Optimization of discharge per unit width of border irrigation based on soil infiltration variability

Abstract: Field soil infiltration variability has brought difficulties to the design and management of border irrigation system. In the previous researches, the effect of spatial variability of soil infiltration on water movement process and irrigation performance was not taken into consideration, which cannot reflect the actual situation in the field, resulting in the limitation of the improvement of border irrigation performance. In order to solve the above problems, based on the available calculation model of irrigation performance indicators of border irrigation under heterogeneity soil conditions, this study extended the range of the model application, and numerical simulation of border irrigation process were conducted by the WinSRFR software. Additionally, the calculation model was verified combined with the experimental data of border irrigation in Wugong county (108°03′06′′E, 34°21′32′′N) of Shaanxi Province and Pengzhuang village (116°22′02′′E, 37°39′N) in Wuqiao county, Hebei Province. Based on the above researches, the calculation model of this study and theoretical analysis were adopted to analyze the influence of heterogeneity soil on the performance of border irrigation. Moreover, taking the maximum geometric average value of the distribution uniformity, application efficiency and storage efficiency as the optimization function, a method to determine the discharge per unit width under the consideration of soil infiltration variability was proposed. The results showed that through the expanded calculation model of border irrigation performance indicators under soil infiltration variation conditions, the proposed model was suitable not only for calculation the performance of border irrigation under the conditions of soil heterogeneity, but also for the calculation under the condition of homogeneous soil. Under the condition of soil heterogeneity, the calculated values of distribution uniformity, application efficiency and storage efficiency were in good agreement with the measured and simulation values by WinSRFR software, and the relative error was less than 8%. However, under the homogeneity soil condition, the error was relative large between the calculated and the measured values of irrigation performance indicators, of which the relative error of distribution uniformity had the largest value of 15.42%. The results indicated that the influence of soil infiltration variability should be taken into account in the process of irrigation performance evaluation. Otherwise, the results would be deviated from the actual situation in the field. While under the condition of homogeneous soil, the calculated values of irrigation performance and WinSRFR software had high consistency, and the relative error was less than 10%. Soil infiltration variation had a great influence on the performance of border irrigation, accounting for 56.71%-95.68%, and the influence should be taken into account in the process of irrigation performance evaluation. By selecting the discharge per unit width as an optimization variable, the effect of infiltration spatial variation on the performance of border irrigation could be reduced, which contributed to improvement of the border irrigation performance. The optimized discharge per unit width of the heterogeneity soil and homogeneity soil meets the 1:1 liner relationship, that is, the optimal discharge per unit width of the homogeneous soil could be used to the design of the discharge water of border irrigation under heterogeneity soil conditions, which guaranteed a high irrigation performance. The method proposed in this study can better reflect the actual performance of border irrigation, and provide theoretical and technical support for the design and management of border irrigation system.