Comparison of Instream Methods for Measuring Hydraulic Conductivity in Sandy Streambeds

Abstract

Streambed hydraulic conductivity (K) values were determined at seven stream transects in the Platte River Basin in Nebraska using different instream measurement techniques. Values were compared to determine the most appropriate technique(s) for use in sandy streambeds. Values of K determined from field falling-and constant-head permeameter tests analyzed using the Darcy equation decreased as permeameter diameter increased. Seepage meters coupled with hydraulic gradient measurements failed to yield K values in 40% of the trials. Consequently, Darcy permeameter and seepage meter tests were not preferred approaches. In the upper 0.25 m of the streambed, field falling-and constant-head permeameter tests analyzed with the Hvorslev solution generally had similar K values that were significantly greater than those determined using the Hazen grain-size, Bouwer and Rice slug test for anisotropic and isotropic conditions, and Alyamani and Sen grain-size methods; median differences between these tests and the Hvorslev falling-head 60 cm diameter permeameter were about 8,9, 17, and 35 rnfday, respectively. The Hvorslev falling-head permeameter test is considered the most robust method for measuring K of the upper 0.25 m of the streambed because of the inherent limitations of the empirical grain-size methods and less sediment disturbance for permeameter than slug tests. However, lateral variability in K along transects on the Platte, North Platte, and Wood Rivers was greater than variability in K between valid permeameter, grain-size, or slug tests, indicating that the method used may matter less than making enough measurements to characterize spatial variability adequately. At the Platte River tributary sites, the upper 0.3 m of the streambed typically had greater K than sediment located 0.3 to 2.5 m below the streambed surface, indicating that deposits below the streambed may limit ground waterlsurface water fluxes. The Hvorslev permeameter tests are not a practical measurement approach for these greater depths. Thus, selection of a method for measuring streambed K needs to consider the vertical location of the sediments that are most likely to limit the rate of ground waterlsurface water interaction.

Designing and Evaluating the Quality and Cost-effectiveness of Saturated Sediment Permeameters

“…We designed our first custom permeameter as a laboratory adaptation of the classic in situ falling-head field method (Landon et al, 2001). Second, we designed and built a constant-head permeameter out of 4" PVC pipe using a U-shape to keep the sediment in place.…”

“…We also measured both head levels using the manometer and calculated their head difference, ΔH. Then we calculated the hydraulic conductivity Equation 1 (Landon et al, 2001),…”

“…Falling-head permeameters are commonly used in field studies (Landon et al, 2001). We modified the method described in Landon et al (2001) for use in a laboratory setting by using a large vase instead of a stream.…”

“…Hydraulic conductivity is typically measured with either a constant-head or falling-head permeameter (Landon et al, 2001;Klute, 1965;Genereux et al, 2008). Both types of permeameters use head differences to create flow through sediment.…”

“…For the constant-head systems, the water levels do not change and the volumetric flow rate through the system is measured. For the falling-head system the higher water level falls and the time it takes to drop is used to calculate K (Landon et al, 2001Conners, 2012.…”