Pre-runoff Soil Infiltration Capacity: a Conceptionand a Technique for Its Determination

摘要

Sprinkle irrigation normally induces uncontrolled surface runoff withsome severe environmental and economic consequences. To deter that in aneffective way it is necessary that the design application depths and operationalones should not exceed the pre-runoff application depths. In that respect pre-runoffmode of infiltration should be recognized from the beginning of infiltration till themoment when stable puddles appear on the soil surface. So the term pre-runoffinfiltration capacity (or infiltrability) was introduced. The term comes to theparameters of an empiric formula, which was derived from wide field researchcarried out in different natural and soil management conditions. The empiricformula allows estimating the duration of pre-runoff mode of infiltration and the prerunoffapplication depths for any practical application rates and impact velocities ofdrops, the latter being expressed via drop diameters. Infiltration theory does notprovide any reliable and applicable to irrigation practice solutions for estimating theduration of pre-runoff infiltration or the pre-runoff application depths. So the methodof direct field research has been chosen and a corresponding technique ofobservation micro-plots has been developed. A rainfall simulator with fixed-headspray nozzles and with rotary impact sprinklers has been used for pre-runoffinfiltration measurements in the field. The rainfall simulator produced rain, whichwas very similar in its characteristics to the rain of real sprinkle systems withapplication rates and drop sizes varying in a wide range.