2022 CSDMS meeting-064


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Insights from new model for river incision accounting for stochastic water and sediment discharge

Clarke DeLisle, (He/Him),Indiana University Bloomington Bloomington Indiana, United States. cdelisle@iu.edu
Brian Yanites, Indiana University Bloomington Bloomington Indiana, United States. byanites@iu.edu

Much of modern tectonic geomorphology focuses on interpreting patterns of bedrock river slope and using this information to make tectonic inferences. At its core, this framework often assumes that rivers are readily able to erode bedrock, and that they respond to tectonic and climatic forcing mostly through vertical incision and slope adjustment. However, bedrock rivers must also transport sediment delivered to them by surrounding hillslopes, which may act to amplify or to inhibit incision into bedrock. Rivers also adjust their width in response to climatic and tectonic controls, often much faster than slope adjustments can occur. While the importance of sediment flux and channel width has been understood for some time, these behaviors are hard to predict mechanistically and thus go unaccounted for in many models of landscape evolution. We present a model of river evolution in which channel slope and width freely evolve to optimize sediment transport and bedrock incision in response to stochastic water and sediment discharge. We investigate the impact of both water and sediment discharge variability under varied tectonic forcing and find that equilibrium channel form is controlled by a combination of water and sediment supply variability. We use the model to document measurement biases in rates of river incision (the Sadler effect) which are observed ubiquitously in real landscapes, and to for the first time examine the drivers of variations in this effect. Our results call into question the assumptions underlying the widely used detachment-limited stream power incision model of river evolution and highlight the importance of considering channel width and sediment flux when modeling river behavior and measuring rates of erosion over landscape evolution timescales.