Abstract:Storm pattern plays a key role on rill erosion processes, and contour ridging has the unique characteristic of rill erosion. In this study, simulated rainfall experiment was conducted to determine the characteristics of rill morphology, runoff and sediment yielding, flow hydraulic characteristics and dynamic mechanisms of rill erosion. Using the runoff box for simultaneously changing the row grade and field slope, four storm patterns (the rising, falling, rising-falling, and falling-rising patterns) were set on cinnamon soil in a contour ridge system. All patterns included three rainfall intensities:30, 60, and 90 mm/h, and comprised the same kinetic energy, total rainfall amount, and average rainfall intensity. Results showed that the differences in rates of headward erosion, bank landslip, and the downcutting of rill bottom among storm patterns greatly changed rill morphology. Compared with the rising pattern, rill width and depth from the rising-falling, falling-rising, and falling patterns increased by158.8% and 38.9%, 115.7% and -27.8%, 21.6% and -33.3% respectively, while the correspondingly increased ratios of width to depth were 14.9%, 60.4%, and 82.6%, respectively. Rill runoff and sediment yield showed significant differences among storm patterns. Runoff ranked in the following order:the rising-falling > falling-rising > falling > rising pattern, and sediment yield was in order of the rising-falling > falling > falling-rising > rising pattern. Regardless of storm pattern, power function relationship was found between runoff rate and sediment yield rate, while the exponent in the rising-falling, falling, and falling-rising patterns increased by 2.52, 2.46, and 1.46 times respectively, compared with the rising pattern. As for rill flow hydraulic characteristics, the largest difference occurred in Reynolds number, and stream power was in dynamic mechanisms parameter. Reynolds number and stream power from the rising-falling, falling-rising, and falling patterns significantly increased by 107.0% and 106.8%, 42.2% and 41.9%, 16.6% and 16.7%, respectively, compared with the rising pattern. These findings would help understand the mechanism of contour ridge influence on rill erosion process, and was of great importance to apply the contour ridge tillage for soil erosion control.