Statistical Distribution of Streambed Vertical Hydraulic Conductivity along the Platte River, Nebraska

Streambed vertical hydraulic conductivity (K_ν) plays an important role in understanding and quantifying the stream-aquifer interactions. While several researchers have discussed the spatial variability of streambed horizontal hydraulic conductivity or K_ν at one or several close-located sites in a river, they did not develop any statistical distribution analysis of streambed K_ν at distant sites along a large river. In this paper, the statistical distribution and spatial variation of streambed K_ν at 18 test sites in a 300-km reach of the Platte River in Nebraska are presented. In-situ permeameter tests using the falling-head method were carried out to calculate the streambed K_ν values. Fine-grained sediments transported by two tributaries, the Loup River and the Elkhorn River, to the Platte River appear to result in lower streambed K_ν values downstream of the confluences between the Platte River and the tributaries. The streambed K_ν values were found to be normally distributed at nearly each test site. When the correlated K_ν values were eliminated from the grid sampling plots, the remaining independent sub-datasets of streambed K_ν values were still in normal distribution at each test site. Furthermore, the combined streambed K_ν values upstream of the first confluence between the Platte River and the Loup River was normally distributed, which may be due to the lack of tributaries in-between and thus streambed sediments were well distributed in this reach and belonged to a single population of hydraulic conductivity values. In contrast, the combined dataset of all measurements conducted downstream of this confluence was no longer in normal distribution, presumably as a result of the mixing of different sediment sources.