Variability of streambed vertical hydraulic conductivity with depth along the Elkhorn River,Nebraska,USA

Determination of streambed hydraulic conductivity is of great importance in the analysis of stream-aquifer interactions and stream ecosystems.In this paper,in situ falling-head standpipe permeameter tests were conducted to determine streambed vertical hydraulic conductivity (Kv) of two connected layers of sediments at 60 test locations from eight sites in the Elkhorn River,Nebraska.Our results show that the Kv values for the upper layer of sediments are generally larger than those in their respective lower layer of sediments.The individual Kv value for the upper layer of sediments from all test locations of the eight sites range from 2.7 to 104.9 m/d,and the average value is 26.6 m/d.The individual Kv value ranges from 0.4 to 73.4 m/d and the average value is 16.1 m/d for the lower layer of sediments.We believe that hyporheic processes can enhance larger streambed Kv in the upper layer of sediments.Inflow and outflow through hyporheic zone produce more porous and permeable sediments and further result in an increasing of streambed Kv.Moreover,we observe that bioturbation activities can destroy the clogging layer of the exposed sediments and create pore spaces in the sediments,which also further increases streambed Kv.