INVESTIGATING THE IMPACT OF DISCONTINUITY ORIENTATION ON FLUVIAL INCISION PROCESSES

The processes by which rivers incise into bedrock, and thereby drive the evolution of entire landscapes, have been a focal point of research within the geomorphology community for several decades. From this growing body of research, bedrock discontinuity networks (fractures, bedding planes, joints, etc.) are emerging as a preeminent influence on the efficiency of fluvial incision. This is expected, due to the control discontinuities exert on plucking - one of the primary mechanisms by which bedrock is eroded in fluvial settings. Recent work has demonstrated that the spacing of discontinuities plays a dominant role in impacting bedrock erodibility by setting the size of pluckable bedrock blocks. However, the impact of discontinuity orientation on susceptibility to fluvial plucking is likely to be nearly as important, but has not yet been examined.

To investigate the role of discontinuity orientation on fluvial incision processes and bedrock erodibility, we are conducting a series of laboratory flume experiments, using stacked ceramic tiles to simulate fractured sedimentary bedrock. Within each experimental run, tiles are held at different orientations relative to flow direction (including upstream-dipping, downstream-dipping, horizontal, and vertically-bedded cases) using 3-D printed support trays placed in the flume. Using high-resolution photo- and video-recording tools, including 3-D images generated with Structure-from-Motion software, we document individual plucking events, knickpoint celerity and expression, and channel morphology. Through these experiments, we hope to demonstrate how the orientation of bedrock discontinuities impacts plucking style and thresholds of erosion, knickpoint behavior, and bedrock erodibility, thereby significantly advancing our understanding of fundamental fluvial incision processes and more fully characterizing the relationships between lithology and bedrock channel morphodynamics.