2023 CSDMS meeting-007

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Modeling the development of wide bedrock valleys as a function of collapsed bedrock block size, bed sediment, and discharge variability

Abigail Langston, Kansas State University Manhattan Kansas, United States. alangston@ksu.edu

Theories for vertical bedrock river incision are well developed and widely applied; however, understanding how bedrock rivers laterally erode their banks and develop into wide bedrock valleys is a frontier topic in geomorphology. I use a modified version of the Landlab lateral erosion component coupled with the sediment-flux dependent vertical incision component in Landlab to explore the fundamental question of how valley width and widening rates are related to sediment on the channel bed. The lateral erosion component widens valleys through lateral undercutting and eventual collapse of bedrock valley walls. The modified lateral erosion component allows the user to set a characteristic block size of collapsed bedrock material. Collapsed material with smaller blocks sizes is rapidly transported away from the valley wall, allowing continued widening, while collapsed material with larger block sizes protects valley walls from further widening until it has weathered into transportable grain sizes. Model simulations show that valleys are wider in landscapes where collapsed material is closer in size to bedload sediment and narrower in landscapes where collapsed material is much larger than bedload sediment. I also use the newly modified lateral erosion/valley widening component together with additional Landlab components to explore the effects of variable discharge and changes in sediment flux on valley width and valley widening rates. This set of model experiments is a step towards a more nuanced and quantifiable framework for describing and predicting bedrock valley widening through time. Numerical models that include physical processes of valley widening are necessary for further advances of geomorphic applications such as numerical modeling of climate-driven strath terrace formation and hillslope–channel coupling.