Understanding tectonics from fluvial topography by using the stochastic‐threshold incision model: Theory and application to the Dadu River basin, eastern Tibetan Plateau

Abstract

The flood distribution and bedrock incision threshold exert important influences on the erosion efficiency, which can result into a nonlinear scaling between channel steepness (normalized channel gradients for the downstream increases in drainage area) and erosion rates. Here, we explore the incorporation of both river incision threshold and discharge probability distribution into erosion efficiency to construct a stochastic‐threshold incision model equation to simulate river power incision and the evolution of fluvial topography. Assuming time‐dependent tectonic uplift, we develop a closed‐form analytical solution to the model equation and derive a linear inverse procedure to retrieve relative uplift rate history from river longitudinal profiles. Application of the inverse scheme to the Dadu River basin in the eastern Tibetan Plateau produces a history with three‐phase increases in the uplift/incision rates during the Cenozoic. We use the inversion results to forward the time‐changed river long profile, which indicates the existence of paleo relief before the Oligocene and significant contributions of the late Miocene regional uplift and early Pleistocene river capture on the present topography.