Abstract:
Abstract: Studies have showed that the high water-saving rate and optimal irrigation can be realized by using the surge flow irrigation. However, the investigation is not sufficient in the rule of water movement under intermittent infiltration in saturated-unsaturated soil condition. In order to explore the effect rule of surge irrigation on the water distribution in the aeration zone under the condition of shallow groundwater, we studied the water distribution and the effect law of infiltration through the combinations of intermittent infiltration and indoor water infiltration with model simulation. The laboratory test aimed to observe and analyze the data about soil moisture, cumulative infiltration and wetting front by irrigation with shallow groundwater during surge flow irrigation (step1). The part of numerical simulation mainly included the determination of the design parameters of soil water movement (step2) and the establishment of the mathematical modeling for intermittent infiltration (step3). Finally, a case was used to test the rationality and validity of the numerical simulation results (step4). The laboratory test included three cycling rate levels of treatment (1/2, 1/3 and 1/4, respectively) and each level of treatment included 3 repeats. Based on the theory of soil water dynamics and the technology of surge flow irrigation method, the one-dimensional water movement model in the intermittent infiltration under the saturated-unsaturated soil condition was established. With the application of the measured data for three treatment levels in the Hydrus-1D software based on finite element modeling for the analysis of water flow and solute transport in variably saturated porous media, the water movement parameters (the parameters of Van-Genuchten model) were calculated with the Hydrus-1D software. Furthermore, according to determined optimal parameters, we established a saturated hydraulic conductivity estimation model under different circulation rates and different intermittent cycles in the process of the intermittent infiltration. At last, by comparing the data of simulation and the data measured in the experiment, the validity of the proposed model was tested by the analysis of the relationship among the soil moisture content, cumulative infiltration and wetting front respectively. The results showed that after the simulation, the estimation model could reflect the correlativity among the three parameters (circulation rate, cycle number and cycle time), and the saturated hydraulic conductivity coefficient was calculated with these parameters. To verify the estimation model, the result of calculated values was compared with the simulated ones, and the relative deviation of saturated hydraulic conductivity was as small as -7.7%-8.9%, showing good consistency between the calculated and simulated data. From the comparison between the spot observation and the simulation data of soil moisture, cumulative infiltration and wetting front, we drew the conclusion that the calculated and simulated data had a similar change tendency by using two commonly-used criteria: root mean square error and coefficient of determination. The coefficient of determination of soil moisture was upon 0.952 and the one of cumulative infiltration was up to 0.953. The coefficient of determination of wetting front was 0.93 at least; root mean square error above was all less than 0.5, reaching an extremely remarkable level. The result of simulation could describe the characteristics of the saturated-unsaturated soil water movement in intermittent infiltration well under the condition of shallow groundwater level. The study of the paper laid a scientific basis for the further development of the surge irrigation.