STREAMBED HYDRAULIC CONDUCTIVITY FOR RIVERS IN SOUTH‐CENTRAL NEBRASKA1

Abstract

ABSTRACT: 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 (Kv), 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 Kv 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 Kv values of sand and gravel in the Platte and Republican Rivers essentially have the same mean; but the Kv values from the Little Blue River have a statistically different mean. Kv is about four times smaller than the horizontal hydraulic conductivity (Kh) for the top 40 cm of sandy streambed. Measured Kh values of the sandy streambed are in the same magnitude as the Kh of the alluvial aquifer determined using pumping tests. The smaller Kv value in the whole aquifer is the result of interbedded layers of silt and clay within the sand and gravel sediments.