Effects of slope and upslope inflow rate on black soil ephemeral gully erosion processes in the Northeastern China

Black soil region in the Northeastern China Ephemeral gullies serve as major sediment sources in Northeast China which can substantially reduce land productivity. Gully erosion processes, hydraulic mechanisms, and threshold values governing the transformation from ephemeral to permanent gullies in black soil regions under water erosion conditions remain insufficiently explained. To address this, laboratory simulations were conducted using an artificial ephemeral gully constructed from black soil, representing conditions in northeastern China. The design incorporated three slope gradients (3°, 6°, and 9°) and five upslope inflow rates (10, 20, 30, 40, and 50 L/min). Data collection involved measuring runoff and sampling sediment to derive hydraulic parameters. Statistical analyses were performed using Spearman rank correlation, multiple regression, and threshold models. Sediment yield increases 4 times more from 6°-9° than from 3°-6°, primarily due to the transition from subcritical to supercritical flow. The sediment yield followed a pattern of initial increase to a peak value, then a gradual decline, while the sediment yield rate demonstrated a stepwise rise with increasing upslope inflow rates. Critical hydraulic thresholds for the transformation from ephemeral to permanent gullies were identified across multiple parameters: mean flow velocity (0.44 m/s), flow shear stress (17.45 N/m²), flow power (8.62 W/m²), and unit flow power (0.05 m/s). This research examines key features and processes of ephemeral gully erosion, establishing a theoretical basis for control strategies in black soil regions. • Above 6°, the effect of increasing slope on sediment yield rate enhanced. • Hydraulic threshold for the transition of ephemeral to permanent gully is revealed. • Thresholds: mean flow velocity (0.44 m/s), flow shear stress (17.45 N/m 2 ). • Thresholds (continued): flow power (8.62 W/m 2 ), and unit flow power (0.05 m/s).