DEM analysis on longitudinal and transverse profiles of steep mountainous watersheds

Longitudinal and transverse characteristics of watersheds are fundamental to describe watershed topography. Only a limited number of studies, however, have analyzed the characteristics of transverse profiles in watersheds, and almost no studies have examined longitudinal and transverse profiles at the same time. How transverse profiles change within a watershed and how longitudinal and transverse characteristics of watersheds are related remain to be examined. To address these issues, this study employs DEMs, GIS and computer programming techniques to acquire a series of longitudinal and transverse profiles of watersheds. Basic morphometric parameters, representing the shape of these profiles, were analyzed. Methods to classify the profiles and to identify points where the morphometric characteristics change abruptly were also developed. These methods were then applied to severely dissected steep watersheds in the Japanese Alps. The results show that spatial change in transverse characteristics reflects two factors: general topography of the watersheds and local differences in channel development. The form of the transverse profiles is also affected by erosion processes that create mature V-shaped valleys with a characteristic slope angle. The longitudinal and transverse profiles play different roles in determining watershed topography, and the overall longitudinal slope exerts a major influence on the mean watershed slope. The discontinuity of the longitudinal and transverse profiles, however, tends to occur at the same location, which may reflect the occurrence of knickzones and their influences on the development of valley-side slopes.