Spatial Variation Coefficient Of Permeability Of Weihe River Bed Sediments On The Research

Streambed hydraulic conductivity affects hydraulic connection between surfacewater and groundwater and water quantity exchange in hyporheic zone. Besides, spatial distribution of hydraulic conductivity of streambed sediments accelerate the surface water and ground water exchange and influence the material reaction in the solute residence time and mixing process. Therefore, the quantitative research on the hydraulic conductivity of streambed sediments and their spatial variability are of great significance in determining the magnitude and scope of the exchange between river water and groundwater and the movement of pollutants and in restoring the river ecosystem. As the biggest tributary of Yellow River, the Weihe River flows through the large and medium-sized cities in Shaanxi Province, including Baoji, Yangling, Yanyang, Xi’an, Weinan, etc., playing a prominent role in the economic development of Guanzhong region. In recent years, the ecological problems of Weihe River are severe, the river is seriously contaminated, and the interaction between the surfacewater and groundwater is notable. Therefore, this research takes Shaanxi section of Weihe River as study region. In this study, the valves of vertical hydraulic conductivity (Kv) for a streambed were derived using falling-head standpipe penneameter tests conducted at shallow sediments layer of76test locations as well as deep sediments layer of8test locations in five test sites including Meixian, Xianyang, Xi’an, Lintong and Huaxian, which are located in the middle and lower reaches of the Weihe River. This thesis adopted the methods of geostatistics and traditional statistics to research the spatial variability of hydraulic conductivity. The measurement results of Kv values were in normal distribution in Yanyang and Lintong test sites; after logarithmic transformation, those in Meixian Lintong and Xianyang sites were in normal distribution. The Kv test values were between0.05～61.32m/d with the average of4.59m/d. The most Kv values were between0～40m/d and the maximum frequency distributions occurred between0～5m/d. The average Kv value in five study sites including Meixian, Xianyang, Xi’an, Lintong and Huaxian were respectively0.96m/d、0.40m/d、19.00m/d、2.54md、0.06m/d. The test values in different test areas varied largely; The spatial distribution of the sediment hydraulic conductivity indicates that the Kv value is the biggest in Xi’an, then in Lintong, the Kv value in the Meixian and Xianyang are relatively small and of little difference, and the smallest in Huaxian. In each study region, the characteristics of spatial distribution is that, along the flow direction, the Kv values in Xianyang gradually decreased, while those in Lintong and Xi’an showed increasing trend, and Kv values in Meixian represented a changing process of firstly increasing and then decreasing. Besides, the values were consistently higher in shallow streambed sediments than in deep streambed sediments at test locations and the particles size distribution of the streambed sediments affected the measured values of the hydraulic conductivity to a large extend for the reason that the Kv values were relatively low in the test sites where the contents of fine particle were higher. With Pearson coefficient method, this thesis arrives at the conclusion that river discharge and water quality index such as total phosphorus, permanganate index, ferrous ion, and total nitrogen and they were positively correlated with the Kv values; then mess percentages of the particles size smaller than0.2mm have a negative linear correlation with Kv values; the particles larger than0.2mm presented linear positive correlation; and the copper, potassium, available phosphorus, and organic matters in streambed sediments were negatively correlated with the Kv values. Using the method of principal component analysis, the multivariate linear Kv model based upon the main physicochemical properties of streambed sediments was preliminarily established. This research attempts to provide theory solutions to qualitative estimation and scope the water exchange and contaminant transport between stream and groundwater.