Water movement in the form of preferential flow does not follow Darcy's Law. Pipe flow is one kind of preferential flow. To study the effect of pipe flow on soil water movement

a natural

secondary

largely undisturbed Pinus massoniana woodland in the granite region of the Three Gorges of the Yangtze River was selected as an experimental plot. Properties of seven soil layers were measured using a double cycle infiltrator. Pipe flow and infiltration was recorded using automatic flowmeters. Rainfall also was observed over the same period. The results show that the infiltration capacity of the soil is related to the higher proportion of weathered granite in this region relative to other areas. Of the seven soil layers measured

the surface layer (0—10cm)

has the lowest infiltration capacity. It is probably due to a higher clay content in the surface layer relative to other layers and a fine texture characteristic. An impervious layer occurs 150—200cm below the soil surface. Pipe flow mainly is generated over this layer. At the initial stage of rainfall

the soil water moves as unsaturated flow. First

continuous flow does not be occur and pipe flow is not generated during this stage. With continued rainfall

the soil becomes saturated and pipe flow begins. The production of pipe flow demands higher soil water content than that resulting from average infiltration in the soil profile.