Scaled Infiltration Equations for Furrow Irrigation

Surface irrigation, especially furrow irrigation, is used more than pressurised irrigation due to low cost, more efficient energy requirements, and better aeration of the root zone. The design, evaluation and simulation of surface irrigation systems relies on a knowledge of the infiltration properties of the soil and of the movement of water over the field. Spatial variation of infiltration rates makes the management of surface irrigation systems a very complex process. Furthermore, the infiltration parameters may be different in furrow irrigation in different inflow rates, furrow geometry and initial soil water contents. Therefore, presentation of a general equation for infiltration is very difficult. One proper way to characterise a general infiltration equation is to use a scaling method. Eight measured infiltration equations in furrow irrigation for six soil series were used to obtain a generalised equation for infiltration. There were four different soil textures in these soil series that consist a wide range of soil textures (sandy loam to clay loam). Using dimensional analysis, a suitable equation was obtained for a characteristic space scale (scaling factor), which was a function of the wetted perimeter, and the saturated and initial soil water contents. Using this scaling factor, the measured cumulative infiltration curves for furrow irrigation were scaled. The results showed that by using scaling factors obtained from dimensional analysis the diverse infiltration curves were able to be merged into a single curve. Furthermore, another scaling factor was presented, which contains furrow width as a readily available parameter. Therefore, using this scaling factor a different scaled infiltration equation was presented. Validation of scaled infiltration equations showed that they are applicable to other furrows in different soils with different hydraulic conditions. Thus, the generalised (scaled) infiltration equations derived in this study can be applied to wide range of soil conditions and hydraulic properties of furrows. Also, the results showed that the scaled equations were able to predict the infiltration under surge irrigation. In surge irrigation, the values of saturated hydraulic conductivity and final infiltration rate were considered as 80% of those in a continuous furrow. It is noteworthy that scaled infiltration equations cannot be applied to a heavily cracked clay soil where initial infiltration occurs in the cracks rather than through t