How does a newly-formed drainage divide migrate after a river capture
event? Insights from numerical simulations and two natural cases
(Yarlung-Yigong, and Dadu-Anning) in the Tibetan Plateau region
Abstract
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.