Bedrock rivers are the pacesetters of landscape evolution in uplifting fluvial landscapes. Water discharge variability and sediment transport are important factors influencing bedrock river processes. However, little work has focused on the sensitivity of hillslope sediment supply to precipitation events and its implications on river evolution in tectonically active landscapes. We model the temporal variability of water discharge and the sensitivity of sediment supply to precipitation events as rivers evolve to equilibrium over 10⁶ model years. We explore how coupling sediment supply sensitivity with discharge variability influences rates and timing of river incision across climate regimes. We find that sediment supply sensitivity strongly impacts which water discharge events are the most important in driving river incision and modulates channel morphology. High sediment supply sensitivity focuses sediment delivery into the largest river discharge events, decreasing rates of bedrock incision during floods by orders of magnitude as rivers are inundated with new sediment that buries bedrock. The results show that the use of river incision models in which incision rates increase monotonically with increasing river discharge may not accurately capture bedrock river dynamics in all landscapes, particularly in steep landslide prone landscapes. From our modeling results, we hypothesize the presence of an upper discharge threshold for river incision at which storms transition from being incisional to depositional. Our work illustrates that sediment supply sensitivity must be accounted for to predict river evolution in dynamic landscapes. Our results have important implications for interpreting and predicting climatic and tectonic controls on landscape morphology and evolution.

Rates of land surface processes provide insights into climatic and tectonic influences on topography. Bedrock incision rates are estimated by dating perched landforms such as strath terraces, assuming a constant bedrock incision rate from terrace abandonment to the next terrace level or present river level. These estimates express biases from the stochastic nature of sediment and water discharge in controlling river incision as well as from using a mobile channel elevation as a reference frame, leading to different incision rates when calculated over different timeframes. We introduce a 1‐D model incorporating fluvial mechanics, tectonics, sediment, and climate variability to predict these biases and assess their sensitivity to climate and tectonics. Findings suggest biases intensify under highly variable climates and slow rock uplift, with climate periodicity being a primary control for our modeled scenarios. Our model provides a mechanism to improve river incision measurement uncertainty, impacting paleoclimate and tectonic geomorphology reconstructions.

Avulsing rivers carve new pathways on the floodplain, and the associated flooding can profoundly impact society ^1-4. River avulsions are thought to occur when the water column becomes perched above the floodplain⁵, or when the slope down the channel's flanks provides a steeper descent than the current path ^6,7. However, neither idea has been suitably field-tested. Here we quantify the topography around avulsing rivers and reveal that these mechanisms work together. Near coasts, rivers avulse when the slope away from the channel is steeper, not because they are perched. The opposite is true near mountain fronts; on alluvial fans, alternative paths are all similarly steep, so rivers avulse when they are perched over the surrounding landscape. We reconcile these findings and present a novel theoretical framework that can predict which rivers are vulnerable to avulsion, and where avulsing rivers will go after they start. By clarifying the rules of river avulsion, it is evident that avulsion risks are underestimated in many coastal environments⁸ and that probabilistic predictions of avulsion pathfinding can efficiently project hazard with minimal information. Applying these principles for risk assessment may have outsized benefit in the world’s poorest nations, which we find are disproportionately impacted by avulsions.

Rates of land surface processes provide insights into climate and tectonic influences on landscape dynamics. River incision rates into bedrock are estimated by dating perched landforms such as strath terraces, assuming a constant bedrock incision rate from terrace abandonment to present. These estimates express biases from the stochastic nature of river incision and from using a mobile channel elevation as a reference frame. No existing mechanistic framework fully addresses these biases. We introduce a 1-D river evolution model incorporating fluvial mechanics, sediment dynamics, tectonics, and climatic factors to predict these biases and assess their sensitivity to climate and rock-uplift rate. Findings suggest biases intensify under highly variable climates and slow rock uplift, with the period of climate being a primary control. Our model improves river incision measurement reliability, impacting paleoclimate and tectonic geomorphology reconstructions.

Methods for landslide volume estimation, channel aggradation mapping, sediment transport modeling, and recurrence estimate.