集水區暴雨強度-延時-頻率模式及其不確定性分析

Abstract

在實際水文模式的應用過程中,工程師經常面對許多不確定性的存在.這些不確定性將直 接影響到水文模式結果的可靠度,間接地,水文模式計算結果之不確定性將影響到水資源規 劃及水工結構設計之成敗.本文針對設計降雨強度常用之降雨強度-延時-頻率公式,利用再 取樣法探討其參數之不確定性.同時針對楊等(1996)所發展出之區域化IDF公式,利用一階 近似法推求其不確定.再者,利用面積加權的概念,結合單站IDF公式,而成一集水區平均IDF 公式,可用以推估集水區之設計降雨強度.台灣大多數高壩皆採用最大可能暴雨(PMP)設計, 但PMP設計本質上屬於定率的.本研究根據所發展之集水區區域平均IDF公式,推估壩址處PMP 其相對應之頻率年,以評估其設計是否恰當. Engineers usually face a variety of uncertainties resided in the practical applications of the hydrological models. These uncertainties will affect directly the reliability of the model output,and indirectly the adequacyof water resources planning and hydraulic structure design.Aiming at the commonly used rainfall intensity-duration-frequency(IDF) formulathis study investigates its parameter uncertainty using the bootstrap resamplingmethod. In the meanwhile, the uncertainty of the regional IDF formaula developedby Yang et al.(1996)is evaluated by the frist-order approximation method.Forthermore, the representative reg ional averaged IDF formula of a given watershed can be obtained by integrating the on-site IDF formula,based on theconcept of area weighting. This regional average IDF formula can be used toestimate the design rainfall intensity of a watershed.Most of the large dams in Taiwan are designed according to the probable maximunprecipitation(PMP). However, the design of PMP is deterministic. This study,basedon the proposed regional average IDF formula, estimates the corresponding returnperiods of the PMP's at several damsites. The results provide useful informationfor the evaluation of dam safety