Study On Three-dimensional Spatial Variability Of Sediment Hydraulic Conductivity In Qingtongxia Section Of Huinong Canal

The hydraulic conductivity of channel bed sediment is an important parameter for the interaction between channel water and groundwater,which directly affects the water exchange and water transport.The irrigation agriculture of Yinchuan plain is developed,the canal system is numerous,and the channel leakage is serious,which leads to a series of ecological environmental problems.It is of great significance to study the hydraulic conductivity of canal bed sediment for the treatment of canal leakage and the evaluation of regional water resources in Yinchuan plain.In this paper,taking Qingtongxia section of Huinong canal as the research object,the hydraulic conductivity and particle size characteristic parameters of the sediment in the canal bed are measured by the vertical pipe test of head drop and the indoor particle test.The traditional statistics,geostatistics,correlation analysis and regression analysis are used to analyze the measured data,and the variability and influencing factors of the sediment hydraulic conductivity of Huinong canal bed in the three-dimensional space of depth,section and flow direction are studied,and the following research results have been achieved:(1)Depth direction:with the increase of depth,the hydraulic conductivity K of coarse-grained soil,mainly gravel and sand,decreases.The average value of K in different depth is 11.34m/d,which changes between 3.22?26.13m/d as a whole.According to the statistical test,K tends to follow the lognormal distribution,and the hydraulic conductivity of variation is 0.778,which is of medium variability.The range value of K with depth is 31.42cm,and the hydraulic conductivity of nugget is 0.86%,showing a strong spatial correlation;the hydraulic conductivity K of channel bed sediment in fine-grained soil section mainly composed of sand and silt decreases with the increase of depth,and the average value of K in different depths of fine-grained soil section is small,only 1.86m/d,varying between 0.36?3.2m/d,K value follows the normal distribution,and the coefficient of variation is 0.606,showing a medium variation opposite sex.The variation of K with depth is 39.37cm,and the nugget coefficient is 1.36%,which also shows strong spatial correlation.At this direction,the spatial variation of sediment hydraulic conductivity is mainly related to sediment lithology.(2)Section direction:the hydraulic conductivity K of channel bed sediment decreases from the middle of channel to both sides of channel in coarse-grained and fine-grained soil sections,but their statistical laws and spatial variation characteristics are different.The average value of K in typical profile of coarse-grained soil section is5.92m/d,which changes between 0.28?25.31m/d as a whole.K value follows lognormal distribution,and the coefficient of variation is 1.12,which shows strong variability.The range value of K in profile scale is 17.79m,and the coefficient of nugget is 7.63%,which shows strong spatial correlation.The average value of K in typical profile of fine-grained soil section is 1.53m/d,which changes between 0.12?3.43m/d.K value is not only the coefficient of variation is 0.59,which shows moderate variability.The range value of K is 8.33m,the coefficient of nugget is 15.09%,which shows strong spatial correlation.In this direction,the spatial variation of sediment hydraulic conductivity is mainly related to hydrodynamic conditions and channel morphology.(3)Flow direction:the hydraulic conductivity K of the sediment in the channel bed fluctuates along the flow direction,but it decreases as a whole.The average value of K is 5.88m/d,and it changes between 0.58?16.66m/d as a whole.The statistical test results show that under the flow scale,the K trend follows the lognormal distribution,and the number of variation coefficient is 0.825,showing a medium variability.The variation of K along the flow direction is 7.15km,and the nugget coefficient is 25.44%,which belongs to the spatial correlation of medium strength.The spatial variation of hydraulic conductivity in this direction is mainly due to the comprehensive effect of hydrodynamic conditions,artificial sand extraction and channel lining.(4)The difference of sediment particle size characteristics is the essential factor affecting the hydraulic conductivity.Pearson correlation analysis method is used to analyze the correlation between the commonly used particle size characteristic parameters d₁₀,d₃₀,d₅₀,d₆₀,C_u,C_C and K.It is found that the hydraulic conductivity K of the sediment in the channel bed of coarse-grained soil section has a good linear correlation with each characteristic particle size except for the nonuniformity coefficient C_u and curvature coefficient C_c.The regression analysis of each characteristic particle size and K shows that the goodness of fit of the coarse-grained soil segment d₅₀ is the best,and the relationship of K can be expressed as:K=12.232d₅₀-0.0737;there is significant or highly linear positive correlation between the fine-grained soil segment K and each characteristic particle size,and the regression analysis results show that the goodness of fit of d₁₀ is the best,and the relationship of K can be expressed as:K=26.071d₁₀-0.1011.There is a weak linear negative correlation between K and C_uand C_c.When C_u<5,the composition of sediment particles is relatively uniform,and there is no obvious relationship between K and C_u.When C_u>5,the composition of sediment particles is relatively uneven,and K decreases with the increase of C_u.When C_c<1,the sediment grading is poor,and there is no significant correlation between K and C_c.when1<C_c<2,the sediment grading is good,and K decreases with the increase of C_c.