Graduate Thesis Or Dissertation


Bedrock River Erosion by Plucking Public Deposited

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  • Plucking is a common erosional mechanism in steep bedrock rivers with well-jointed, layered bedrock. Where active, plucking is one of the most efficient erosional mechanisms. However, the influence of bedrock layering and jointing on the evolution of rivers carved into layered landscapes has yet to be properly addressed at the process level. Rivers carving into fractured and jointed rock commonly display sharp steps in the bed separated by flat reaches between the steps. At the edges of these steps, blocks are vulnerable to plucking by both sliding and toppling. In this work, I seek to constrain the roles of block geometry and flow physics on the susceptibility of such blocks to entrainment. I use numerical modeling to demonstrate how blocks play an important role in setting the pace of river evolution, and therefore should be accounted for in landscapes where plucking is active. I first employ a computational fluid dynamics model to constrain the pressure and shear forces on blocks under different flow conditions. I use the results of this model to inform calculations of the susceptibility of blocks to entrainment and find that accounting for the pressure differences around blocks in force calculations significantly reduces entrainment thresholds. I then use these numerical results to inform a process-based 1-D model of bedrock river evolution that accounts for the entrainment probability of individual blocks in a jointed bed. I find that in the absence of external forcing, jointed beds will self-organize into a series of steps that is set by the baselevel lowering rate and block heights. Adding layers consisting of larger blocks stalls erosion at the contact between the large blocks and smaller blocks. Further, the large blocks prevent any signal of changes in baselevel lowering from being transmitted upstream until the large blocks are able to be plucked. Finally, I test this model with a spillway erosion case study from Canyon Lake, Texas, where an 8 m deep canyon was carved during a three-day flood event. The work presented here demonstrates the importance of properly accounting for block physics in river evolution models.
Date Issued
  • 2021-05-24
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  • 2022-03-06
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