水文頻率分析及設計降雨概念之檢視探討

Abstract

在都市水文模擬中，設計降雨往往是作為產生雨量時間序列的主要方法之一，而現今設計降雨通常是使用IDF曲線決定降雨總量以及修正位序法等設計雨型方法產生雨型，然而這些設計降雨通常沒有考量到不同延時的降雨對於都市致災性的差異，在這種情況之下，取決於都市的防洪能力，同回歸年但延時不同的設計降雨往往也會造成不同程度的淹水深度，因此如何考量都市排洪能力對於不同延時雨型設計的影響並且改善現在降雨設計之方法就成了此論文的兩個主要目標。 有了以上考量，此論文必須要有一個好的降雨定義給不同降雨事件藉此考量降雨事件更為全面並修正以往的設計降雨方法。以都市防洪為主，本論文提出一個改良的降雨設計方法於一個理想集水區且已知其防洪能力。在此集水區中，定義降雨深度超越的防洪設施的排水能力則此滯留於集水區中的降雨深度為淹水深度，並且使用此深度作為淹水嚴重性的指標。有了這個概念，我們結合降雨深度以及降雨延時兩個降雨特徵並進行水文頻率分析,藉此考量不同延時之降雨深度機率密度分布。結合機率密度函數和都市排洪能力，此論文提出期望超越深度來評估不同延時降雨之期望的致災能力。最後考量設計降雨與事件降雨之期望災害不同進行事件降雨修正，並且重新產生設計雨型，並且給予都市水文模擬一個更佳的雨量時間序列。

For engineering practice, the determination of design storms mainly applies the intensity-duration-frequency method or revised ranking method with a fixed given duration based on the long-term rainfall record. However, this kind of method does not address the influence of storm duration. Both long duration or short-duration storms are combined together in performing rainfall design. As a result, in some cases, the peak intensity of a short duration design storm might be overestimated by traditional methods. Consequently, how to incorporate the concept of duration to improve current frequency analysis and design storms are the two main purposes of this research. With this concern, this study tries to find a better definition of the rainfall characteristics based on different durations, and generate a revised design storm in the consideration of more comprehensive rainfall patterns. For the purpose of flood control, this study tries to propose the improved method based on a conceptual watershed with known drainage capacity. In the watershed, when the rainfall total depth exceeds the capacity of the drainage system, the accumulation of the water depth will become the flood. Considering this situation, the total depth of storm plays an important role in the severity of flooding. For this concern, this study tries to incorporate two parameters, the rainfall duration and the rainfall total depth which indicate the severity of storms in frequency analysis. Following, to avoid the under/over-estimation of rainfall peak intensity without considering the influence of duration, we propose the expected value of over depth to composed a design storm by combining different duration of rainfall events. More specifically, if the expected value of the rainfall event is higher than the design storm, the rainfall of events will have a lower ratio to shape the rainfall total depth of design. With this process, we can obtain the suitable rainfall events for our design storms under known drainage capacity. Based on this revised event, we could generate a new design rainfall by the revised ranking method. Finally, this study will propose a method of design storms which offers a better application for flood protection plan and management.