Horizontal hydraulic conductivity of shallow streambed sediments and comparison with the grain-size analysis results

Streambed horizontal hydraulic conductivity (K _h) has a substantial role in controlling exchanges between stream water and groundwater. We propose a new approach for determining K _h of the shallow streambed sediments. Undisturbed sediment samples were collected using tubes that were horizontally driven into streambeds. The sediment columns were analysed using a permeameter test (PT) on site. This new test approach minimizes uncertainties due to vertical flow in the vicinity of test tube and stream stage fluctuations in the computation of the K _h values. Ninety-eight PTs using the new approach were conducted at eight sites in four tributaries of the Platte River, east-central Nebraska, USA. The K _h values were compared with the nondirectional hydraulic conductivity values (K _g) determined from 12 empirical grain-size analysis methods. The grain-size analysis methods used the same sediment samples as K _h tests. Only two methods, the Terzaghi and Shepherd methods, yielded K _g values close to the K _h values. Although the Sauerbrei method produced a value relatively closer to K _h than other nine grain-size analysis methods, the values from this method were not as reliable as the methods of Terzaghi and Shepherd due to the inconsistent fluctuation of the average estimates at each of the test sites. The Zunker, Zamarin, Hazen, Beyer, and Kozeny methods overestimated K _h, while the Slichter, US Bureau of Reclamation (USBR), Harleman, and Alyamani and Sen methods underestimated K _h. Any of these specific grain-size methods might yield good estimates of streambed K _h at some sites, but give poor estimates at other sites, indicating that the relationship between K _g and K _h is significantly site dependent in our study.