In-situ infiltration-runoff characterization of slopes under the influences of different rainfall patterns and slope gradients

The infiltration-runoff process plays a crucial role in hydrological studies. The influences of rainfall patterns and slope gradients on the infiltration-runoff process are not yet fully understood, particularly under field conditions. In-situ monitoring and experiments were conducted to investigate the effects of a uniform rainfall pattern (UR, q = 17.5 mm h⁻¹ and q = 35 mm h⁻¹), the Chicago rainfall pattern (CR), and different slopes (β = 5° and 25°) on the infiltration, runoff, and sediment yield. The CR pattern is a mathematical model used to simulate natural rainfall based on historical rainfall data for a specific region. The results show that the response times of both the volumetric water content (VWC) and matric suction are directly proportional to depth, whereas their magnitudes are inversely proportional. The soil water characteristic curve (SWCC) obtained using the van Genuchten (vG) model can be established based on monitoring data for the drying path. The rainwater transformation is altered by the CR pattern, prolonging the initial runoff time and reducing rainfall infiltration. The infiltration and runoff rate curves, which mirror the rainfall pattern, exhibit peak values that increase both the cumulative runoff and sediment yield. The runoff rate, shear stress, and hydraulic power are significantly increased by increasing the slope angle. This positively contributes to the runoff and sediment yield and reduces the rainfall infiltration. The soil water profile during infiltration can be qualitatively divided into three stages. A time correction parameter, which is highly related to the initial runoff time, is incorporated into the Kostiakov model to more precisely predict the infiltration process. This paper presents a novel approach for applying the CR pattern to hillslope hydrology. Our findings improve the understanding of the effects of rainfall patterns and gradients on rainwater transformation and sediment yield and provide a scientific reference for hydrological modelling.