Laboratory Experiment And Numerical Simulation Study On Hydraulic Factors Of Field Pipe Network System Under Subsurface Drip Irrigation

Subsurface drip irrigation (SDI) that has a wide application prospect is one of the high efficiency water-saving irrigation techniques. Because the emitters were buried in soil, the hydraulic characteristics of SDI subunit pipe network were affected by soil physical properties. But the research on this problem was inadequate at present. In the paper, the laboratory test and the combined methods in both numerical simulation and theoretical analysis were carried out for the research on the variation and influencing factors of hydraulic factors of SDI emitter, lateral and field pipe network. The principal results are as follows:(1) A new method of emperiment test was put forword, and corresponding laboratory test system for hydraulic factors of SDI emitter and lateral pipe was established. The weight values of SDI emitters'water output were tested by weighing sensors; the pressure values of SDI field pipe network were measured by pressure transmitters. Then these tested data was automatically collected, transmitted and stored by the data acquisition system and a personal computer. The test precision of the laboratory test system could meet test requirement, so it became an effective mean of experiment test for research on the hydraulic characteristics of SDI emitter and lateral.(2) Based on three independent variables that were work pressure of non-compensated emitter, soil bulk density and initial soil water content, the experience formula for calculating SDI emitter discharge was established according to the test data. The analyses show that when work pressure is increased, the SDI emitter discharge is increased. The bigger work pressure, the closer emitter discharges of both SDI and drip irrigation (DI). Pressure head is main factor to affect SDI emitter discharge; soil bulk density and initial soil water content play faint restrictive effects on SDI emitter discharge. (3) An experimental scheme was proposed for test SDI lateral hydraulic factors. The nonlinear equations of SDI lateral hydraulic calculation were established based on test data of SDI lateral hydraulic factors. Using MATLAB programming, the every emitter's discharge along SDI lateral and the increasing coefficient of local head loss in SDI lateral could be calculated under experimental condition. On the basis, the numerical simulation model of SDI lateral hydraulic calculation was build. Through using the model, the variation of SDI lateral hydraulic factors under different conditions could be analysed. The results shows that the bigger soil bulk density and initial soil water content, or finer soil texture, then the lower SDI emitters' discharges and lateral frictional head loss, while the greater pressure along SDI lateral. But the differences of SDI lateral pressure and emitters'discharges among different soil bulk density, or different initial soil water content, or different soil texture, are not significant. The bigger soil bulk density and initial soil water content, or finer soil texture, then the lower pressure head and flow deviation rates of SDI lateral. The relationship between pressure head deviation rate and flow deviation rate of SDI lateral can be approximately expressed by that of DI lateral.(4) The numerical simulation model for hydraulic calculation of SDI field pipe network was build. Using the model, irrigation uniformity field pipe network under different combination condition was analysed. The results show that irrigation uniformity of SDI field pipe network is higher than that of DI field pipe network, and the higher pressure, the closer both. Generally, to different drip irrigation pipes, when the arrangement mode of submain pipe and lateral are unchanged and pipes laying in flat slope, irrigation uniformity of DI field pipe network is increased with the submain inlet pressure increasing. But irrigation uniformity of SDI field pipe network may be increased, and may be also decreased with the submain inlet pressure increasing. This is due that the sensitivity of different drip irrigation pipes to soil physical properties are different. When other conditions are similar, the finer soil texture, or the bigger soil bulk density and initial soil water content, then the higher irrigation unirformity. But generally, soil texture, soil bulk density and initial soil water content have little influence on irrigation unirformity.The analyses show that the bigger soil bulk density and initial soil water content, or the finer soil texture, then the lower pressure head and flow deviation rates of SDI field pipe network, and the better irrigation quality. But the effects of soil texture, soil bulk density and initial soil water content on pressure head and flow deviation rates are less obvious. Irrigation quality of SDI field pipe network is slightly better than that of DI field pipe network under the same codition. The relationship between pressure head deviation rate and flow deviation rate of SDI field pipe network can be approximately expressed by that of DI field pipe network.