由於地理資訊系統能提供操作便利、資料準確、高效率且能展示分析地理位置上等多項功能，使研究區域之環境背景資料建置與環境問題之分析更方便進行。本研究利用合理化公式，配合地理資訊系統，探討集水區流域在颱風期間，其逕流係數與逕流量所衍生的集流時間和坡度間的變化關係，並由坡地土地利用開發程度判別開發區與逕流係數間關係。本研究彙整1995-2004年間三峽河、新店溪、基隆河上三處具流量站之小集水區，由每年最大日逕流量與日降雨量資料，求出逕流係數與集流時間，結果顯示，在直線迴歸分析與對數迴歸分析中除介壽橋集水區外其餘集水區之相關性較佳，所以未來在進行類似之研究分析時，為求有較合理之數據或結果，需依照不同集水區特性，選擇適合之回歸分析方法。利用GIS軟體，將數值地形模型(DTM)區分為1-3級的緩坡和4-7級的陡坡兩類來分析，得知坡度和集流時間不一定呈現反比關係；由山坡地土壤圖，研究區域土壤以探討土壤滲入性和逕流量之關係。依土地利用情形探討逕流係數受開發程度影響，判別集水區開發情形和平均逕流係數的相關性，結果顯示三處集水區開發情形和逕流係數成正比關係。 Since GIS can offer operation convenience, accuracy of the materials that the GIS may generate, dealing the geographical analysis with high efficiency. Therefore it is convenient to carry on the research about environmental problems. This research makes use of rational formula to analyze the relation between runoff and river discharge during the typhoon period. With the help of GIS, this study analyzed the effects on the relation between runoff and river discharge due to the slope and the time of concentration. Data of three different smaller watersheds which are the Sanshia river, Sindian river and Keelung river were thus collected during the period of 1995-2004. In every year the biggest daily discharge and rainfall in these 10-year period was used to calibrate the runoff coefficient. The results of the regression analyses showed that the logarithm regression was better fitted. Therefore in the future with similar research, the model should be carefully chosen. In GIS application on DTM, two type of slope ,mild and steep, were use to study the slope effects on the relation between river discharge and surface runoff. From the analyses’ results, the time of concentration was not directly proportional to the degree of slope. The texture of soil and the type of land use in different watershed area were also examined and analyzed in order to find out how these factors have affected on the surface runoff and the river discharge.