Use and Hydrological Robustness of Time-to-Incipient-Ponding

Using a nondimensional analytic form for time-to-ponding, t_p, for rainfall rates, R, greater than about 1.5 times the saturated hydraulic conductivity, K_s, t_p is relatively robust. Only in the region K_s ≤ R ≤ 1.5 K_s is t_p sensitive to small changes in R/K_s. A comparison between field measurements of t_p using a rainfall simulator on a structurally unstable, sodic and saline gravelly silty clay loam and those predicted using the analytic expression and measured values of K_s and sorptivity determined under ponded conditions with disc permeameters are shown. Results indicate that both the determination and prediction of t_p are soundly based provided R > 1.5 K_s. The analytic expression for t_p is used in the inverse sense to determine the soil's sorptivity, hydraulic conductivity and characteristic mean pore size, a measure of soil pore structure, from values of t_p, R and the steady state runoff during rainfall. These hydraulic properties agree well with those measured under a constant head. Concludes that t_p is a useful and hydrologically robust property provided R(t_p) > 1.5 K_s. -from Authors