在利用數值地形模型粹取河川網路過程中，排水匯集量臨界面積，常是影響河川 網路粹取結果的重要因素之一，其功用主要在決定河川網路之密度。本文旨在探討不同的臨 界面積對河川網路粹取之影響，並以福山兩個陡坡小集水區作為研究對象。結果顯示，河流 級數、支數及長度，均隨臨界面積之增加而減少，河溪長度比及河溪面積比，變動範圍較大 ，與臨界面積無密切相關，此外，排水密度與河川頻率取對數後，與臨界面積成直線負相關 ，對排水密度與臨界面積關係而言，福山一號集水區比福山二號集水區較為敏感，但對河川 頻率與臨界面積之關係而言，則恰好相反，福山二號集水區則比福山一號集水區較為敏感， 此現象可能與集水區形狀及坡度密切相關，但尚待進一步之探討。 When extracting stream networks from a digital terrain model (DTM), the flow accumulation threshold area is used to determine the density of stream networks, and it is an important factor that it often has great influence on the results. This paper evaluates the effects of different threshold areas on the extraction of stream networks. In particular, two small steep watersheds in Fu-Shan are chosen as the study sites. The results reveal that the stream order, stream number, and stream length decrease as the threshold area increases. Both ratios of stream length and stream area vary in wide range, which are not correlated with the threshold area. Furthermore, the logarithm of stream density and stream frequency have negative linear relationship with the threshold area. The Fu-Shan watershed No.1 is more sensitive to the relationship between stream density and threshold areas, while the Fu-Shan watershed No.2 is more sensitive to the relationship between stream frequency and threshold areas. This phenomenon probably relates to the shape and slope of the watersheds, however, further study is needed.