| 01 Oct 2026
Friction over gravitational forcing: Disentangling the controls of Hortonian overland flow and erosion through energy-centred process modelling
Abstract. This study investigates the coupled dynamics of Hortonian overland flow (HOF) and sediment transport observed during rainfall simulations at the plot scale using the process-based Catflow model with an energy centred approach. A hierarchical calibration strategy was applied to reproduce overland flow generation, flow velocities in sheet and rill domains and sediment detachment sequentially, allowing the dominant controls on HOF and erosion processes to be identified.
The results show that antecedent soil moisture and surface roughness are the primary controls on HOF generation, whereas rainfall intensity and slope had no significant effect within the investigated range. Increasing surface roughness reduced surface runoff and total sediment export, while simultaneously increasing the ratio between rill and sheet flow velocities, indicating enhanced flow concentration into preferential pathways. No clear relationship was observed between flow velocities and slope, demonstrating that overland flow dynamics are primarily limited by friction rather than gravitational forcing.
The model reproduced overland flow generation, flow partitioning and total eroded sediment with good consistency. The results indicate that sheet flow primarily governs sediment detachment and energy dissipation, whereas rills function as efficient sediment transport pathways. Increasing surface roughness promoted flow concentration into rills, where the greater hydraulic radius reduced relative frictional losses and enabled a more efficient conversion of potential into kinetic energy. Consequently, downslope kinetic energy transport became increasingly dominant within the rill domain, while the overall system remained friction dominated. This energetic interpretation links overland flow generation, flow organisation and erosion dynamics through the balance between energy input, dissipation and redistribution.
Overall, the study highlights the importance of frictional resistance as prime limitation of overland flow velocities, flow organisation and domain-specific flow representation for modelling infiltration‑excess overland flow and erosion dynamics.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Hydrology and Earth System Sciences.
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