Sediment Cover Modulates Landscape Erosion Patterns and Channel Steepness in Layered Rocks: Insights From the SPACE Model

Erosional perturbations from changes in climate or tectonics are recorded in the profiles of bedrock rivers, but these signals can be challenging to unravel in settings with non‐uniform lithology. In layered rocks, the surface lithology at a given location varies through time as erosion exposes different layers of rock. Recent modeling studies have used the Stream Power Model (SPM) to highlight complex variations in erosion rates that arise in bedrock rivers incising through layered rocks. However, these studies do not capture the effects of coarse sediment cover on channel evolution. We use the “Stream Power with Alluvium Conservation and Entrainment” (SPACE) model to explore how sediment cover influences landscape evolution and modulates the topographic expression of erodibility contrasts in horizontally layered rocks. We simulate river evolution through alternating layers of hard and soft rock over million‐year timescales with a constant and uniform uplift rate. Compared to the SPM, model runs with sediment cover have systematically higher channel steepness values in soft rock layers and lower channel steepness values in hard rock layers. As more sediment accumulates, the contrast in steepness between the two rock types decreases. Effective bedrock erodibilities back‐calculated assuming the SPM are strongly influenced by sediment cover. We also find that sediment cover can significantly increase total relief and timescales of adjustment toward landscape‐averaged steady‐state topography and erosion rates. Plain Language Summary Changes in climate and tectonics over thousands to millions of years cause local erosion and deposition along rivers, affecting river elevations and slopes as one travels downstream. Because different rocks erode at different rates, changes in rock type also impact river slopes. Ideally, we could “read” rock strength and the past history of climate and tectonics from river elevation profiles. To achieve this, we need models—equations—that describe how climate, tectonics, and rock strength influence river evolution. In this study, we compare two numerical models for predicting river erosion over time. The simpler model, commonly used to interpret climate, tectonics, and rock properties from real landscapes, assumes the river bed is entirely bedrock, without any sediment. The other model includes both erosion and sediment deposition on the river bed, which affects erosion rates. We calculate river erosion through alternating strong