A laboratory and field study of border check irrigation

Abstract

Field and laboratory results of infiltration advance are presented. They are compared with results from equations that derive from the Lewis-Milne equation after substitution of infiltration relations based on independently determined parameters obtained from infiltration experiments. In the laboratory, change of slope, change of supply rate, prewetting of the surface, and restriction of vertical air escape were studied in various combinations for two homogeneous materials. Change of supply rate, q, affected the rate of advance, x, while change of slope and prewetting the surface had only second order effects with a change of q. Results are compared in terms of the ratio x/q. Agreement between theory and experimental results is good. The effect of restriction of air escape vertically ahead of the wetting front was marked, even though the measured increase in air pressure was small, and effectively reduced the parameters, sorptivity and hydraulic conductivity. An innovation is to introduce a further term-the 'instantaneous' crack-filling volume. This slightly modifies the equations used for homogeneous materials and provides very good descriptions of irrigation advance phenomena for a cracking grey clay, a duplex red-brown earth, and for laboratory simulated duplex profiles consisting of two thicknesses of coarse sand overlying fine sand. The movement of water into the layered sand systems showed that infiltration is not entirely vertical as equired by the Lewis-Milne equation. The implications of the experimental results and the use of infiltration-advance equations in studies of the irrigation of field soils are briefly discussed.