Variability in alluvial river width driven by intermittent bank collapse.

Area of Science:

• Fluvial geomorphology
• River dynamics
• Remote sensing

Background:

• Hydraulic geometry theory traditionally describes equilibrium channel dimensions based on flow discharge.
• Natural alluvial rivers exhibit dynamic planforms and fluctuating widths, with mechanisms of variability poorly understood.
• High-resolution datasets highlight the need for refined understanding of river width dynamics.

Purpose of the Study:

• To investigate spatial patterns of river width variability in a global set of alluvial rivers.
• To identify geomorphic features associated with different wavelengths of width variability.
• To elucidate the role of intermittent bank collapse in river morphodynamics.

Main Methods:

• Analysis of high-resolution satellite imagery from a globally distributed set of alluvial rivers.
• Normalization of channel width data by mean channel width.
• Application of Fourier analysis to examine width variability patterns and their relation to channel curvature.
• Numerical modeling to assess the impact of intermittent bank collapse on river morphodynamics.

Main Results:

• Identification of three characteristic wavelengths of width variability linked to meander bends, mid-channel bars, and intermittent bank collapse.
• A strong inverse relationship found between intermittent bank collapse-driven width variability and bend-average curvature, particularly in mildly curved rivers.
• Numerical models confirmed that intermittent bank collapse accelerates lateral river migration and enhances floodplain reworking.

Conclusions:

• Intermittent bank collapse is a significant geomorphic mechanism driving river width adjustment, particularly in less curved river sections.
• These findings refine classical fluvial geomorphology theory by incorporating bank collapse dynamics.
• The results have implications for river restoration strategies and estimating organic carbon fluxes in a changing climate.