The cycle of bedrock valley widening and narrowing, driven by changes in sediment supply relative to sediment transport capacity, leads to the formation and preservation of strath terraces, where lateral erosion typically plays a key role. However, in uplifting valleys, lateral erosion may be limited, and dynamic channel width could become more influential. Because valley widths were mostly ignored assuming one grid cell in most landscape evolution models, few models can explain how strath terraces in bedrock valleys form under external forcings. Here, we present a modified fluvial erosion-deposition landscape evolution model considering dynamic channel widths scaled by upstream water discharge. Our model shows that increased channel widths can amplify the influences of climate signals on fluvial sediments. Wider channels lead to greater sediment deposition because the same water discharge is distributed across more channel nodes, reducing the transport capacity as water discharge per node decreases. Moreover, our modeling shows that strath terraces form as the climate shifts from wet to dry conditions by incorporating dynamic channel widths and a sediment deposition term. We show that this planation occurs within confined valleys, different from the widely accepted framework where lateral planation of a bedrock surface typically takes place in broad valleys. Instead, our model produces a planation surface by channel widening, with bedrock straths subsequently exposed during channel narrowing. Our model has the potential to elucidate the evolution of bedrock valleys, including the influences of tectonics, climate, rock properties, and sediment thickness on valley geometry.
