On the basis of a dimensionless form of a fundamental equation given by combining RICHARDS' equation with functional relationships of soil-water properties (water retention and permeability), properties of a base-flow recession are examined using a two-dimensional saturated-unsaturated flow model. Physical conditions are represented by four dimensionless parameters: α, β, γ, and δ. For a saturated-flow model, the fundamental equation includes one parameter, δ. For a one-dimensional, vertical-flow model, it includes two parameter, α and β. α and β are the parameters which feature unsaturated flow, and γ and δ are topographic parameters related to the slope length, soil depth, and slope gradient. The influences of these parameters on dimensionless recession-hydrographs are examined by numerical solutions. The fundamental equation can be converted to a simple form having one parameter, β, in almost all cases with the usual hillslope topographies and soil-water properties. In the simple form, parameter β, an exponent reflecting the relationship between hydraulic conductivity and moisture content, is the indicator of nonlinearity in kinematic law. This simple form of the equation can be used for further examination of the base-flow recession.