單場事件降雨逕流關係與河川退水特性之研究

Event-Based Rainfall Runoff Response and Flow Recession

歷線分離為獲取逕流係數等流量反應參數主要方式，其中圖解法以其簡便特性至今仍為歷線分離常用手段。然而使用圖解法往往面臨決定退水結束時間點過於經驗，易忽略集水區環境、降雨特性等問題。此外，台灣河川坡陡流急，中、小型集水區河川暴雨流量多在一天之內即可呈現穩定狀態，故以時尺度雨量、流量資料觀察暴雨流量變化特性應較傳統日尺度資料為宜。本研究由橫溪、稜角以及觸口集水區近十年中央氣象局與水利署時雨量、時流量資料選取單場降雨流量事件，以退水係數呈現連續三小穩定狀態之時間點作為退水結束時間進行歷線分離以析取各項流量參數，並運用典型相關分析（Canonical Correlation Analysis）探討臨前、降雨等輸入參數與逕流反應輸出參數間作用情形。研究顯示各集水區濕季退水結束時間皆明顯小於傳統應用上以N-Day法所得數值，而透過典型相關分析可發現逕流參數與退水結束時間受降雨特性影響較大，且皆為正相關關係，代表集水區排水能力主要隨降雨規模或降雨強度變化，而臨前狀態僅對稜角集水區影響較明顯，此外，降雨特性以降雨量影響最大，降雨強度則以最大2小時降雨量較為重要。

Hydrograph separation techniques are useful tools for determining runoff coefficients from storm events. Among them, especially for single event-based hydrograph separations, graphical technique is the most common approach. However, when it goes to set up the time of the end point, where direct runoff ceases and streamflow is entirely consisted of baseflow, whether by fixed criteria or just set it arbitrary, the doubt that antecedent or rainfall characteristics of specific events could be neglected emerges. Taiwan, characterized by high, steep mountains and strong rainfalls in wet season, the flow rate of recession limb could return to steady status within 24 hours after rainfall. It implies more natures of rainfall-runoff relationship could be filtered out by analyzing hourly hydrograph instead of traditional daily data. This study attempts to discuss correlations between antecedent conditions and rainfall characteristics as input factors and flow characteristics of watershed responses as output factors by analyzing single event-based hydrographs withdrawing from 10 years’ hourly rainfall and flow records from Central Weather Bureau and Water Resource Agency respectively. After the time of the end point, where the recession coefficient is approximately constant by 3 hours is identified, all flow parameters are derived by applying graphical hydrograph separation and then put into Canonical correlation analysis for further study. Of the events studied, Less recession times are found in all studied watersheds compared to values of N-Day method. Through canonical correlation analysis, runoff parameters and the time of the end point are in positive correlation to rainfall characteristics but not clear to antecedent conditions. And among rainfall characteristics, rainfall amount and max 2 hour rainfall are the two most important parameters which trigger flow responses.