Hydraulic Conductivity And Macrodispersivity And Their Spatial Variability Of Floodplain Sediments In The Weihe River

The interactions between surface water and groundwater are important research focusand cutting-edge topics. Rivers are parts of the surface water systems that drain runoff, andwhere surface water and groundwater exchange frequently.. The Weihe River in ShaanxiProvince flows through the Guangzhong Plain; it is hydrologically connected to the adjacentaquifers. Especially in summer, the Weihe River is flood-prone.The hydraulic properties ofthe floodplain sediments in the Weihe Riverplay a significant role in the river waterinfiltration to the groundwater.This research took the Xianyang section of the Weihe River as a study area. Weconducted permeameter tests using the standpipe method in a floodplain in the Weihe River todetermine the vertical hydraulic conductivity (Kv). The floodplain consists of an unsaturatedzone of about50to100cm in thickness and a saturated zone below it. We conducted68testsin the saturated zone and900tests in the unsaturated zone. After the permeameter tests,sediment samples were collected for grain size analyses. The principle of geological statisticswas applied to analyze the spatial correlation of the hydraulic conductivity for the saturatedand unsaturated zones. The spatial correlation information was then used to calculate themacrodispersivity of the floodplain which is an important parameter in the modeling ofcontaminant transport..The results show that:(1) The average Kvvalue of the saturated zoneis0.021cm/s using the standpipe method, and the average Kvvalue of the unsaturated zone is0.012cm/s. The hydraulic conductivities have a strong spatial variability.(2) The Kvvaluesdetermined based on the grain size distribution methods for the saturated zone were verydifferent from the Kvvalues of the standpipe method. The USBR method and the Sauerbreimethod only can be used to approximate the hydraulic conductivity of the unsaturated zone inthe study region.(3) Sediment sieving analyses suggest that the content of medium size sand for the unsaturated zone is the highest by weight, the next size group is coarse sand, andthe sediment sorting is good. The mean particle diameter is0.4722mm. The particledistribution curve of the sediment show positive skewness. The sediments consist mainly ofmedium to coarse sands. The kurtosis of sediments are sharp relatively.(4) The hydraulicconductivities of the saturated and unsaturated zones belong to lognormal distribution.(5) Thecorrelation length of Kvfor the saturated zone is2.94m and the correlation length of Kvforthe unsaturated zone is7.42m. But the correlation length for each row is smaller than thecorrelation length for all rows.(6) The spatial variability of the saturated and unsaturated zonehydraulic conductivities is intermediate.(7) The longitudinal macrodispersivity (AL) wascalculated based on the variance and correlation length of lnK for the Weihe Riverfloodplain. The ALvalues of the saturated and the unsaturated zones are3.6m and9.7m,respectively. Moreover ALvalues are related to study scales.