Layer averaged Richardʹs equation with lateral flow

In this paper a formulation for layer averaged sub-surface moisture transport, that models the lateral flow, is developed using the Richardʹs equation. This formulation is consistent with the approach currently adopted in contemporary models used in land–atmosphere interaction studies. Explicit expressions are derived for layer averaged lateral transport contribution from diffusion, gravity, dispersion, and convergence due to land–surface curvature. It is argued that lateral contribution can be a significant component of the total soil-moisture flux. Ignoring these contributions can result in significant model error leading to inaccurate prediction or unrealistic calibration of parameters that compensate for these errors.