由縱剖面特徵初探園尾坑西北側蝕谷之發育作用

A Preliminary Discussion on the Development Process of Ravines near Yuanweikeng Based on the Characteristic of Longitudinal Profile

本研究藉由縱剖面特徵的分析，對於園尾坑西北側以出露頭嵙山礫岩為主之四處集水區的蝕谷發育作用進行初探，結果反映了滲流侵蝕作用主導的強烈性在研究區中呈現自北向南遞降的趨勢，由岩層結構推斷，滲流水源乃來自於棲留地下水。上述作用空間差異的形成可能與礫岩層中礫岩比率的多寡有關，而研究區部分一級蝕谷呈現出不同於主要發育作用的縱剖面特徵，則顯示研究區蝕谷在整體發育過程中相對重要性較低之作用對於形貌的影響並非全然不存在。又本研究發現，研究區中谷系密度由北向南遞減，似意涵滲流侵蝕作用主導者具有較高的蝕谷密度，此與地表逕流侵蝕作用主導者谷系密度較高的既有經驗歸納結果有所差異，其原因有待日後更多的個案研究以進一步地探討。

In this paper, the characteristic of longitudinal profile is examined for preliminarily inferring the development process of ravines within four small watersheds near Yuanweiken where the conglomeratic facies of Toukoshan Formation is exposed. The result suggests seepage erosion caused by perched groundwater seems to play a critical role in the whole development of ravine network in northern study area. In contrast, relative importance of surface runoff erosion is more evident in southern study area. Spatial difference of dominant process mentioned above could be attributed to the variation of the exposed volume of conglomerate probably. Some branching ravines’ morphology implies the influence of non-dominant process also exists within the part of watersheds. In addition, the more intense dissection of surface appears in the watersheds where the seepage erosion may be dominant in this study. It is not coincident with the inductive conclusion in existing literatures that higher drainage density is related to surface runoff erosion. A further research is necessary in order to find the reason.