Lateral Flow in a Layered Profile of an Infinite Uniform Slope

Abstract

A numerical solution was used to calculate vertical infiltration of rainfall into a periodic layered profile of an infinite uniform slope. The calculated pressure‐head distribution within the profile was then used to evaluate transient un saturated lateral flow in the slope which is not limited to the existence of an impervious barrier. Because of the pressure‐line distribution within the layers, the horizontal component of the lateral flow changes direction from one layer to another. As a result, the net discharge across the profile can be directed upstream during the initial stages of infiltration into a relatively dry profile. Over longer times it is always directed downstream, and its value is proportional to the slope. This indicates that the layered soil profile behaves as an anisotropy media on the point scales and on the average. For a two‐periodic layered profile the total volume that passes in the direction parallel to the slope is very nearly proportional to the square of the total rainfall, and it is represented versus the accumulated rainwater by one curve for all rainfall intensities. Thus the total rainfall is controlling the rate of lateral flow rather than the rainfall intensity. The thickness of the soil layers has only a secondary effect on lateral flow. The net volume that moves horizontally is a potential source for water accumulation at concave parts of a regular slope. This water accumulation can form saturated or near‐saturated wedges that may contribute to surface‐runoff generation at these partial areas for cases of low rainfall intensities and short ponding times. These wet zones of the hillslope may also contribute massive recharge of water and chemicals (if exist) to groundwater in narrow columns.