Streambed hydraulic conductivity for rivers in south-central Nebraska

This paper presents hydraulic conductivities of streambeds measured in three rivers in south-central Nebraska: the Platte, Republican, and Little Blue Rivers. Unlike traditional permeameter tests in streams that determine only the vertical hydraulic conductivity (K-v), the extended permeameter methods used in this study can measure K in both vertical and horizontal as well as oblique directions. As a result, the anisotropy of channel sediments can be determined from streambed tests of similar sediment volumes. Sandy streambeds with occasional silt/clay layers exist in the Republican and Platte Rivers. The average K-v values range from about 15 to 47 m/day for the sandy streambed and about 1.6 m/day for the silt/clay layers. Statistical analyses indicated that the K-v values of sand and gravel in the Platte and Republican Rivers essentially have the same mean; but the K-v values from the Little Blue River have a statistically different mean. K-v is about four times smaller than the horizontal hydraulic conductivity (K-h) for the top 40 cm of sandy streambed. Measured K-h values of the sandy streambed are in the same magnitude as the K-h of the alluvial aquifer determined using pumping tests. The smaller K-v value in the whole aquifer is the result of interbedded layers of silt and clay within the sand and gravel sediments.