Tectonic and/or climatic perturbations can drive drainage adjustment. The capture events, significantly changing the river network topology, are the major events in river network evolution. While they could be identified through field observations and provenance analysis, reconstructing this evolution process and pinpointing the capture time remain challenging. Following a capture event, the steady-state elevation of the captor river will be much lower than that of the beheaded river. Then, the newly-formed drainage divide will migrate towards the beheaded river, a process also known as river-channel reversal. The migration of the newly-formed drainage divide provides a new perspective for identifying the reorganization of the river network. Here, we employ numerical modeling to reproduce the characteristic phenomena of drainage-divide migration following capture events and analyze the effects of different parameters on the migration rate. We find that (1) the migration of newly-formed drainage divides can last for tens of millions of years, with the migration rate decreasing exponentially over time; (2) larger captured area, higher uplift rate, and lower erosional coefficient, all of which cause a higher cross-divide difference in steady-state elevation, will cause higher migration rate of the newly-formed drainage divide. This insight was further applied to the Dadu-Anning and Yarlung-Yigong capture events. We predict the present Dadu-Anning drainage divide would further migrate ~65–92 km southward to reach a steady state in tens of millions of years. The Yarlung-Yigong capture event occurred in the early-middle Cenozoic, which implies that the late-Cenozoic increased exhumation rate is not related to the capture event.

Landscape evolution is controlled by tectonic strain, bedrock lithology, and climatic conditions, and is expressed in the spatial and temporal variations in river channel networks. In response to tectonic and climatic disturbance, river networks shift both laterally and vertically to achieve a steady state. Several metrics are available to assess the nature of river network disequilibrium, upon which the direction of drainage divide migration can be interpreted. However, to link this information to other observational, theoretical, and experimental data requires the knowledge of the rate of migration, which is still lacking. Here we develop a modified method based on Gilbert metrics to calculate the transient direction and rate of drainage divide migration from topography. By choosing a high base level, linear or quasi-linear χ-plots are obtained for rivers on both sides of the drainage divide, and the elevation-χ gradient is proportional to the average normalized steepness index (ksn). In turn, the velocity of divide migration can be quantified theoretically from the cross-divide comparison of χ. We applied this method to eastern Tibet and obtained a uniform, westward migration pattern for 29 points along two drainage divides with rates between 0.02 and 0.66 mm/yr, which is consistent with the great river capture events in the region. The ongoing reorganization of the river network in eastern Tibet is caused by the Cenozoic growth and eastward expansion of the Tibetan Plateau, the strengthening of the precipitation and regional extension throughout East Asia, and the local fault activities.