The Study of Wtershed Characteristics of Keelong River and Flood Disasters

Abstract

民國89年秋末，象神颱風夾帶豪雨侵襲基隆河集水區，造成基隆市、台北縣市部分地區嚴重淹水，並造成上百人死亡，其淹水的水位與面積比76年的琳恩、87年的瑞伯與芭比絲颱風嚴重。在這段期間，甚多報導指出基隆河上游雨量過大（火燒寮24小時累積雨量高達723公釐-已超過200年頻率；五堵3天累積雨量達752公釐-為150年頻率），加上與上漲潮汐交互作用之結果，導致下游地區五堵水位站遭到淹沒，其水位高達17.98公尺，已超過200年洪水頻率，幾成水鄉澤國，嚴重影響國計民生與生命財產之安全。 本研究由自然與人為因子方面著手，並比較近年來造成基隆河沿岸重大淹水災害的歷次颱風事件(琳恩、瑞伯、芭比絲、象神)，利用地理資訊系統軟體(Arc/info、Arcview)、遙感探測軟體(Imagine)與集水區資訊系統(Wingrid)，分析並整合集水區之DEM及SPOT衛星影像資料，探討潮汐水位與颱風的關係，以及人為因子對基隆河集水區所造成的影響，以彰顯造成基隆河集水區歷年洪水與土砂災害最具影響的關鍵因素，最後提出改進方法及檢討人類在無意中犯錯而不自知的經驗，期能提供有關單位做為決策時能夠達到減災防洪的參考。 研究結果發現：基隆河淹水的原因在於下游地勢平坦，加上截彎取直後，河道變短、河寬變窄、蓄水容量大為降低；若再遇上每年10月的颱風與東北季風前進時所產生的地形效應，以及潮汐作用交互的影響，其淹水機率必定更大為增加。另一方面，由於人為不斷地破壞原有自然環境之地形與地表植被，且不斷與河川爭地的結果，導致地表不透水比例逐年增高，終使洪峰流量急遽增加，更是一個不可忽略且必須重視的重點。

Xangsane typhoon brought heavy rainfall when she was invading Keelong River watershed and caused serious flood in some areas include Keelong city and Taipei city and Taipei country, and brought hundreds of people to be dead in 2000 late autumn. Compared to the water level and the extent of the flood drown area with Lynn typhoon in 1987, Zeb and Babs typhoons in 1998, the drown area was much larger. During this period, there were quite many reports indicated that the rainfall on the upper Keelong River was too heavy, when combined with the raising tide. The flood level of the lower Keelong River area was too high. Eventually, the three cities along Keelong River was drown seriously that caused people lived poorly and the life and property was forced to danger. This research began with the natural and manmade factors, and then compared with the four mentioned typhoon events (Lynn, Zeb, Babs, Xangsane) which caused serious flood disasters recently around Keelong River. This research used the GIS software (Arc/info, Arcview), RS software (Imagine) and Wingrid system to analyze and integrate all the data of the watershed, finally to investigate the relationship between the tide and typhoons, besides the effect on Keelong River which is caused by manmade reason. Finally, we show the most important factors those caused the flood disasters and debris disaster in Keelong River, and then mention the improvement methods to review and discuss the experience that human beings make mistakes accidentally; and can be referred by government on trying to achieve the goal of reducing the disaster caused by typhoon storms. The results of this research indicate that the reason of flood disaster around Keelong River is that the slope of downstream is too mild. After the construction of cutting the curve river to get straight, the length of river got shorter, the slope of riverbed got steeper, and the capacity of water storage also got lower. In case the typhoon happened on October accompanied with northeast trades and the tides, the probability of causing flood disaster would get raising absolutely. Otherwise, owing to the destruction of natural environment and get land from river causing by human beings continuously and purposely. It induces the runoff volume, the discharge of flood peak and the ratio of waterproof from ground to get larger year by year. So it's one more important point which is unable to be ignored and must pay much attention to.