Layer averaged Richard's 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 Richard's 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.