Overland Flow Dynamics on a Cracked Soil Slope Under Drying‐Wetting Cycles: An Integrated Hydrological and Infrared Thermographic Study

Abstract

Although overland flow strongly governs soil erosion and sediment transport, its response to desiccation cracking induced by drying‐wetting cycles is not fully understood. This study addresses this gap through laboratory rainfall simulations on a slope model subjected to three drying‐wetting cycles. Soil moisture and suction were monitored at shallow depth, crack patterns were quantified through image processing, and runoff and sediment yields were measured during rainfall events. Infrared thermography was applied to capture flow velocity and spatial organization. Results show that drying‐wetting cycles accelerated moisture loss, steepened suction gradients, and promoted the initiation and propagation of cracks. Crack ratio and total crack length increased markedly during the first two cycles but stabilized in the third, indicating that the slope surface had reached a state of structural equilibrium. Runoff generation was influenced by both antecedent moisture and crack development: higher initial moisture reduced infiltration capacity and produced rapid, high‐magnitude runoff, while progressive cracking enhanced infiltration and weakened runoff response in later cycles. Sediment yield closely followed runoff intensity, peaking in the second cycle due to the influence of reduced infiltration and structural weakening. Infrared thermography showed that leading‐edge velocity declined during rainfall while the continuity‐derived equivalent runoff depth increased, reflecting different responses of local tracer‐front propagation and integrated runoff generation to evolving flow connectivity and effective hydraulic resistance. Across cycles, leading‐edge velocity rose initially and then declined, consistent with the transition from high antecedent moisture and structural weakening to stabilized crack networks. Spatial indices further confirmed this shift, indicating progressive increases in surface roughness, enhanced flow dispersion, and shortened effective flow paths.