Determination of the anisotropy of an upper streambed layer in east-central Nebraska, USADétermination de l’anisotropie de l’horizon supérieur d’un lit fluviatile dans le Centre-Est du Nebraska, USADeterminación de la anisotropía de una capa superior de un cauce en el centro-este de Nebraska, EEUU美国内布拉斯加中东部河床上层沉积物各向异性比的确定Determinação da anisotropia da camada superior dos sedimentos do leito de rios no Centro-este de Nebraska, EUA

Information on the anisotropy of streambed hydraulic conductivity (K) is a necessity for analyses of water exchange and solute transport in the hyporheic zone. An approach is proposed for the determination of K, developed from existing in-situ permeameter test methods. The approach is based on determination of vertical and horizontal hydraulic conductivity of streambed sediments on-site and eliminates the effects of vertical flow in the hyporheic zone and stream-stage fluctuation, which normally influence in situ permeameter tests. The approach was applied to seven study sites on four tributaries of the Platte River in east-central Nebraska, USA. On-site permeameter tests conducted on about 172 streambed cores for the determination of vertical hydraulic conductivity (Kv) and horizontal hydraulic conductivity (Kh) at the study sites indicate that the study sites have relatively small anisotropic ratios, ranging from 0.74 to 2.40. The ratios of Kh to Kv from individual locations within a study site show greater variation than the anisotropic ratios from the mean or median K at each of the study sites.