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 (K_v) of two connected layers of sediments at 60 test locations from eight sites in the Elkhorn River, Nebraska. Our results show that the K_v values for the upper layer of sediments are generally larger than those in their respective lower layer of sediments. The individual K_v 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 K_v 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 K_v 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 K_v. 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 K_v.