THE ROLE OF REDISTRIBUTION AND HYSTERESIS IN THE SURGE IRRIGATION PHENOMENA
ABSTRACT An implicit one-dimensional infiltration model based on Richard's equation with an option to select a nonuniform grid spacing is written. A hysteresis algorithm is added to the model based on Mualem's 1984 theory. Data for Rubicon sandy loam soil are used in the model to simulate infiltration events under continuous flow (CF), surge flow (SF), and surge flow with hysteretic soil hydraulic properties (SFH). The nominal cycle on-times for the surge simulations are 20 min with a cycle ratio of 0.5. Simulation results indicated that hysteresis effects (SFH) decrease cumulative infiltration when compared to redistribution only (SF), however the combined effects of redistribution and hysteresis are not thought to be the cause for reduced infiltration rate under surge irrigation. Larger pressure head gradients during the first 5 min of subsequent surges are the reason for differences in simulated cumulative infiltrations. Hysteresis tends to cause an increased storage within the upper zone of soil profile. The depth of water penetration is greater in the absence of hysteresis.