Abstract

Preferential flow is an ordinary phenomenon of rapid and non-equilibrium transport of water in most of soil, which causes a latent pollution of the groundwater by transporting poisonous chemical substance rapidly towards it, reduces the nutritious substance adaptable to plants and water quantities in root system, affects the process of water permeating and soil permeability and influences indirectly runoff yield and flow concentration. The paper chooses the coniferous forest of upper reach area of Yangtze River as the study area. Due to the fact that there are heavy accumulation of litters and moss at the study site, researchers undertook a systematic analysis on the impact of litters and moss on the soil preferential flow by doing in-door soil column experiment. Calculation and analysis of Re shows that Re of soil in the differential succession forest of study area are all over 10, which reveals the fact that the coniferous forest of upper reach area of Yangtze River is a typical area for the soil preferential flow, and that the preferential flow in this area belongs to a transitional type somewhere between laminar flow and turbulence. The analysis of the impact of liters and moss on the soil preferential shows that although litters and moss are able to keep water to a large extent, it has a certain limit. As rainfall intensity increases and time elapses, litters and moss tend to stop absorbing water when it reaches a certain limit. Water in zones of litters and moss, spurred by the initial energy, will then move downwards along the zones of soil and becomes water route. Water then passes the route into the preferential flow zone in the unsaturated zone of the soil, and continues to move downwards along the paths of the preferential flow.

Keywords: the coniferous forest of upper reach area of Yangtze River; litters and moss; preferential flow