台灣地區逕流係數分佈之探討

Abstract

集水區之水文規劃與管理經營中，逕流係數的應用常扮演著一個重要的角 色，因此，全面且有系統地決定集水區的逕流係數值就相當的重要。本研 究乃結合地理資訊系統技術與合理化公式，以建立台灣地區逕流係數分佈 圖，其架構係先依據台灣本島之地理與水文特性，將其劃分成三個地區， 再以地理資訊系統軟體ARC/INFO與ArcView求取集水區面積、坡度及河川 長度等相關參考地文因子值。在集水區設計尖峰流量值的求取上，則是採 用上述求得之具獨立代表性的地文因子，以複迴歸方法去求得100年頻率 年之設計尖峰流量。由複迴歸分析所得結果顯示，所劃定之地區內的集水 區具有相當的水文均一性與區域分佈特性。另一方面，各集水區之降雨強 度與集流時間可藉由運動波控制方程式推導之集流時間計算式與降雨強度 計算式聯立求得。最後，將求得之參數代入合理化公式中，即可反求出台 灣地區集水區100年頻率年之逕流係數值與繪製逕流係數等值線分佈圖。 整體而言，台灣地區集水區逕流係數的分佈是由東西兩沿海地區向中央山 脈呈現逐漸遞減趨勢。在中央山脈地區，逕流係數曲線呈現封閉環狀分佈 ，其值介於0.55至0.7間；而在河川中下游平原地區之外圍曲線逕流係數 值為0.8，其值即可視為台灣地區河川中下游平原的逕流係數上限值。同 時，本研究之作業流程皆架構於地理資訊系統軟體ArcView中，並以其所 支援之Avenue物件導向程式語言，建構使用者介面以自動化與人性化地求 取集水區之尖峰流量、集流時間、降雨強度及逕流係數值。

In general, runoff coefficient plays an important role in watershed hydrologic designs and managements. Therefore, to systematically determine individual watershed runoff coefficient is quite necessary. This study is thus to combine GIS and rational formula to establish a runoff coefficient distribution map over Taiwan area. Firstly, the entire Taiwan island is divided into three major areas according their geomorphologic and hydrologic properties, the related physiographic factors such as watershed area, slope, stream length ---, etc., can all be generated through GIS software ARC/INFO and ArcView analyses. As for the estimation of watershed design peak flow rates, multi-regression method is used to obtain the 100-year frequency design peak flow rate from the above physiographic independent variables. The results shows the hydrogeneity for the watersheds selected in each area and proves the zonal distributed properties in Taiwan area. On the other hand, rainfall intensity and time of concentration for individual watershed can be solved simultaneously through kinematic-wave governing equations and rainfall-duration formula. These parameters are then fitted into rational formula, runoff coefficients can be obtained and the associated distribution map can then be produced. In summary, the runoff coefficients distribution over the island declines from both east and west coast toward inland mountain areas. In central mountainous area, the values are in closed ring forms with the range 0.55-0.7.The outer value of runoff coefficients in the plain area is 0.8 and it can be considered as an upper value of watershed mountain zones.Also, the general framework of this study is constructed on ArcView GIS software. Since ArcView software employs AVENUE object-oriented programming, the proposed method also contains a group of user interfaces to automatically, user-friendly calculate the outcomes of watersheddesign peak flow rate, time of concentration, rainfall intensity as well as runoff coefficients.