control capacity of Keelung River are affected by these seven factors such as the flooding discharge of Keelung River, the flooding discharge Tamsui River, the water level at the Tamsui River’s river mouth, mangroves, Manning’s n values, river siltation, river channel broaden. According to the sensitivity analysis of each factor, the flooding discharge of Keelung River is most sensitive. In this study, choked flow effect caused by bridges such as SheHou Bridge, Jiangbei Bridge and Chang'an Bridge, has been proved to be the major cause of flooding risk in Xizhi river section, and simulating demolition case of three old bridges shows that the water level can be reduced by almost 140cm. This study compared the flood control advantages of following cases: flood diversion scheme, tributary river closure scheme, floodway, tributary detention flood pool, tributary dam and underground detention river. Among these cases, either the Sijiaoting flood diversion scheme or the Sijiaoting flood diversion scheme with the left tributary diversion scheme is the most effective flood reduction measure, which can max reduce flood about 580 cms and 760 cms. In Sijiaoting flood diversion case except Zhongshan Bridge section, the reduced flood is almost equivalent with the discharge during Nari typhoon. On May 29th 2018, Legislative Yuan approved Draft Revision of the Water Act. following, it is announced by Presidential Order No. Hua-Zong-Yi-Yi 10700066601 on June 20th 2018. With this revision, a new chapter of “runoff allocation and outflow control“ have been added into the Water Act. In response to the scheme, runoff allocation, this study has estimate the preliminary runoff allocation volume of Keelung River, which is around 4,160,000 cubic meter and the flood reduction effect of runoff allocation scheme up to about 350cms. The improvement program in the Keelung River is includes short-term 5-year and mid-term 15-year and long-term plans. In short-term, the goal for the upstream section of the Nanhu Bridge, conducting dredging and improving embankment will be conducted to prevent 200-year flood risk analyzed in 2015. The mid-term goal is reducing 200-year flood risk analyzed in 2015 to the river permitted flow by conducting runoff allocation scheme. The long-term goal is to remain the permitted flow. Except for promoting disaster prevention systems, non-engineering measures should cooperate with the runoff allocation and outflow control in land development programs to achieve the sustainable management for Keelung River.