Study On Soil Water Transport Law And Characterization Model Of Gravity Subsurface Hole Irrigation

Water shortage and soil erosion are two bottlenecks that restrict the sustainable development of the Loess Plateau,and they are also the fundamental reasons that lead to ecological fragility in this area.In order to control rainfall runoff,realize rainwater resource utilization and reduce soil erosion,a gravity underground hole irrigation system was developed.In order to facilitate the evaluation of soil water transport law of gravity underground hole irrigation and increase the wide applicability of the system.In this paper,based on the theory of soil hydrodynamics,HYDRUS-2D/3D software is used to simulate the infiltration process of soil water under different combinations of influencing factors,and the empirical model is established by analysis and fitting,and the reliability of the empirical model is verified by experimental data.The main results are as follows:(1)The double logarithmic coordinate plot of cumulative infiltration amount and irrigation infiltration time was analyzed,and the results showed that the cumulative infiltration amount increased gradually with the increase of soil saturated hydraulic conductivity,seepage hole diameter,and seepage hole depth.increase and decrease slightly.(2)The simulation data of cumulative infiltration is studied by using origin software,and Kostiakov empirical model and Philip empirical model are established in the form of power function to express the change process of cumulative infiltration.The results show that the exponential variation interval of the Kostiakov model in the form of a power function is small,and the average value is b=0.911;the coefficient also has a good power function relationship with soil texture,seepage hole diameter,seepage hole depth,and soil matrix potential.Therefore,a Kostiakov empirical model of cumulative infiltration in the form of power function multiplication is established.The experimental data verified the Kostiakov empirical model and found that the MAE was between 0.009 and 0.019 L,the RMSE was between 0.002 and 0.005 L,and the NSE was greater than or equal to 0.998,indicating that the model fitting accuracy was high.(3)When establishing the Philip empirical model of cumulative infiltration,the analysis found that in Philip’s formula,the imbibition rate has a power function relationship with soil texture,seepage hole diameter,seepage hole depth,and soil matrix potential.The diameter and burial depth of seepage holes are in a power function relationship.After further analysis,a Philip empirical model of cumulative infiltration is established.The experimental data verified the Philip empirical model and found that the MAE was between 0.016 and 0.023 L,the RMSE was between0.004 and 0.006 L,and the NSE was greater than or equal to 0.895,indicating that the model had a good prediction effect.(4)By analyzing the graph of the wetting front migration distance,we know that the cumulative infiltration amount is one of the main factors affecting the wetting front migration distance.When the cumulative infiltration amount is constant,the influence factors on the wetting front migration in different directions are different.The nonlinear power function empirical model 1 and model 2 are established by fitting the simulated data.The comparative analysis shows that the nonlinear power function empirical model 1 has higher fitting accuracy.The experimental data verified the empirical model 1 and found that the vertical downward direction MAE≤0.320 cm,RMSE≤0.089 cm,NSE≥0.979;horizontal direction MAE≤0.060 cm,RMSE≤0.017 cm,NSE≥0.998;vertical upward direction MAE≤0.351 cm,RMSE≤0.097 cm,NSE≥0.963.It shows that the model estimation effect is good.(5)The contour maps of soil moisture content under different schemes are similar in shape,and they are all"ellipsoid"around the seepage surface;With the increase of the diameter of the seepage hole,the water content of the same coordinate point of the wetting circle decreases;with the increase of the buried depth of the seepage hole,the position of the wetting circle moves down,and the water content of the same coordinate point in the circle decreases;with the initial soil matrix potential gradually increased(Ψ_mincreased from-7500 cm to-3750 cm),and the soil moisture content at the same coordinate point gradually decreased.