EVALUATION OF PARAMETRIC INSATURATED FLOW MODELS FOR DRAINAGE

Abstract

Recharge due to infiltration is described mathematically by Richard's equation for unsaturated flow which is a non-linear second order differential equation. Solution to this equation is complicated. Quasianalytical solution to this equation is possible only for very simple hypothetical boundary conditions. For field conditions normally encountered solution of this equation is prohibitive because it would involve complicated numerical methods and require much computer memory and time. Therefore simpler parametric models have been used and one of such models is the Nash Cascade, a two parameter linear transfer function often used for routing runoff in surface hydrology. This study examines the applicability of the Nash Cascade in modelling groundwater recharge due to infiltration. The chief assumption when applying the Nash Cascade is that the response (groundwater recharge) is a linear function of the input (infiltration) and thus liutiar• sysLam operations i.e. (i) principle of proportionality and (ii) principle of superposition could be applied.