2026 CSDMS meeting-015
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Quantifying grain size control on fluvial erosion and topographic expression of tectonics
Sayan Das,
(he/him),Indiana University Bloomington Bloomington Indiana, United States. sayand.es2709@gmail.com
Brian Yanites, Indiana University Bloomington Bloomington Indiana, United States. byanites@iu.edu
Earth’s topography is actively shaped by rivers, which serve as dynamic conduits for source
to-sink routing of water and sediment. While models aiming to decode the mechanisms that drive river evolution exist, they often neglect sediment dynamics, process stochasticity, and landscape heterogeneity. Previous research has shown that fluvial erosion rates vary with the extent of bedrock exposure. In exposure-limited models that account for sediment cover, steady-state channel steepness is less sensitive to increases in uplift than in detachment-limited models without sediment. Additionally, exposure-limited rivers exhibit initial narrowing in response to transient rock uplift followed by long-term widening, whereas detachment-limited models predict continuous channel narrowing. However, the extent to which variability in grain size distributions modulates bedrock erosion and river morphology during tectonic perturbations remains poorly constrained. Here, we present a 1-D river profile model in which channel slope and width evolve to optimize bedrock incision while accounting for temporal variability in discharge and sediment supply. We test multiple grain size distributions by varying headwater grain sizes and downstream abrasion rates. For preliminary simulations, we consider a 50-km-long oversteepened river profile with temporally constant channel width under uniform discharge and sediment supply, and examine slope responses to increased uplift rates. For 2x increase in uplift rate, channels with 0.1 m headwater grain size exhibit larger slope adjustments (~1.16x) at 15 km downstream than channels with a 0.2 m grain size (~1.04x). Similarly, under a 5x increase in uplift, fine-grained channels undergo greater slope increases (~1.8x) than coarse-grained channels (~1.25x). These results indicate that slope sensitivity to uplift is muted for coarser grain sizes, highlighting the buffering effect of alluvial cover. Future steps will include dynamic width adjustment under stochastic discharge and sediment supply to quantify how grain size variability influences river morphological responses to tectono-climatic forcing in steep, eroding landscapes.
