Fig. 4. Idealized movement of recharge water and solutes beneath a region A in an irrigated field. Recharge water infiltrating at a given time descends as a plane through the vadose zone. After reaching the water table, its movement is predominantly horizontal but a downward component remains, which accounts for the tilt in V's vertical axis. Recharge originating between two dates occupies an oblique prism bracketed by elevations z₁ and z₂.