The Effect of Rainfall Duration on Preferential Flow in Coal Mining Subsidence Areas of the Middle Reaches of the Yellow River Basin

Underground coal mining has resulted in a large number of collapse areas and ground cracks in the mining area. The cracks provided the preferred pathway for soil water infiltration. Preferential flow caused by cracks resulted in severe water content reduction in the surface soil layer, destructing vegetation and land. Three cracks of identical width (3 cm) were selected from the coal mining subsidence area of the Shenfu‐Dongsheng Coalfield, located in the middle Yellow River basin. Dye‐tracing experiments were conducted under a constant rainfall intensity of 125 mm/h, with varying durations of 10 min, 20 min, and 30 min, to analyse the preferential flow characteristics of cracks under different rainfall durations. The results indicated that: (1) for rainfall durations of 10, 20, and 30 min, the average maximum water infiltration depths were 21.32 cm, 40.50 cm, and 41.40 cm, respectively. As rainfall duration increased, the morphology of the soil dyed area ratio shifted from an ‘S’‐shaped pattern to a uniformly descending trend, accompanied by an increase in the width and depth of the dyed pathways. (2) During a 10‐min rainfall duration, soil water flow was primarily characterised by high interaction large pore flow, which constituted 54.29%. As the duration extended to 20 and 30 min, the dominant flow type shifted to homogeneous matrix flow, with proportions of 58.57% and 61.41%, respectively. Furthermore, extended rainfall duration facilitated the emergence of heterogeneous finger flow, complicating the hydrological transition from homogeneous matrix flow to large pore flow. (3) As rainfall duration increased, the average initiation depths of preferential flow zones were 6.62 cm, 16.08 cm, and 25.90 cm, indicating an increasing trend. In contrast, the average proportions of preferential flow zones were 41.68%, 40.06%, and 21.94%, which reflect a decreasing trend. This suggests that matrix flow expands more rapidly than preferential flow. (4) Deep cracks create preferential pathways that enhance water conductivity, promote preferential flow, and increase the penetration depth of dyed pathways. This study provides a scientific basis for land reclamation management in coal mining areas.