Bedrock incision by bedload transport

In most river or landscape evolution models (like the Stream Power Law), the bedload of rivers is not modelled explicitely, though it represents one of the main factors of incision in a bedrock river. Pebbles transported within the bedload layer regularly impact the bedrock and contribute to its abrasion.

We performed direct numerical simulations of the trajectories of a number of solid particles entrained by a turbulent stream. This model, based on the discrete element method, allows us to directly compute the amount of energy that the impacts deliver to the bedrock.

This energy can then be converted into an effective incision rate: in accordance with existing lab experiments, our model shows that the incision rate first increases with the sediment load (the more pebbles, the more impacts on the bedrock), but then reaches a maximum before decaying to zero (when the sediment load is too high, the bedrock is entirely covered and therefore protected from impacts). From our simulations we are able to predict the incision rate as a function of both the sediment load and the water discharge. Though we only simulate the trajectories of pebbles over a few minutes, we are able to predict a realistic value for the long-term incision rate of a river.

Participants: G. Aubert, P. Allemand, V. Langlois.
References: Aubert et al., Earth Surf. Dynam. (2016).