Stream analysis of small drainage basins in an ancient landform, Korean Peninsula

• The knickpoints corresponded to fault zones.
• The fault activity affects the concavity and steepness.
• The ancient landform may not have been as stable during the Quaternary as expected due to faulting.

Much of the topography of Korea is ancient, but many Quaternary fault outcrops and marine terraces have been observed in the southeastern part of the Korean Peninsula. Sufficient evidence of a Quaternary fault is lacking in the geological features of the commercially developed Jukbyun and Uljin areas. Knickpoints that develop on streams can be formed by tectonic activity such as faulting and folding, or can result simply from the differential erosion rates of bedrock. In this study, we investigated the relationship between stream steepness and faults in the Jukbyun area. Stream profile analyses of the Bugu and Namdae basins were performed using a digital elevation model to estimate Quaternary tectonic movements. Stream parameters obtained from analysis of the longitudinal stream profiles of the Bugu and Namdae drainage basins in the northeastern part of the Korean Peninsula indicated neotectonic movement. Thirty of the thirty-nine knickpoints that developed in the downstream areas of the fluvial channels corresponded to fault zones. It is thought that fault activity results in knickpoints in river systems. The normalized relative slope (Ksn) value (54.9) of the BS1 stream in the Bugu drainage basin was higher than that (28.8–36.3) of the other streams in both basins, despite a similar lithology to NS1 and NS2. Therefore, we concluded that stream steepness might be a result of tectonic forcing rather than a product of rock strength in the study area and that stream parameters could provide indirect evidence of Quaternary tectonics in ancient landforms.