Steady state lateral water flow through unsaturated soil layers

The effects of gravity on flow through variably saturated soil layers are investigated quantitatively using two new analytical solutions and a numerical model. In all cases, steady state flow occurs laterally through a tilted, rectangular layer of soil with a constant hydraulic head on either end. The first solution is for gravity-driven flow through a tilted layer with sublayering parallel to the slope. As intuitively suggested by earlier investigators, flow occurs parallel to the floor of the layer and the pressure head is a simple function of the normal distance from the floor of the layer. The second analytical solution is for a tilted soil layer described by a Gardner soil model with both gravity and pressure head gradients. Flow velocities remain parallel to the layer floor, which is confirmed by numerical simulations. This is in contrast with chosen non-Gardner examples for which the flow does not necessarily remain parallel to the floor.