Study On The Relationship Between Fractal Of Soil Structure And Hydraulic Properties In Ziya River Basin

Based on the National Natural Science Foundation of China-"Research on the Relationship between Fractal of Soil Structure and Hydrodynamic Characteristics"?41302186?,this paper selects six typical regions in the Ziya River Basin and uses a laser particle size analyzer to measure soils at different depths in each typical region.The fractal dimension and particle size range of the particle size were obtained through indoor and outdoor joint monitoring and measurement methods,and the matrix suction and water content at the corresponding points were obtained,so as to obtain the soil water characteristic curve in the study area.Based on the measured values of soil fractal dimension and hydraulic properties,a correlation was established between them.The optimal soil moisture characteristic curve model was selected through error analysis and model verification.Based on this,the geostatistics are used to characterize the spatial variation of the soil structure and its hydraulic properties?water characteristic curve?fractal characteristics in the watershed,and to analyze the mechanism of the occurrence of the variation,for the study of soil water movement and shallow groundwater recharge in the basin Provide scientific evidence.The main results of the paper are:?1?Select six areas along the watershed to determine the fractal dimension of the soil particle size and analyze the range of particle size,discuss the fractal characteristics of the soil,and explore the relationship between the fractal dimension and soil texture.Studies have shown that the soil fractal dimension is closely related to the soil texture,and the soil fractal dimension is related to the sand content,silt content and clay content.And the fractal dimension can be used to describe the uniformity of the soil texture.The larger the fractal dimension of the soil,the higher the soil clay content;the smaller the fractal dimension,the lower the soil clay content.?2?Taking Luancheng area as a typical area,in-situ tests using neutron and negative pressure meters to obtain soil matrix suction and water content,and analyze the characteristics of soil hydraulic properties in Luancheng area.The Ku-pf test method was used in other research areas to determine the soil matrix suction and water content of the soil,and the change law of soil water characteristics in each study area was analyzed within the watershed.Then,four models were selected for soil water content in the study area by RETC The characteristic curve is fit and verified to determine the appropriate model.The research shows that except for the Binhai New Area,which uses the DP model,the rest of the areas use the VG model to establish a soil moisture characteristic curve model.The texture and pore size of the soil determine the water holding capacity of the soil and affect the shape of the soil-water characteristic curve.The trend of the curve of the Binhai New Area is as follows:in the low suction stage,the water content drops sharply;in the middle and high suction sections,with the increase of the matrix suction,the change trend of the soil water content slows down and gradually stabilizes.The characteristic curve of soil moisture in other areas basically shows three sections:when the substrate suction is in the low suction section,the soil water content changes little with increasing substrate suction.When the middle suction section is reached,the soil moisture content decreases sharply with the increase of soil matrix suction,and basically shows that the larger the slope of the curve,the greater the water loss.When the substrate suction reaches the high suction stage,the tendency of soil moisture content to decrease with the increase of substrate suction becomes slower,and the trend of water content change becomes stable.?3?Analyze the fractal model of the soil moisture characteristic curve,select the Menger sponge model fractal model,and study the relationship between the fractal dimension of soil particle mass and the fitted value of the fractal model of the soil water characteristic curve.It was found that the relationship between the fractal dimension of soil particle mass fitting at point 1-2 and the fractal dimension of soil particle size measured was D₁=0.6595D_??+0.6188?₂D=0.876D_??+0.2496,and the correlation coefficient was above0.9.?4?A fractal model of soil water characteristic curve was established in the watershed.The research shows that the model has a high degree of fit,the fitted values and the measured values basically coincide,the correlation coefficients are all above 0.9,and the maximum RMSE is 0.211.The correlation analysis between Pearson and Spearmen found that the measured fractal dimension of each sampling point was significantly correlated with the model fractal dimension,and the relative error was less than 10%.The model can be used to study the fractal characteristics and Relationship between hydraulic properties.?5?The spatial variability of the fractal characteristics of the soil structure in the Ziya River Basin has been studied.Classical statistics show that the fractal dimension of the soil particle size in Shijiazhuang shows weak spatial variability,while the rest of the areas show moderate variability.Geostatistics shows that the coefficients of the semi-variance fitting function range from 0.263 to 0.927,and the gold block coefficients of Luancheng,Shijiazhuang and Hengshui areas range from 25%to 75%,showing a medium spatial correlation.The gold block coefficient of Hejian,Dacheng and Binhai new area is small,close to 0,showing a strong spatial correlation.?6?The spatial variability analysis of the fractal dimension of the soil water characteristic curve under the same area and the same depth in the Ziya River Basin revealed that the fractal characteristics of the soil hydraulic properties in the Ziya River Basin have weak spatial correlation in the same area.Luancheng,Shijiazhuang,Dacheng and Binhai New Area showed weak spatial variability,and Hengshui and Hejian areas showed moderate spatial variability.The spatial variability of the lag distance in each study area is particularly obvious within 0-0.4m.As the lag distance gradually increases,the spatial variability of the fractal characteristics of soil hydraulic properties becomes weaker and weaker,which may be due to external disturbances such as irrigation methods and crop cultivation.The impact of the resulting soil structure changes.The fractal characteristics of soil hydraulic properties in the same depth range showed medium spatial variability,with coefficient of variation between 0.25?0.75 and strong spatial autocorrelation.The coefficient of variation increases with the increase of depth,indicating that the spatial variability of Ziya River Basin increases with the increase of depth,and the hydraulic properties of soil are easily affected by the variation and randomness of soil texture.