臺北市地狹人稠，市區內大部分開發為商業區與住宅區，鮮少設置大規模之休閒空間，臺北市政府為提高市民生活品質，在辦理市轄各河川整治工程時，對於堤外高灘地一併規劃設置為公園綠地、運動場、停車場等公共休閒運動空間，並在堤防適當地點設置疏散門，以提供颱洪期間河水淹漫高灘地前人車疏散及平時做堤外公共設施維護、河道疏浚等工程車輛進出使用。 由於在颱風來襲期間疏散門必須適時的予以關閉，以確保堤內居民生命財產安全。目前臺北市政府關閉防洪疏散門時機係以中央氣象局發佈陸上颱風警報後，淡水河臺北橋水位達2.4公尺或基隆河大直橋水位達3.1公尺時，即通知臺北市政府災害防救中心發佈新聞稿，並立即關閉全市疏散門。但根據歷年來颱洪資料顯示，目前關閉疏散門之戒備水位偏於保守仍有提高之空間。 本研究以歷史颱洪事件之水文資料做統計分析，對於現行疏散門啟閉機制合理性做一探討，並重新推求疏散門最佳啟閉之水位，另外由於水利工程在規劃設計時水文資料不確定性或各工程變數等因素，往往使水利工程設置完成後仍有風險存在，本研究亦將從歷史颱洪水文事件中，以水位與颱洪次數之累積機率做迴歸分析，探討防洪疏散門關閉水位及河水淹漫高灘地之風險機率。 The Taipei City is crowded with a large population today. Most areas in the City were developed for commercial or residential use. Very few considerations have been given to reserving massive spaces for leisure activities. In order to enhance the living quality for citizens, the Taipei City Government plans to utilize the upper platforms of outer riverside levees as open public facilities such as parks, sports fields, or parking lots. These planning activities are often carried out at the initial design phase of maintenance projects for rivers that are classified as City-governed. Evacuating gates on the levees are established at proper spots. Through those evacuating gates, people and vehicles can be evacuated before the rivers overflow the platforms during the typhoon or flood seasons. At normal times, the same evacuating gates are used as entrances for engineering trucks when maintenance of those public facilities are carried out. When a typhoon attacks, evacuating gates must be closed in time to secure the lives and properties inside the levees. At present, the Taipei City Government relies on information provided by the Central Weather Bureau (CWB) to determine the right timing for closing evacuating gates. The Taipei City Government will inform Taipei City Government Disaster Response Center to issue press releases and close every evacuating gates in the City when the following criteria are met: a) CWB issues a terrestrial typhoon alert, b) either the water level of Tamshui River at Taipei Bridge exceeds 2.4 meters, or that of Keelung River at Tachih Bridge exceeds 3.1 meters. However, according to the data for typhoons and floods in past years, the warning water levels upon which decisions for closing evacuating gates were made are considered conservative, and could be properly adjusted. This study analyzes the hydraulic data resulting from typhoons and floods in past years. It evaluates the appropriateness of current practice for closing evacuating gates, and suggests new water levels for closing those gates. Due to the uncertainties of hydrology and uncontrollable engineering factors when planning hydraulic engineering projects, it is quite likely that risks still exist after the projects are completed. This study also carries out recursive analysis with accumulated probability of both water levels and the number of typhoons and floods. It probes into the probability of risks associated with different water levels for closing gates, as well as the probability of risks associated with overflowed platforms.
