The vertical heterogeneity of soil detachment by overland flow on the water-level fluctuation zone slope in the Three Gorges Reservoir, China The vertical heterogeneity of soil detachment capacity

Periodic submersion and exposure due to the operation of the Three Gorges Reservoir (TGR) alter the soil properties and plant characteristics at different elevations within the water level fluctuation zone (WLFZ), possibly influencing the soil detachment capacity (D-c), but the vertical heterogeneity of this effect is uncertain. Soil samples were taken from 6 elevation segments (5 m per segment) along a slope profile in the WLFZ of the TGR to clarify the vertical heterogeneity of D-c. Scouring experiments were conducted at 5 slope gradients (17.6%, 26.8%, 36.4%, 46.6%, and 57.7%) and 5 flow rates (10, 15, 20, 25, and 30 L min(-1)) to determine D-c. The results indicate that the soil properties and biomass parameters of the WLFZ exhibit strongly vertical heterogeneity. D-c fluctuates with increasing elevation, with maximum and minimum average values at elevations of 145-150 m and 165-170 m, respectively. Linear equations accurately describe the relationships between D-c and hydrodynamic parameters, for which the shear stress (tau), stream power (omega), and unit energy of water-carrying section (E) perform much better than the unit stream power (U). Furthermore, a clear improvement is achieved when using a general index of flow intensity to estimate D-c. Furthermore, D-c is significantly and negatively correlated with the mean weight diameter (MWD, p < 0.05) and organic matter content (p < 0.01) but not significantly correlated with other soil properties (p > 0.05). The rill erodibility at elevations of 145-150 m and 170-175 m is greater than that at other elevations. The critical hydraulic parameters were highest in the 165-170 m segments. Both the rill erodibility and the critical parameters fluctuate vertically along the sloping surface. This research highlights the vertical heterogeneity of D-c and is helpful for better understanding the mechanisms responsible for soil detachment in the WLFZ of the TGR.