Study on non-Darcian flow and solute transport characteristics through a filled single fracture

In this study, well-controlled laboratory experiments on flow and solute migration through a Filled-Single Fracture (FSF) of 3 mm aperture size were performed for different flow rates. Non-Darcian flow conditions prevailed throughout the experiment, which can be effectively explained using Forchheimer or Izbash’s equations. The constant mode was utilized to inject a conservative solute (NaCl) evenly through the FSF, following which the resulting Breakthrough curves (BTCs) were developed for three different average flow velocities. The computed BTCs were simulated by the conventional Convection-Dispersion Equation (CDE); and the single rate Mobile-Immobile (MIM) Model. A non-Fickian trend was observed for the attained BTCs, which cannot be interpreted by the Fickian CDE; however, the CDE model serves as the comparing base. MIM model was found much better than the CDE in fitting BTCs for three different average values of pore velocities. Statistical analysis on the goodness-of-fit further confirmed the suitability of MIM as much greater correlation coefficients were observed compared to the CDE model. Further, the BTCs were found to fit better at lower velocities. The greater computed dispersivity values are compatible with Taylor who suggested that much stronger dispersion occurs under non-Darcian flow conditions.