Improved geohydraulic characterization of river bed sediments based on freeze-core sampling - Development and evaluation of a new measurement approach

- Horizontal and vertical, small-scale, layer-by-layer determination of K-values.
- New approach based on freeze-core samples of river bed sediments.
- Evaluation of our results using comparative methods.
- In situ permeameter tests and results obtained by freeze-core tests are consistent.
- Results confirm that methods based on grain-size distribution are not suitable.

SummaryPrior to hydraulic engineering work, it is essential to know the geohydraulic properties of river bed sediments as precisely as possible in order to predict and minimize potential effects on adjacent aquifers. Many different methods are available, but all have limitations. Some destroy the natural sediment structure, others lack a small-scale resolution, and all fail to determine anisotropy. In this study, we present a new measuring approach to determine hydraulic conductivity (K) and anisotropy at a detailed scale. Frozen, undisturbed sediment samples taken with the freeze-core technique form the basis of our approach. Orientated core cutter samples are taken from the freeze-cores at different depths and examined by means of falling-head lab permeameter tests, in order to obtain detailed profiles of vertical and horizontal K values and anisotropy. The approach was tested with natural sediment samples from the bed of a channel near Potsdam, Germany, and with samples from an experimental container. For comparison and evaluation, hydraulic conductivities were also determined by means of in situ permeameter tests and empirically, on the basis of grain-size distribution (GSD). The results show a large discrepancy between the empirically determined hydraulic conductivities and the directly measured hydraulic conductivity with lab and in situ permeameter tests. We conclude that empirical methods based on GSD are not suitable for determining in situ conductivity of river bed sediments. Our new approach enables an improved geohydraulic characterization of river bed sediments including the determination of anisotropy.