Formation and dynamic equilibrium mechanisms of parallel drainage networks in tectonically active areas: Numerical simulations based on feedback mechanisms in the Three Rivers Region

The "Three Rivers Region" in the southeastern margin of the Tibetan Plateau is a significant converging zone that evolved due to the collision of the Indian and Eurasian plates. Its prominent parallel drainage system (Nujiang, Lancang, and Jinsha rivers) has been substantially preserve differential uplift and incision at the plateau margin. Traditional views are typically inferred from river longitudinal profiles and thermochronological data. However, river networks are inherently dynamic systems: both tectonic uplift and crustal compression affect landscape evolution. This dynamic process complicates the correspondence between landforms and tectonics, leading to long-standing debates over the origin of the parallel drainage pattern and uncertainty about its primary controlling factors. Therefore, this study employs a 3D geodynamic-landscape evolution model to systematically evaluate 48 parameter combinations, including uplift rates, horizontal compression, and bedrock erodibility. Our results identify a specific "stability window"-defined by moderate uplift rate (~0.4 mm/yr), high erodibility (~1×10⁻⁶), and sustained compression (20-30 mm/yr) -that is most most conducive to maintaining the stable "Three-Rivers-Parallel" pattern. Within this regime, the three trunk rivers achieve an equilibrium in stream power and catchment area. Deviations from these parameters cause the drainage system to either fragment into multi-river networks or collapse into a single trunk river. The study reveals a coupled internal-external geomorphic mechanism: tectonic uplift and compression intensify stream power, triggering a positive feedback of rapid incision and bedrock fragmentation. Simultaneously, erosion-induced sediment unloading promotes local tectonic uplift, further fueling incision. Conversely, continuous erosion reduces topographic gradients, leading to a decline in erosion rates that eventually balances with tectonic uplift through negative feedback. The interplay between these feedbacks sustains the stable parallel architecture. This study provides a quantitative framework for understanding the coupling between drainage reorganization and tectonic forces, offering new insights into the landscape evolution of active plateau margins.