Origin and interpretation of knickpoints in the Big South Fork River basin, Kentucky–Tennessee

Abstract

This study investigates the causes of knickpoints and knickzones in the bedrock-controlled streams of the Big South Fork River basin in Kentucky and Tennessee. Knickpoints in the Big South Fork River area vary in form and apparent origins. While some are likely related to base level change and incision in the Cumberland River drainage system, the locations and drainage relations of the knickpoints are not consistent with transmission of an incision signal throughout the network. Local controls predominate in forming steeper channel segments, with no single factor dominant. Knickpoints in the study area are characterized by polygenesis and multiple causality, though several archetypes can be identified. These include rock fall rapids, created by mass wasting from adjacent valley slopes; structurally controlled headwater cliffs; and lithological knickpoints. A fourth category, local incision knickpoints, may be attributable to a variety of factors influencing force:resistance relationships. These results imply that the simple presence of a knickpoint cannot be attributed to any particular cause or history without consideration of the local controls. This further implies that factors such as the spacing of knickpoints may not be an indication of migration rates or that migration has even occurred. However, the analysis of individual profile convexities can shed light on various controls (such as lithology and structure) and other processes (such as valley side mass wasting and local bed incision) important in evolution of fluvially dissected landscapes.