| Abstract: Preferential flow is a kind of non-equilibrium movement of soil water. It influenced greatly on the formation and movement of surface runoff and underground (subsurface) runoff. As a kind of special movement form of soil water, preferential flow is one of the most important and difficult problems in current research about hydrology.In this paper, the Quxi watershed of Zigui county, Hubei province, was selected as the experimental site. In a slope of forestland, the distribution characteristics of preferential flow were analyzed by the method of irrigating. The moving characteristics of preferential flow, the factors influencing preferential flow, and the effect of preferential flow on infiltrated flow and surface runoff were also analyzed. Based on that, the preferential flow model was modified. The main conclusions were as the following:(1) Preferential flow is very common in the granite area of the Three-Gorges, Yangtze River. Its Re is bigger than 10, which shows that the movement of preferential flow does not follow Darcy-Law. There exist two kinds of preferential paths in this area, namely original preferential paths and secondary preferential paths. Preferential paths mainly exist in the soil layer of 0.8~1.0m under ground, which is gatherly distributed with index of 6.0-19.0. The mean number of existed preferential paths is 5~7/m.(2) The process of preferential flow is obviously divided into 3 phases: increasing phase, peak, and decreasing phase. Its increasing phase is very short, while decreasing phase is very long. Normally, preferential flow appeared 5-95.5h later than precipitation. Its duration time is 7-170h. Most preferential flow reach their peak l~2h after their appearance. In the condition of abundant antecedent rainfall, preferential flow will appear even with little precipitation.(3) Precipitation and soil characteristics are the most important factors influencing preferential flow. The main factor influencing the amount of preferential flow is the amount of rainfall, which is evidently positively related to the amount of preferential flow. The main factors influencing the duration of preferential flow are the duration and the amount of rainfall. The duration of preferential flow is very evidently positively related to the duration of rainfall, and evidently positively related to the amount ofrainfall. The main factor influencing the peak of preferential flow is the amount of rainfall, which is evidently positively related to the peak of preferential flow. The soil characteristics of different soil layers are very different, which induced the lateral preferential flow.(4) The ratio of preferential flow to infiltrated flow may reach 2.4%~48.72%. Its shuifentongliang may be 17200 times of that of infiltrated flow, which shows that preferential flow has great effect on the quick infiltration of precipitation. Preferential flow could increase the moving velocity of infiltrated flow and increase the shuifentongliang of soil water in a great extent.(5) Comparing the amount of preferential flow and amount of surface runoff, it is found that they have the positively linear related relationship. The equation is as the following:y = 0.7761x + 0.0379 (R2=0.8294, R=0.9107)In one rainfall, the more the amount of preferential flow is, the more the amount of surface runoff is. So do the inverse situation. In one rainfall, the increase of the amount of preferential flow induced the decrease of the amount of surface runoff. The appearance of preferential flow delayed the appearing time of the peak of surface runoff, increased the increasing duration of surface runoff, and prolonged the total duration of surface runoff.(6) Based on the data measured in lab and in the field, the preferential flow model is set up as the following equation:The simulated value matched better with measured value in surface soil than it does in deep layers. The simulated results showed that the effective path-length is 150mm in the soil layer 83-110cm, the longest of all the soil layers, which meant that pre... |
PDF Full Text Request