DEVELOPMENT AND TESTING OF SHELBY TUBES AS AN IN-SITU DISCHARGE AND HYDRAULIC CONDUCTIVITY MEASUREMENT DEVICE

The Shelby tube (a.k.a. thin walled soil sampler) has been used since the 1940’s as an undisturbed soil core collection device. In this study, a Shelby tube has been repurposed to measure specific discharge (q) and hydraulic conductivity (K) in shallow surface waters. Data needed to determine q and K are the head as a function of time inside the Shelby tube , and the stream head outside the Shelby tube .

Laboratory testing of the Shelby tube was conducted in seepage tanks at the University of Utah and the USGS Denver Federal Center. Utah tests were conducted in fine glass beads and coarse irregular sand. For both the beads and sand the Shelby tube discharge matches the bucket-gauged pumping rate (R²=0.95, m=0.96, n=10, q=1 to 0.6 m day^-1; R²=0.998, m=1.07, n=38, q=50 to -50 m day^-1, respectively). Denver tests were conducted in a medium sand and Shelby measured discharge agrees with controlled seepage rates (R²=0.994, m=1.06, n=13, q = -0.47 to 0.6 m day^-1). K comparisons made at Utah indicate that the Shelby calculated hydraulic conductivity (K_s) agrees well with falling head permeameter tests (K_f) for the beads (K_s=16 m day^-1, SD=2.7, n=10; K_f=14.2 m day^-1, SD=0.2, n=5) and sand (K_s=228 m day^-1, SD=52, n=38; K_f=158 m day^-1, SD=10.4, n=5).

Field-testing will compare the Shelby tube with Darcian methods. Interpolation of Darcian measurements correlate well with discharge from bromide tracer tests. We suggest that reach scale discharge can be measured using Shelby tubes.