About: Turowski et al., (2024), Earth Surface Dynamics (link)

What sets the width of river valleys? In a paper published today, we propose a new model for the width of river valleys. It considers valley width as a competition of lateral channel motion and the uplift and erosion of valley walls. Here is the equation:

W is valley width
q_L is the lateral sediment transport capacity
q_H is the lateral input of sediment from hillslopes
U is the uplift rate
W₀ is the channel belt width
W_C is the channel width

A dimensionless “mobility-uplift number, M_U” expresses that competition where:

The model implies that valley width varies between two extremes: At a minimum, valleys are as wide as the channel. Such narrow valleys occur where rivers drain rapidly uplifting landscapes. At a maximum, valleys encompass wide channel belts. These two extremes are connected by a logarithmic function of the mobility-uplift number.

Despite its conceptual simplicity, the model compares surprisingly well to several datasets including experiments and a large compilation of valley widths in the Himalaya.

This model explains valley width in a landscape that has reached steady state. How do valleys evolve over time and what sets the maximum width of valleys? We are working on these questions in an upcoming publication.