The epoxy-resin model used in this study replicates a specimen of upper Pleistocene, Biscayne aquifer limestone gathered from southeastern Florida that is riddled with cm-scale ichnogenic macroporosity primarily related to Ophiomorpha. Specific discharge through the model was controlled using a constant head reservoir and a peristaltic pump.
The region of useful, minimally distorted NMRI images measured 9 cm in length along the z-axis parallel to the predominant flow direction and 10 cm in both transverse directions. Axial and transverse resolution of the images was 0.118 cm and 0.418 cm, respectively. The time needed to collect NMRI data for all three Cartesian components of velocity was about 7.5 hours for each experiment.
NMRI measurements of velocity were collected at two steady-state values of specific discharge. Average axial components of velocity (0.016 cm/s and 0.04 cm/s) are within the range of advective flow expected in the Biscayne aquifer. In both experiments, the velocity field is nearly proportional as might be expected in a low Reynolds number, laminar-flow regime (for water with kinematic viscosity= 0.01 cm2/s moving with a velocity=0.04 cm/s in macropores with diameter=1.5 cm, Reynolds number=6). Exponential functions fit the distributions of the axial velocity. Distributions of the transverse velocities are symmetric but wider tailed than Gaussian functions.