Affecting factors of preferential flow in the forest of the Three Gorges area, Yangtze River

Abstract

In order to study the factors affecting preferential flow, a 2.9 m-long, 2.6 m-deep soil profile was dug in the Quxi watershed, Yangtze River. To analyze the influence of rainfall on preferential flow, the preferential flow process was observed when the rainfalls were recorded. Soil physical and infiltration characteristics were also measured to study their effect on preferential flow. The results showed that the rainfall amount that could cause preferential flow was over 26 mm. There are four types of rainfall in the Three Gorges area, namely gradually dropping rain, even rain, sudden rain and peak rain. Preferential flow process was found to be relevant to the rainfall process. It was determined that with different rainfall types, preferential flow appeared at different times, occurring first in peak rain, followed by sudden rain, gradually dropping rain, and then even rain. Preferential flow would appear when the rainfall intensity was over 0.075 mm/min. In the studied area, the coarse soil particles increased with the soil depth, and for the deeper soil layer, the coarse particles promote the formation of preferential flow. Preferential flow accelerates the steady infiltration rate in the 83–110 cm soil horizon, and the quickly moving water in this horizon also enhanced the further formation and development of preferential flow.